Studying the evolution characteristics of a gust front and the physical mechanisms of extreme winds behind it using multiple types of radar products is of great reference significance for improving the forecasting and early warning capabilities of catastrophic gale weather. Using conventional upper-air and surface observational data, ERA5 reanalysis data of the European Center for Medium-Range Weather Forecasts, S-band dual-polarization radar data and X-band phased-array radar data, the characteristics of radar products of a gust front and the extreme wind process behind the gust front in Shaoxing of Zhejiang Province on July 10, 2023 were analyzed. The results show that this process occurred under the background of southwest airflow at both high and low altitudes. The upper air was at the edge of the subtropical high, and at 925 hPa, it was in the convergence area of southwest wind speeds. The atmospheric thermal instability and uplift conditions were better. After multiple convective cells merged into a multi-cell storm, the gust front was formed at the outflow boundary of it. The gust front underwent three stages: development, rupture, and weakening. At the weakening stage, a new mesoscale convective zone was triggered behind it, and the backward propagation characteristics were obvious. The maximum wind speed induced by the gust front occurred during its weakening stage, while the extreme wind of the process occurred during the eastward movement and northward lifting of the mesoscale convective band triggered by the gust front. The internal vortex structure of the convective cells which generated the extreme winds only existed at an altitude of 800 m, and the convergence of wind direction and speed was mainly at the middle and upper levels. The gusts of 6-7 levels were generated when the vortex circulation weakened and disappeared, and the core of the reflectivity factor decreased, and the lower levels of the storm turned into downdraft. The extreme wind was generated later when the inflow behind the storm turned back into updraft and converged with the downdraft at middle levels. It was also accompanied by radial convergence in the middle layer horizontally, which indicated an increase in sinking airflow. Due to the relatively small contribution of downward momentum transfer, the extreme wind was mainly caused by strong sinking airflow.

Based on the precipitation data from Shaanxi Province from 2016 to 2021 and real-time products of two-source and three-source precipitation from the CMA Multi-source Precipitation Analysis System (CMPAS-V2.1) during 2018-2021, the spatial and temporal characteristics of short-term heavy rainfall in Shaanxi Province over the past 6 years were analyzed. Furthermore, statistical tests were applied to evaluate the accuracy of the multi-source precipitation products, with the aim of providing reference for correction of multi-source precipitation products in short-term heavy rainfall processes. The results are as follows:(1) In Shaanxi Province, the short-term heavy rainfall frequency peak was at 19:00 pm, with heavy precipitation primarily occurring from 16:00 to 02:00 in a day and predominantly in the months of June to August. The diurnal extreme value of heavy rainfall shows relatively higher from 17:00 to 01:00 and from 04:00 to 07:00 in the morning. Short-term heavy rainfall is more frequent in southern Shaanxi compared to Guanzhong and northern Shaanxi. The regions with relatively larger extreme values include northern Shaanxi, eastern Guanzhong, and central-eastern of southern Shaanxi. (2) Both two types of precipitation products tend to underestimate precipitation compared to observed values. The mean absolute errors of the three-source product exhibit smaller in southern of northern Shaanxi, most part of Guanzhong and southern of southern Shaanxi, while the two-source product performs relatively better in other region.The mean absolute error increases with precipitation increase. For heavy precipitation ranging from 20 to 50 mm, three-source product is recommended, while two-source product is more suitable for heavy precipitation above 50 mm. (3) The diurnal variations in mean absolute errors for both two types of multi-source products are relatively larger from 13:00 to 19:00, 23:00 to 01:00 and from 04:00 to 06:00, and relatively smaller from 08:00 to 12:00, 20:00 to 22:00 and from 02:00 to 03:00. The three-source product outperforms two-source product from May to August, while two-source product performs better from September to October. (4) The accuracy rate of multi-source precipitation products increases as the threshold of short-term heavy rainfall decrease. Both mean absolute error and accuracy rate indicate that the three-source product outperforms two-source product. Multi-source precipitation products exhibit higher accuracy from September to October compared to May to August.

Xin’an River Basin is a typical water-abundant area. Characteristics exploration of the drought events and study on the response of hydrological drought to meteorological drought in Xin’an River Basin largely benefits the scientific reference for basin water management. This study calculated the Standardized Precipitation Index (SPI) and Standardized Runoff Index (SRI) with the monthly data of inflow runoff and precipitation from 1960 to 2022 in Xin’an River Basin. Based on SPI and SRI, the evolution of meteorological and hydrological droughts under different time scales and the seasonal response of hydrological drought to meteorological drought were analyzed. The results are as follows: (1) From 1960 to 2022, meteorological and hydrological droughts in the Xin’an River Basin mainly occurred in the 1960s, late 1970s to mid-1980s and early 2000s. Meteorological and hydrological droughts have rarely occurred since the 21st century; dry and wet alternated frequently over the remaining periods of time. (2) Mann-Kendall trend test results show a wetting trend during the past 63 years, and the effects of drought have mitigated. While in winter and summer, it showed drought decreasing trend in the basin. The hydrological trend of becoming wet was more obvious than that of meteorological. (3) The correlation between hydrological drought and meteorological drought in Xin’an River is high. Also, the hydrological drought lags behind the meteorological drought for 1-3 months. The seasonal response of hydrological drought to meteorological drought in flood season shows higher correlation and faster speed than that in dry season. Because of the quick response of hydrological drought to meteorological drought in flood season, more focus and targeted steps should be taken on the drought state of the basin in the flood season.

Based on hourly meteorological and environmental monitoring data in Cangzhou of Hebei Province from 2014 to 2020, this paper analyzed the aggravation of ozone (O₃) pollution and its relationship with meteorological factors. The results are as follows: (1) The pollution of O₃ in Cangzhou had been increasing and O₃ had become the primary pollutant. The pollution of O₃ concentrated from May to September, and the diurnal variation of O₃ mass concentration showed single peak and single valley type, and the maximum concentration occurred around 16:00 BST. (2) During the period of O₃-8 h maximum value from May to September, the average temperature, maximum temperature, relative humidity and total radiation irradiance were strongly correlated with the O₃ mass concentration, while the correlation between station atmospheric pressure, water vapor pressure, mean wind speed and the O₃ mass concentration didn’t pass the significance test. (3) During the period of O₃-8 h maximum value from May to September, when the average temperature of 8 h was above 30.9 ℃, the maximum temperature of 8 h was above 32.7 ℃, the average relative humidity of 8 h was below 42.1% and the average total radiation irradiance of 8 h was above 505.8 W·m^-2, the probability pollution of O₃ was up to 84%. (4) Meteorological factors were not sufficient conditions for rapid increase of O₃ hourly mass concentration.

Based on hourly meteorological and environmental observation data from Cangzhou of Hebei Province from 2014 to 2019, the influences of precipitation on atmospheric pollutant concentration were further discussed by using wind and background concentration correction method. The results show that the correction method about wind and background concentration could better remove the own diurnal variation characteristics of pollutant concentration and eliminate the influence of wind speed, and the influence of precipitation on atmospheric pollutant concentration could be acquired more accurately. Under the condition of wind force and background concentration correction, the removal effect of rainfall on PM_2.5, PM₁₀, O₃ and NO₂ was better, but for SO₂ and CO it wasn’t obvious. The removal effects of rainfall with different intensities on PM_2.5, PM₁₀ and NO₂ were better, and the removal rate increased with enhance of rainfall intensity. The removal effect of rainfall intensity less than 8.0 mm·h^-1  on O₃ was significant, while the rainfall intensity above 6.0 mm·h^-1 had removing effect on SO₂. With the duration of rainfall, the mass concentration of PM_2.5, PM₁₀, NO₂ and O₃ continuously decreased, and the removal efficiency dropped, the removal effect wasn’t obvious when the mass concentration of pollutant dropped to a certain threshold.

Based on temperature and precipitation data from 68 national meteorological stations in Zhejiang Province from 1988 to 2017, mean summer temperature and precipitation were interpolated using thin-plate smoothing splines （ANUSPLIN), inverse distance weighting (IDW) and ordinary kriging interpolation methods. In order to explore the optimal interpolation method of meteorological elements under complex terrain and climate in Zhejiang Province, the cross-validation method was applied to evaluate the accuracy of three methods, and the spatial error was analyzed. The results are as follows: (1) The interpolation accuracy of temperature and precipitation was generally close by using three methods, and the spatial distribution was relatively consistent. However, ANUSPLIN method was significantly better than IDW and ordinary kriging methods in detail for areas with large heterogeneity of element. (2) The interpolation accuracy of air temperature and precipitation based on ANUSPLIN was higher than that based on IDW and ordinary kriging. For example, the mean absolute error (MAE)and root mean square error (RMSE) of air temperature interpolation were both less than 0.5 ℃. The RMSE (0.381 ℃) of temperature interpolation based on ANUSPLIN was smallest, it was second based on ordinary kriging（0.459 ℃）, and it was biggest （0.463 ℃） based on IDW. The RMSE (37.8 mm) of precipitation interpolation based on ANUSPLIN was smallest, it was second (42.2 mm) based on the ordinary kriging, and it was biggest (49.1 mm) based on IDW. (3) The average interpolation error of temperature in plain area was lower than that in mountainous area. The average interpolation error of precipitation in the coastal area had largest error, showing an obvious low estimation. In conclusion, ANUSPLIN was more suitable for the spatial treatment of meteorological elements in Zhejiang  Province under complex terrain and climate background.

From the view of climate system complexity, the nonlinear characteristics of drought were discussed in Northwest China from 1962 to 2017. Based on the monthly meteorological observation data at 159 stations of Northwest China, the standardized precipitation evapotranspiration index (SPEI) was calculated, firstly. Then, the temporal and spatial distribution of drought was analyzed by using empirical orthogonal function (EOF). And on this basis the abrupt change of decomposed time coefficient of SPEI was detected by using moving cut data- approximate entropy (MC-ApEn) method. Finally, the complexity of drought was discussed by using approximate entropy (ApEn) method in Northwest China. The results are as follows: (1) The first EOF mode of SPEI was consistently positive in Northwest China from 1962 to 2017, while the second EOF mode was positive in the east and negative in the west of Northwest China. Compared with time coefficient of the second mode, the climate was wetter in the west and drier in the east than that before the abrupt change, and the change point was approximately in 1980. The drought existed 2-3 a period in Northwest China during 1962-2017. (2) The complexity of drought increased after the abrupt change of 1980 in Northwest China as the whole, so the predictability of drought decreased. Moreover, the complexity of drought in autumn and winter was greater than that in spring and summer in Northwest China from 1962 to 2017, and the complexity was the largest in winter and the smallest in summer.