The formation and evolution of haze involve multi-scale atmospheric physical and chemical processes. “High humidity” is a typical pollution-related meteorological characteristic of the Sichuan Basin and an important influencing factor for haze development. Based on ERA5 reanalysis data from 2015 to 2018 and ground-based conventional environmental meteorological observations, this study systematically analyzed the evolution characteristics of water vapor and its relationship with atmospheric visibility during winter haze processes in the Sichuan Basin. The results show that: 1) The mean regional net water vapor budget during winter haze processes in the Sichuan Basin is (3.40±2.92)×106 kg·s-1, indicating an overall water vapor surplus; the western and southern boundaries are the main water vapor input pathways, the eastern boundary shows net output, and water vapor transport across the northern boundary exhibits uncertainty. 2) As the haze processes evolve from the formation to the development and persistence stages, the lower-tropospheric (below 700 hPa) water vapor content increases continuously, and the water-vapor high-value tongue extends northward with an expanding coverage. 3) The increase in lower-tropospheric water vapor facilitates the hygroscopic growth of near-surface aerosols, thereby increasing the mass extinction coefficient and consequently reducing atmospheric visibility.
The complex influence of snow cover on surface energy processes constitutes a critical source of uncertainty in wintertime numerical simulations over complex terrain and therefore warrants further investigation. Comparative simulation experiments were conducted for a snow-covered period (18-26 February) and a snow-free period (11-19 January) in 2014 over the Lanzhou New Area using the Weather Research and Forecasting (WRF) model version 4.3. Four land surface models (LSMs), SLAB, Pleim-Xiu, RUC, and NoahMP were systematically evaluated against observations from four meteorological towers to reveal the impact of snow cover on simulation accuracy and scheme sensitivity. Satisfactory performance was achieved during the snow-free period: correlation coefficients (R) of air temperature ranged from 0.80 to 0.97, with normalized centered root mean square errors (NCRMSE) of 0.27-0.60. The R of wind speed ranged from 0.46 to 0.82, and the absolute bias was generally below 0.5 m·s-1, successfully reproducing slope wind circulation. Conversely, simulation accuracy declined significantly during the snow-covered period. R of air temperature for half of the LSMs decreased below 0.80, cold biases exceeded 5.00 ℃, and NCRMSE increased to 0.38-0.79. Wind speed NCRMSE increased to 0.77-2.52, while wind direction frequency errors doubled. Taylor diagram analysis demonstrated that snow cover enhanced the sensitivity to LSMs, indicated by increased dispersion in normalized standard deviation among the schemes. NoahMP exhibited the superior performance with the lowest cold bias under snow-covered conditions (R≈0.9; NCRMSE<0.5), emphasizing the significance of accurate snow process representation for improving winter meteorological simulation in complex terrain.
From 25 to 29 November 2024, Heilongjiang Province experienced an extreme precipitation event associated with a northeast cold vortex (NECV), during which precipitation at multiple observation stations exceeded historical records. Using hourly observations from surface meteorological stations in Heilongjiang Province and ERA5 reanalysis data from the European Centre for Medium-Range Weather Forecasts (ECMWF), the evolution characteristics of the NECV and the formation mechanisms of sustained heavy precipitation were investigated. The results indicate that the cold-core structure of the NECV initially appeared in the mid-troposphere, extended downward during its development, and retreated to the mid-levels during the weakening stage. During the development and mature stages, subsidence dominated on the southern side of the vortex, while pronounced upward motion and deep moist layers were present on the northern and eastern sides. Throughout the heavy precipitation period, the precipitation center remained on the eastern side of the NECV. The southeasterly low-level jet and super low level jet acted as warm conveyor belts, continuously transporting moisture and heat to the precipitation area, and exhibited a pronounced diurnal variation, with jet intensification and downward extension of strong winds from early morning to afternoon, accompanied by significant vertical wind shear. Heavy precipitation showed a strong correspondence with the 925 hPa moisture convergence zone. The long-term maintenance of sustained moisture transport and convergence near Hegang was a necessary condition for the occurrence of extreme precipitation. In addition, terrain-induced convergence and uplift, together with the coupling of upper- and lower level jets, significantly enhanced low level ascent, leading to prolonged and extreme precipitation. Extreme precipitation mainly occurred on the windward slopes of the eastern foothills of the Xiaoxing’an Mountains.
To deepen the understanding of precipitation patterns in complex mountainous terrain, hourly precipitation data from three meteorological observation stations at different altitudes on the eastern side of the Fanjing Mountain in Guizhou Province in the flood season from May to October during 2022-2023 were used to analyze the diurnal variation characteristics of precipitation at the foot, mid-slope and summit stations. The results show that the amount and intensity of precipitation from night to morning increase with increasing altitude, while both decrease with increasing altitude from afternoon to evening. The periods with the large precipitation amount at stations on the foot and middle of the mountain occur from the late afternoon to evening, while at the summit station it concentrates from the early morning to morning. The precipitation at three stations mainly originates from rainfall events lasting from 2 to 18 hours. At the summit station, the precipitation amount during rainfall events lasting less than 8 hours is greater at night than during the day, while at the foot and mid-mountain stations, this characteristic is only observed in rainfall events lasting less than 3 hours.The peak period of precipitation shows a systematic delay with altitude increasing. From the night to the morning at the station at the foot of the mountain, then from the night to the noon at the station on the middle of the mountain, and finally transitioning from the noon to the early morning at the top station of the mountain, it exhibits a trend of “spreading from the morning to the noon and then to the early morning”. Short duration heavy precipitation (with precipitation amount greater than or equal to 25 mm) mostly occurs in the morning and has the highest frequency, while long duration precipitation has the highest proportion of precipitation amount.
To gain an in-depth understanding of the fine-scale characteristics of short-term heavy precipitation under Zhengzhou’s complex terrain, based on hourly precipitation data from national and regional stations from 2013 to 2022, conventional observation data, and high-precision geographic information data, this study systematically analyzes the multi-temporal scale variations and spatial distribution patterns of short-term heavy precipitation in Zhengzhou and quantitatively explores the relationships between precipitation intensity, frequency and topographic factors. Combining the case study of the extreme torrential rain event occurring in July 2021 (“21·7”) in Zhengzhou, the study reveals the thermodynamic mechanisms through which terrain triggers and enhances short-term heavy precipitation. The results indicate that the station-based frequency of short-term heavy precipitation in Zhengzhou shows a fluctuating increasing trend, July and August are the peak occurrence periods. The active period is between 14:00 and 20:00 (Beijing Time, the same as below), peaking from 18:00 to 20:00. The probability of daytime occurrence in mountainous areas is significantly higher than in plains. The short-term heavy precipitation events with rainfall intensity greater than or equal to 20 mm·h?¹ occur mostly in mountainous areas, whereas extreme events with rainfall intensity greater than or equal to 50 mm·h?¹ are more likely in the Zhengzhou main urban area and Xinmi City, reflecting a spatial distribution pattern where mountainous areas experience higher frequency but relatively lower intensity, while urban areas exhibit stronger extremity. Circulation classification shows that under weak synoptic-scale forcing backgrounds, the number of station occurring short-term heavy precipitation in mountainous areas is significantly greater than that in plain areas. Terrain’s influence on rainfall intensity distribution of short-term heavy precipitation is not significant, but it has a clear impact on its frequency. During the “21·7” torrential rain process, the triggering effect of the terrain convergence line and the mechanism of convective enhancement caused by the uplift on the windward slope and the thermal difference of the underlying surface are particularly prominent.
Based on hourly precipitation data from high-density regional automatic stations and national stations in Shaanxi Province during 2009-2023, the spatiotemporal characteristics of short-term heavy rainfall (hourly precipitation greater than or equal to 20.0 mm) in different regions of Shaanxi were comparatively analyzed to provide a scientific basis for refined forecasting and early warning of short-term heavy rainfall. The results show that: (1) The frequency and precipitation extremes of short-term heavy rainfall in Shaanxi generally increase from north to south, with the highest values occurring in southern Shaanxi, where the maximum hourly precipitation reaches 108.7 mm. (2) The normalized frequency of short-term heavy rainfall exhibits a significant increasing trend in the Guanzhong region; short-term heavy rainfall in all regions is mainly concentrated from June to August, with a peak in late July. From April to June and in September, short-term heavy rainfall in southern Shaanxi is significantly more frequent than that in Guanzhong and northern Shaanxi. Precipitation extremes in all three regions show increasing trends, and the occurrence time of peak extremes is progressively delayed from south to north. Precipitation intensity increases in Guanzhong and southern Shaanxi, with the maximum intensity in all regions occurring in early August. The variation characteristics of the normalized frequency of extreme short-term heavy rainfall are generally consistent with those of short-term heavy rainfall. (3) The diurnal variation of the normalized frequency of short-term heavy rainfall in all regions reaches its maximum at 19:00. Northern Shaanxi exhibits a bimodal pattern, with a primary peak during 14:00-23:00 and a secondary peak during 03:00-05:00. Guanzhong shows a unimodal pattern, with a high-frequency period from 16:00 to 01:00 of the following day. Southern Shaanxi displays pronounced nocturnal rainfall characteristics, with a high-frequency period from 16:00 to 04:00 of the following day, and short-term heavy rainfall during the late night mainly occurring in the central and western parts of the region. Compared with short-term heavy rainfall, the peak period of extreme short-term heavy rainfall is delayed by approximately 1 hour in Guanzhong and advanced by approximately 1 hour in southern Shaanxi.
Shaanxi Province is located in the northeast of the Tibetan Plateau, which is dominated by complex terrain of the Qinba Mountains, river valley and the Loess Plateau. Rainstorms are frequent and intense in Shaanxi, and often lead to floods and secondary disasters. Based on data of direct disaster reports from 2008 to 2023, this paper analyzes the spatial and temporal distribution of rainstorm floods and secondary disasters. Taking the disasters in the Qinba Mountains area as an example, this paper explores the triggering mechanism of heavy precipitation on extreme floods and secondary disasters. The results are as follows: (1) The frequency of rainstorm and flood disasters and their secondary disasters in Shaanxi Province decreases from south to north. Hanzhong and Ankang in the hinterland of the Qinba mountainous area are high-risk areas for disasters, followed by Shangluo in the eastern section of the Qinling Mountains and Yan’an in the Loess Plateau. (2) The heavy rainstorms and floods in Shaanxi Province occur mainly from July to August, and there are significant inter-annual variations, and 2013 was the year with the most frequent and severe disasters in recent years. (3) Intense and persistent heavy rain is the root cause of secondary disasters such as floods and mudslides in the Qinba mountainous area. The synoptic meteorological analysis of historical disasters indicates that the combined influence of the westward developing of the subtropical high in the middle troposphere and the eastward movement of the mid-latitude trough has continuously transported water vapor and heat to the Qinba mountainous area, and coupled with the high temperature, high humidity in the lower layer and the instability of convection, leading to the continuous occurrence of heavy rainstorms. The gap terrain of the east-west transition in the Qinba Mountains displays a significant role to increase the precipitation, forming a strong “rain pocket” in the center of rainstorm.The mountainous terrain causes surface runoff to converge rapidly, which promotes landslides and mudslides in Hanzhong and Ankang, as well as strong disasters of the damage of reservoirs and bridges and other secondary disasters.
Using conventional ground-based meteorological observations, the China Meteorological Administration (CMA) best-track dataset of tropical cyclones (TCs), the National Centers for Environmental Prediction/National Centers for Atmospheric Research (NCEP/NCAR) reanalysis data, and the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model, statistical and composite analyses were conducted for tropical cyclone remote precipitation (TRP) events affecting Zhumadian during 2001-2023. The results show that TRP events in Zhumadian mainly occur from mid to late July and in August, and most of them are associated with the TC intensification or mature stages. According to the spatial distribution characteristics of TC center locations, the TRP events are classified into two types. Composite analyses indicate that the primary circulation systems influencing TRP in Zhumadian include the TC， subtropical high， and midlatitude westerly trough configuration, as well as upper- and lower-level jet streams. The background differences between the two TRP types are mainly reflected in the relative positions of the TC, subtropical high, and westerly trough, as well as in the moisture transport pathways. At 24 hours prior to TRP occurrence, both types exhibit a circulation pattern characterized by upper-level divergence and lower-level convergence, but the intensity is weaker than that at the time of TRP occurrence. Further analysis reveals that the relative positions of the key influencing systems and whether a remote TC can establish an effective moisture transport channel with the local region play a decisive role in the occurrence of TRP. Meanwhile, the vertical motion induced by the coupling of upper- and lower-level jet streams is the key dynamical factor controlling TRP intensity. Based on these results, forecasting approaches for the two types of TRP events in Zhumadian are summarized.
To investigate the formation mechanisms of heavy precipitation during landfalling typhoons, explore the application of high-resolution data in persistent heavy rainfalls, and analyze the synergistic effects of dynamic and thermodynamic factors, the observational characteristics and thermodynamic causes of the torrential rainstorm process that occurred in the Beijing-Tianjin-Hebei region from 29 July to 1 August 2023, were analyzed using ground meteorological station precipitation data, reanalysis data from the European Centre for Medium-Range Weather Forecasts, raindrop spectrum data, and dual-polarization radar data. The results are as follows: 1) The high-pressure dam formed by the subtropical high and the continental high-pressure ridge blocked the residual circulation of the Typhoon Doksuri, and the east-high-west-low circulation configuration provided a stable circulation background for the torrential rain. 2) Raindrop spectrum analysis revealed precipitation dominated by small raindrops with high number concentrations. The normalized number concentration increased with rain intensity, indicating that the torrential rainfall was primarily driven by high particle concentration, presenting typical tropical precipitation characteristics. 3) Frontogenesis, driven by shear deformation and horizontal divergence, triggered secondary frontal circulation, generating intense vertical motions that prolonged rainfall duration. 4) Latent heat release enhanced upward motion and moisture convergence through positive feedback, synergizing with frontogenesis to sustain the rainstorm. The relationship among the three indicates that the microphysical characteristics of small raindrops with high number concentration are regulated by the warm cloud collision-coalescence and breakup, and the frontogenesis effect provides the conditions for dynamic uplift, while the release of latent heat of condensation further strengthens the dynamic circulation by heating the atmosphere, thus forming a “microphysics-dynamics-thermodynamics” coupled mechanism for rainstorm intensification.
The plateau vortex is one of the important weather systems causing heavy rainfall and short-duration intense precipitation in Qinghai Province. Based on the plateau vortex dataset, precipitation observation data of meteorological stations in Qinghai, and the ERA5 reanalysis data from the European Centre for Medium-Range Weather Forecasts (ECMWF) from 1979 to 2021, this study investigates the proportion of plateau vortex days, plateau vortex precipitation, and environmental field characteristics over Qinghai by using the plateau vortex precipitation correlation method and dynamic composite analysis method. The results show that the spatial distribution of the proportion of plateau vortex days in Qinghai increases from northeast to southwest, with an annual maximum of 15.37%. The annual maximum proportion of plateau vortex precipitation to total precipitation reaches 37.92%. The annual maximum proportion of plateau vortex extreme precipitation days to the total extreme precipitation days is observed in southwestern Qinghai (63.69%). Meanwhile, the annual maximum proportion of plateau vortex extreme precipitation days to plateau vortex days occurs in the region from eastern Haixi Prefecture to southern Hainan Prefecture (10.73%). Although the number of plateau vortex days is relatively small in these areas, such systems often induce intense precipitation. The larger proportion of plateau vortex days over Qinghai is mainly concentrated in the period from April to October, and the eastward movement of plateau vortices exerts a more significant impact on precipitation. The frequency of heavy rain dynamically composited relative to the plateau vortex center shows an asymmetric distribution (wider in the zonal direction and narrower in the meridional direction). Heavy rain occurrences are predominantly concentrated in the northeastern and southeastern quadrants, with the maximum frequency occurring within a distance of 0.50-1.25 latitude degrees from the vortex center.
To gain an in-depth understanding of the circulation characteristics, formation mechanisms, and transport features of strong wind-dust weather processes, this paper employs conventional meteorological observation data and ERA5 reanalysis data from the European Centre for Medium-Range Weather Forecasts (ECMWF). Combined with simulations from the HYSPLIT (Hybrid Single Particle Lagrangian Integrated Trajectory) model, as well as observational data from aerosol lidar, and wind profiler radar observations, a comparative analysis is conducted on two severe dust events that occurred in the Hexi Corridor during the spring of 2023 (the 20 March event and the 18 April event). The results are as follows: (1) The 20 March event followed a westerly pathway, triggered by the southward movement of split cold air behind a Mongolian cyclone; the 18 April event took a northwesterly route, driven by a Mongolian cyclone and an associated cold front moving southward. (2) Both events involved long?range transport of pollutants. In the 20 March event, particulate matter transported externally played a dominant role, whereas in the 18 April event, dust particles generated locally constituted the primary dust source. (3) During the early stage of external dust input, the 18 April event exhibited faster long-range transport of dust particles, a significantly lower proportion of coarse particles, and a lower depolarization ratio compared with the 20 March event. However, during the outbreak phase, the near-surface replenishment of dust particles was more pronounced in the 18 April event.
Investigating the response routine of saltwater intrusion-drought compound risk to climate change provides a scientific basis for safeguarding regional water supply security. This study focuses on the Modaomen waterway in the Pearl River Estuary. Utilizing daily drought data from the Guangdong section of the Xijiang River Basin and salinity monitoring data from the Guangchang Pumping Station in the Modaomen Estuary, this study applies a compound risk assessment model to calculate, evaluate, and project the saltwater intrusion-drought compound risk index for Modaomen. The results show that the chloride concentration in the Modamen waterway of the Pearl Rver Estuary has a significant nonlinear negative correlation with the 8-day antecedent average drought index in the Guangdong section of the Xijiang River Basin. When the drought index is less than or equal to -0.69, the threshold condition for saltwater intrusion is met.The saltwater intrusion-drought compound events risk index in Modaomen is higher from November to March of the following year, with the peak risk occurring from mid-December to late January of the next year. Under the future medium emission scenario (SSP2-4.5), the saltwater intrusion-drought compound events risk index shows a marked increasing trend in autumn, most notably in November, followed by spring. From 1970 to 2099, the saltwater intrusion-drought compound events risk index in Modaomen of the Pearl River Estuary generally shows a fluctuating upward trend. Compared with the recent 20-year period (2001-2020), the risk index will increase by 1.9%, 8.4%, and 9.6% in the near-term (2021-2040), mid-term (2041-2060), and late-21st-century (2080-2099), respectively. The start dates of saltwater intrusion-drought compound events will advance by more than 10 days, and the end dates will delay by more than 9 days in different future periods. Under future climate change scenarios, the duration of compound saltwater intrusion and drought events in the Pearl River Estuary will lengthen, the cross-seasonal risk will show an increasing trend, and the probability of such events occurring consecutively in autumn, winter, and spring will rise significantly.
To reveal the response characteristics of different underlying surfaces to climate change in the Taklamakan Desert, this paper adopts linear trend analysis, the Mann-Kendall test, and correlation analysis to comparatively investigate the meridional variation characteristics of surface meteorological elements in this region over the past 30 years, based on the meteorological observation data from three stations located in the northern margin (Luntai), hinterland (Tazhong), and southern margin (Minfeng) of the desert during 1997-2024. The results are as follows: (1) Significant regional differences exist in the interannual variations of all meteorological elements. Temperatures in Luntai and Tazhong first decreased and then increased, while Minfeng experienced continuous warming, with Tazhong showing the fastest rate of increase. Precipitation significantly decreased in Luntai, slightly increased in Tazhong, and first increased and then decreased in Minfeng. Wind speeds significantly increased in Luntai, while Tazhong and Minfeng exhibited phased turning points. Sunshine duration significantly decreased only in Minfeng, and slightly increased at the other two stations. Relative humidity slightly increased in Luntai and Tazhong, while slightly decreasing in Minfeng. (2) Seasonal variations exhibited distinct regional patterns: Luntai showed pronounced autumn warming, significant wind speed increases in four seasons, and relative humidity increases in spring; Tazhong exhibited marked summer warming, substantial spring-summer wind speed fluctuations, and summer-autumn relative humidity increases; Minfeng demonstrated significant spring warming, pronounced sunshine duration decreases in four seasons, and autumn-winter relative humidity decreases. Precipitation at all three stations concentrated in summer, with Tazhong exhibiting the highest proportion (approximately 64%) of summer precipitation. (3) The correlations among various meteorological elements also exhibited regional differences: temperature and relative humidity showed a negative correlation at all three stations, while relative humidity and precipitation presented a positive correlation; temperature and precipitation were positively correlated at Luntai and Minfeng Stations but negatively correlated (-0.33) at Tazhong Station; temperature and wind speed showed a negative correlation at Luntai Station, a positive correlation at Tazhong Station, and nearly no correlation at Minfeng Station; temperature and sunshine duration were positively correlated at Luntai Station but negatively correlated at both Tazhong and Minfeng Stations. These differences highlight the complexity of climate change over different underlying surfaces in arid regions.
The macro- and micro-structural characteristics of rainstorm cloud clusters exhibit pronounced variations under different geographical environments and synoptic circulation conditions. The Inner Mongolia section of the Yellow River Basin is a semi-arid region characterized by complex topography and highly transient, intense rainstorms. Utilizing Precipitation Measurement Radar (PMR) data from the Fengyun-3G (FY-3G) satellite, combined with ERA5 (ECMWF Reanalysis version 5) reanalysis data provided by the European Centre for Medium-Range Weather Forecasts (ECMWF), this study conducts a comprehensive analysis of the three-dimensional structure of cloud clusters and their circulation background during the rainstorm event on August 8 2024 over the Yellow River Basin in Inner Mongolia. The results indicate that the rainstorm occurred under the combined influence of a strong subtropical high and a westerly trough, with the 700 hPa low-level jet, pronounced vertical wind shear, and strong ascending motion of warm and moist air providing favorable dynamic conditions for rainfall formation. Both stratiform and convective cloud clusters coexisted in the precipitation system. The convective clouds exhibited higher average particle number concentration, effective particle diameter, and precipitation rate compared with stratiform clouds, and the vertical distributions of particle number concentration and effective diameter corresponded well with the unstable energy field. Enhanced reflectivity zones were observed above and below the 0 ℃ layer, and the latent heat release of convective clouds at approximately 5 km altitude was about twice that of stratiform clouds, indicating that convective cloud clusters were the primary contributors to this extreme rainstorm and played a decisive role in precipitation efficiency and intensity. The cloud-top height of the precipitation system increased gradually from west to east, and the horizontal distributions of cloud-top height and 0 ℃ level height in the extreme rainfall region were closely related to topographic variations.
Typhoon Doksuri (No.2305) caused an extremely rare torrential rainfall over Putian City, Fujian Province. Based on multi-source observational data, including surface meteorological observational data of Fujian Province, radar and satellite data, as well as reanalysis data from ECMWF (European Centre for Medium-Range Weather Forecasts), the stages and intensity characteristics of the extreme rainfall induced by Typhoon Doksuri were analyzed. The main conclusions are as follows: The entire rainfall process was consisted of three seamlessly-linked stages. The first stage was the typhoon eyewall rainstorm, which had the characteristics of intense short-term rainfall and uniform spatial distribution. The second stage was the spiral rainband rainstorm, which was characterized by significant differences in hourly rainfall intensity and distinct rain peaks. The third stage was the monsoon-enhanced rainstorm, with the characteristics of a wide range of heavy rain and a long duration. The heavy rain in Putian caused by Typhoon Doksuri exhibits remarkable extremeness, with specific manifestations as follows: extremely intense heavy rainfall, a wide impact range of extremely heavy rainfall, large cumulative rainfall, high frequency of short-term heavy precipitation, and long duration. Among these, the 24-hour rainfall at Putian Station reached 561.7 mm, breaking the historical record of Fujian Province, and its extreme characteristics are particularly prominent. The continuous maintenance of typhoon warm shear line, low-level southerly jet and monsoon system is an important weather background for the three stages of rainstorm to achieve “seamless connection”. The uplift and contraction of the southerly jet caused by the terrain of Xinghua Plain “surrounded by mountains on three sides and opening to the south” is an important factor for the rainstorm center to be located in the Xinghua Plain to the northeast mountainous area.
Aiming at a significant heavy rainfall event that occurred in Inner Mongolia in July 2021, the paper conducfed a set of convection-allowing ensemble prediction (CAEP) experiments to evaluate its forecasting capability for intense precipitation processes, and compared the results with the global ensemble forecasts from the European Center for Medium-Range Weather Forecasts (ECMWF), the National Centers for Environmental Prediction Global Ensemble Forecast System (NCEP-GEFS), and the China Meteorological Administration Regional Ensemble Prediction System (CMA-REPS). The results show that the ensemble mean of global ensemble forecasts tended to underestimate the intensity of heavy precipitation centers, although ECMWF provided relatively accurate predictions of their locations. Both CMA-REPS and CAEP precipitation intensities forecasts close to observations but with some positional deviations, whereas NCEP-GEFS performed poorly in forecasting both the location and intensity of heavy rainfall. The Probability Matching Ensemble Mean (PM) effectively improved the simulated precipitation intensity compared with the traditional ensemble mean, leading to a notable increase in the threat score (TS), particularly for ECMWF and CAEP. The CAEP outperformed both global and regional ensemble forecasts in predicting the magnitude and temporal evolution of single-station precipitation. Objective verification indicated that ECMWF, CMA-REPS, and CAEP ensemble members exhibited certain forecasting capability for 25 mm·(6 h)-1 precipitation, while NCEP-GEFS performed poorly. For 60 mm·(6 h)-1 precipitation, CAEP achieved the highest TS, the lowest Brier score, and the highest AROC score among the ensemble systems, demonstrating its superior capability in forecasting heavy rainfall over the Inner Mongolia region.
The Tongchang Reservoir in southern Xinjiang is a medium-sized river-blocking reservoir in the Kuche River Basin, where heavy rainfall is the primary factor contributing to reservoir-induced floods. Studying the quantitative meteorological and hydrological indicators of the reservoir is of great significance for the flood warning and prediction of the reservoir. Based on hourly precipitation data from 19 automatic weather stations in the Kuche River Basin, the three-source integrated precipitation product (China Meteorological Administration Multi-source Merged Precipitation Analysis System, CMPAS), as well as the inflow volume and water level of the reservoir, nine flood events caused by heavy rainfalls in the reservoir were selected and classified into circulation types, and the meteorological and hydrological characteristics of two typical rain and flood events in the reservoir were analyzed. The results are as follows: (1) The circulation patterns of the rain-flood processes in the reservoir can be classified into two types: low vortex (trough)-shear line type (the type I) and low vortex (trough)-cyclone type (the type II). (2) The intensity of precipitation, the rainfall area, and the duration all determine the rate of water level rise in the reservoir. The type I process is characterized by short-term heavy precipitation and rapid water level rise, while the type II process is characterized by long-duration weak precipitation and slow water level rise. The water level rise speed during the type I process is faster than that during the type II process. (3) The increase in the inflow into the reservoir is related to the magnitude of the hourly areal rainfall. When the hourly areal rainfall is less than 0.5 mm, the variation range of the inflow into the reservoir is not significant, while the hourly areal rainfall is greater than 2.0 mm, the inflow into the reservoir increases significantly. (4) The water level rise of the reservoir has a lagging response to the meteorological conditions. For the type I process，the start time of water level rise and the occurrence time of the peak inflow of the reservoir are 3-4 hours behind the start time of precipitation, and the occurrence time of the highest water level in the reservoir is 4 to 5 hours later than the starting time of precipitation, and 1 to 2 hours later than the peak inflow flood into the reservoir. The start time of the flood rise during the type II process, the peak inflow, and the time when the highest water level occurs are all later than those during the type I process to varying degrees.
A comprehensive understanding of the spatio-temporal characteristics of extreme precipitation and exploring its key influencing factors can help better defend against the adverse effects of extreme precipitation. Based on the standardized daily precipitation data from 58 national meteorological stations in Gansu Province from 1961 to 2022, the spatio-temporal characteristics of extreme precipitation in Gansu Province were analyzed by using 12 extreme precipitation indices, and the contribution rate of large-scale climate factors to extreme precipitation was quantified using the Geodetector. The results are as follows: 1) In the past 62 years, the consecutive dry days (CDD) and consecutive wet days (CWD) in Gansu Province showed a decreasing trend, while the other indices representing intensity and frequency of extreme precipitation showed mainly insignificant increases. The frequency of extreme precipitation events had the highest increasing rate of 2.38 times·(10 a)-1. The extreme precipitation presented a significant increasing and intensifying trend, with an abrupt change detected around 2010 in the Hexi region. The extreme precipitation events in Gansu Province occurs from March to November, especially in July and August. The months with an increasing and strengthening trend of extreme precipitation are predominant, and in June the rate of increase is the maximum. 2) The stations where the extreme precipitation indices showed an increasing trend are mainly located in the most of Hexi region and Lanzhou, the central and northern parts of Baiyin, Linxia, the southeastern part of Longdong region, and the southern part of Longnan. 3) The Indian Ocean Basin-Wide Index and Nino Eastern Pacific index contribute the most to extreme precipitations in the Hexi region (29%) and the Hedong region (33%), respectively. The warming of sea surface temperature in the tropical Indian Ocean is conducive to an increase and intensification of extreme precipitation in the Hexi region, while the Eastern Pacific El Niño event is unfavorable for the occurrence and development of extreme precipitation in the Hedong region. Moreover, the contribution rate of two-factor interaction to extreme precipitation is significantly greater than that of single-factor action.
The synoptic classification of short-duration heavy rainfall (SDHR) circulation patterns is of great significance for improving forecasting and early warning capabilities, as well as enhancing meteorological disaster prevention and mitigation. Based on hourly precipitation data from May to September during 2005-2022 and ERA5 reanalysis data, this study employs the obliquely rotated T-mode principal component analysis to investigate the circulation patterns, precipitation characteristics, and environmental parameter differences associated with SDHR events in the Shaying River Basin. The results indicate that SDHR events during the warm season can be categorized into five circulation types: the pre-trough southwesterly flow pattern, the southwesterly flow pattern on the periphery of the subtropical high (STH), the northwesterly flow pattern, the low vortex shear pattern, and the typhoon low pressure pattern. Among them, the pre-trough southwesterly flow pattern occurs most frequently, while the typhoon low pressure pattern is the least. In terms of precipitation intensity, the pre-trough southwesterly flow pattern shows a relatively uniform distribution; the southwesterly flow pattern on the periphery of the STH exhibits strong local characteristics; the northwesterly flow pattern produces stronger precipitation in the southwest; the low vortex shear pattern features higher intensity in the northern and central parts; and the typhoon low pressure pattern shows maxima mainly in the western and northern high-altitude areas. Regarding precipitation probability, the low vortex shear pattern exhibits higher probabilities in mountainous areas and northern regions, whereas the other four types display opposite spatial tendencies. On the monthly scale, the pre-trough southwesterly flow pattern dominates in May, the northwesterly flow pattern prevails in June, both the pre-trough southwesterly flow pattern and low vortex shear pattern are dominant in July, the northwesterly flow pattern becomes most prominent in August, and both the southwesterly flow pattern on the periphery of the STH and pre-trough southwesterly flow pattern are predominant in September. The diurnal variations reveal that the pre-trough southwesterly flow pattern, the southwesterly flow pattern on the periphery of the STH, and the low vortex shear pattern exhibit bimodal structures with differences in peak frequency and duration; the northwesterly flow pattern shows a single afternoon peak, while the typhoon low pressure pattern has no obvious diurnal variation. Analysis of individual physical parameter indicates that the southwesterly flow pattern on the periphery of the STH and the typhoon low pressure pattern are characterized by abundant water vapor; both the southwesterly flow pattern on the periphery of the STH and the northwesterly flow pattern feature significant thermal instability, manifested as high convective available potential energy (CAPE) and a large 850-500 hPa temperature difference; the low vortex shear pattern and the typhoon low pressure pattern exhibit strong low-level convergence and upward motion; and all five circulation types are associated with weak vertical wind shear. Joint probability density analysis of environmental parameters further reveals that different SDHR types tend to develop under distinct combinations of thermodynamic and dynamic conditions, corresponding to different precipitation formation mechanisms.
Convective cloud systems, characterized by complex and variable structures, are key targets for atmospheric water resource exploitation through artificial rain enhancement in the South China. Reasonably evaluating the seeding operation process through numerical models and further studying their catalytic mechanisms is a necessary approach to establishing and improving seeding operation techniques, and it is also an effective means to assess the actual effects of artificial rain enhancement operations. In this study, based on the Weather Research and Forecasting (WRF) model coupled with a silver iodide (AgI) seeding module, a catalytic simulation was conducted for the case of the artificial rainfall enhancement experiment in Gutian, Fujian Province on May 4, 2021. The catalytic mechanism of AgI nucleation, the impact of the catalysis on the macro and micro characteristics of the cloud system, the precipitation mechanism, and the evaluation of the rainfall enhancement effect were analyzed. Numerical simulation results indicate that the dispersed AgI particles spread in a band-like patterns within the clouds. During the initial catalytic stage (09:00-11:00 UTC), the increment of ground precipitation increased slowly. Then (from 11:00 to 13:00 UTC), the precipitation increment increased significantly and showed sharp fluctuations, after 13:00 UTC, the increment of precipitation was mainly negative. Deposition nucleation was identified as the dominant AgI activation mechanism, sustaining effective catalysis for approximately 40 minutes. After AgI was dispersed, it mainly increased the number concentration of ice crystals through sublimation nucleation (by 3 to 9 particles per liter). The majority of the increased ice crystals transformed into snow crystals, and then the melting of these snow crystals increased the mass concentration of raindrops in the cloud. The impact of seeding persisted for about four hours, resulting in an absolute increase in precipitation ranging from -0.78 to 1.24 mm, the rainfall enhancement rate was approximately -8.3% to 12.1%, and the total precipitation increase was 4.64×105 tons. The rainfall enhancement effect was significant.
Lodging is a major meteorological disaster that significantly affects the yield of summer maize. Investigating the impact of lodging during the milk stage on water use efficiency (WUE) and yield is crucial for accurately assessing lodging-induced losses and guiding summer maize production. Based on crop, meteorological, disaster survey, and CO2/H2O flux data collected at the Zhengzhou Agro-meteorological Experimental Station during the 2016-2017 growing seasons, this study constructed models of net ecosystem productivity (NEP) and evapotranspiration (ET) to simulate the population-level WUE. A wind-induced lodging event that occurred in Zhengzhou on August 25, 2016 was analyzed using the model validated by 2017 observations. The results show that under normal conditions, the simulated WUE values agreed well with flux observations, with a mean absolute error of -0.08 mg C·g-1 H2O and a relative error of -5.39%. After lodging, the simulated WUE values were markedly lower than those under non-lodging conditions, with a daily average decrease of 0.31 mg C·g-1 H2O, corresponding to a reduction of 20.37%. At the yield level, WUE decreased by 3.87%. Both NEP and ET declined following lodging, with a larger reduction in NEP than in ET, leading to a decrease in WUE. Lodging also reduced the hundred-grain weight by 2.8% and the grain weight per plant by 10.8%, resulting in an overall yield reduction of approximately 5.0%.
Under climate warming, asymmetric day-night temperature increases and atmospheric CO2 concentration rising are two key features altering the distribution of water and heat resources, driving changes in the planting structure and boundaries of the three major grain crops (wheat, corn, and rice). Studying their responses to global warming is vital for food security. Using high-density meteorological station data, the paper analyzes thermal resource changes before and after 1990 during a 30-year period and their possible impacts on the potential planting areas of China’s three major grain crops using statistical method. In addition, the results from multi-site “Free-air temperature increase (FATI) under field conditions” and “Open-top chamber (OTC) experiments with controlled temperature and CO2” are summarized, and combined with the literature meta-analysis method to explore the effects of climate warming on the growth periods and yields of the three major crops. Results are as follows: 1) Agricultural thermal resources in China are generally increasing, with the duration of the farming period and accumulated temperature significantly rising, and the frost-free period extending. The number of extreme hot days has generally increased, and in some regions (such as Shaanxi, Gansu and Ningxia), the number of extreme cold days during the farming period has also increased, intensifying the risk of extreme meteorological disasters. 2) The northern boundaries of the three major crop-growing areas have shifted northward to varying degrees, resulting in an increase in the potential suitable planting area. 3) In the early stage of climate warming, it is beneficial for winter wheat to grow. However, excessive warming will lead to earlier development, increased frost risk, shorter growth period and reduced yield for spring wheat. Although an increase in CO2has a yield-enhancing effect, it is difficult to offset the adverse impacts induced by high temperatures. 4) Climate warming shortens the growth period of corn, reduces the number of grains per ear and the weight of 1 000 grains, thereby inhibiting the formation of yield. Nighttime warming further exacerbates the decline in yield. The effect of increasing CO2 concentration on corn growth and yield is limited, with warming being the dominant factor. 5) Warming alone has an inhibitory effect on the yield of early rice but a promoting effect on that of late rice. Warming for early rice reduces the yield-increasing effect of CO2, while for late rice it shows a synergistic promotion and increasing the yield.
This paper took winter wheat in the Huang-Huai-Hai region as the research object, where agricultural droughts occur frequently with warming climate and increasing evaporation, and defined the water shortage index (k) to classify drought year types based on the data from 1981 to 2020. Taking three stations in Henan Province as examples, this paper used the World Food Studies (WOFOST) model to analyze the cost-benefit of drought resistance under different drought year types, in order to provide a reference for improving agricultural output value and agricultural insurance business. The results show that during the study period, the three stations were easy to experience water stress with varying degrees during the growth period of winter wheat, and the drought that occurred in the middle to late stages of the growing season (from early April to harvest) had the greatest impact on yield formation. In order to ensure the safety of national food, agricultural irrigation in the study areas is the main way to keep high yields of winter wheat. According to the cost-benefit analysis, the northern region of Henan Province needs to irrigate 5 times in severe drought years, and irrigate 4 times in general drought years to achieve the maximum benefit. The water conditions in eastern Henan are relatively better than others, with a low probability of severe drought and 3 times irrigation should be needed in general drought years.
To reveal the influence mechanisms of weather patterns and meteorological factors on air pollution in arid and semi-arid regions, this study utilized the fifth-generation atmospheric reanalysis dataset (ERA5) provided by the European Centre for Medium-Range Weather Forecasts (ECMWF) from 2016 to 2022. The Self-Organizing Map (SOM) neural network was employed to classify weather patterns based on the 700 hPa geopotential height field and wind field, combined with quadratic curve fitting to analyze the nonlinear relationships between meteorological factors and pollutants in typical cities across different climatic zones of Gansu Province. The results indicate that: 1) PM10 and PM2.5 mass concentrations generally exhibit a negative correlation with temperature, while for O3 its mass concentration increases nonlinearly with rising temperature. Under low wind speeds (<1 m·s-1) and high wind speeds (>4 m·s-1), PM10 and PM2.5 mass concentrations are elevated, which attributed to local accumulation under calm conditions and dust transport under strong winds, respectively. In contrast, wind speeds between 1 and 4 m·s-1 favor precursor accumulation, leading to higher mass concentration of O3. Pollutant concentrations are generally higher under relative humidity between 25% and 75%, though regional differences exist. For instance, in Jiuquan, the PM10 concentration is higher at humidity below 25% due to frequent dust events, the PM2.5 concentration increases with the rise of relative humidity due to the hygroscopic growth effect, while O3 concentration decreases with declining humidity owing to reduced consumption under dry conditions. 2) In winter and spring, the dominant weather patterns are the southwestern high-pressure type and the eastern trough type. Under the southwestern high-pressure pattern, strong northwesterly winds in western regions create pollutant transport pathways, whereas the eastern trough pattern results in poor diffusion conditions and stable atmospheric conditions in Gansu, facilitating pollutant accumulation and significantly increasing of PM10 and PM2.5 concentrations. 3) In summer and autumn, high-pressure systems dominate, with abundant solar radiation and high temperatures elevating the boundary layer height. Coupled with warm, moist air transport, these conditions provide a favorable environment for photochemical reactions, leading to higher O3 concentrations.
Based on the hourly precipitation analysis data of the China Meteorological Administration multi-source merged precipitation analysis system (CMPAS) and the hourly precipitation data predicted by the China Meteorological Administration mesoscale weather forecast system (CMA-MESO)， the distribution characteristics of precipitation in the Beijing-Tianjin-Hebei region under special topographic conditions from June to September 2021 were analyzed, and the prediction performance of CMA-MESO was discussed. The results are as follows: (1) The observational maximum centers of mean hourly precipitation in the Beijing-Tianjin-Hebei region were primarily located in 100-600 m altitude on the windward slopes of the eastern Taihang Mountains and the southern foothills of the Yanshan Mountains, while the maximum centers predicted by the CMA-MESO were located on the side of the windward slope leaning towards the plain in front of the mountains. The observational hourly precipitation frequency and intensity were similar to precipitation amount, but the maximum center of hourly precipitation frequency was located on the windward slopes of the Taihang Mountains, leaning towards the mountainous side, while the maximum center of precipitation intensity was mainly distributed on the windward slopes in front of the mountains and the plain areas of the eastern Beijing-Tianjin-Hebei region. (2) The observational regional average hourly precipitation amount on the windward slopes in front of mountains of the Beijing-Tianjin-Hebei region exhibited a bimodal diurnal pattern, with the primary peak occurring from afternoon to evening and the secondary peak in the early morning. The primary peak predicted by the CMA-MESO was colse to observations, but the regional average hourly precipitation amount was significantly overestimated. (3) On the windward slopes in front of the mountains, the peak period of precipitation above 10 mm·h-1 occurred from the afternoon to the early morning and the early hours of the next day. The CMA-MESO forecast indicated that the precipitation above 10 mm·h-1 in the afternoon to evening period was slightly higher, while the precipitation in the early hours of the next day was slightly lower. (4) Precipitation events on the windward slopes from afternoon to early nighttime were mainly short-term precipitation events within 3 hours. The CMA-MESO taked the characteristic, but the amount of short-term precipitation events predicted by it was relatively high. (5) The CMA-MESO successfully forecasted the topographic enhancement of precipitation on the windward side of the mountains. However, the specific humidity below 850 hPa was underestimated, and the convective available potential energy value at 14:00 (Beijing Time) was significantly underestimated. These biases contributed to the existence of a negative precipitation bias center over the windward slopes.
Low-temperature spring flooding over Northeast China refers to a meteorological phenomenon characterized by persistently low temperatures and excessive precipitation in spring, primarily from March to April, which severely hinders spring agricultural operations, particularly plowing and sowing. In this paper, based on monthly temperature and precipitation data of 104 national meteorological stations in Northeast China during 1961-2020, and the monthly reanalysis data of the National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR), combined with the sea surface temperature and the atmospheric circulation indices with significant correlation, a case study is carried out. The low-temperature spring flooding events and their judgment indexes are defined, and the multi-factor synergy of temperature, precipitation and other factors at the cross-seasonal scale, as well as the influence mechanism of atmospheric circulation and sea surface temperature anomalies in the same period and in the early stage are preliminarily revealed. The results show that persistent cold and rainy conditions in spring are key contributors to the occurrence of such events, and the abnormal increase of accumulated precipitation in autumn in the previous year is the key factor resulting in severe low temperature and spring flood events. In addition, the negative phase of the Arctic Oscillation (AO) in the preceding winter, the stronger-than-normal Siberian High in spring, and the active Northeast China cold vortex and cold waves are important dynamical conditions. Furthermore, abnormal warming of sea surface temperatures, especially associated with El Niño events in the previous autumn and winter, is in favor of the occurrence of low-temperature spring flooding. These events are often followed by alternating drought and flood conditions in Northeast China, typically manifesting as a “drought-flood-drought” pattern during late spring to early summer, midsummer, and winter, respectively.
The variation trend and potential causes of short-term heavy rainfall (STHR) in Jiangxi Province were studied to enhance the forecasting and early-warning capabilities about extreme precipitation events, particularly for STHR. Baud on hourly precipitation data from 84 national meteorological stations in Jiangxi Province during 1979-2019 and ERA5 atmospheric reanalysis data from the European Centre for Medium-Range Weather Forecasts (ECMWF), anomaly normalization, linear tendency estimation, the Mann-Kendall test, and correlation analysis were employed to investigate the variation trend of STHR in Jiangxi Province and its potential influencing factors. The results are as follows: (1) STHR in Jiangxi Province exhibits distinct seasonal characteristics. From April to September, the frequency and proportion of such events account for 95.7% and 92.4% of the annual totals, respectively. (2) According to the hourly rainfall（R）, STHR was classified into three levels: 20≤R<30 mm, 30≤R<50 mm, and R≥50 mm, referred to as levels I, Ⅱ, and Ⅲ, respectively. The spatial distribution of levels I and Ⅱ shows higher frequencies in the eastern regions than in the western regions, with great activity observed over mountainous terrain than over plains and basins. By contrast, level III STHR exhibits no distinct spatial pattern. On the whole, the annual frequency and annual proportion of STHR across all levels show an increasing trend, with a significant shift observed at the onset of the 21st century. (3) The anomaly of high precipitable water vapor and the anomaly of low-level atmospheric pseudo-equivalent potential temperature were significantly positively correlated with the annual mean frequency anomaly and annual proportion anomaly of STHR in Jiangxi Province. Moreover, the correlation coefficient gradually decreases as the intensity level of STHR increases. Composite analysis of strong and weak STHR years indicate that when the Western Pacific Subtropical High and the Ural High are abnormally strong, accompanied by an anomalously strong low-level southwesterly flow, the frequency of STHR events in Jiangxi Province increases; conversely, the opposite circulation configuration leads to fewer STHR occurrences.
Extreme snowstorms with freezing rain are rare in Inner Mongolia, and studying such weather is of great significance for forecasting and disaster prevention. Based on the conventional meteorological observation data, ERA5 reanalysis data of the European Centre for Medium-Range Weather Forecasts and Doppler radar data of Tongliao, Inner Mongolia, the environmental conditions and causes of an extreme snowstorm with freezing rain in the southeast of Inner Mongolia on November 5-6 in 2023 were analyzed. The main conclusions are as follows: The 500 hPa upper-air cold vortex, the 700 hPa warm shear line, the 850 hPa easterly jet stream and the northward-moving surface Jianghuai cyclone were the main influencing systems of this process. When the freezing rain occurred, the vertical direction showed a “cold-warm-cold” stratification structure. There was a melting layer at 925-875 hPa, and a bright band of the 0 ℃ layer was observed on the radar base reflectivity imagery. The supercooled water particles and ice crystals entered the melting layer through the 0 ℃ layer bright band, and then fell to the ground, which conformed to the characteristics of melting freezing rain. The mid-level southwest jet climbed over the lower-level easterly cold cushion, generating strong dynamic frontogenesis, which provided robust dynamic lifting conditions for the extreme snowstorm. The existence and long-term maintenance of strong upward motion were important conditions for the extreme snowstorm. The maximum specific humidity in the lower layer over the blizzard area reached 4-6 g·kg-1, and long-lasting strong water vapor convergence in the lower layer provided sufficient moisture for the extreme snowfall. In summary, the extreme snowstorm with freezing rain in the southeast of Inner Mongolia was the result of the interaction between the upper and low level systems, the vertical uplifting mechanism triggered by dynamic frontogenesis, and the continuous water vapor transport.
To improve the accuracy of summer regional rainstorm forecast and the precision of affected area prediction in Zhejiang Province, this study utilizes precipitation observations from 75 national meteorological stations in Zhejiang Province, the fifth-generation ERA5 reanalysis data (0.25°×0.25°) from the European Centre for Medium-Range Weather Forecasts from 2010 to 2023, and the ObjectiveConsensus Forecast (OCF) model precipitation products (0.05°×0.05°) from 2020 to 2023, to analyze 187 summer regional rainstorm events in Zhejiang, conduct synoptic classification, adjust OCF model products for different precipitation types, and verify the correction effects. The results indicate that: 1) The frequency matching method significantly improves precipitation forecasts through categorical adjustment, with downward corrections for precipitation of 30 mm or below and upward compensations for precipitation more than 30 mm. The threat score (TS) for rainstorms and above increased by 4.2%, and the hit rate improved by 14.3%. 2) Based on synoptic classification, rainstorms are categorized into six types, including stationary front rainband, warm shear, subtropical high, typhoon, typhoon inverted trough and cold trough. The correction performance of frequency matching varies significantly among different rainstorm types. Specifically, for warm shear, typhoon inverted trough, and cold trough types rainstorms, the TS increased by 11.8%, 39.1% and 15.4% (with the OCF model completely missing these events), respectively, while the hit rate for typhoon inverted trough type rainstorm improved to 60.0%, and the missing rates for warm shear and cold trough type rainstorms decreased by 20.0% and 26.0%, respectively. 3) The classification correction strategy effectively enhanced the TS and hit rate of various types of rainstorm forecasts, and significantly improved the prediction accuracy of rainstorm areas.
High spatiotemporal resolution wind profile radar data are of significant value in the nowcasting and early warning of short-duration heavy precipitation. Based on conventional meteorological observations, regional automatic station data, reanalysis data from the National Centers for Environmental Prediction (NCEP), and wind profile radar network observations, this study analyzes the first large-scale heavy rainstorm event in Shandong Province following the onset of the 2023 flood season. The results indicate that, this event was jointly influenced by an upper-level trough, a low vortex, a low-level jet (LLJ), and a mesoscale shear line. Convection on June 27 occurred in the warm sector, while short-duration heavy rainfall on June 28 was primarily induced by the low vortex. The heavy precipitation mainly occurred on the right side of the mesoscale shear line, within regions of positive vorticity advection and above convergence centers. The vertical configuration of low-level convergence and upper-level divergence provided favorable dynamic conditions for strong convection. Variations in the near-surface wind field below 1 km were indicative of heavy rainfall. The downward extension of the LLJ and enhanced horizontal wind perturbations were positively correlated with precipitation intensity. Within 1 hour prior to the onset of heavy rainfall, both the LLJ index and vertical wind shear increased significantly. Before the cessation of rainfall, vertical wind shear weakened rapidly, and strong low-level shear appeared near the surface. Wind profile radar showed clear advantages in identifying precursor signatures for nowcasting short-duration heavy rainfall events.
To enhance the effectiveness of thunderstorm gale warning signals and achieve a scientific balance between accuracy and lead time, this study systematically evaluates the warning signals based on observation data from 245 automatic weather stations in Shanghai from 2016 to 2023 and warning signals issued by nine district meteorological stations, using the percentile method and synoptic classification. Results show that thunderstorm gales mainly occur from April to August, with the highest frequency in July; their diurnal variation is characterized by frequent occurrence from afternoon to nighttime; extremely strong gales are prone to appear in coastal and riverside areas; and the issuance of warning signals generally precedes the peak occurrence of gales by about 1 hour. The overall effectiveness score is 14.1 points (out of 100), and the average score for extremely strong thunderstorm gales is 28.2 points, with the warm shear type scoring the highest (49.2 points) and the stationary front shear type the lowest (12.1 points). During subtropical high-edge and stationary front shear processes, the western Pacific subtropical high tends to be stronger and displaced westward. Case studies indicate that extremely strong thunderstorm gales associated with the upper-level cold vortex under the influence of the northeast cold vortex achieve relatively higher scores. However, similar to other processes, when the wind force reaches beaufort scale force 12 or above, warnings are often issued later than the actual occurrence. Subtropical high-edge gales have a relatively wide impact range, and warnings are generally issued in a timely manner across districts, resulting in overall higher effectiveness scores.
It is of great significance to study the formation mechanisms of extreme rain-to-snow weathers under the background of explosive cyclones for improving winter precipitation forecasting and snow disaster prevention. Based on conventional meteorological observation data and ERA5 reanalysis data, this paper compares and analyzes the causes and characteristics of two extreme rain-to-snowstorm processes in Liaoning Province from November 6 to 9, 2021 (Process I), and from November 5 to 7, 2023 (Process II), from the perspectives of influencing systems, water vapor conditions, dynamic mechanisms, and thermal effects. The results show that the combined influence of an upper-level cold vortex and a surface explosive cyclone is the key factor in the formation and development of both events. The coupling of upper and lower level jet streams provides strong dynamic support for extreme precipitation, with heavy rain and snow mainly occurring on the northern side of the surface cyclone. Conditional symmetric instability is identified as the primary dynamic mechanism. Well-developed frontal zones in the lower troposphere, together with the alignment of water vapor convergence zones and fronts, are conducive to the occurrence of heavy precipitation. The phase differences among low-level uplift motion, frontal zones, and water vapor convergence zones are the main reasons for the differences in precipitation center intensity between the two events. The combined effects of dynamic and moisture conditions, along with thermal structures, determine the phase of precipitation. Specifically, the intensity of low-level cold fronts and the timing of cold air intrusion significantly influence the phase transition of precipitation and the spatial distribution of rain and snow.
The heavy precipitation occurred in the northeastern region of Liaodong Peninsula from 20:00 on 3 to 14:00 on 5 August 2017, with the daily rainfall breaking historical records. Based on observations from automatic weather stations, radiosonde and Doppler weather radars, FY-2G temperature of brightness blackbody product, and European Centre for Medium-Range Weather Forecasts ERA5 reanalysis data, diagnostic analyses are made on the torrential rain processes in Liaodong Peninsula during 3-5 August 2017. The synoptic background, mesoscale environment and triggering mechanism of the mesoscale convective systems (MCSs) are focused. The results show there were two stages of this extreme rainstorm and it was influenced by upper trough, low-level shear line, the warm and moist flows in the border of the subtropical high near Japan, the intrusion of north cold-dry current, and the surface convergence line. The differences in short-term heavy precipitation between the two stages are significant, which is closely related to the low-level moisture, vertical shear of the environmental wind, and the intensity of frontogenesis. When there is abundant low-level moisture, large vertical shear of the horizontal wind, and strong frontogenesis, there is more precipitation. Frontogenesis process in the lower layer and the coupling dynamic structure of positive vorticity center and the divergence center over Liaodong Peninsula, further uplift the air, thus enable those initial convective cells to move northeastward alongside the shear line, to merge and develop, promoting higher organization and more stronger of the convection system. As shown on the surface wind field in Liaodong Peninsula, there were two north-south convergence lines and at their meeting location, convective cells merged and intensified, which was the main cause of extreme short-term heavy precipitation (hourly precipitation ≥50 mm). The surface convergence line was formed by the cold-dry current from the northeastern of Liaodong Peninsula spreading southwestward and the southerly airflow on its eastern side. In addition, the terrain blocking effect and the cold pool effect caused by heavy precipitation promoted the southward extension of the northeasterly or northerly air flow, and the backward propagation of convective cells, which was conducive to the maintenance and intensification of heavy precipitation.
The comparative analysis of local physical processes of rainfall with different intensities under similar circulation background is an effective way to improve the accurate forecasting ability of heavy precipitation events in the region. Based on multi-source data, this paper analyzed the thresholds of physical quantities of sudden increase of rainfall intensity during three heavy rainfall processes under the background of cold vortex in Tianjin on June 28 (hereinafter abbreviated as the “6·28” process), July 1 (hereinafter abbreviated as the “7·1” process) and July 26 (hereinafter abbreviated as the “7·26” process) in 2022. The results show that during the "6·28" process, the synergistic effects of extremely strong water vapor convergence (-8.0×10-7 g·hPa-1·cm-2·s-1), low lifting condensation level (962 hPa), and deep warm cloud layer (4.0 km), combined with the mesoscale vortices triggered by cold pool outflow and low-level convergence, as well as low-quality storms and the training effects, collectively resulted in a maximum rainfall intensity increase of 96.6 mm·h-1.During the “7·26” process, the higher ambient temperatures (32.1 ℃) and convective effective potential energy (CAPE) (2 464 J·kg-1) promoted the vertical development of high quality storms. However, the increasing proportion of ice phase particles limited the increase in rainfall intensity (88.8 mm·h-1). During the “7·1” process, the weak vertical wind shear (1.3 m·s-1) and insufficient cold pool strength (21.9 ℃) were impossible to trigger new convection, with the lowest increase in rainfall intensity (55.3 mm·h-1). There are common thresholds of physical quantities before the sudden increase in rainfall intensity in the three processes: the CAPE greater than 1 200 J·kg-1, the warm cloud layer thickness greater than 3.1 km, total atmospheric precipitable water greater than 47.5 mm, and the occurrence time of the surface convergence line being 1.5-2.0 h ahead of the occurrence time of heavy precipitation. The correlation coefficient between ET, CR, VIL and rainfall intensity increment exceeded 0.90, while the correlation coefficient between dew point change in the first hour and rainfall intensity increment was -0.90 during the extreme heavy rainfalls.
In order to strengthen the application of densified automatic station data in rainstorm forecast in the eastern Helan Mountain foothills, based on hourly surface meteorological observations and ERA5 reanalysis data, 17 rainstorm events in this area from 2016 to 2021 were classified into cold-warm air convergence type, warm-sector type, and weak cold air intrusion type, according to the intensity of cold air. The precipitation distribution, circulation characteristics, and the evolution of surface meteorological elements were then comparatively analyzed. The results show that cold-warm air convergence rainstorms are characterized by a deep upper-level trough and an extensive low-level high-humidity zone, but with relatively weak southerly winds and water vapor flux. These storms exhibit a wide precipitation area and high average rainfall, but the precipitation efficiency is lower than that of warm-sector rainstorms. Warm-sector rainstorms have the strongest low-level southerly winds and moisture flux, but the upper-level divergence is the weakest and the high-humidity zone is fragmented. These storms are marked by high precipitation efficiency, strong locality, and extreme intensity. In weak cold air intrusion rainstorms, the low-level warm and moist conditions are better than in the cold-warm air convergence type, and the precipitation and convective intensity which triggered by upper-level cold air are stronger than those of the cold-warm air convergence type. One hour before the onset of precipitation, all three types of rainstorms exhibit temperature drop, pressure rise, and increased wind speed, with temperature changes being the most significant, while dew point temperature varies between cases. In the five hours prior to precipitation, temperature decreased and relative humidity increased, with the most pronounced changes occurring one hour before rainfall onset. After precipitation began, these variables tended to stabilize. However, the timing and magnitude of temperature drops and the rate of relative humidity increase differed among the storm types. Dew point temperature first increased and then decreased, peaking from 1 hour before to 2 hours after rainfall onset. Wind speed variations also differed across storm types. The indicators developed in this study performed best for warm-sector type rainstorms, achieving a TS (threat score) of 48.65%, followed by the cold-warm air convergence type, with the weakest performance in the weak cold air intrusion type. The prediction accuracy of humidity, pressure, and dew point temperature indicators was relatively high (mostly exceeding 50.00%, some over 55.00%), indicating potential for enhancing rainstorm monitoring and early warning. In contrast, indicators based on temperature change (less than 50.00%) and wind speed variation (around 30.00%) showed weaker predictive capability, indicating the need for further optimization.
Study of the influence of urbanization on the climate environment can provide a basis for urban adaptation to climate change. Based on the data of meteorological stations in urban and suburban areas of Xi’an from 1961 to 2022, the impacts of urbanization in different stages on local climate were analyzed by comparison between urban and suburban areas, linear tendency estimation and Mann-Kendall (M-K) test. The results show that the urban heat island (UHI) effect in Xi’an has been significantly enhanced since the 1990s, and it was stronger in winter and spring. The UHI exhibits distinct diurnal and seasonal variations. The relatively stable high-value and low-value periods occur from 21:00 on the same day to 06:00 the next day, and from 11:00 to 16:00, respectively. The maximum value in winter appears 2-3 hours earlier than that in summer, while it ends 2-3 hours later than in summer. The contribution rate of urbanization development to the minimum temperature (Tmin) was greater than that to the maximum temperature (Tmax). The contribution rate of urbanization development to Tmax, Tmin and diurnal temperature range (DTR) was the largest in spring, while that to average temperature (Tave) was the largest in summer. The urban rain island (URI) effect primarily occurs during winter and spring. During the rapid urbanization period (1991-2022), the URI effect intensified, characterized by increased frequency and intensity of moderate-to-heavy precipitation in urban areas, alongside a reduction in light precipitation. The urban turbidity island (UTI) and urban dry island (UDI) effects were more pronounced in both winter and spring. For the entire year, the absolute difference in sunshine duration (SD) between urban and suburban areas during the rapid urbanization period was 0.73 h, and the absolute difference in relative humidity (RH) was 4.38%. The contribution rate of urbanization development to SD and RH was the largest in spring and summer, respectively.
To explore the spatiotemporal evolution of climate comfort in Guizhou Province and support regional tourism development planning, this study utilized daily meteorological data from 77 national stations spanning from 1974 to 2023. Two evaluation models, the comprehensive comfort index (CCI) and the outdoor weather comfort index (OWCI), were employed in combination with the least squares method, Pearson correlation analysis, and Mann-Kendall (M-K) mutation test. The results indicate that both indices effectively capture the spatiotemporal characteristics of climate comfort across Guizhou. The CCI is more effective at reflecting long-term climate variability and incorporates clothing adjustment capacity, making it more suitable for annual-scale assessments. In contrast, the OWCI responds more responsive to environmental meteorological conditions change and performs better at the monthly scale. Climate comfort days showed a significant increase in March and November, and a significant decrease from June to September. The proportion of stations with a significant increasing trend in climate comfort days is highest in March, while the proportion of stations with a significant decreasing trend is highest in July and August. Overall, climate comfort is favorable in southern low-altitude areas from January to March and November to December, in western high-altitude regions from May to September, and across most of the province in April and October.
It is of great significance to scientifically assess the risk of drought disaster during the key growth period of apples to reduce the loss of apples due to drought. Based on multi-source data such as meteorological data, apple planting data, elevation, river density, and vegetation coverage data in Hebei Province, this paper systematically evaluated the characteristics of drought disaster risk during key growth period of apples in Hebei Province by analyzing the risk factors of drought disasters, the sensitivity of disaster prone environments, and the exposure of disaster bearing bodies. The results show that the total probability of drought occurrence during the sprouting and young fruit stage of apples in Hebei Province was the highest, generally above 60%, and was mainly severe drought and extreme drought. The risk of disaster causing factors was ranked from high to low as follows: germination and young fruit stage, coloring and maturity stage, fruit swelling stage, and the northwest region was a high-risk area in all stages. The sensitivity of pregnancy disaster environment showed a spatial distribution characteristic of increasing from southeast to northwest. The exposure of disaster bearing bodies was relatively high in some areas in the east and south. The regions with drought disaster risk indices greater than 0.800 during the germination young and fruit stage, fruit swelling stage, and coloring and maturity stage account for 20.8%, 8.7%, and 8.5%, respectively, and the northwest region was a high-value area of risk indices in all growth stages. The high-value, median, and low value areas of the drought disaster risk in the whole growth period of apple accounted for 14.2%, 27.2%, and 58.6% of the total area, respectively, and shows a gradually increasing trend from southeast to northwest. Therefore, it is necessary to focus on the prevention of drought disasters in high-risk areas in the northwest of Hebei Province, and provide a scientific basis for drought resistance and disaster reduction in the apple industry.
The study of the adaptability of meteorological drought indices in alpine grassland is of great significance to improve the accuracy of drought monitoring of natural vegetation on the Qinghai-Xizang Plateau, protect alpine grassland ecosystems, and promote the sustainable socio-economic development of pastoral areas. In this study, the drought monitoring accuracy of indices such as Precipitation Anomaly in Percentage (PA), Standardized Precipitation Index (SPI), Meteorological Drought Composite Index (MCI) and Palmer’s Drought Severity Index (PDSI) in the alpine grassland at the eastern edge of the Qinghai-Xizang Plateau was evaluated by using the day-by-day measured soil moisture data from 2010 to 2022, and combining with the Pearson’s correlation coefficient and the method of drought identification. The PDSI index with higher drought identification accuracy was selected for local calibration, and based on the PDSIimproved obtained from the calibration, the monthly drought conditions of the study area in 2022 were analyzed. The results show that: 1) The drought identification accuracies of the four meteorological drought indices (PA, SPI, MCI and PDSI) in the study area were 48.21%, 38.79%, 37.42% and 59.16%, respectively. Among them, the PDSI responded better to the drought condition of the alpine grassland in the study area, but in the case when the relative soil humidity was less than or equal to 60% and the number of drought days was not consecutive, it was prone to omission or over-measurement. 2) By establishing the correspondence between the relative soil humidity and the PDSI value, and performing the localized calibration of the PDSI and the threshold adjustment of drought level, the improved PDSI can improve the drought identification accuracy by 12.15%, reaching 71.31%. 3) The PDSIimproved was used to monitor the drought situation in the study area in 2022. The results show that the drought mainly occurred in the low-lying areas in the southeast of the study area at an altitude of 3 300-3 700 m, and the drought had obvious seasonal characteristics, which was mainly concentrated in winter and mainly characterized by severe drought and extreme drought.
To reveal the spatio-temporal differences and atmospheric circulation causes of summer meteorological drought in the Sichuan-Chongqing region, based on daily observational data and meteorological drought composite index (MCI) of 188 meteorological stations in Sichuan and Chongqing during 1981-2023, the spatio-temporal evolution characteristics of summer drought in Sichuan and Chongqing are analyzed. In addition, monthly reanalysis data from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) and climate system monitoring indices are employed to investigate the drought formation mechanisms from the perspectives of circulation patterns, water vapor transport, westerly jet streams, and vertical motion. The results show that droughts in the Sichuan-Chongqing region exhibit strong synchronicity and significant regional differences. Drought in Sichuan mainly concentrates in June and August, while that in Chongqing is more severe from July to August. The drought centers are primarily located in the Sichuan Basin, with a certain degree of synchrony between eastern Sichuan and Chongqing, whereas the drought in the western Sichuan Plateau is relatively weak. During typical drought years, the South Asian High moves northward and strengthens, the Western Pacific Subtropical High is abnormally located further north, water vapor transport at 700 hPa is weakened, and the region is controlled by subsidence motion, resulting in significantly less precipitation. Distinct atmospheric circulation anomalies in different types of drought years are the main cause of the spatial variability of drought in the region.
