Founded in 1982
Sponsored: Northwest Institute of ecological environment and resources, Chinese Academy of Sciences
Sponsor: Chinese Academy of Sciences
Editor-in-chief: Wen Jun
Considering the important influence of freeze-thaw processes on land-air interactions， this paper couples an improved freeze-thaw parameterization scheme into the BCC_CSM2_MR model and conducts a one-year simulation experiment， dividing the simulation period into four stages： beginning of freezing， complete freezing， beginning of ablation and complete ablation according to the annual change of soil layer， and analyzing the soil temperature， soil temperature， near-surface wind field on the plateau and the meteorological elements of soil temperature， soil temperature， near-surface wind field and precipitation were analyzed.The results show that the new freeze-thaw scheme has good improvements for both shallow and deep soil temperatures， especially in the central part of the plateau.The improvement of the optimized freeze-thaw parameterization scheme for soil moisture is significant， and the root mean square error and bias of the new scheme are significantly reduced across the Tibetan Plateau in all four freeze-thaw periods， mainly in the central part of the plateau.The wind speed deviation in the northern and central parts of the plateau is reduced during the freezing and thawing phases， which is closer to the comparison data.The correlation coefficients have been improved.The results of the study show that the improved soil freeze-thaw parameterization scheme has a corresponding improvement over the original scheme in the BCC_CSM， and has a positive impact on the simulation of the climate and major circulation systems in China.
Accurate estimation of cloud cover is the basis for understanding the spatial and temporal characteristic of cloud parameters on the Qinghai-Xiznag Plateau （QXP）.The dynamic changes in cloud distribution on the Qinghai-Xiznag Plateau are analyzed by the correlation analysis， regression analysis and trend analysis method.Using the MODIS cloud daily product （MOD08_D3） data and ERA5 reanalysis data from 2000 to 2020， the temporal and spatial characteristics of cloud distribution and cloud parameters in different phases over the Tibetan Plateau are analyzed.The results show that the high cloud cover center is located in Medog County （77.3%）， and Nyingchi （72.5%） is the maximum cloud cloud-covered area.The total cloud cover over the QXP has decreased by 0.04% in the past 21 years.Regarding seasonal distribution， the probability of liquid water clouds present in Summer is the highest （31.7%）， and the probability of ice clouds present in Spring is the highest （26.5%）.The ice cloud occurrence per year is about 2% more than liquid cloud.Under the background of global warming， the atmospheric water vapor over the QXP shows a decreasing trend， whereas the cloud water content shows a gradually increasing trend.The annual average cloud water vapor is about 0.01 cm higher than the total atmospheric water vapor， and the total cloud water vapor increased by about 0.04 cm.This study provides a basis for understanding the influence of cloud water resources on global climate change and the water cycle over the QXP.
Based on vegetation type map， leaf area index and meteorological data for northern Xizang from 1990 to 2019， the relationship between the transition zone of alpine meadow and alpine grassland in northern Xizang and dry-wet climate boundary （1.5 on the dry-wet index， which is the boundary between semi-arid and semi-humid regions） and 400 mm Isohyet was compared to explore the response characteristics of vegetation distribution to different dry-wet boundaries.The results show that the precipitation in northern Xizang decreases from southeast to northwest， the dry-wet index increases， and the surface evolves from wet to dry； from 1990 to 2019， the precipitation increases， and the dry-wet index decreases， showing a wetting trend； the annual LAI value of vegetation increased significantly， indicating that the environment for vegetation growth in 30 years has been improved， and the improvement degree of alpine meadow is higher than that of alpine grassland； the consistency between dry and wet climate boundary and the transition zone of alpine meadow and alpine grassland is high， indicating that the dry wet index can better characterize the vegetation distribution in northern Xizang， while the 400 mm Isohyet is generally to the West； LAI in the east of dry wet boundary is more than 0.6， and LAI in the west of 400 mm Isohyet is less than 0.1； from the correlation analysis among annual LAI value， annual precipitation and annual dry wet index， the increase of precipitation and wet surface conditions in most areas are conducive to vegetation activities.
Based on the knowledge that the main sources of summer water vapor on the Qinghai-Xizang （Tibet） Plateau are the Arabian Sea， the Bay of Bengal， and the South China Sea， a simulation study of the effects of different water vapor sources on the eastern-type and western-type precipitation on the Qinghai-Xizang （Tibet） Plateau in summer was carried out.Numerical simulations of water vapor content reduction at different water vapor source locations were conducted using conventional observations， NCEP/NCAR global reanalysis data， and the mesoscale numerical model WRF for two intense precipitation processes on the Qinghai-Xizang （Tibet） Plateau from June 28 to July 2， 2016 （eastern type） and from July 19 to 23， 2018 （western type）， by separately integrating the Arabian Sea， Bay of Bengal， and South China Sea By comparing three sets of sensitivity experiment and control experiment， the relative humidity at the Arabian Sea， the Bay of Bengal and the South China Sea was reduced by 70%， 60%， 50%， 40% and 30% from the ground to 100hPa respectively， and the effects of the reduction of water vapor content at different water vapor sources on summer precipitation on the plateau were explored in depth from the perspectives of circulation field， water vapor transport and precipitation changes， and the following main conclusions were obtained： （1） The reduction of water vapor content at three water vapor sources has an effect on The reduction of water vapor over the Bay of Bengal significantly reduced the summer precipitation of the Qinghai-Xizang （Tibet） Plateau by about 10% in 2016 （eastern type） and 2018 （western type） compared with the controlled experiment， while the reduction of water vapor over the South China Sea had minimal effects on the two summer precipitation processes of the Qinghai-Xizang （Tibet） Plateau.Reducing the water vapor over the Arabian Sea plays a catalytic role in the precipitation of the western type of the plateau， increasing the precipitation by about 10% relative to the controlled test； and inhibiting the precipitation of the eastern type of the plateau， making the precipitation decrease by about 5% relative to the controlled test.（2） Changing the water vapor conditions over the Bay of Bengal source has the most obvious effect on the precipitation on the Qinghai-Xizang （Tibet） Plateau.The possible reason is that reducing the water vapor conditions over the Bay of Bengal makes the low value system on the southern side of the plateau weaken， and the southerly wind on the plateau weakens， resulting in weaker water vapor transport， resulting in less precipitation on the plateau.（3） The difference of water vapor revenue and expenditure in the plateau region was not obvious in the control experiment and three sensitivity experiment at the beginning of the simulation， but with the increase of simulation time （after about 48 h）， there were obvious differences in water vapor revenue and expenditure in the Qinghai-Xizang （Tibet） Plateau， and there was an obvious correlation between water vapor revenue and expenditure and daily precipitation.
The hinterland of the Qinghai-Xizang （Tibet） Plateau is affected by two major circulation systems， Westerly Wind and Indian Ocean monsoon.The average altitude of the region is high， and the terrain is complex and changeable.It is extremely complicated that the temperature and precipitation conditions in this region as a comparison to other areas of the Qinghai-Xizang （Tibet） Plateau.In order to accurately obtain the temporal and spatial changes of temperature and precipitation in this region and predict future temperature and precipitation changes， based on the CN05.1 observation dataset， the ability of CMIP6 data to simulate temperature and precipitation in the hinterland of the Qinghai-Xizang （Tibet） Plateau was evaluated.CMIP6 was corrected using Spatial Disaggregation and Equidistant Cumulative Distribution Functions Method Temperature and precipitation conditions of 5 climate models and 7 scenarios in 2015-2100 were estimated.The results show that： （1） In the historical period （from 1961 to 2014）， the temperature and precipitation observation values of CMIP6 data have little deviation from the simulation values， and have strong space-time correlation.（2） In the future （from 2021 to 2100）， the annual average temperature and precipitation will show an overall upward trend.The percentage of temperature anomaly and precipitation anomaly in 2021-2100 of SSP3-7.0 and SSP5-8.5 scenarios increased significantly.The high value of temperatures anomaly is concentrated in the Qaidam Basin， and the high value of precipitation anomaly is located at the source of the Lancang River in the southeast.（3） In the future， the temperature will continue to increase in the four seasons， the precipitation will also show an overall trend of rise in four seasons.However， the degree of precipitation increase is distinct in different seasons and different scenarios.In the four seasons， the temperature increase of SSP5-8.5 scenario is the largest.The temperature of SSP5-8.5 scenario increases fastest in autumn； The precipitation of SSP3-7.0 scenario increases fastest in summer and winter， while that of SSP5-8.5 scenario increases fastest in spring and autumn.（4） Except for the SSP1-1.9 scenario， the temperature of each scenario from the recent period to the end of the period shows strong temporal and spatial similarity.Against to the historical period， the spatial distribution of temperature in spring and winter showed a consistently rising tendency is similar， and that in summer and autumn is similar.The precipitation increase is the largest in summer and the smallest in winter.Compared with the historical period， the spatial distribution of precipitation anomaly percentage shows a strong seasonality and regional feature.The high value area is mainly distributed in the southeast of the study area.
The heterogeneity of the underlying surface affects the accuracy and representativeness of the land-atmosphere flux observation.The study on the flux footprint distribution of complex underlying surface over Qinghai-Xizang Plateau （QXP） is of great significance to the observation and simulation of land-atmosphere interaction and its influence on weather and climate.Flux footprint analysis plays a pivotal role in investigating the spatial representativeness of flux observation information.The Flux Footprint Prediction （FFP） model represents a proficient methodology for computing the flux footprint.Based on the observation data from multiple research stations， including the Qomolangma Atmospheric and Environmental Observation and Research Station， the Ngari Desert Observation and Research Station， the Nam Co Monitoring and Research Station for Multisphere Interactions， the Muztagh Ata Westerly Observation and Research Station， the Southeast Tibet Observation and Research Station for the Alpine Environment in 2013， the FFP model was utilized to investigate the sensitivity of model parameters concerning flux footprint distribution.Additionally， the spatiotemporal characteristics and specific influencing factors of flux footprint distribution at different stations were discussed， thereby providing valuable insights for the erection of future observing stations.The results reveal that the primary determinants of flux footprint are measurement height， wind speed and wind direction.Characterized by an underlying surface of evergreen coniferous forest， flux footprint at Linzhi station exhibits greater sensitivity to measurement height and planetary boundary layer depth compared to the other stations.In the QXP， the spatial extent of the flux footprint derived from the ultrasonic anemometer measurements ranges from approximately 250 m to 500 m.Among the five stations， Qomo station exhibited the lowest frequency of stable stratification times during daytime， representing 15.69% of the daytime data points， whereas Ali station had the lowest occurrence of unstable stratification times during nighttime， comprising for 13.32% of the nighttime data points.At these five stations on the TP， the nocturnal flux footprints demonstrate greater width and extent compared to their daytime counterparts.In summer， due to the influence of monsoon， the axis of flux footprint tends to be more consistent.Lake-land breeze at Nam Co station is the main factor affecting flux footprint， whereas glacier wind at Qomo station is the dominant factor.Linzhi station possesses the smallest footprint due to the smallest mean wind speed， thus demonstrating the highest level of representativeness among these five stations.Lowering the height of observation instruments at Qomo and Nam Co stations could potentially enhance the representativeness of in situ measurements.
Rainfall can cause significant changes in the hydrothermal state within the active layer of the permafrost regions， and the rainfall in the Qinghai-Xizang （Tibet） Plateau has obvious seasonal characteristics.In order to analyze the effects of seasonal rainfall characteristics on the hydrothermal state of permafrost active layer， the meteorological data and the changes of soil heat flux， water content， and temperature within the active layer were monitored in the Beiluhe area of the central Qinghai-Xizang （Tibet） Plateau.The results show that the Beiluhe area is mainly characterized by the light rain events， supplemented by the moderate rain events， and the light rain events accounted for about 90% of the rainfall events from March to November.In addition， the heavy rain events and sustained rain events occur in summer and autumn， respectively.Among them， the rainfall events in each season leads to an overall decrease in surface net radiation， and the impact of the heavy rain events on the net radiation in summer is more obvious.The sustained rain events in autumn lead to a trend of first increase and then decrease in net radiation， and the change trend of soil heat flux consistent with changes in net radiation.Rainfall changes the soil heat flux by affecting the surface net radiation， thus causing changes in the water field and temperature field within soil.Among them， the heavy and moderate rain events in summer can significantly increase shallow soil water content， while spring and autumn rainfall have little effect on soil water content.The effect of the light rain events on soil temperature in each season can be ignored， but the moderate rain， heavy rain and sustained rain events can significantly alleviate the warming trend of shallow soil， and the effect of the rainfall events on alleviating soil warming gradually weakened with the increase of depth.The research results have certain guiding significance for solving regional ecological environment problems and engineering building disease prevention and control problems in permafrost regions.
Based on two ozone concentration data sets from the European Center for Medium-Range Weather Forecasts （ECMWF） 43a （from 1979 to 2021） and the National Aeronautics and Space Administration （NASA） 42a （from 1980 to 2021）， combined with high pressure， mean sea surface temperature， and circulation field data from South Asia， this study examines the spatial and temporal distribution of ozone in the Upper Troposphere and Lower Stratosphere （UTLS） over the Qinghai-Xizang Plateau （QXP）.The study found that ozone depletion occurs over the QXP in summer， forming a bicentric structure known as the QXP Ozone Valley.The study also shows that typical El Ni?o events contribute to ozone depletion in the UTLS region over the QXP， while typical La Ni?a events have the opposite effect， weakening ozone depletion.Under the influence of El Ni?o， a negative sea surface temperature （SST） anomaly forms in the western Pacific Ocean， generating a Rossby wave at 200 hPa height that transports westward to the Indian Ocean.This strengthens the Bay of Bengal trough behind the QXP， causing lower airflow to converge and rise， shifting air from the troposphere to the lower stratosphere.At the same time， southward pressure and high pressure strengthen， resulting in a smaller Total Column Ozone （TCO*） zonal deviation than the multi-year anomaly and a decrease in ozone content.In contrast， under the influence of La Ni?a， anomalous warming of the sea surface in the western Pacific Ocean causes air flow over the QXP to sink and wind field to blow from the stratosphere to the troposphere.The weakening of southern pressure high pressure leads to a larger TCO* value than the multi-year anomaly and an increase in ozone content.Therefore， El Ni?o enhances ozone depletion over the QXP， while La Ni?a weakens it.
Using observed hourly precipitation data and disaster records of flooding in Qinghai， we adopt the ratio weight method to construct the disaster index of flood disaster events based on the direct economic loss， disaster-affected population， collapsed houses， agricultural economic loss and agricultural disaster area.According to the percentile method， flood disasters are graded into general， heavy， severe， and extra heavy.The disaster distribution characteristics and differences of the four ranks are analyzed and compared with the precipitation characteristics in Qinghai.Principal component analysis， box-whisker plot and correlation analysis are employed to investigate the main factors that lead to flood disasters in Qinghai and the differences among regions.Results show that flood disasters occur frequently， and losses caused by floods increase.The frequency of severe and extra heavy disasters increases significantly after 2016， and the periods of July and August are the most frequent periods of flood disasters in Qinghai every year.The eastern part of Qinghai is an area of frequent floods and the most serious disasters.The Hainan Prefecture has the most flooding frequency and the Haidong City suffers the most serious disaster losses.The flooding disasters in Qinghai are mainly induced by rainfall processes that are more serious than heavy rainfall.The process of flood-causing precipitation in Qinghai can divide into two categories， one is short-lived but has a high rainfall intensity， which has a rainfall duration of 12 h and can cause high accumulated precipitation.The other can also induce high accumulated precipitation， and its rainfall duration is generally longer than 12 h.The flood disasters occurring in eastern cities like Hainan， Huangnan， Haibei， Xining and Haidong are mainly induced by the first category of precipitation process mentioned above.The second category of rainfall process is mainly found in Haixi and Yushu Prefecture， and Huangnan， Haibei， Xining and Haidong are also affected by this precipitation process.The accumulated precipitation and 24 h precipitation are closely associated with flood disaster losses， and longer precipitation duration can further aggravate flood disaster losses.
The quasi-stationary front in Yunnan and Guizhou is one of the most important weather systems in Guizhou in winter， and it is difficult to forecast.This paper analyzes the winter climate characteristics of the quasi-stationary front in Yunnan and Guizhou and frontal rainfall characteristics of different magnitudes in Guizhou by using the daily ground conventional observation station data of five provinces （cities， districts） of Yunnan， Guizhou， Sichuan， Chongqing， Guangxi from 2007 to 2021 and the daily precipitation data of Guizhou from 08:00 to 08:00.The results show that： （1） There are 52.8 days of the quasi-stationary front weather in Guizhou in winter on average.The impact of the quasi-stationary front is most serious in January， followed by February and December.（2） In winter， the front direction of the quasi-stationary front in Yunnan and Guizhou is the most south-north type， averaging near Qujing； The second is the northwest southeast type， which is located in the west of Guizhou on average； There are few east-west types； The moderate intensity quasi-stationary front is the most and tends to occur in the early winter， the strong quasi-stationary front is the second and tends to occur in the late winter， and the weak quasi-stationary front is the least.（3） The frontal precipitation is dominated by rainfall （rain or freezing rain）.The stronger the quasi-stationary front is， the fewer the days of frontal precipitation are， and the proportion of the days of frontal precipitation increases with the weakening of the quasi-stationary front； The frontal rainfall is mainly concentrated below 5.0 mm， and the frontal rainfall probability is inversely proportional to the rainfall and is proportional to the rainfall range.When the frontal rainfall is weak， the frontal rainfall probability is unimodal with the increase of rainfall and bimodal with the expansion of rainfall range.（4） The results of EOF and REOF classification show that there are two types of frontal precipitation with different magnitudes that affect Guizhou： the frontal precipitation in the central and eastern regions is mostly in the early winter and more south-north， with moderate or weak intensity and prone to large-scale rainfall of 0.1~1.0 mm magnitude； The southwest type frontal rainfall is mostly in the late winter， and it is mostly north-south type or north-west southeast type.The intensity is strong， and the small-scale rainfall of 1.1~5.0 mm is easy to occur.（5） The climate tendency rate of the average annual rainfall in the middle-east type is negative， and the cumulative anomaly changes are roughly in the "M" shape； The climate tendency rate of annual average rainfall in the southwest type is positive， with obvious stage characteristics， and the cumulative anomaly changes are roughly "W" shaped； Both of them have quasi 4 years and quasi 8 years periodic oscillations； In recent years， the frontal rainfall in the middle-east has decreased， while that in the southwest has increased.The results can provide an important climate background for the prediction of quasi - stationary front weather in winter in Guizhou.
Under the background of global warming， summer extreme rainstorm events occurred frequently in Inner Mongolia.As an important ecological security barrier in northern China， the sensitivity of the climate change in this area is increasing.Based on the daily precipitation observation data of National Meteorological Station from 1981 to 2020 and China's first-generation Global Atmospheric Reanalysis product （CRA40）， the variation regularity and dynamic factors of summer extreme rainstorm in Inner Mongolia in the past 40 years were studied.The conclusions are as follows： （1） The spatial distribution of summer precipitation in Inner Mongolia is gradually increasing from west to east， the difference between east and west is obvious， which is closely related to the distribution of the terrain.Hetao area and the southeast of Inner Mongolia are the areas with frequent rainstorm.In the past 40 years， the summer precipitation of most stations in the whole region were decreasing， and the significant decreasing stations of precipitation reached 36.44%.（2） The summer extreme rainstorm in Inner Mongolia mainly occurred in July and August and had obviously interannual variation.The frequency of extreme rainstorm decreased after 2000， but began to increase significantly after 2016.There have been 12 extreme rainstorm processes in the whole region in the past 40 years， which mainly affected the Hetao region in the west and the southeast region of Inner Mongolia.（3）During the extreme rainstorms happened in the Hetao region and the southeast， the large value area of dynamic factor basically coincides with the strong rainfall area， the dynamic factor of the precipitation area in the eastern region is significantly larger than that in the western region.The four dynamic factors had good indicative significance for typical extreme rainstorm process in southeast， but in typical extreme rainstorm process in west， the moist thermodynamic advection factors and the thermodynamic wave activity density performed better.（4） CRA40 reanalysis data showed that during the extreme rainstorm in the western and southeastern regions， the subtropical high was obviously stronger， and 500 hPa was affected by the circulation system with higher east and lower west， obviously water vapor channel was established between them also with significant water vapor convergence.Combined with the remarkable vertical ascending movement and the large value area of generalized potential temperature， meanwhile add the effect of the terrain that both lead to the improvement of precipitation efficiency， the extreme rainstorm events occurred.
Using ERA5 reanalysis data， automatic weather station data， FY4A satellite data， Doppler radar and Laser raindrop spectrometer data， the macro and micro characteristics of the extreme rainfall process in Jincheng， Shanxi Province on July 11， 2021 are analyzed. The results show that： （1） This extreme rainfall in Jincheng is the second highest rainfall in July since 1961. The strong divergence on the right of the upper jet entrance， the convergence of wind speed at the exit of lower jet， and the strong convergence near the warm shear line of the low vortex are the macro dynamic conditions of the extreme rainfall. The water vapor transfer by the low-level jet and the whole layer precipitable water above 65 mm， are the macro water vapor conditions， while 500 hPa trough is ahead of the cold shear lines on 700 hPa and 850 hPa is the macro dynamic unstable condition for this extreme heavy rainfall. （2） The extreme heavy rainfall is located in an irregular quadrilateral area surrounded by 500 hPa trough， 850 hPa and 700 hPa warm shear lines and ground dry line， which overlaps with the areas controlled by 500 hPa T-Td≤4 ℃， 700 hPa T-Td≤3 ℃， 850 hPa T-Td≤2 ℃， K index≥38 ℃ and Si index≤-1 ℃. The maximum extreme precipitation occurs in the large value area of the brightness temperature gradient on the southwest side of the convective cloud cluster and the low brightness temperature area in the southwest of the cloud cluster， which is within 0~30 km of the surface dry line and surface mesoscale shear lines. （3） The meso-α-scale warm shear line on 850 hPa， ground dry line and meso-β-scale surface shear lines and convergence lines triggered this extreme heavy rainfall in Jincheng. The strengthened easterly air flow on the surface layer is forced to converge and lift when it meets the trumpet shaped terrain opening eastward formed by Zhongtiao Mountain， Wangwu Mountain， Xionger Mountain and Song Mountain， promoting the convergence and rising movement in extreme precipitation areas and increasing the precipitation. （4） The lightning is located in the area where the cloud top brightness temperature is ≤220 K and the large value area of cloud top brightness temperature gradient. The peak value of lightning frequency is 10~35 minutes ahead of the peak value of precipitation， which is very significant for early warning of precipitation peak value. （5） The meso-α-scale low vortex warm shear system stimulates the development of the meso-α-scale vortex cloud system. The development and evolution of convective cloud clusters are backward development type. In the meso-α-scale vortex warm shear line cloud system， there are several organized meso-γ-scale convective cells with independent echo， which are guided by the southwest air flow moving to the northeast and form a train effect in the extreme precipitation area. The convective cell that leads to the largest rain peak in Manghe scenic area has the typical supercell storm structural characteristics. （6） The significant increase of cloud water content promotes the enhancement of precipitation intensity， and the high area of supercooled water content in -20~0 ℃ layer corresponds to the extremely heavy precipitation area on the ground. The extreme precipitation in Jincheng is stratiform and cumulus mixed cloud precipitation， and the particle size distribution of raindrops is wide. Small and medium raindrops with high concentration are the main contributors of extreme heavy precipitation. Compared with the typical continental convective precipitation process， the average range of the average generalized intercept common logarithm （lg（NW ）） of raindrops in this extreme heavy precipitation process is large， but the mass weighted average diameter （DM ） is slightly smaller than the average range.
The microphysical characteristics is important for the formation mechanism of rainstorm which is the result of multi-scale conditions and the interactions of macro and micro physical processes.From 15:25 （Beijing Time， the same as after） to 17:27 on July 20， 2021， a strong mesoscale convective system affected Zhengzhou， and the accumulated precipitation was 312.1 mm， which was referred to as extreme rainstorm.Excluding the period of extremc rainstorm， from 08:00 to 20:00 on the July 20， the accumulated precipitation was 183.4 mm， which is referred to as rainstorm.Based on the observations data of disdrometer at Zhengzhou station， the characteristics of raindrop size distributions（DSDs） and integral parameters of extreme rainstorm and rainstorm are analyzed.The results showed that： （1）In rainstorm， the average DSDs increased with the increase of rain rate.The concentrations of diameter less than 1 mm increased less， and concentrations of large diameter which is greater than 2 mm increased faster.In extreme rainstorm， the average DSDs increased with the increase of rain rate， and the concentrations of each diameter increased significantly.Meanwhile， the differences between the concentrations of average DSDs at different rain rate were complex.Somewhile there were distinct differences in the concentrations of small raindrops， and there were also great differences in the concentrations of large raindrops.The differences of average DSDs of different rain rate categories lead to different parameters variation with the increase of rain rate.For rainstorm， the D m increased with the increase of rain rate， while lgN w increased slightly， indicating that the main source for the increase of rainstorm intensity was the increase of particle diameter， and the secondary factor was increase of particle concentrations.For extreme rainstorm， when the rain rate was between 50 and 100 mm·h-1， D m（lgN w） increased （decreased） with the increase of rain rate， while the rain rate was greater than 100 mm·h-1， D m and lgN w increased slightly with the increase of rain rate， suggesting that the formation mechanisms of DSD in different rain rate categories of extreme rainstorm may be different.（2）The distribution of lgN w-D m showed that the DSDs of rainstorm were mainly continental-like， and its formation mechanism was mainly warm-ice mixture process and a small amount of ice-based process.The scatter plot of lgN w-D m ofextreme rainstorm with rain rate less than 100 mm·h-1 mainly clustered on the upper and right side of the continental-like area， and the formation mechanism of extreme rainstorm was mainly warm-ice mixture process and ice-based process； the scatter plot of lgN w-D m of extreme rainstorm with rain rategreater than 100 mm·h-1were mainly distributed on the upperside of the continental -like area， and the formation mechanism was mainly warm-ice mixture process.（3）There were a small proportion（about 2.8%）of the equilibrium raindrop size distribution（EDSD） and a large proportion （about 60.5%）of transition DSDs in rainstorm.There was no EDSD in the extreme rainstorm， while the transition DSDs had a very high proportion （about 83.9%）， indicating that the breakup process played a much more role in the extreme rainstorm.
"21·7" severe torrential rain occurred in Middle-North of Henan Province from 18 to 22 July 2021， which has been studied by many scholars.Affected by the northward movement of the weather systems in “21·7” torrential rain， a regional heavy rainstorm occurred subsequently in the middle section of Taihang Mountains from 20 to 22 July.Based on 0.25°×0.25° hourly ERA5 reanalysis data and multi-source high-resolution observation data from 2508 ground dense automatic weather stations， Doppler radar， wind profile radar， L-band radiosonde， ground-based GPS water vapor and so on， the characteristics and synoptic analysis of the heavy rain in the middle section of Taihang Mountains from 20 to 22 July 2021 were analyzed.The results show that： （1） The main weather systems were subtropical high， upper-tropospheric low vortex， shear line， low-level jet， moreover the long-distance water vapor transport of double typhoon of "In-Fa" and "Cempaka" was favorable to the heavy rain.The main synoptic background was stable atmospheric circulation and long-term maintenance of low-level easterly wind.（2） The locations of surface convergence line， surface dew point temperature front area， the strong echo area with reflectivity factor greater than 30 dBz， and short-term heavy precipitation zone of hourly precipitation greater than 10 mm were nearly consistent and stably maintained at the eastern foot of Taihang Mountains with less movement and long duration.During heavy precipitation phases， the easterly component of low-level winds increased， and the maximum height of east wind decreased.Farther， the maximum easterly component was 8 to 11 m·s-1， the maximum height of east wind was 510 m.The maximum height of low-level easterly jet was 510 m to 2310 m， the maximum low-level jet index was 33.1×10-3 s-1； The maximum vertical wind shear of 0~1 km and 0~3 km were 11.9 m·s-1 and 16.9 m·s-1 respectively.The easterly wind and Taihang Mountains made a horizontal convergence on windward slope， also the obvious terrain effect induced the increase of precipitation.（3） The deep wet layer extended from the ground to 400 hPa.During the precipitation process， the condensation height was close to the surface.The convective effective potential energy in the early stage of precipitation was 1925.5 J·kg-1.In the stage of heavy precipitation， when the GPS water vapor was higher than 50 mm， the start time of high water vapor was 5~6 hours ahead of the precipitation.The large value of water vapor flux of the middle and lower layers in the western mountainous area lasted for more than 10 hours， and the water vapor convergence was significantly higher than that in the East.Heavy precipitation presented as a band shape in front of Taihang Mountains.（4） The centroid of radar echo was low， and the strong echo area with reflectivity factor greater than 30 dBz lasted for 20 hours， the characteristics of train effect and warm-cloud precipitation were obvious in the western mountainous area.
The role of warm conveyor belts （WCBs） on the development of cyclones and precipitation and their relationship to occluded fronts are investigated for extratropical cyclones causing snowstorms in northeastern China during 2006 -2021， using ERA5 reanalysis data and Lagrangian Analysis Tool （LAGRANTO）.Main results show that： （1） The correlation coefficient of 0.63 which could pass significance test of α=0.01 implies strong correlation between cyclone intensification and WCB strength.Most of cyclones have occluded in the 24 h period of strongest deepening， and these occluded fronts are mainly warm-type occlusions.（2） Rapidly intensifying occluded cyclones typically have strong WCBs， which low-level inflow mainly locates in the center and warm sector of cyclones， while the outflow has two branches： some trajectories rise to the high levels northwest of the cyclone， and others ascend to the downstream of cyclone following the upper westerly winds； the interaction between low-level potential vorticity （PV） and upper-level PV in cyclone occluding stage eventually forms a PV tower throughout the troposphere.（3） Non-occluded cyclones also have strong WCBs and positive low-level PV anomalies， but lack of significant upper-level PV forcing.The development of these cyclones is weak.Weakly intensifying occluded cyclones have a PV tower， but their WCBs and precipitation are weak.（4） Cyclones with strong （weak） warm conveyor belts cause more （less） precipitation， and the distribution of rainfall is closely related to the location of warm conveyor belts.The WCB trajectories moving towards to cyclone center play an important role for cyclone development.The warm advection and low-level diabatic PV production generated by these trajectories both enhance the low-level circulation and contribute to the cyclone intensification.
In order to enhance the understanding of the environmental field characteristics of the convective regeneration triggered by thunderstorm gust fronts.Based on Beijing sounding observation， automatic stations， S-band Doppler radar and new detection data to analyse environmental field characteristics of two typical cases in which convection initiation triggered by thunderstorm gust fronts.The results show that： （1） One type is convection triggered by collision of multiple gust fronts or the encounter of gust fronts with other boundary layer convergence lines in the region with high Convective Available Potential Energy （CAPE） and sufficient water vapor （collision triggering）.In this type， the vertical velocity of two collision gust fronts is much larger than that of a single gust front.Strong upward movement is easy to provide good lifting conditions for the triggering of convection， and convection is easy to trigger.（2） The other type is the gust front triggers convection in the unstable region （non-collision trigger）.In this type， the low-level wind direction is perpendicular to the gust front， which is conducive to the strong convergence between the ambient wind near the ground and the gust front.Meanwhile， the updraft of the convection triggered by the gust front tends to be vertical， which is beneficial to convective initiation.（3） By comparing the environmental field of gust fronts trigger and non-trigger Convective Initiation （CI） cases， the results show that there are deep wet convection potential with high CAPE and low Convective Inhibition （CIN） of the environment field in these cases which CI are triggered by gust fronts.The wind profile and microwave radiometer observations indicate that there are cold dry advection at the upper level and warm wet advection at the lower level in most cases CI triggered by the gust fronts.In most cases which gust fronts trigger CI occur at the wind speed or wind direction convergence areas with high CAPE.（4） In cases which non-triggered CI， vertical distribution of environmental field is not conducive to the regeneration and development of convection， and gust fronts pass the area which are divergence or there are low CAPE and high CIN.These conditions are adverse to convection triggering.
Based on ERA5 reanalysis data and CLDAS land grid precipitation data from the National Meteorological Information Center， a systematic WRF numerical simulation and precipitation mechanism diagnosis of a typical systematic precipitation process in the Qilian Mountains are carried out in this paper.The dynamic diagnosis results of the circulation background field show that the interaction between the mesoscale upper trough system and the local lower flow around and flow over provides important dynamic conditions.The mesoscale dynamic uplift in front of the trough caused by the development of the upper trough determines the distribution of the heavy precipitation belt during the precipitation process， while the lower flow around and flow over provide direct dynamic conditions for local heavy precipitation.The further diagnosis results of water vapor transport and budget show that the water vapor source of this precipitation mainly comes from the Sichuan Basin.The flow around will transport abundant water vapor for the precipitation area in front of the windward slope， and the flow over will promote the reverse gradient transport of water vapor along the terrain height and converge near the precipitation center.In the stage of heavy precipitation， the vertical transport of water vapor contributes the most to the water vapor budget， followed by the convergence of water vapor， and the local variation of water vapor can be basically ignored.Finally， the diagnostic results of atmospheric stratification characteristics show that when both atmospheric dynamic conditions and water vapor conditions are conducive to precipitation， combined with the enhancement of the instability of low and medium tropospheric stratification， it is easier to trigger convection and enhance precipitation in front of the windward slope.
Based on the data of networked wind profiles and Doppler radars， ground automatic weather observation station， radiosonde and FY-4 satellite， combined with the ECMWF ERA5 1 h 0.25°×0.25° reanalysis data， this paper analyzes the spatial structure， formation， maintenance and function of PMDV that occurred in boundary layer to lower troposphere in North China during the blizzard weather on 14 February 2020.Besides， the moisture transported by multiple air flows and the net inflow are calculated and compared.The results indicate that PMDV was located in the front of the 500 hPa cold vortex， within the 850 hPa warm inverted trough and on the noutheast backflow.The PMDV was suspended vortex， with a horizontal range of 100~300 km and a vertical thickness of 1.2 km and a life span of 17 h.It first appeared in the boundary layer and then extended to higher altitudes（top at 2 km） and finally disappeared in the boundary layer.One of the reasons for formation of PMDV was that the strong and persistent east-northeast wind blew westward and then turned counterclockwise after being blocked by the Taihang Mountains running from northeast to northwest.Another reason was that the stronger frontogenesis appeared at PMDV primary position and it had maintained about 4 h ahead of complete cyclonic wind field circulation formed.The reason for maintenance of PMDV was under the common action of decompression （caused by warm advection）， weaker frontogenesis （caused by dense temperature gradient） and release of latent heat of internal condensation.The PMDV promoted the strengthening of low-level jet and the increase of positive vorticity in the southeast of its northeast side （blizzard area）， causing the upward movement， water vapor transport and aggregation in the study area to increase.Most moisture transported in the blizzard area was originated from multiple air currents below 850 hPa， among which the southeast branch contributed most， accounting for 86.4% of the total net inflow.The wet layer carried by the northeast branch airflow was concentrated in the 850 hPa layer， but the northwest airflow maintained dry all the time.Though the wet layer of southwest branch airflow was deep， the net inflow of water vapor above 700 hPa was very small.
Drought is one of the most widespread and harmful natural disasters in the world.The standardized precipitation Index （SPI） is one of the most widely used meteorological drought indexes in the drought monitoring operation and research.At present， China has built a large number of high-density regional automatic weather stations， which can not be used to calculate the SPI due to the lack of long history sequence data.How to use these short-term data to carry out refined drought monitoring and assessment is the focus of attention.Based on the daily precipitation data of 2032 national meteorological stations from 1960 to 2020 and 1009 regional stations in Yunnan Province from 2010 to 2020， 31 national stations are selected as the method test stations.The SPI（Iab） is constructed by the Gamma distribution parameter interpolation method to fit the regional stations， compared with the commonly neighbor station substitution method and multiple linear regression method， and cross-test and error analysis were carried out.By comparing the correlation coefficient， root mean square error and average absolute error between the fitting value and the true value， it can be concluded that the fitting value Iab is significantly better than the fitting results of the other two methods except in the areas with sparse stations in Northwest China.In different seasons and different time scales， the SPI （Iab） obtained by parameter interpolation is the best.In Mid-Eastern China， the average error of Iab decreases from 0.02 to 0.30 compared with the other two methods.The maximum error change of fitting value Iab and true value Iz in Beijing and Kunming over the years is 0.16， less than half the drought grade 0.25.The correlation coefficient of Iab and the true value （Iz） is above 0.999， passed the significance test of 0.001.The monitoring results of the drought process of the regional stations using this method show that the drought index SPI calculated by the high-density regional stations is closer to the actual drought disaster than the SPI obtained by the interpolation of the national stations.In general， the gamma distribution parameter interpolation method can be used to calculate the drought index SPI from the precipitation data of high-precision short series regional stations， so as to realize the precise monitoring， prediction and evaluation services of meteorological drought.
Low-level wind shear significantly impacts aviation safety and operational efficiency.Zhongchuan Airport， located in a mountainous inland region， experiences the influence of complex terrain and weather systems.Wind shear is frequently observed during the summer season.This study analyzes the spatial and temporal characteristics of low-level wind shear events at Zhongchuan Airport using aircraft reports spanning from 2009 to 2018.During the observation period from May 2016 to November 2017， a total of 18 low-level wind shear events were confirmed through aircraft verification.Two methods， namely the fixed and adaptive window methods， were compared to identify wind shear events using LIDAR data from the Windcube 400s-at instrument.The study also explored the continuous evolution and spatial characteristics of the three-dimensional wind shear structure.The results indicate that the frequency of low-level wind shear events has increased at a faster rate compared to the flight volume at Zhongchuan Airport over the past ten years.The peak months for low-level wind shear events at Zhongchuan Airport are April-July and August-October， influenced by local weather patterns.The peak months for low-level wind shear events at Zhongchuan Airport are April-July and August-October， influenced by local weather patterns.Wind shear induced by convective weather occurs in the weak or non-echo region surrounding the convective cloud， resulting from the convergence of updrafts and downdrafts outside the cloud， or the formation of a gust front following the downdraft's contact with the ground.The wind shear factor is correlated with the intensity of radar echoes.Compared to the fixed window method， the adaptive window method had a larger recognition range due to the different data sets included in the recognition window.Therefore， the adaptive window method was found to be more suitable for studying the three-dimensional evolution of wind shear structures.Therefore， the adaptive window method is better suited for studying the evolution of the three-dimensional wind shear structure.The wind shear in the vicinity of Zhongchuan Airport is characterized by a low spatial distribution， small horizontal scale， and short duration， primarily concentrated in the small-scale and γ mesoscale.In other words， the wind shear events occurred at relatively low altitudes， with horizontal scales mostly ranging between 1000~1500 m and 2000~2600 m， lasting less than 20 minutes.Furthermore， 40.5% of the wind shear events were attributed to the movement of the wind， primarily influenced by the background wind.The findings of this study contribute to a better understanding of the characteristics of wind shear， offering valuable insights for the identification， mechanisms， forecasting， and early warning of low-level wind shear events at Zhongchuan Airport.
The Global Constellation Observing System for Meteorology， Ionosphere， and Climate （COSMIC） radio occultation （RO） from 2007 to 2009 were collocated with the CloudSat nadir-pointing cloud profiling radar （CPR） in time and space in this study.We investigated the characteristics of fractional refractivity differences between COSMIC RO and the analysis of the European Centre for Medium-Range Weather Forecasts （ECMWF） and the National Centers for Environmental Prediction （NCEP） within the different clouds. and indicate the fractional differences of refractivity between COSMIC RO and ECMWF， and COSMIC RO and NCEP analysis， respectively.The maximum values of within cumulus， stratocumulus， altocumulus and altostratus are 1.2%， 0.2%， 0.5%， and 0.2%.The highest values of are 1.8%， 0.5%， 0.5% and 0.4%， respectively.In the lower troposphere， the value of is positive and increases with the liquid water content， whereas the value of is negative.From the perspective of global distribution， large positive refractivity differences for both ECMWF and NCEP analyses are shown in the equatorial convergence zone， which is highly correlated with the positive bias of water vapor and the negative bias of temperature in space.
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