Global warming has led to rapid changes in the sea ice of the Antarctic and Arctic， triggering a number of climate feedbacks.Turbulent heat exchange between the polar seas and the air plays an important role in these feedbacks.Solar radiation， as the main energy source at the polar sea surface， is mainly used for sea ice melting and air-sea heat exchange， but the higher albedo of sea ice results in low radiation absorption.Air-sea heat exchange is influenced by temperature and humidity gradients between the sea surface and the atmosphere， with sensible heat dominating at the sea-ice edge and latent heat farther from the sea ice.In the Arctic， air-sea heat exchange is dominated by sensible heat， whereas in the Antarctic it is dominated by latent heat.The air-sea heat fluxes at the north and south polar seas vary seasonally.Sea ice can also inhibit air-sea heat exchange to some extent.Accurate parameterization of the turbulent heat exchange between the sea and the atmosphere in the sea ice regions is crucial for simulating air-sea interactions， however， in situ observations remain extremely rare due to limitations of the polar environment， and accurately representing the turbulent air-sea exchange in polar oceans remains a challenge.In the future， the network of air-sea flux measurements in polar seas should be strengthened， especially in the marginal ice zone， which are necessary and crucial for a deep understanding of the role of air-sea interactions in polar regions on global climate change， and for reducing the uncertainty in climate models.Secondly， the dynamics and thermal properties of ice must be fully considered to optimize the parameterization scheme or develop new models to improve the simulation accuracy.Furthermore， the influence of waves on the air-sea heat exchange in the sea ice region should be clarified to fill the research gaps.Finally， the contribution of the air-sea heat exchange to climate change in the polar regions should be evaluated further to improve the understanding of the role of polar oceans in climate change.

Based on the China snow depth time series data set and high resolution ground meteorological element driven dataset， this study analyzes the spatial and temporal variation of snow depth on the Qinghai-Xizang （Tibetan） Plateau by watershed and elevation gradient during the 1980 -2020 snow season considering different river basins and elevation gradients.Additionally， the study investigates the response of snow depth to climate change in the context of hydrothermal factors.The results show that： （1） Spatial difference in snow depth on the Qinghai-Xizang （Tibetan） Plateau was obvious， showing a distribution pattern of high in the west and low in the east， and greater in the high-altitude mountain areas than in the basin plains， with the average snow depth in the high-altitude mountain areas generally greater than 10 cm.The average snow depth decreased at a rate of 0.25 cm/decade， 64.74% of the regions showed a declining trend， with statistically significant decreases in 29.09% on the Qinghai-Xizang （Tibetan） Plateau during the snow season from 1980 to 2020.（2） There is a clear vertical zonation of snow depth and its trend as influenced by altitude.Below an altitude of 4.2 km， average snow depth increased with elevation.Between 4.2 km and 4.8 km， average snow depth decreased as elevation rises.Above 4.8 km， average snow depth again increased with elevation.A decreasing trend in snow depth was observed across all elevation bands， with the rate of decrease initially increasing and then decreasing with elevation， exhibiting a threshold at approximately 5.0 km.The most rapid decrease in mean snow depth ［3.36 cm·（10a）^-1］occurred in the 5.0~5.2 km elevation band.The interannual variation of mean snow depth exhibited a pronounced altitude-dependent pattern， the rate of snow depth reduction was significantly higher at higher elevations than at lower elevations， especially at 4.8~5.5 km.（3） Climate change on the Qinghai-Xizang （Tibetan） Plateau is ‘warmer and wetter’ overall， but ‘warmer and drier’ in the north-west and south during the snow season from 1980 to 2020.However， there are watershed differences and elevation differences in the response of snow depth to climate change.Specifically， in the Nujiang， Ganges， Amu Darya， and Indus River basins， the warming and aridification of climate conditions have contributed to a reduction in snow depth.Conversely， temperature has a more pronounced effect on snow depth in the Yarlung Tsangpo River， the interior plateau， as well as the Yangtze River basins， the Qaidam Basin， and the Tarim Basin.Additionally， precipitation plays a more significant role in influencing snow depth in the Yellow River， Heihe River basin.In regions with altitudes below 3.5 km， climate conditions characterized by warming and aridification have led to a reduction in snow depth.However， in areas with altitudes above 3.5 km， temperature has a more pronounced influence on snow depth.The altitude-dependent warming of temperature accounts for the altitude-dependent reduction in snow depth.

The Qinghai-Xizang Plateau summer monsoon is an important component of the Asian monsoon system， significantly influencing the energy and moisture cycles in the plateau and its surrounding regions.This study uses JRA-55 monthly reanalysis data from 1980 to 2020 and GPCC monthly precipitation data， combined with the Qinghai-Xizang Plateau Monsoon Index.Various statistical methods， including correlation analysis， regression analysis， composite analysis， and dynamic diagnostics， are used in this study.This paper focuses on the impact of the summer monsoon over the Qinghai-Xizang Plateau on water transport， such as precipitation， atmospheric circulation， and water budget.The results show that： （1） When the Qinghai-Xizang Plateau summer monsoon is strong （weak）， precipitation in the central and eastern parts of the plateau increases （decreases）.（2） From the perspective of water vapor transport， when the summer monsoon over the plateau is stronger， there is an anomalous anticyclonic circulation over central India， an anomalous westerly airflow to the south of the plateau， and the water vapor transport over the plateau is primarily dominated by the westerly water vapor transport channel.（3） Analysed in terms of moisture budget， when the Qinghai-Xizang Plateau summer monsoon is strong （weak）， moisture inflow at the southern and western boundaries of the plateau increases （decreases）， while moisture inflow at the northern boundary decreases （increases）， resulting in an increase （decrease） in regional net moisture budget.（4） The impact of the Qinghai-Xizang Plateau summer monsoon on moisture convergence/divergence is mainly driven by the contribution of the wind’s dynamic component， while the thermal component from moisture advection is relatively small.

The freeze-thaw cycle of near-surface soil in the perennial permafrost region of the Qinghai-Xizang （Tibetan） Plateau plays a crucial role in regulating water and energy exchange between the soil and the atmosphere.Investigating its spatiotemporal characteristics and response to climate change is essential for understanding the mechanisms driving climate change on the plateau.In this study， we calculated near-surface freeze-thaw parameters-including the start and end times of soil freezing， thawing duration， and freezing duration-across the perennial permafrost region of the plateau from 1980 to 2017 using the Common Land Model 5.0 （CLM5.0）.We further analyzed their spatiotemporal variations and correlations with temperature， precipitation， snow depth， and vegetation index.The results show that： （1） The onset of near-surface soil freezing in the plateau’s permafrost region occurs between September and mid-to-late October， while the thawing period ends between February and May.Semi-humid regions have the longest thawing duration， whereas semi-arid regions have the shortest， with an average difference of 15 days.The freeze-thaw status of permafrost soil on the plateau exhibits significant changes.Except for areas near the Karakoram Mountains， most permafrost regions show a decreasing trend in freezing duration and an increasing trend in thawing duration.The average growth rate of soil thawing duration across the plateau is 2 d·（10a）⁻¹， with the most significant increase observed in semi-humid regions， reaching 4 d·（10a）⁻¹.（2） The freeze-thaw parameters of the plateau's permafrost are associated with geographical factors.In the latitude range of 29°N -36°N and longitude range of 82.5°E -103°E， the thawing duration shows an increasing trend； however， the rate of change decreases in some areas while increasing in others.Additionally， as elevation increases， the growth rate of thawing duration declines.（3） The duration of permafrost thawing is significantly correlated with snow depth， near-surface temperature， precipitation， and vegetation index， though these relationships vary across different climatic regions.Near-surface temperature exhibits a strong positive correlation across all regions， making it the primary driver of freeze-thaw changes.Precipitation and snow depth show positive and negative correlations， respectively， with particularly strong correlations in semi-humid areas.The vegetation index is positively correlated with thaw duration in all regions， with the strongest correlation observed in semi-arid areas.（4） The relationship between thawing duration and seasonal climatic factors varies.Near-surface air temperature exerts a significant influence on the freeze-thaw process at seasonal scales， with the most pronounced impact occurring in spring.Precipitation is positively correlated in summer but negatively correlated in winter.Both snow depth and vegetation index are significantly correlated with thawing duration in semi-arid and semi-humid regions during spring， exhibiting negative and positive correlations， respectively.（5） Near-surface temperature influences the freeze-thaw cycle in the plateau’s perennial permafrost region during both dry and wet seasons.However， the effects of snow depth， precipitation， and vegetation index are more pronounced during the wet season.

Using effective bias correction methods and transforming non-stationary data to stationary can enhance the scientific accuracy of temperature analysis， allowing for a deeper understanding of its temporal and spatial distribution characteristics and evolution patterns.This study utilizes the ERA5_Land near-surface （2 m） monthly mean temperature observation dataset covering the period from 1970 to 2014.Initially， it employs the Taylor diagram， Taylor index， interannual variability skill score， and rank scoring method to evaluate and select among six climate models from the International Coupled Model Intercomparison Project Phase 6 （CMIP6） and the multi-model ensemble （MME） average models.Subsequently， the superior models are refined using the Delta bias correction method and the Normal distribution matching method.Finally， the study analyzes the temporal and spatial temperature variation characteristics of the Qinghai-Xizang Plateau from 2015 to 2100 under the SSP1-2.6， SSP2-4.5， and SSP5-8.5 scenarios.The results indicate that： （1） Among the six CMIP6 models and the multi-model ensemble （MME） average models analyzed in this study， the EC-Earth3 model demonstrates the most effective performance in simulating temperature.（2） When comparing the Delta bias correction results of the EC-Earth3 model with observational data， the regional averages of the coefficient of determination （R²） and the Nash-Sutcliffe efficiency coefficient （NSE） are 0.992 and 0.983， respectively.After applying the Normal distribution matching method for correction， the regional average values of R² and NSE are 0.990 and 0.978， respectively.This comparison reveals that the Delta bias correction method exhibits superior correction efficacy for the model's monthly temperature.（3） According to the combination of EOF-EEMD， the annual temperature of the first typical field of the three scenarios changes uniformly in the whole region， and there is a common sensitive area of temperature change under SSP1-2.6 and SSP2-4.5 scenarios， that is， the central region of the Qiangtang Plateau.The temperature dynamics in the second typical field reveal a gradual reverse-phase change from the upper reaches of the Zhaqu River to surrounding areas.Under the SSP1-2.6 scenario， the plateau experiences overall cooling in the east and warming in the west.Conversely， under the SSP2-4.5 and SSP5-8.5 scenarios， the plateau initially warms in the east and cools in the west， followed by a subsequent cooling in the east and warming in the west.This study provides a reference for bias correction methods that enhance the accurate application of climate model data in the Qinghai-Xizang Plateau region and offers essential foundational information for a comprehensive assessment of the impacts of temperature changes on water resources， ecosystems， and the environment in this area.

The central Qinghai-Xizang Plateau is located in the transition zone between the mid-latitude westerlies and the Asian monsoon， with complex circulation systems and water vapor sources.In the studies of lake-atmosphere interaction in the Qinghai-Xizang Plateau， little attention has been paid to the dependence of lake effect on background circulation to understand the mechanism of lake affecting extreme precipitation.To further understand the mechanism of lake influence on extreme precipitation， this study objectively classifies the dominant synoptic patterns responsible for the regional extreme precipitation events in autumn over the central Qinghai-Xizang Plateau with lakes densely distributed to analyze the characteristics and differences of lake effects under different dominant synoptic patterns.Based on the CMFD precipitation data and ERA5 reanalysis data during 1979 to 2018， 1358 regional extreme precipitation events were detected in autumn over the central Qinghai-Xizang Plateau， and it was found that the regional extreme precipitation events contributed more than 40% of the total autumn precipitation in most parts of the central Qinghai-Xizang Plateau with the large centers of regional extreme precipitation amount mainly concentrated in the Nam co basin and the small lakes in the north， that is also the region with high occurrence probability of extreme precipitation when regional extreme precipitation event occurs.Then， the spectral clustering method was used to analyze the atmospheric circulation over the central Qinghai-Xizang Plateau during the regional extreme precipitation events and identified three dominant synoptic patterns responsible for the regional extreme precipitation events in autumn over the central Qinghai-Xizang Plateau： precipitation in the southern mountainous areas caused by weak convergence airflow （P1 type）， precipitation in the northeast downstream under the control of monsoonal southwest airflow （P2 type）， and precipitation near lakes under the influence of southwest airflow in front of the westerly trough （P3 type）.They lead to 48.8%， 42.3% and 8.8% of the total occurrences of regional extreme precipitation events in autumn， respectively.P1 and P2 types mainly occur in September， and P3 type mainly occurs in October.The physical mechanism of the regional extreme precipitation occurrences is explained by analyzing the high and low level configuration of large-scale circulation fields and their anomalies under different synoptic patterns.Furthermore， multiple sensitivity experiments were conducted to reveal the relative importance of the influence of lake clusters in the central Qinghai-Xizang Plateau on regional extreme precipitation events under different synoptic patterns， and found that the lake clusters can lead to the precipitation amount averaged over the central Qinghai-Xizang Plateau reduced by 2.37%， increased by 12.11% and increased by 138.37% under the P1， P2 and P3 types， respectively.The lake effect under the P3 type is the most significant among the three synoptic types， making it a synoptic pattern prone to lake effect.Further mechanistic analysis shows that the enhancement of low-level instability and water vapor convergence over the lake and surroundings areas induced by the heating and moistening effect of lake play an important role in the formation of the regional extreme precipitation under the synoptic pattern P3.This research has identified the dominant synoptic patterns responsible for the regional extreme precipitation events over the central Qinghai-Xizang Plateau in autumn and revealed the relative importance of lake effects on regional extreme precipitation under different dominant synoptic patterns， providing necessary reference for further improving the prediction level of regional extreme precipitation.

Compound heatwave events are heatwaves that occur simultaneously during the day and at night， which not only threaten human health but also impede sustainable socio-economic and ecosystem development.In recent years， the frequency of compound heatwave events in the Sichuan-Chongqing （SC） region has increased significantly， and an advanced understanding of the plausible factors of compound heatwave variations over the SC region is of great importance for a better understanding of their impacts.Based on observational and reanalysis data， the relationship between the summer compound heat wave frequency （HWF） in SC and the anomalous atmospheric heat source （AHS） over the Qinghai-Xizang （Tibetan） Plateau （QXP） is statistically analyzed in the present study.Then， this study evaluates the performance of 28 climate models from the Coupled Model Intercomparison Project Phase 6 （CMIP6） in simulating the relationship between the SC HWF and the QXP AHS of 1985-2014 and explores the key factors causing the differences in the simulation capability among the models.The results show that both the climate mean and the standard deviation of the HWF have relatively large values in the eastern SC， where the HWF variability shows a significant negative correlation with the summer AHS over the southeastern QXP.When the AHS over the southeastern QXP is weaker in summer， an anomalous anticyclone is present over the eastern SC， leading to an anomalous downward motion.This anomalous descent induces cloud cover and surface shortwave changes， leading to the formation of heatwave events over the eastern SC.Most CMIP6 models can essentially simulate the spatial distribution characteristics of the observed climate states of the summer HWF in the SC region and the summer AHS in the QXP.However， the models perform better in simulating the standard deviation of the AHS over the QXP than in simulating the HWF in the SC regions.There are significant differences in the simulated relationship between the SC HWF and the QXP AHS between different models.This is mainly due to the different abilities of the models to simulate the anomalous vertical motions over the SC regions corresponding to the anomalous summer AHS over the QXP.Further analysis shows that a good performance of the models usually depends on their ability to simulate the anomalous vertical motions and cloudiness in the SC regions， which can lead to air temperature variations.Therefore， the simulated vertical motion and cloudiness anomalies in the eastern SC in response to the QXP AHS anomalies are the key circulation factors affecting the model’s performance in simulating the HWF-AHS relationship.

Based on daily observations from ground-level stations and daily NCEP/NCAR reanalysis dataset， the circulation anomalies of the winter persistent regional haze events for the years 1980 -2021 in Guanzhong region of Shaanxi and their precursor signal are analyzed.The winter persistent regional haze events in Guanzhong region is found to be closely connected with a pronounced atmospheric teleconnection pattern from the North Atlantic to Euraisa.A positive North Atlantic Osciilation （NAO+） phase and a positive East Atlantic/West Russia（EA/WR+） phase are observed as important part of this teleconnection pattern， the NAO+ pattern act as the origin of the atmospheric transmission.Approximately 75% of the NAO positive phase days from 15 to 5 days before the occurrence of persistent regional haze events are greater than 5 days， with a daily NAO index greater than or close to 0 and an average intensity greater than 0.There is a clear EATL/WRUS+ pattern in the Eurasian continent at 500 hPa three days prior to and after the occurrence day of persistent regional haze events in Guanzhong during winter.On the 1^ST to 6^th day， a clear positive geopotential height anomaly extends from Northeast China to the Sea of Japan at 850 hPa， which reflects the positive anomaly pressure gradient from the Korean Peninsula to central China accompanied with stronger southeast wind in Guanzhong.The stronger southeast wind anomaly intensifies the convergence in Guanzhong region and Southern Shaanxi， and transport the aerosol from central and eastern China to Shaanxi Province.

Aircraft icing is a high-impact weather phenomenon that poses a serious threat to aviation safety while also offering valuable opportunities for flight testing under complex meteorological conditions.Verification flight tests of civil aircraft in stratiform cloud icing environments are critical for airworthiness certification.A deeper understanding of the cloud microphysical characteristics in such conditions is essential to support the airworthiness certification of domestic civil aircraft.To investigate the cloud microphysical properties and airworthiness compliance of icing environments in Northwest China， this study analyzes in situ aircraft measurements， geostationary satellite observations， ERA5 reanalysis data， and sounding data collected during a non-precipitating stratiform cloud icing experiment over eastern Shaanxi Province on 8 December 2021.The synoptic background， cloud microphysical characteristics， and icing intensity were examined， and the compliance of the observed environmental data with airworthiness requirements was further evaluated.The results show that： （1） Under the combined influence of a 500 hPa upper-level trough， a 700 hPa shear line， and a surface cold high-pressure system， southwesterly warm and moist airflow generated extensive stratiform clouds in eastern Northwest China.An inversion layer at the cloud top facilitated the accumulation of supercooled liquid water.（2） The stratiform clouds were distributed between 2.8 km and 4.2 km in altitude， with temperatures ranging from -4 °C to -11 °C.An inversion layer approximately 100 m thick existed at the cloud top.The liquid water content （LWC） increased with altitude， from about 0.1 g·m⁻³ near the cloud base to a maximum of 0.39 g·m⁻³ at the bottom of the inversion layer near the cloud top.At 3.7~4.2 km and 3.0~3.3 km， small cloud droplets （10~15 μm） and larger particles （50~75 μm） dominated， with elevated LWC， median volume diameter （MVD）， and spectral width of small cloud droplets.In contrast， at 3.3~3.7 km， droplets were primarily 5~10 μm， with peak number concentrations but lower MVD.（3） The distribution trends of the average particle spectra across different height layers in the upper part of the cloud layer are relatively consistent.Small cloud droplets below 50 μm exhibit a bimodal distribution， while larger cloud particles above 50 μm display a unimodal distribution.The “Khrgian-Mazin” distribution fits the small droplet portion well.The region of high LWC near the cloud top correlates well with several factors： higher albedo （38%~44%）， smaller cloud effective radius （7~12 μm）， warmer cloud tops （ -15 °C）， and high optical thickness （40%~100） from the Himawari-8 satellite data.These satellite products are valuable for identifying the icing environment of single-layer stratiform clouds.（4） During three horizontal flight legs at different altitudes， the aircraft primarily encountered moderate icing.Temperature， droplet MVD， and LWC remained horizontally stable.The cumulative average LWC reached 40%~60% of the certification envelope value at -10 °C， with all icing conditions falling within the envelope.Overall， the microphysical characteristics of this non-precipitating stratiform cloud icing case met the environmental requirements for airworthiness certification flight testing， with particularly favorable conditions observed within the inversion layer beneath the cloud top.

Based on the observation time series data of Guizhou DSG1 precipitation phenomenon instrument from 2018 to 2023， the particle number distribution and scale spectrum characteristics of rain， snow and hail three types precipitation were compared and analyzed， and an integrated determination algorithm for precipitation phenomenon type identification was established based on the particle number， particle spectral width， and particle plurality， and the applicability of the algorithm was evaluated.The specific conclusions are： （1） The diameter spectrum widths of rain， snow， and hail droplets are concentrated in the ranges of 1~8 mm， 1~12 mm， and 5~12 mm， respectively.The velocity spectra are concentrated in the ranges of 3~15 m∙s^-1， 3~5 m∙s^-1， 12~15 m∙s^-1， and the particle plurality velocities are 4.4 m∙s^-1， 1.1 m∙s^-1 and 4.4 m∙s^-1.respectively.The rain and snow precipitation types can be effectively recognized by the particle falling velocities.（2） The percentages of rain particles in the raindrop and hail drop spectrum accounted for 50.1% and 64.3%， and the number of snow particles in the snowdrop spectrum accounted for 70.2%， which exceeded half of the total number of particles.The percentage of hail particles in the hail droplet spectrum is 0.19%， which is significantly higher than the short-term heavy precipitation （0.005%）.（3） Particles with particle diameters greater than 3 mm and particle velocities of less than 5 m∙s^-1 mainly exist in the process of snowfall.Particles with particle diameters greater than 5 mm and particle velocities greater than 10 m∙s^-1 mainly exist in the process of hailstorms and short-term heavy precipitation.Increasing the velocity limit can improve the accuracy of hail particle recognition.（4） By evaluating the integrated determination algorithm for precipitation phenomenon type recognition， the accuracy of single precipitation type recognition reaches more than 95%， and the false alarm rate of hail is only 1.7%， which can effectively reduce the cases of misrecognition as hail in short-term heavy precipitation.

Based on the hourly precipitation data of 3454 stations with dense space in Sichuan Province and DEM （Digital Elevation Model） data with horizontal accuracy of 30 m， the temporal and spatial distribution characteristics of extreme hourly precipitation in 7 regions of Sichuan Province in recent 10 years were analyzed， and the relationship between high frequency extreme precipitation and complex terrain was discussed.The results showed that： （1） In recent 10 years， the frequency of extreme hourly precipitation with hourly rainfall ≥100 mm in Sichuan Province has increased significantly with the growth rate of 6.4 times·（10a）^-1.（2） The sub-seasonal variation of extreme hourly precipitation frequency was more significant than that of extreme rainfall intensity， with the maximum monthly increase of 3.7 times and 0.2 times， respectively.In addition， the occurrence time of peak frequency was delayed with the increase of extreme hourly precipitation threshold.（3） The frequency of extreme hourly precipitation was significantly higher at night than during the day， and the occurrence time of peak-valley value and high-frequency concentration period were different in different regions， and the frequency peak appears gradually from south to north and from west to east.（4） The diurnal variation of extreme rainfall intensity was much weaker than that of extreme hourly precipitation frequency， and the extreme rainfall intensity of most stations in the basin was higher than the regional average， but the opposite was true in western Sichuan Plateau and Panxi area.（5） The distribution characteristics of extreme hourly precipitation frequency and cumulative rainfall in different regions were closely related to topographic uplift and topographic convergence in this region， and the increase of extreme hourly precipitation caused by topographic forced uplift in the western part of the basin was roughly below 1400 m.（6） The slope of high frequency extreme hourly precipitation sites in the basin was mainly eastward， and the slope of high frequency sites in the southwest of the basin was larger than that in the northwest of the basin.The number of maximum extreme hourly cumulative rainfall sites in the Western Sichuan Plateau and Panxi area increased first and then decreased with the slope， and the peak value was located in the slope， but the decrease was more rapid in Panxi area than in the Western Sichuan Plateau.

The variability of Arctic sea ice is closely linked to anomalous winter temperature changes over the Eurasian continent， while the frequent activity of winter cold high-pressure systems directly influences temperature reductions in Siberia and East Asia.In the context of "Arctic amplification" and projected Arctic sea ice retreat scenarios， it is worth delving into how near-surface anticyclone activity in Siberia will change.This study utilizes a Mask R-CNN anticyclone objective identification algorithm based on deep learning to identify winter synoptic-scale anticyclones over the Eurasian continent.It further investigates the potential impacts and mechanisms of anomalous autumn sea ice changes on anticyclone and cold air activities under the backdrop of rapid future Arctic sea ice retreat， using data from the European Centre for Medium-Range Weather Forecasts （ECMWF） ERA5 reanalysis， the National Oceanic and Atmospheric Administration （NOAA） OISST V2.1 daily sea ice concentration dataset， and outputs from the MIROC6 model.The results indicate that the sea ice index in the Barents-Kara Sea （BKS） region declined during autumn from 1981 to 2022， accompanied by significant temperature drops in the mid-to-high latitudes of the Eurasian continent， particularly in Siberia， where anomalous accumulations of cold air mass occurred， and the cold air mass carried by anticyclone activity increased.Utilizing model data from the Polar Amplification Model Intercomparison Project （PAMIP）， the study statistically analyzed the variability of anticyclone activity over the Eurasian continent under scenarios of reduced Arctic sea ice in the future.It was found that under conditions of sea ice reduction， Siberia is one of the main regions influencing the formation and dissipation of anticyclones over the Eurasian continent.Anticyclones in this region exhibit local activity characteristics， significantly contributing to the quasi-stationary Siberian cold high and the accumulation of cold air in the cold pool region.Temperatures increased along the northern edge of the Eurasian continent but significantly decreased at mid-latitudes， accompanied by an increase in extremely cold days across most of the Eurasian continent.Further research revealed that autumn BKS sea ice conditions can serve as a precursor factor influencing subsequent winter anticyclone activity and temperature anomalies.The sea ice conditions in this region result in a significant reduction in the meridional gradient of regional potential vorticity， thereby increasing the frequency of blocking events in the upstream Eastern European Plain， directing cold air to build up over Siberia.This favors the enhancement of anticyclone activity and the transport of cold air， exacerbating the winter cold trend in East Asia.

Based on daily precipitation gridded data from CN05.1 ground observation data， the monthly NCEP/NCAR reanalysis data and sea surface temperature （SST） data from the Japan Meteorological Agency （JMA） spanning 1961 to 2021， this study uncovers the synergistic influence of the North Pacific and North Atlantic SST on the interannual anomalies of regionally consistent anomaly patterns in Xinjiang during winter.The findings obtained from the analysis are presented as follows： （1） Winter precipitation in Xinjiang is predominantly concentrated in the north of the Tianshan Mountains and Kashgar， and EOF analysis identifies three main interannual anomalous modes， namely regionally consistent anomaly， north-south antiphase anomaly and tripolar anomaly patterns.A shift from low to high precipitation occurred around 1987， with a significant increase in interannual variability post-2000.（2） This study identifies the key circulation systems and three transport pathways of cold air and water vapor facilitating increased interannual winter precipitation in Xinjiang.These include the Polar east of Novaya Zemlya-Western Siberia-Aral Sea-Northwest and northern Xinjiang northerly cold air and water vapor path， the tropical and subtropical Atlantic-Mediterranean-Black Sea-Caspian Sea-Xinjiang westerly water vapor paths and the equatorial Indian Ocean-Arabian Sea-Red Sea-Persian Gulf-Southern Caspian Sea-Xinjiang southwestern water vapor path.（3） The “relay” mechanism by which North Pacific and North Atlantic SST influencing the interannual anomalies of winter precipitation in Xinjiang is described.From pre-spring to pre-autumn， Rossby wave energy excited by the SSTA like a Pacific Decadal Oscillation （“+PDO” -like） Sea Surface Temperature Anomalies （SST Anomalies， SSTA） propagates eastward from the North Pacific Ocean over the North Atlantic， triggering corresponding atmospheric teleconnection wave trains.The North Atlantic SST， along with the atmospheric anomalies’ signals， drives its SSTA toward the “+” “-”， and “+” tripolar pattern.In winter， the North Atlantic tripolar SSTA releases its stored energy， exciting a longitudinal tripolar anomalous wave train （North Atlantic Oscillation with negative phase in the lower layers） and two downstream energy branches.The northeastern branch contributes to the development of a positive Scandinavian Pattern （SCA）， while the southeastern branch promotes an anticyclonic circulation from North Africa to the northern part of the Arabian Sea， fostering the development of a upper-level weak temperate jet stream and a strong subtropical jet stream.These meteorological conditions converge warm and cold air currents in Xinjiang， particularly in its northwestern regions， leading to an increase in precipitation levels.The precursor “+PDO” -like SSTA can be an interannual predictive signal for winter precipitation surpluses in Xinjiang.

Using the day-by-day average temperature， maximum temperature， and minimum temperature data from a total of 70 ground-based conventional observatories in the Northwest Sichuan Ecological Demonstration Area as well as its peripheral areas from 1961 to 2022， and adopting the climatic propensity rate， EOF（Empirical Orthogonal Function） analysis method， and Morlet complex wavelet method， we analyzed the temporal and spatial change characteristics of the extreme temperature indices in the Northwest Sichuan and its peripheral areas， and the results show that： （1） The extreme temperature warm indices and extreme value indices in the study area show an increasing trend， the extreme temperature cold indices show a decreasing trend， and the DTR（Diurnal Temperature Range） change is not obvious； the warm and cold indices have similar magnitude of change， the rate of change of the night indices is greater than that of the day indices， and the climate change of the extreme temperature indices of the neighboring areas is more significant compared to that of Northwest Sichuan.（2） Extreme temperature indices in Northwest Sichuan have 2~3 main cycles in 2~30 years； neighboring areas have 2~3 main cycles in 2~20 years.Most of the indices in Northwest Sichuan have a sudden change of cycle around 2000， and the frequency of alternation between short and medium cycles is increasing.The cycles of FD0（Frost Days）， TN10P（Cold Nights）， TX10P（Cold Days）， and CSDI（Cold Spell Duration） in the neighboring regions changed abruptly around 1990， and the frequency of short- and medium-cycle alternation decreased； the cycle changes of the extreme temperature indices in Northwest Sichuan have lagged compared with those in the neighboring regions.（3） TNx（Max TN）， TXx（Max TX）， and TR20 （Tropical Nights ） show an increasing trend in the northern part of the study area； TXn（Min TX） shows an increasing trend in the eastern part of NW Sichuan as well as in the neighboring areas； ID0（Ice Days） and TN10P decrease over the whole area； FD0 decreases in NW Sichuan and increases in the neighboring areas； TNn（Min TN）， TN90P（Warm Nights）， and DTR decrease in NW Sichuan and increase in the neighboring areas； CSDI and SU25（Summer Days） increase in the east and decrease in the west， and WSDI（Warm Spell Duration） is the opposite.CSDI and SU25 increased in the east and decreased in the west in the study area， while WSDI was the opposite.（4） In the study area， the extreme temperature cold indices mainly show a decreasing trend， the extreme value indices change less， and the rest of the indices mainly show an increasing trend； the overall warming trend is shown， and the indices change in the study area respond well to the global warming， with the peripheral areas showing more significant changes.

Flood disasters are among the most serious natural disasters in the Haihe River Basin， inflicting substantial damage on infrastructure， electricity， transportation， agriculture， and other critical sectors.It has always been given great attention and concern by various flood control decision-making departments.The western and northern parts of the Haihe River Basin are mountainous and plateaus， while the southeastern part is the North China Plain with gentle terrain.The transition zone between the mountainous area and the plain is relatively short， and the river channels have short sources， rapid flow， and large flood flow velocity.The propagation time of floods is short， with the longest time from rainfall in the mountainous area to the occurrence of floods at the river outlet not exceeding 1~2 days， and the shortest time being only a few hours.This makes floods in the basin characterized by a short lead time and strong suddenness.Heavy rain is the most direct and fundamental cause of flood disasters.In this study， hydrological and meteorological data are used to select and analyze the characteristics of historical flood-causing rainstorms in the Haihe River basin.Based on hydrological monitoring data in the Haihe River Basin， daily precipitation data from national meteorological stations， and ERA5 global reanalysis data， refered to the recommended design flood revision results and corresponding peak discharge design values specified in the Haihe River Water Conservancy Commission's "Recommended Results Table of Design Flood Revision in the Haihe River Basin"， historical extreme floods， major floods， and moderate floods in the Haihe River Basin since 1952 were selected and analyzed.According to the number of hydrological stations with flood and the time interval between flood occurrences， the flood can be divided into regional flood and local flood.Analysis on the frequency of flood with time and the frequency distribution of historical flood in different river systems， The temporal and spatial characteristics of historical flood in Haihe River Basin are obtained.The results indicate that extreme floods， major floods， and moderate floods in the basin over the past 70 years all occurred in July and August， and there are two peak points in the frequency of flood occurrences， which is related to the movement and intensity changes of the summer monsoon climate； Geographically， the occurrence of floods in the basin shows a northeast-southwest trend， with the characteristics of more occurrences in the south and fewer in the north， and more occurrences in the west and fewer in the east.Analysis of the basin's topographical features shows that the river systems on the leeward slopes in the mountainous areas， with long river sources and large drainage areas， are relatively easy to control， while the river systems on the windward slopes have dispersed tributaries， short sources， rapid flow， and strong suddenness， making them relatively difficult to control.Moreover， the windward areas of the Taihang Mountains and the Yan Mountains are also concentrated areas of heavy rain， leading to sharp rises in river levels， concentrated flood volumes， high flood peaks， and short historical durations.Therefore， extremely large floods are most likely to occur in the central and southern parts of the basin.Furthermore， statistical analysis on the historical flood distribution and interannual variation of precipitation anomaly in the Haihe River Basin from 1952 to 2020 shows that over 80% of individual flood events and 100% of regional floods occurred in years with above-average precipitation.The inter-decadal fluctuations in the number of historical floods exhibit a "more-less-more-less" stage-wise characteristic， which is consistent with the characteristics of summer precipitation changes in North China.Finally， based on the analysis of the weather chart on the day and the past 4 days of the extreme rainfall events causing floods occurrence， selected Haihe River Basin （111°E-121°E， 34°N-43°N） as a key area， with analyzing the influencing system and occurrence mechanism of the heavy rain in the key area， the extreme rainfall events causing floods in the Haihe River Basin can be roughly classified into five synoptic patterns： northward typhoon pattern， northeast cold vortex + southwest vortex pattern， low vortex pattern， upper-level trough pattern， and Mongolian cold vortex pattern.Among them， the proportion of extreme rainfall events caused by typhoons in the Haihe River Basin is the highest， accounting for 42.4%， followed by cold vortices and low vortices， accounting for 27.3% and 15.2% respectively.The three regional extreme floods that occurred in the basin were also influenced by typhoons and low vortices.

The investigation of the impact of hydrothermal variation on the water conservation function of forests holds substantial scientific importance for formulating rational ecological protection policies and water resource management strategies.The present study focuses on the hydrothermal variation of Picea crassifolia forests in Qinghai province， aiming to elucidate how different hydrothermal conditions influence the water conservation capacity of these forests.Long-term hydrothermal data spanning over 21 years were analyzed using regression fitting models and water balance models.The findings can be summarized as follows： （1） The average water content of moss and soil at various elevations （2600， 2700， 2900， 3100， and 3300 meters） was examined.The results showed that the average water content of moss and soil at these elevations was 100.76%， 27.42%， 86.94%， and 33.18%， respectively.Regression analysis revealed that the trends in water content followed quadratic and exponential functions.Moss exhibited significant long-term water absorption， retention， and storage capacities， indicating a robust water conservation function.These results highlight the crucial role of moss in maintaining the water conservation capacity of the forest ecosystem.（2） The study analyzed the relationship between soil temperature and elevation.Soil temperature decreased with increasing elevation at a rate of 0.39% per 100 meters， with a significantly linear decline.The elevation of 2900 meters emerged as a critical threshold： above this point， soil temperature remained below 0 ℃， while below 2900 meters， soil temperature was above 0 ℃.Additionally， air temperature exhibited a fluctuating pattern with increasing elevation， following a significant quadratic polynomial trend.These findings underscore the influence of elevation on thermal conditions， which in turn affect the hydrological processes in the forest ecosystem.（3） The mean water conservation capacity of the study area was calculated to be 159.63 mm·m^-2·a^-1， with a significant quadratic trend within the 2600~3300 m elevation range.Correlation analysis showed that precipitation and soil moisture were significantly positively correlated with water conservation capacity （R ²=0.994 and 0.988， P0.01， respectively）， while soil temperature and forest evapotranspiration were significantly negatively correlated with water conservation capacity （R ²=0.96 and 0.98， P0.01， respectively）.These results indicate that precipitation and soil moisture promote water conservation， while temperature and evapotranspiration from the forest floor inhibit it.Therefore， precipitation and temperature are key determinants of vegetation growth and water conservation function in the Picea crassifolia forests of Qinghai province.The findings emphasize the importance of considering elevation， temperature， and precipitation in formulating effective ecological protection policies and water resource management strategies for these forest ecosystems.

In this paper， the vertical structure of the atmospheric boundary layer in Chongqing on summer afternoon is analyzed using the sounding data with intensive observation.The general features of the vertical structure of the atmospheric boundary layer under different weather conditions are also given.The results show that the atmospheric boundary layer depicts a typical convective boundary layer structure under clear and cloudy conditions.On clear days， the development of convective boundary layer is very vigorous， the surface transpiration/evaporation is strong， and there is obvious upward water vapor transport.The near-surface superinsulation layer is thick， and the potential temperature lapse rate is large.The height of the boundary layer can reach 1.5 km on average and up to 2.1 km， while the height under cloudy conditions is relatively low， with an average height of 1.0 km.Under sunny and cloudy conditions， the wind speed in the boundary layer is generally low with the values less than 5.0 m·s^-1.On cloudy days， the atmospheric boundary layer presents a classic morning boundary layer structure， which means that there is a stable boundary layer and a residual mixed layer between the convective boundary layer and the entrainment layer.Under this condition， the thickness of the convective boundary layer is relatively low， with a magnitude of less than 0.8 km.The specific humidity profile presents a feature opposite to the potential temperature profile， and the boundary layer wind speed is relatively low.When it rains， the potential temperature depicts a neutral stratification feature and shows no obvious convective boundary layer structure.Due to the influence of different weather systems and processes， the characteristics of specific humidity and wind profiles are relatively complex and changeable.

The BCC_AVIM model neglects the effects of molecular diffusion rate， vegetation litter and dry surface layer thickness on water vapour conductivity in the simulation of latent heat fluxes at the land surface.Based on this， this paper considers the above detailed physical processes for the simulation of latent heat fluxes at the land surface， and focuses on the effects of these processes on the simulation.The physical processes considered mainly include （1） the diffusion rate of molecules through the soil pores to the drying surface layer and the effect of plant apoplastic cover on the water vapour conductivity （Sakaguchi and Zeng， 2009， hereafter referred to as the S-Z scheme）； （2） the effect of the thickness of the drying surface layer of soil on the water vapour conductivity （Swenson and Lawrence， 2014， hereafter referred to as the S-L scheme）； and （3） the effect of physical processes on water vapour conductivity in the combined S-Z and S-L schemes， hereafter referred to as the SZ-SL scheme.In order to better study its sensitivity in different subsurfaces， observations from the flat and uniform alpine meadow Maqu station and the complex topography of Si'e Mountain station in Southern Sichuan Forest were selected to examine the simulated effects of different parameterisation schemes.The results are as follows： （1） The BCC_AVIM model can better reproduce the trends of soil temperature and humidity， sensible latent heat fluxes and other elements at Si'e Mountain and Maqu stations， but the simulated values deviate from the measured values to a certain extent； （2） Based on the BCC_AVIM model， the simulated latent heat fluxes at the two stations are significantly improved by the introduction of more detailed physical processes， with the simulated results of the S-Z scheme being the closest to the measured values， and the simulated results of the S-Z scheme being the closest to the measured values.were closest to the measured values， with the Pearson's correlation coefficient （R） of Si'e Mountain station improved from 0.68 to 0.74， the mean absolute percentage error （MAPE） reduced by 10.7%， and the root mean square error （RMSE） reduced by 4.0 W·m^-2； the R of Maqu station was improved from 0.15 to 0.62， the MAPE was reduced by 5.7%， and the RMSE was reduced by 11.2 W·m^-2； （3） the simulation results of the two stations' soil temperature and humidity simulation results show that compared with the original scheme， the scheme after considering more detailed physical processes increases the simulated values of soil temperature and soil humidity and enhances the correlation with the measured values， of which the S-Z scheme is the optimal scheme for soil temperature simulation at the two stations， the S-L scheme is the optimal parameterization scheme for soil humidity simulation at Si'e Mountain station， and the SZ-SL scheme is the optimal parameterization scheme for soil moisture simulation at Maqu station.scheme； （4） by considering more detailed physical processes， not only the simulation accuracy of latent heat fluxes is significantly improved， but also the simulation ability of soil temperature and soil moisture is enhanced， but the improvement of sensible heat fluxes is still limited.

The India-Burma Trough （IBT）， a semi-permanent low-pressure system situated on the southern flank of the Qinghai-Xizang （Tibetan） Plateau during the winter half-year， plays a crucial role in modulating winter and spring precipitation patterns across China.To quantitatively characterize IBT activity， researchers have proposed multiple indices from diverse methodological perspectives.While data source selection and isobaric surface choices exert limited influences， the principal distinctions among these indices stem from their utilization of different atmospheric variables， notably geopotential height， relative vorticity， and vertical velocity fields.The regionally mean geopotential height index of the IBT is particularly susceptible to the isobaric surface uplift caused by global warming.Its persistent weakening trend essentially reflects the increasing geopotential height of tropospheric isobaric surface under global warming.Consequently， this necessitates the implementation of zonal correction procedures to accurately capture the trough’s activity charcteristics and its interannual-to-decadal variability.The revised index demonstrates interannual and decadal variation patterns comparable to those derived from relative vorticity and vertical velocity， while effectively mitigating the confounding effects of climate warming on geopotential height fields.It reveals a robust correlation between IBT intensity and winter precipitation in South China， with coherent decadal-scale fluctuations observed in both parameters.This revised geopotential height-based index achieves dual objectives： （1） Effectively eliminating global warming-induced isobaric surface uplift artifacts， and （2） Maintaining clear physical interpretability by capturing the localized geopotential height depression characteristic of meridionally elongated trough systems like the IBT.Notably， while detrending methods can reduce climate changes impacts on geopotential height indices， they may inadvertently introduce spurious weakening trends in interannual variability due to discrepancies between short-term atmospheric fluctuations and long-term climate trajectories.This study highlights a critical implication that the validity of regional mean geopotential height as a climate system metric requires rigorous verification.And the isobaric surface rising effects by global warming must be explicitly accounted for to distinguish genuine climate system characteristics from warming-induced artifacts.

Based on GPM data from March 2014 to July 2023， the spatial and temporal distribution characteristic of mesoscale convective systems （MCSs） and sub-mesoscale convective systems （sub-MCSs） in East China are studied.Then the macro and micro structure characteristics of MCSs and sub-MCSs are studied based on six cases from June to August 2022 which classified by the area of systems.The results show that MCSs occur most frequently in June.The magnitude of diurnal variation of MCSs is relatively flat， and the life history is longer.The sub-MCSs occur most frequently in August.The period of 14:00 -15:00 （Beijing time） are the time when sub-MCSs most likely occurring.The geographical distribution of convection is closely related to the topography.The concentrated distribution area of MCSs in summer has a trend of changing from south region to north region.The sub-MCSs mainly distributed in Fujian and Zhejiang Province and mountainous area in Jiangxi Province in summer.According to precipitation types， MCSs and sub-MCSs can be divided into convective precipitation， stratiform precipitation and other precipitation.The particle concentration of convective precipitation in MCSs is lower than that of stratiform precipitation in general， but the particle size is larger.The average near-surface rainfall rate of convective precipitation in MCSs is almost four to five times as much as the stratiform precipitation.The particle size of sub-MCSs dominated by convective precipitation is as much as convective precipitation in MCSs， but the particle concentration is much lower， which leads to the average near-surface rainfall rate of sub-MCSs is much lower than that of convective precipitation in MCSs.Precipitation intensity is determined by many factors such as particle size and particle concentration.The precipitation particle size increases when descending form the air above 5 km altitude and the growth rate of convective precipitation is stronger than that of stratiform precipitation.The precipitation particle size decreases when descending form the air below 4 km altitude.The particle concentration of stratiform precipitation has no significant change when descending， while the convective precipitation is generally associated with the increase of particle concentration.

In order to study the applicability of China΄s first generation global atmospheric reanalysis（CRA） precipitation dataset in Sichuan region.The applicability of CRA has been evaluated with the precipitation observations from 155 national meteorological stations in Sichuan region and further compared with the ERA5 and CFSR datasets in terms of spatial distribution of precipitation， temporal variations， error analysis.The mean error（ME）， root mean square error（RMSE）， Standard deviation（STD）， Correlation coefficient（R） of the three reanalysis datasets are computed to compare the accuracy and evaluate the application.The comparative results suggest that： （1） In the simulation of the spatial distribution of annual precipitation， the distribution of less precipitation in the western Sichuan Plateau and more precipitation in the Sichuan Basin can be simulated by the three reanalysis datasets， but the location and magnitude of the extreme precipitation area can only be better simulated by CRA； （2） In the simulation of the spatial distribution of four seasons precipitation， CRA is almost consistent with the observations， and the summer precipitation of CRA is less than the observations， the location and magnitude of ERA5 and CFSR is mostly inconsistent with the observations， and the precipitation of ERA5 and CFSR is larger than the observations； （3） In the characteristics of temporal changes in precipitation， the seasonal variation of precipitation can be simulated by the three reanalysis datasets， but annual variability of the monthly and seasonal precipitation can be only be simulated by CRA.Compared with ERA5 and CFSR， the linear variation characteristics of Sichuan precipitation can be better reflected by CRA； （4） In the spatial distribution of daily precipitation RMSE， the RMSE of CRA is the smallest， the RMSE of ERA5 and CFSR in different regions are different.In terms of correlation coefficient， standard deviation， and root mean square error for precipitation in four seasons， CRA has the largest correlation coefficient in all seasons， and the smallest standard deviation， root mean square error.On the whole， CRA is better than ERA5 in the simulation of precipitation in Sichuan region， ERA5 is better than CFSR.And CRA can be used to replace ERA5 and CFSR.