Severe convective weather under the Northeast Cold Vortex is characterized by strong locality and challenging predictability, with cold air incursions often serving as indicators for triggering such weather events. This study employs ground observations from densified automatic weather stations, ERA5 reanalysis data from ECMWF, and wind profile radar data to analyze the dynamics and thermodynamics of two heavy precipitation events under cold vortices background on June 30, 2016, and August 3, 2020. Both events were influenced by a Mongolian cyclone on the ground, creating favorable dynamic conditions from the surface up to higher altitudes. Before the precipitation, it was clear in the morning with cold air penetration at mid to high levels and high near-surface humidity, forming an unstable atmospheric layer with dry and cold air above and warm and moist air below. Before the heavy rainfall, a dry intrusion moved from west to east at mid-levels, and a downward extension of the upper-level high potential vorticity area enhanced convective instability. Mid-level potential vorticity nearing 1×10^-6 m²·K·s^-1·kg^-1 can act as an indicator for the onset of heavy precipitation. The dry intrusion index, showing a dipole distribution, reflects the interaction between cold, dry and warm, moist air masses. Heavy rainfall often occurs within areas of dense dry intrusion indices. When positive values of the mid to upper layer dry intrusion index propagate to lower levels, they trigger the release of unstable energy. The dry intrusion index is indicative of heavy rainfall locations and the amplification of localized heavy rainfalls.

Based on the monthly maximum frozen soil depth at 68 meteorological stations in Shanxi Province during 1960-2018, the temporal and spatial distribution characteristics of the annual maximum frozen soil depth in Shanxi were studied by using EOF and wavelet analysis methods. The results are as follows: (1) The average annual maximum frozen soil depth at 68 stations in Shanxi during 1960-2018 was 71 cm, the extremely maximum value was 192 cm, and the extremely minimum value was 7 cm. In the past 59 years, the average annual maximum frozen soil depth at 68 stations in Shanxi showed a significantly decreasing trend with a climate tendency rate of -1.394 cm per decade, and it mutated in 1986. (2) The quasi-4-year period of average annual maximum frozen soil depth at 68 stations in Shanxi was detected. (3) The annual maximum frozen soil depth showed a spatial distribution characteristics with shallow in southern and deep in northern Shanxi, shallow in eastern and deep in western Shanxi. (4) The accumulated variance contribution rate of the first two modes of the annual maximum frozen soil depth in Shanxi reached 58.4%. The spatial pattern of the first mode was consistent in the whole province, while that of the second mode was reverse in southern and northern Shanxi.

The typical fog and haze episode in the Sichuan basin from December 16, 2014 to January 27, 2015 was selected according to the method of determination of fog and haze days at a single station and the regional fog and haze process. Based on air quality index (AQI), mass concentration of pollutant, meteorological element characteristics and atmospheric circulation, the characteristics and mechanism of the generation, evolution and transformation of this continuous fog and haze weather were studied. The results are as follows: (1) The fog and  haze process was characterized by strong intensity, long duration and wide range. (2) Both mass concentration of pollutant and AQI were highly consistent with the fog and haze weather process, and the main pollutant in this fog and haze process was PM2.5, followed by PM10. (3) It can be seen from the process of formation, evolution and transition of a longlasting severe fog and haze episode that there were stages of pollutant accumulation with different intensities, reaching the peak value and rapidly weakening. Therefore, the intensity of fog and haze weather process was closely related to weather situation and vertical structure of boundary layer. The average temperature was 1.24 ℃ higher than the normal years, the rainfall was 34.77% lower than the same period, relative humidity was 2.67% lower than the same period, sunshine hours was 10.33 hours more than the same period, and wind speed was close to or slight higher than that of the normal years. The stable atmospheric circulation feature provided favorable environmental field for fog and hazy weather and heavy air pollution. Strong temperature inversion layer, sinking motion in the boundary layer and convergence in weak wind fields on the ground prevented water and pollutants from diffusing to the upper air.

Atmospheric precipitable water vapor (PWV) is an important factor affecting rainfall. Based on ground-based GPSretrieved PWV data, ground meteorological observations, sounding data and ERAInterim reanalysis data from 2010 to 2019, the seasonal, monthly and diurnal variation characteristics of water vapor resources over Fujian were analyzed. Moreover, the spatial and temporal characteristics of PWV were assessed by using the empirical orthogonal function (EOF), MannKendall test and the sliding t test. The results show that the accuracy of the groundbased PWV was higher compared with ERAInterim reanalysis data. The water vapor resource over Fujian was largest in summer, followed by spring, autumn and winter. The monthly distribution of PWV presented an inverted Ushaped, and the diurnal variation of PWV changed significantly on sunny day and rainy day. The PWV of the eastern coastal areas was generally higher than that of the western mountainous areas, but the precipitation conversion rate of PWVthere was lower than that of the inland mountainous areas. The first mode of EOF decomposition of PWV presented the main characteristics with a variance contribution rate of 80.06%. The eigenvalues were positive in the whole region, which indicated that the spatial change of PWV had good consistency. The oscillation intensity of PWVstrengthened from northwest and southwest to the east, and the corresponding time curve characterized the significant seasonal changes of PWV. The mutation test of MannKendall and the sliding t test showed that the water vapor resources over Fujian had not undergone abrupt change in the past 10 years.

Plant litter is an important part of ecosystem in Mu Us sandy land, and its stock volume and redistribution process play important roles in affecting nutrient cycling between surface soil and plant and soil erosion resistance. Based on the field survey and sampling data, the spatial distribution characteristics of litter of Salix psammophyla normal plant were studied in typical sand dunes of southeastern edge of Mu Us sandy land. The results show that the distribution patterns of Salix litter approximately appeared concentric circle, fan-shape and crescent-shape with the centre of Salix base under the long-term influence of the northwest wind, and the biomass of litter decreased significantly with the increase of the distance (30 cm, 60 cm and 90 cm) from the Salix base. Compared with the concentric circle pattern, the biomass of litter for crescent-shaped and fan-shaped patterns decreased in the northwest of base and increased in the southeast of base, especially for the crescent-shaped pattern the changes were significant. The northwest wind played an important role in migration and redistribution of leaves and fruits in Salix communities, so the northwest wind was main reason for the formation of three pattern of litter. These results might provide scientific basis for vegetation optimization layout and ecological reconstruction in wind-sandy area of northern China.

Based on conventional ground observation data of weather stations and pollutant mass concentration observation data from environment monitoring stations in Liaoning Province, ECMWF reanalysis data with 0.5°×0.5° spatial resolution, a heavy pollution process caused by straw burning from 7 to 10 November 2015 in Liaoning Province, the differences and its causes of pollution among different cities were analyzed. The results are as follows: (1) CO was main pollutant during the heavy pollution process. The mass concentration of PM2.5 appeared two peak stages, and it was well corresponded to CO and NO2 mass concentrations. The visibility was mainly affected by PM2.5 concentration and relative humidity. (2) The effect of previous weak precipitation more than 1.0 mm on wet deposition of pollutants was obvious in Yingkou and Panjin, while the precipitation in other cities was smaller, and the high humidity environment was conducive to moisture absorption and growth of pollutants. (3) The horizontal wind speed from ground to 700 hPa during the heavy pollution was close to 4 m·s-1, the atmospheric stratification was stable, and the temperature inversion was obvious, which was beneficial to inhibit the vertical diffusion of pollutants. (4) The warm layer around 0 ℃ between 850 hPa and 900 hPa over cities except for Jinzhou maintained for a long time, which might provide favorable environment for the melting, collision and growing of pollutant particles. (5) There were many fire points in Jilin and Heilongjiang Province during the pollution process. Therefore, the main sources of pollution in central Liaoning Province came from the wide straw burning upwind, so it was necessary to strengthen the control of local and external pollution sources under the favorable weather conditions to the pollutants accumulation.

The monthly change of the potential evapotranspiration Wills an alyzed based on the meteorological observations during 2000—2005 in the Ulan Buh Desert．The potential evapo transpiration calculated by Penman equation，Thornthwaite formula and Holdridge method were compared and an alyzed，and the result indicated that the potential evapotranspiration calculated by Penman equation WaS conspicuously correlated to the water surface evaporation，and it could be used to evaluate the water evaporation characteristic．Th e re—search showed that the monthly change of the potential evapotranspiration Was similar to the monthly average temperature，the largest value appeared in July and August，and the total potential evapotranspiration in a year Was 3 041 mm．