Current Issue

• Comparative Analysis of Coupling Relationship Between Land Surface Processes and Atmospheric Boundary Layer Evolution in Nagqu Area in Different Seasons
• Guantian WANG, Zeyong HU, Genhou SUN, Yaoxian YANG, Lianglei GU, Chunwei FU, Weiwei FAN, Di WU, Ruijia NIU, Hongyu LUO
• 2023 Vol. 42 (6): 1361-1371.  DOI:10.7522/j.issn.1000-0534.2023.00020
• Abstract ( ) PDF (4389KB) ( )

• The coupling relationship between land surface processes and atmospheric boundary layer is one of the key links and difficulties in understanding the thermal effect over the Qinghai-Xizang Plateau.Based on the surface and radiosonde observation data of Nagqu Plateau Climate and Environment Observation and Research Station in May， July and October 2019， this paper analyzes the surface energy budget， the daily and seasonal variations of vertical profile of atmospheric temperature and humidity， in Nagqu Area of the Qinghai-Xizang Plateau， and discusses the evolution law of the atmospheric boundary layer height in different seasons in this region.The results show that the convective boundary layer is 2842 m high in sunny days due to the influence of diurnal net radiation intensity during the observation period in May.It is 1481 m high in cloudy day， which is relatively low， and the strong convective weather may change it into a stable boundary layer.In the meanwhile， the exchange between the sensible heat and the latent heat in the near surface atmosphere provides energy support for the maintenance and development of the atmospheric boundary layer.The vertical profile of potential temperature and specific humidity can correctly reflect the seasonal difference of atmospheric boundary layer height in gqu Area.The height of the convective boundary layer is highest in May， less high in October and the lowest in July while the stable boundary layer is highest in July， less high in May and lowest in October.

• Spatio-Temporal Changes of Key Climatic Elements in the Upper Yellow River Water Conservation Area in Recent 60 Years
• Zihan ZHANG, Xuejia WANG, Meixue YANG, Lanya LIU, Jichun LI, Guoning WAN
• 2023 Vol. 42 (6): 1372-1385.  DOI:10.7522/j.issn.1000-0534.2023.00011
• Abstract ( ) PDF (2797KB) ( )

• The upper Yellow River water conservation area is an important section for ecological protection and high-quality social-economic development in the Yellow River Basin.The impact of climate change on the spatio-temporal distribution of its water resources will exacerbate the occurrence of natural disasters， which in turn will affect China's regional ecology and even the living environment of human beings.Based on the CN05.1 gridded air temperature， precipitation， and wind speed data from 1961 to 2016 and the actual evaporation data of GLEAM V3.5a from 1981 to 2020， this paper analyzed the changes of key climatic elements in the water conservation area of the upper Yellow River Basin in the past 60 years.The results are as follows： （1） The air temperature in the research area increased significantly， the variation trend of the air temperature can reach 0.34 °C·（10a）^-1， and the largest temperature rise occurred in winter.Maqu county and surrounding areas in Heihe region have seen the most dramatic warming.（2） The regional precipitation increased as a whole， the variation trend of the precipitation is about 9.3 mm·（10a）^-1.The growth rate was relatively rapid in spring and summer， and the slowest occurred in winter.The growth trend gradually decreased from the northwest to the southeast， with a significant increase in the arid regions of the west， and a relative decreasing trend in the humid regions of the southeast.（3） After experienced an anomalous rise in the early 1970s， the near-surface wind speed continued to decline， the variation trend of it is about -0.11 m·s^-1·（10a）^-1， and the wind speed decreased in most regions of the study area， especially in the northern Datong River area.（4） The actual evaporation showed an increasing trend， the variation trend of it is 11.89 mm·（10a）^-1， of which the relatively large increases occurred in spring and winter， and the growth rate showed a trend of gradual increasing from east to west.Among them， the increase of the actual evaporation in Zhaling Lake， Eling Lake area and the western part of Datong River area was the most significant， and only a few places in the middle and southeast decreased.（5） From the perspective of precipitation and evaporation， the growth rate of precipitation is slightly higher than that of the actual evaporation during the same period （from 1981 to 2016）， therefore the water conservation area in the upper reaches of the Yellow River Basin also has the trends of warming and wetting as the climate warms.

• A Comparative Study on the Impact of MWHS-2 and MHS Data Assimilation on the Simulation of Rainstorm in the Three Rivers Source Area
• Xu CHEN, Lei WANG, Xiehui LI, Haobin ZHONG, Xuhui DENG
• 2023 Vol. 42 (6): 1386-1401.  DOI:10.7522/j.issn.1000-0534.2023.00024
• Abstract ( ) PDF (6056KB) ( )

• Based on the mid-scale WRF （Weather Research and Forecasting） numerical model， this study uses the direct assimilation module data from the FY-3C satellite MWHS-2 （Micro-Wave Humidity Sounder 2）， and the WRF-3DVAR （Three Dimensional Variation） method to conduct assimilation comparison experiments on two precipitation processes in the Three Rivers Source area.Moreover， this study extensively compares the effects of two assimilation data sets on simulation results： data from the MWHS-2 （microwave humidity instrument carried by FY-3C） and data from the MHS （Microwave Humidity Sounder） carried by NOAA-18 （National Oceanic and Atmospheric Administration-18）.Results of the study show consistent simulation results for MWHS-2 and MHS data assimilation.For instance， regardless of whether assimilation is conducted or not， the simulated precipitation range is overestimated for precipitations less than 30 mm.However， the simulated range and amount are underestimated for precipitations higher than 30 mm.Furthermore， data assimilation strengthens the 500 hPa southwest wind field， increases the intensity of water vapour transport， shifts the high-altitude trough to the southwest， and strengthens the 300 hPa wind field disturbance， all of which increase the precipitation range above 30 mm and， to a certain extent， improve the precipitation level results.However， compared to the actual situation， the precipitation area is biased southward.Satellite data assimilation significantly improves the range of the water vapour flux field and specific humidity field precipitation areas， but its effects on the intensity improvement are not obvious.At the same time， changes in the water vapour flux field and specific humidity field change the precipitation forecast area and intensity.As for the temperature field， the WRF simulation includes significant errors.Satellite data assimilation shows a certain improvement effect on the temperature field and a more significant improvement effect on the humidity field.In other words， MWHS-2 or MHS satellite data assimilation improves the precipitation forecast in the Three Rivers Source area.These conclusions provide significant guidance for improving the precision of precipitation forecasting in the Three Rivers Source area.

• Influence of Different Development Periods of the Strong and Weak South Asian Monsoon on the Vertical Circulation over the Qinghai-Xizang （Tibetan） Plateau
• Yufei PEI, Minhong SONG, Shaobo ZHANG
• 2023 Vol. 42 (6): 1402-1415.  DOI:10.7522/j.issn.1000-0534.2023.00022
• Abstract ( ) PDF (8435KB) ( )

• In order to explore the role of the changes in the strength and weakness of the South Asian monsoon on the vertical circulation of the Qinghai-Xizang （Tibetan） Plateau， the South Asian monsoon index WYI was calculated using the high-resolution JRA55 reanalysis data for the past 30 years from 1990 to 2019 and the strong and weak years of the South Asian monsoon were selected， and the effects of the changes in the strength and weakness of the South Asian monsoon on the vertical circulation of the Qinghai-Xizang （Tibetan） Plateau were analyzed by comparing the three different periods of the pre-monsoon outbreak， outbreak period and late outbreak.The following main conclusions were obtained： （1） The strength and extent of updrafts on the southern side of the plateau in May in WYI strong years are greater than in weak years， the intensity of updrafts on the main and southern sides of the plateau increases in July， and the difference between strong and weak years is not obvious.（2） In May and October， both mass and energy converge to the plateau from the south and north sides of the plateau， while in July， it turns to dissipate mass and energy from the plateau to the north and south sides.the intensity of the upper-level radiation dispersion in the south side of the plateau in the WYI strong year is greater than that in the weak year， and the difference of the irradiation intensity in the lower level is smaller.The difference in the intensity of energy and mass transfer between WYI strong and weak years is greatest in May and least in July.（3） In the WYI strong year， the 100 hPa South Asian high pressure shifts to the western type in October， and the 500 hPa West Pacific subalpine lifts northward， so the wind field on the southern side of the plateau shifts and raises the high altitude temperature， while in the WYI weak year this phenomenon occurs in May， indicating that the South Asian monsoon changes the horizontal circulation situation at high altitude and thus affects the vertical circulation of the plateau.The surface temperature of the main body of the plateau in May， July and October in WYI strong years is greater than that in weak years， indicating that under the influence of the warm and humid airflow brought by the South Asian monsoon， the updraft from the southern side of the plateau lifts to the plateau， and the surface temperature of the plateau increases significantly， and the surface heat of the plateau increases which in turn affects the vertical circulation of the plateau.

• Water and Heat Flux Characteristics of Alpine Wetland and Alpine Steppe under Grazing Enclosure on the Northern Xizang
• Zhuangzhuang WANG, Yaqiong LÜ, Da WEI, Yahui QI, Xiaodan WANG
• 2023 Vol. 42 (6): 1416-1428.  DOI:10.7522/j.issn.1000-0534.2023.00005
• Abstract ( ) PDF (6132KB) ( )

• Grazing enclosure has been extensively employed as a direct and effective management measure for grassland restoration on the Qinghai-Xizang Plateau.Enclosures significantly increased vegetation coverage and affected the water and heat exchange between the land surface and the atmosphere.However， there is still a lack of quantitative research on how enclosures regulates water and heat fluxes in typical alpine ecosystems.Based on continuous data observed from eddy covariance system from July 2019 to June 2021 at alpine steppe and alpine wetland of the Northern Xizang， the changes of surface energy flux after enclosure was analyzed by using the eddy covariance method.The results show that： The water and heat fluxes in alpine steppe and alpine wetland shows significant unimodal diurnal variations.The exchange of land-atmosphere in alpine steppe is mainly dominated by sensible heat （Bowen ratio： 1.60） except in Summer， while wetland mainly transfers energy to the atmosphere by latent heat （Bowen ratio： 0.31） whole year.Grazing enclosure decreased the surface fluxes in alpine steppe， the sensible heat flux reduced by 5.99 W·m^-2 and the latent heat flux increased by 4.84 W·m^-2.Grazing enclosures increased the surface fluxes in alpine wetland， the sensible and latent heat raised by 3.04 W·m^-2 and 30.95 W·m^-2， respectively.The daily and average sensible and latent heat fluxes decreased in alpine steppe but increased in alpine wetland.The effect of enclosure on surface energy fluxes was stronger during the day and weaker at night.The collected literature data demonstrated that fencing decreased soil temperature and increased soil water holding capacity.Given the data of soil temperature， soil moisture， latent heat flux， and sensible heat flux， our study shows the cooling potential of enclosure on alpine steppe and alpine wetland.

• Comparative Analysis of Convection Permitting Model and Cumulus Parameterization for Simulation of Summer Precipitation over Qinghai-Xizang （Tibetan） Plateau
• Ying CHEN, Xianyu YANG, Yaqiong LÜ, Jun WEN, Jianing ZHU
• 2023 Vol. 42 (6): 1429-1443.  DOI:10.7522/j.issn.1000-0534.2023.00016
• Abstract ( ) PDF (8759KB) ( )

• The Qinghai-Xizang （Tibetan） Plateau is known as the Asian water tower.The change of its water resources has an important impact on the weather and climate in the lower reaches.Precipitation is a key role in the water cycle.Therefore， it is of great significance to accurately simulate plateau precipitation for water resources security in China.In recent years， some studies have found that the convection-permitting model （the cumulus parameterization scheme could be turned off when grid scale is less than 4 km） could improve the precipitation simulation over the Qinghai-Xizang （Tibetan） Plateau.However， the previous studies only selected 1~3 cumulus parameterization schemes for comparison.It is still unknown whether convection-permitting model is superior to any cumulus parameterization scheme.In this paper， the ability of nine cumulus parameterization schemes in WRF and convection-permitting model （CPM） in simulating the precipitation over the Qinghai-Xizang （Tibetan） Plateau in the summer of 2009 was evaluated.The results showed that the simulations overestimate the summer precipitation over Qinghai-Xizang （Tibetan） Plateau in 2009， and the error was about 0.4~2 mm·d^-1.The over simulation of CAPE and latent heat flux in Qinghai-Xizang （Tibetan） Plateau may be one of the reasons for the overestimations.Among all simulations， the G3 cumulus parameterization scheme has the best simulation of the mean precipitation the mean precipitation and the dinural cycles precipitation and it can can better capture the precipitation intensity， spatial distribution， precipitation area and diurnal cycles of the mean precipitation.CPM showed overall the second best precipitation simulation following G3 cumulus parameterization scheme， which can not effectively improve the simulation of diurnal cycles of precipitation， but can improve the simulation of precipitation frequency.In different plateau ecological regions， all simulations cannot reasonably simulate the precipitation in the desert area and the southern foot of the Himalaya， but compared with the cumulus parameterization schemes， CPM can greatly reduce the error in the desert area.In other regions， CPM and Tiedtke cumulus parameterization scheme performed well.Considering the mean precipitation and precipitation frequency， the CPM， Tiedtke and G3 cumulus parameterization scheme have the minimum simulation error for precipitation in different regions and intensity.Therefore， we recommend to adopt G3 or Tiedtke cumulus parameterization schemes in simulating summer precipitation over the Qinghai-Xizang （Tibetan） Plateau， and when the computational resources are allowed， the high-resolution CPM can be considered to improve the precipitation frequency simulations.

• Temporal and Spatial Variation Characteristics of Daytime and Nighttime Precipitation in Monsoon and Westerly Regions of the Loess Plateau from 1961 to 2020
• qi REN, Yuanfa GONG, Xueyu LIU
• 2023 Vol. 42 (6): 1444-1456.  DOI:10.7522/j.issn.1000-0534.2023.00009
• Abstract ( ) PDF (10739KB) ( )

• Based on the day and night precipitation data of 64 stations in the Loess Plateau of China from 1961 to 2020 from the National Meteorological Information Center， the Loess Plateau is divided into two regions （monsoon region and westerly region）.The variation characteristics of daytime and nighttime precipitation days and precipitation in the two regions in two seasons （wet-season and dry-season） were analyzed using methods such as linear trend and t test.The main conclusions are as follows： There are significant seasonal differences in daytime and nighttime precipitation between the monsoon region and the westerly region of the Loess Plateau.The number of daytime and nighttime precipitation days in the wet-season （May-September） in the monsoon region accounts for 60% of the whole year， and the precipitation is more than 75%.In the westerly region， the proportion of daytime and nighttime precipitation in the whole year is nearly 70%， and the precipitation is more than 80%.The Loess Plateau tends to get wet in the westerly area and dry in the monsoon area.Among them， the most prominent feature is that in the westerly region， The number of stations which measured increase in daytime accounts for 77.8% of the total.in the wet-season， and more than 50% in the dry-season.In the monsoon area， the number of stations in daytime and nighttime which measured decrease in precipitation days and precipitation account for more than 80% and 50% respectively in the wet-season， and more than 95% and 80% respectively in the dry-season.

• Influence of Developing Phase of Eastern Pacific El Niño Events on the Autumn Extreme Precipitation in China
• Yuli PU, Juan FENG, Jianping LI
• 2023 Vol. 42 (6): 1457-1467.  DOI:10.7522/j.issn.1000-0534.2023.00004
• Abstract ( ) PDF (7905KB) ( )

• Using the daily surface precipitation data and NCEP/NCAR monthly reanalysis data over the period of 1961 -2020， the impacts and possible physical mechanism of the developing phase of eastern Pacific El Ni?o on the autumn extreme precipitation in China were examined.The results indicated that the eastern Pacific El Ni?o events exhibit significant impacts on the extreme precipitation over the central and southern China during the developing autumn， resulting in increased extreme precipitation in southern China and decreased extreme precipitation in central China.The involved physical process is explored.The result indicated that when the eastern Pacific El Ni?o is in the developing autumn， significant positive sea surface temperature anomalies （SSTA） are seen in the central and eastern Pacific， which are associated with anomalous ascent in the tropical central and eastern Pacific and anomalous sinking in the western Pacific.Associated with the SSTA， southern China is controlled by anomalous convergence， which creates favorable dynamic conditions for precipitation.In addition， anomalous anticyclonic circulation is observed from the South China Sea to the western Pacific， and the water vapor transport via the southwest flow is enhanced， which promotes the occurrence of extreme precipitation in southern China.As to the central China， however， it is characterized with anomalous northerlies wind and water vapor divergence， which is not conducive to the occurrence of precipitation.These results provide scientific clues for understanding the physical mechanism of extreme precipitation events in eastern China.

• Analysis of Flood Season Precipitation and Extreme Precipitation in Gansu Province Based on Data from Different Types of Meteorological Stations
• Feng FANG, Jing WANG, Weiping LIU, Youheng WANG, Xin WANG, Jingjing LIN, Xing WANG
• 2023 Vol. 42 (6): 1468-1477.  DOI:10.7522/j.issn.1000-0534.2023.00008
• Abstract ( ) PDF (3894KB) ( )

• In this paper， the data quality control of the flood season precipitation and extreme precipitation of the regional meteorological stations and national meteorological stations in Gansu Province from 2011 to 2020 has been carried out， and 1253 regional meteorological stations and 75 national meteorological stations have been selected to analysis the precipitation characteristics.The results show that the average precipitation amount of the regional meteorological stations in Gansu Province is very close to that of the national meteorological stations， and there is no significant difference.The average precipitation of the regional meteorological stations in flood season in Gansu province is 382.9 mm， and that of the national meteorological stations is 379.7 mm.The average monthly precipitation of regional meteorological stations distributes from 31.7 mm to 87.1 mm， and that of national meteorological stations distributes from 30.4 mm to 86.4 mm.However， there are significant differences in the extremes of precipitation between the two types of meteorological stations.The maximum of total precipitation at regional meteorological stations in flood season even reaches 917.5 mm， the maximum monthly precipitation reaches 776 mm， and the maximum number of rainstorm days reaches 46 d·（10a）^-1.However， those of national meteorological stations is 710.7 mm， 541 mm and 17 d·（10a）^-1， respectively.The spatial locations of precipitation maxima of regional meteorological stations and national meteorological stations are close to each other， but the numerical values of regional stations are significantly higher than those of national stations.The spatial trends of precipitation at the two stations are very consistent， and the correlation coefficient of flood season precipitation of two types stations is 0.95， the correlation coefficient of monthly extreme precipitation is 0.92.Moreover， regional meteorological stations show many higher and less value centers of small patches than national stations； the spatial precipitation difference between the two types of meteorological stations are clearly in the east and south of Gansu Province.Overall， the regional meteorological stations describe the precipitation characteristics of Gansu Province in a more detailed way.More extreme precipitation events are monitored in those regions with complex terrain， and the extreme value of precipitation is larger than that of national meteorological stations.The rainstorm and flood disaster prevention in these regions should be based on the data of regional meteorological stations to enhance the disaster risk prevention ability.

• The Impact of Assimilating Himawari-8 Radiance Data on the Prediction of a Severe Storm over Sichuan-Chongqing Region
• Hao LIANG, Dongmei XU, Aiqing SHU, Xuewei ZHANG, Lixin SONG
• 2023 Vol. 42 (6): 1478-1491.  DOI:10.7522/j.issn.1000-0534.2022.00112
• Abstract ( ) PDF (14688KB) ( )

• Himawari-8 is a new generation of stationary orbit imager， AHI （Advanced Himawari Imager） onboard is able to is able to provide observations with high spatial and temporal resolution to detect weather systems continuously over Sichuan - Chongqing Region.In this study， a numerical simulation is conducted for a severe regional storm event over Sichuan-Chongqing region on April 19， 2019 based on the weather Research and Forecasting （WRF） model.Furtherly， several radiance data assimilation experiments were performed for the storm with the WRF data assimilation （WRFDA） system from Himawari-8 AHI water vapor channels.Infrared radiance quality control and cloud detection procedures are conducted firstly.Cycling data assimilation schemes are further designed to investigate the impact of assimilating AHI radiance on the analyses and prediction of the weather system.The results show that the simulated brightness temperature of AHI water channels based on the radiative transfer model of CRTM in the analysis is more consistent with the observed brightness temperature than the those simulated from the background.It is also found that that assimilation of Himawari-8 AHI water vapor channels contributes to better describing the model initial conditions including the wind field， the water vapor field， and the radar reflectivity on multiple levels.Compared to the control experiment without any data assimilation， the forecast skill is enhanced in terms of predicting the main patterns of the precipitation after assimilating the AHI water vapor radiance data.To be specific， the assimilation experiment could capture the position of the main rainband and the center of heavy precipitation better.Through the AHI water vapor data assimilation， the heavy precipitation centers that are missed in the control experiment are successfully predicted.In addition， AHI radiance data assimilation experiment effectively improves the overestimated heavy precipitation from the control experiment in eastern Sichuan and southeastern Gansu for both the range and intensity.This study aims to provide the useful reference for the pretreatment and assimilation of geostationary infrared radiance data in the rainstorm system in numerical models over Sichuan-Chongqing Region.

• Analysis of the Difference between Rainstorm Accompanied by Easterly Low-level Jet in Tarim and Rainstorm without Easterly Low-level Jet in Tarim in Southern Xinjiang
• Xia YANG, Hongkui ZHOU
• 2023 Vol. 42 (6): 1492-1503.  DOI:10.7522/j.issn.1000-0534.2023.00003
• Abstract ( ) PDF (5322KB) ( )

• Most of the regional heavy rain processes in the monsoon region of China are related to the low-level jet.However， in arid and semi-arid regions， the low-level jet stream is not necessarily associated with every rainstorm process.Based on the daily precipitation data from May to September from 1971 to 2020， hourly precipitation data from 2011 to 2020， and the radiosonde data from Ruoqiang Station twice a day， the observational characteristics of heavy rain with and without easterly low-level jet in southern Xinjiang in recent 40 years were analyzed by statistical methods.The results show that the number of rainstorm days accompanied by easterly low-level jet is slightly less than that without easterly low-level jet in southern Xinjiang in recent 40 years.Both of them showed an increasing trend in the past 40 years， but the increasing trend of the number of rainstorm days accompanied by the easterly low-level jet was more significant.In the past 40 years， the proportion of rainstorm days accompanied by easterly low-level jet to the total rainstorm days in southern Xinjiang showed an increasing trend， while the proportion of rainstorm days without easterly low-level jet showed a decreasing trend.In the warm season of southern Xinjiang， the number of rainstorm days accompanied by easterly low-level jet was the highest in May， while the number of rainstorm days without easterly low-level jet was the highest in July， and both of them were the least in September.From the 1970s to the 1990s， the heavy rain in the warm season in southern Xinjiang was mainly accompanied by the easterly low-level jet， and from the 2000s to the present， the heavy rain was mainly accompanied by the easterly low-level jet.The number of rainstorm days is relatively higher in the western part of southern Xinjiang， and the rainstorm is mainly accompanied by easterly low level jet stream.The proportion of short-time heavy precipitation events in the rainstorm without the easterly low-level jet in the warm season in southern Xinjiang is significantly higher than that in the rainstorm with the easterly low-level jet.The rainstorm accompanied by the easterly low-level jet is dominated by night rain， while the rainstorm without the easterly low-level jet is dominated by day rain.In the warm season of southern Xinjiang， the periods of maximum precipitation and maximum occurrence of the rainstorm with the easterly low-level jet mainly occurred around midnight， while the periods of maximum precipitation of the rainstorm without the easterly low-level jet mainly occurred from late afternoon to late afternoon.The maximum cumulative frequency of the rainstorm without the easterly low-level jet is similar to that of the rainstorm with the easterly low-level jet occurred around midnight.The maximum intensity of both types of torrential rain occurs from mid-afternoon to late afternoon.The peak value of rainstorm precipitation with easterly low-level jet in the warm season in southern Xinjiang was mainly caused by the frequency of precipitation in the early night， while the sub-peak value of rainstorm precipitation around evening was mainly caused by the intensity of precipitation.The diurnal variation characteristics of rainstorm precipitation without easterly low-level jet in the warm season in southern Xinjiang are similar to its precipitation intensity， and the difference between it and its precipitation frequency is great.There is a great difference between the rainstorm with easterly low level jet and the rainstorm without easterly low level jet in the warm season of southern Xinjiang.At present， the research on the formation mechanism of rainstorm in southern Xinjiang with the coordination of easterly low level jet from Tarim is relatively mature， while the formation mechanism of rainstorm without the coordination of easterly low level jet from Tarim is still unclear.

• Comparative Analysis of Individual Water Vapor Sources in Dry and Wet Year in Southwest China
• Jianing ZHU, Xianyu YANG, Yaqiong LÜ, Jun WEN, Ying CHEN
• 2023 Vol. 42 (6): 1504-1517.  DOI:10.7522/j.issn.1000-0534.2023.00001
• Abstract ( ) PDF (21360KB) ( )

• The climate of Southwest China is wet all year round， but the frequent drought disasters in recent years have caused huge economic losses such as crop yield reduction and forest fire.In order to fully understand the anomalies of water vapor transport in drought years in Southwest China and provide reference for early warning of drought disasters in this area in the future， this study used TRMM and APHRODITE precipitation data to analyze the interannual variation of precipitation and the interannual variation of precipitation in various seasons in Southwest China from 1998 to 2019， selected the summer dry year （2011）， autumn dry year （2009） and 2008， which were relatively wet in summer and autumn.Using Lagrangian transport model FLEXPART， we tracked the paths of water vapor transport and water vapor sources in the two extreme dry seasons （the autumn of 2009 and the summer of 2011）， and compared with the summer and autumn of the wet year （2008）， respectively.The results showed that： （1） The paths of water vapor transport in dry and wet year are consistent， and the paths in southwest China in summer can be divided into three main paths： the southwest path， the southeast path and the northwest path， among which the most dominant is the southwest path， so the main water vapor source area are the Arabian Sea——the Bay of Bengal.In autumn， the main paths can be divided into two： the southeast path and the northwest path， of which the most important is the southeast path， so the main source of water vapor is South China Sea——the Pacific Northwest.（2） There are differences in the strength of water vapor transport between dry and wet years.The reason for the drought in Southwest China in summer is that the water vapor transported by the southwest route is weak， while the reason for the drought in Southwest China in autumn is that the water vapor transported by southeast route is weak.

• Climate Extremes in a Typical Glacier-related Debris Flow Watershed of Southeast Tibet During 1979 -2018
• Hao LI, Shuang LIU, Kaiheng HU
• 2023 Vol. 42 (6): 1518-1528.  DOI:10.7522/j.issn.1000-0534.2023.00014
• Abstract ( ) PDF (2692KB) ( )

• Heavy rainfall and high air temperature are the main factors inducing glacial debris flows.In-depth understanding of the variation of disaster-pregnant meteorological conditions of glacial debris flows in small watersheds can provide basis and basic data for early warning and disaster prevention of glacial debris flows.Based on the China Meteorological Forcing Dataset （CMFD） （1979 -2018）， the inter-annual and intra-annual variation characteristics of rainfall， air temperature， and extreme climate index in Kada valley are analyzed using several methods， including Sen's slope， Mann-Kendall trend and mutation test， Sliding t-test， Morlet wavelet transform， coefficient of variation （CV）， and precipitation concentration index （PCI）.The results show that： （1） Both the average annual air temperature and the warm days showed a significant rising trend at rates of 0.05 ℃·a^-1 and 1.46 d·a^-1， respectively， but the inter-annual variance of the warm days was very high.Both the average annual air temperature and the warm days exhibited quasi-periods of 32 a and mid to short-term scale periods.（2） The air temperature in spring， summer， autumn and winter increased significantly at rates of 0.044 ℃·a^-1， 0.039 ℃·a^-1， 0.049 ℃·a^-1 and 0.06 ℃·a^-1， respectively.The air temperature increased significantly in all months， with March and November showing significant inter-annual fluctuations.（3） The decreasing trend of annual rainfall was not significant.Although no significant trend in extreme rainfall days was observed， it fluctuated considerably from year to year， with a sudden change occurring in 1988.Both annual rainfall and extreme rainfall days exhibited multiscale periods of 16~22 a， 8~10 a， 4~6 a， 2~5 a and 2~3 a.（4） The intra-annual distribution of rainfall is generally more balanced.The overall changing pattern of seasonal and monthly rainfall was not significant， except for a noticeable decline in rainfall during June and July， at rates of 1.44 mm·a^-1 and 1.15 mm·a^-1， respectively.In general， the climate in the Kada valley is transitioning from hot and humid to dry and hot.Additionally， it is in the rainy period of multiscale periodic strong amplitude centers superposition of 2~3 a and 4~6 a， as well as the high air temperature period of 8~11 a.At the same time， the warm days， extreme rainfall days， and monthly rainfall have moderate or greater variation， increasing the likelihood of extreme drought and flood events.The combination of extreme hydrothermal conditions raises the risk of glacial debris flow outbreak in the Kada valley.

• The Best Reference Latitude for the Eddy Heat Flux Approximation in the Lower Stratosphere
• Fenghua YANG, Renqiang LIU
• 2023 Vol. 42 (6): 1529-1535.  DOI:10.7522/j.issn.1000-0534.2022.00113
• Abstract ( ) PDF (3561KB) ( )

• Stratospheric atmosphere is jointly affected by dynamical， radiative and chemical processes.Since the 1970s， the greenhouse gas emission and ozone depletion caused by anthropogenic activities have driven significant stratospheric cooling， so the tropospheric warming and the stratospheric cooling are both important criteria for global climate change.Observational and modeling studies disclosed that the formation of polar stratospheric clouds at very low stratospheric temperatures is an important condition for rapid ozone depletion.The weak polar vortex event related to the stratospheric sudden warming can even propagate downward to the troposphere and induce the tropospheric circulation anomaly， further leading to the extreme cold event in the middle and high latitude continents.Therefore， it is necessary to clearly understand the causes of stratospheric temperature changes at the background of global warming.Under quasigeostrophic scaling， the eddy heat flux approximation theory within the transformed Eulerian-mean framework is usually used to calculate the dynamical and radiative heating contributions of the Arctic stratospheric temperature changes， but this may bring certain errors.In this paper， according to a new area-weighted averaged thermodynamic equation by Liu and Fu （2019） within the Eulerian-mean framework， a monthly temperature change equation is constructed by time-sliding accumulation.Then using the European Centre for Medium-range Weather Forecasts fifth reanalysis data （ERA5） during 1980-2019， we calculate the climatological monthly temperature increment， dynamical heating， diabatic heating and convective heating term （W term） in the Arctic lower stratosphere， respectively， during the whole period 1980-2019 and two sub periods （1980-1999 and 2000-2019）， and discuss the best reference latitude for the eddy heat flux approximation theory.The results show that the newly derived W term reduces the imbalance between the Arctic temperature increment term and the sum of cumulative dynamical and diabatic heating by half in winter and spring.At 100 hPa， W term changes with month and latitude， nontrivial especially in winter and spring.Therefore， the best reference latitude for the eddy heat flux approximation should be near the zero contour line of the W term.Further verification shows that the reference latitude can be taken at 50°N.

• Radar Climatological Characteristics of Warm Season Convection in Southeast of Gansu
• Wei XIAO, Weicheng LIU, Zhao FU, Wenxue LI, Jie FU, Shang GOU, Wei ZHANG
• 2023 Vol. 42 (6): 1536-1547.  DOI:10.7522/j.issn.1000-0534.2023.00023
• Abstract ( ) PDF (9727KB) ( )

• The radar climatology characteristics of convection in southeastern Gansu Province during the warm season （June to August）were investigated using Tianshui Doppler radar data that filtered by “Maximum Method” and tracking statistics by “TITAN”（Thunderstorm identification Tracking Analysis and Nowcasting） algorithm.The frequency of convective activity showed large value in high altitude mountains with the Great value center located in windward slope of Western Liupanshan Mountain and undulating region of western Qinling Mountains， and the peak time in August.The convective storm mainly propagated from northwest to southeast， meanwhile the propagation characteristics presented a difference in different months and it spreads fastest in June and slowest in August.The diurnal variation of convective activity showed a unimodal distribution of frequency with peak region at 16:00 -17:00 （Beijing Time）.It's also showed in the occurrence and development of convection in different terrain occurrence and development in different terrain conditions with the high frequency of thermal convection mainly at high altitude area in the afternoon and presentation in the mountain， river valley， basin and plain respectively at night.The diurnal variation of convective storms in different months was obviously different.The influence of solar heating and topographic forcing on convective storms in the afternoon of June was the most significant， while the response of convective storms in the night of July and August was higher to the complex topography of the plateau slope.The propagation direction of the well-organized storm in the afternoon was closely related to the extension and slope direction of the mountain， and was closely related to the prevailing winds at 500 hPa at night.More than 90% convective storms lasted less than 36 minutes， and only 1% lasted longer than 1 hour.

• The Connections between the Establishment and Maintenance of Ural Blockings in Winter and Intra-seasonal Oscillation of Geopotential Height
• Binyu XU, Suxiang YAO, Qingfei SUN
• 2023 Vol. 42 (6): 1548-1561.  DOI:10.7522/j.issn.1000-0534.2023.00006
• Abstract ( ) PDF (4199KB) ( )

• The Ural blocking high （UB） in winter is an important influence system leading to widespread cold snap in China.Exploring exploring the connections between its establishment and maintenance processes and intra-seasonal oscillations of geopotential height can provide reference factors for extended range forecasting and short-term climate prediction.By using the ERA5 daily reanalysis data provided by European Centre for Medium-Range Weather Forecasts （ECMWF） from 1979/1980 to 2019/2020， 114 winter UB events were selected by using a combined subjective and objective method， in which the cumulative number of blocking high days reached 591.The connections between the Ural blockings and the intra-seasonal oscillations of the 500 hPa geopotential height were analyzed by using power spectrum analysis， correlation analysis， synthesis analysis and other statistical methods.The results show that： （1） Geopotential height over the Ural Mountains has significant periods of 10~20 days， 30 days and 45 days during the last 41a winter.Through multi-scale analysis， we find that different time scale components of the geopotential height contribute differently during the establishment and maintenance processes of the Ural blockings， where the largest contribution to the establishment of Ural blocking highs is the quasi-biweekly geopotential height anomaly （10~20 days）， and the maintenance of blocking high events is determined by intra-seasonal oscillations with a scale of 20~80 days.During the establishment and maintenance processes of blockings， the quasi-biweekly geopotential height anomaly propagates from west to east， while the intra-seasonal oscillations of the geopotential height anomaly have no significant propagation.（2） According to the time intervals between the occurrences of two events， blockings are classified into continuous blocking high events and other blocking high events.Through multiple case synthesis analysis and typical individual case analysis， we find that for continuous blocking high events， the intra-seasonal oscillations of the geopotential height anomaly contribute most to their establishment and maintenance processes， but have no significant propagation.The geopotential height anomaly shows a westward propagating signal on the quasi-biweekly scale.The connections between other non-continuous blockings and atmospheric circulation at different time scales are similar to the results of all blocking high events.

• The Applicability Performance of the ERA5-Land Precipitation Datasets in Southwest China
• Xiaolong HUANG, Wei WU, Jianhui XU, Shiying LI, Yuhe JIANG, Bin DU, Liwei WANG
• 2023 Vol. 42 (6): 1562-1575.  DOI:10.7522/j.issn.1000-0534.2023.00012
• Abstract ( ) PDF (7125KB) ( )

• ERA5L precipitation reanalysis datasets were provided by the European Centre for Medium-Range Weather Forecasts（ECMWF） Fifth Generation Land Surface Reanalysis （ERA5L）. An investigation of the applicability of ERA5L precipitation reanalysis datasets produced for Sichuan， Chongqing， Guizhou， Yunnan and Xizang in Southwest China has been conducted.Statistical metrics， including Pearson correlation coefficients （CCs）， mean relative deviations （MREs）， root mean square errors （RMSEs）， probability of detections （PODs）， false alarm rates （FARs）， and critical success indices （CSIs）， were employed to assess the features and accuracy of ERA5L precipitation data using 441 national ground stations of the China Meteorological Administration between 2018 and 2020.The characteristics and deviations of ERA5L precipitation data were analysed in aspects of different regions， stations， altitudes， and timescales （monthly and seasonal） in our assessment phase.The following insights were revealed： （1） ERA5L better represents precipitation changes in the southwestern region； however， it tends to show higher precipitation levels than the in-situ observations， especially in Xizang.（2） In the Sichuan Basin， high correlation has been found between ERA5L precipitation data and in-situ observations， with a small error.The areas of Xizang， Yunnan， Guizhou and Western Sichuan are characterized by complex terrains and mountainous regions.The ERA5L data here has a relatively higher error.（3） The ERA5L exhibits a clear monthly variation in error， with a decline in overall precipitation leading to higher MRE， lower POD， and increased FAR from July to February.The MRE decreases， the POD increases， and the FAR rate decreases as precipitation increases from February to July.The quality of ERA5L varies between provinces and seasons.There is excellent precipitation quality in Chongqing during spring and autumn， and in Guizhou and Sichuan during summer and winter.（4） ERA5L precipitation is overestimated compared to in-situ observations in light rain magnitude， but underestimated in moderate and above-moderate rain.The underestimate becomes more severe as the rain intensity increases.As a whole， ERA5L has the potential for various applications in Southwest China.The hierarchy of ERA5L precipitation quality from high to low occurs in the following order： low altitude， medium altitude， and high altitude.In the context of five provinces， the order of applicability from high to low is as follows： Chongqing， Guizhou， Sichuan， Yunnan， and Xizang.

• Sub-seasonal Forecasting Skills Assessment and Deviation Analysis of CFSv2 for Summer Precipitation in Sichuan and Chongqing
• Ying XIAO, Yishu PANG, Zhenfeng MA, Quanliang CHEN, Zhengjie ZHANG
• 2023 Vol. 42 (6): 1576-1588.  DOI:10.7522/j.issn.1000-0534.2023.00007
• Abstract ( ) PDF (10641KB) ( )

• In this paper， the hindcast precipitation fields of the NCEP's second-generation climate prediction system （CFSv2） and the observed precipitation data of 182 meteorological stations in Sichuan and Chongqing from 2000 to 2009 were utilized.Sub-seasonal forecasting ability for summer precipitation and its anomaly in Sichuan-Chongqing region of this model was evaluated by use of Temporal Correlation Coefficient （TCC）， Anomaly Correlation Coefficient （ACC）， Root Mean Square Error （RMSE）， sign coincidence rate （SCR） and PS scores methods.Meanwhile， bias characteristics on probability density and frequency of precipitation was analyzed.The results show that the available forecast lead time for summer precipitation in Sichuan and Chongqing is about 3 pentads， which can simulate the high-value center of summer precipitation well， but the magnitude is too large.The high-value areas of forecasting skills are mainly located in the northwestern Sichuan Basin and northeastern Chongqing， and some forecasting skills are also available for the southern Panxi region and parts of the western Sichuan Plateau.The model can also better grasp the trend of abnormally less precipitation in summer in the Sichuan-Chongqing region， and the effective forecasting skill is within 2 pentads.The precipitation probability densities predicted and observed in each time period of the model are mainly concentrated in the order of magnitude below 10 mm； compared with the actual situation， the precipitation frequency of each magnitude predicted by the model is significantly higher， and with the extension of the forecast time， the deviation is greater， and the most obvious one is the light rain frequency.

• Influence and Mechanism of Indian Ocean Basin Model on the Asymmetry of Pacific Subtropical High in the Northern and Southern Hemispheres
• Yuxin YANG, Chaoxia YUAN, Yan LI
• 2023 Vol. 42 (6): 1589-1603.  DOI:10.7522/j.issn.1000-0534.2023.00010
• Abstract ( ) PDF (17105KB) ( )

• Subtropical anticyclone has an important influence in weather and climate in China， which is affected by the tropical sea surface temperature （SST） anomaly in the Indian Ocean for its formation.However， there is limited studies for the corresponding influence mechanism.In order to probe impact as well as the mechanism of the SST anomaly over the Indian Ocean on the subtropical high， the El Nino-Southern Oscillation （ENSO） signal is filtered out.By using the reanalysis data from the National Centers for Environmental Prediction/National Center for Atmospheric Research （NCEP/NACR） from 1980 to 2020， this study tries to explore the influence and mechanism of the Indian Ocean basin model （IOBM） on subtropical high in the Pacific Ocean through dynamical diagnose in perspective of energy， and verifies the results by numerical model simulation by the Geophysical Fluid Dynamics Laboratory Atmospheric Model （GFDL AM2.1）.The results show that eastern-spreading of the Kelvin wave is motivated by the SST anomaly in the Indian Ocean in summer.Meanwhile， low-level anticyclone anomaly appears in the northwest Pacific Ocean， resulting in the subtropical anticyclone is stronger than the climatological mean.Thus， the precipitation is less in regions from the South China Sea to Eastern Philippines.In winter， during the positive phase of the IOBM， the east wind anomalies are stimulated in Australia， resulting in large-area negative anomalies of precipitation occurred over the western Pacific.Non-uniform distribution of precipitation is caused by the asymmetry in circulation of subtropical high over the Pacific Ocean in the northern and southern hemispheres.Result by the dynamical diagnose reveals that when the phase of IOBM is positive， the wind field convergence zone is superposed by the disturbance energy growth area， whereas in winter such two regions do not cooperate with each other.As a result， the subtropical high is abnormally strong in the northwestern Pacific in summer and with indistinct abnormally in Australia in winter.The numerical simulation verifies that the asymmetry of anticyclonic circulation and precipitation anomalies are closely related to the symmetrical SST anomaly in Indian Ocean along the equator， both in its position and intensity.The result of model simulation demonstrates the reliability of the conclusions of synthesis analysis and energy diagnosis.Thus， the IOBM plays a significant role on the symmetrical structure of the Western Pacific subtropical high in northern and southern hemispheres， as well as in the precipitation in East Asia and Australia regions， which provides a theoretical basis for formation mechanism of the asymmetry of the Pacific subtropical high in the southern and northern hemisphere during the warming of the entire Indian Ocean basin.

• A Statistical Test of Station Thunderstorm Days Based on Lightning Location System and Its Evolution Characteristics
• Bo PANG, Biao ZHU, Huihuang LAI, Binbin LIN, Bing LIU
• 2023 Vol. 42 (6): 1604-1614.  DOI:10.7522/j.issn.1000-0534.2023.00013
• Abstract ( ) PDF (8101KB) ( )

• To research the continuity and climate evolution characters of station lightning data in Fujian Province， the paper established the calculation model based on Lightning Location System.The data sorted to thunderstorm days by observed（1982 -2013） and by Lighting Location System（2011 -2020） were used respectively.The paper determined the monitoring radius of lightning Location System that best matches the manual observation Combined with the T test and F test results.On this basis， the maximum penalty F test （PMFT）method was used to test the continuity of thunderstorm daily data from 66 stations in Fujian Province， and the passing rate under different monitoring radius and the mean square error of observation and monitoring were compared to obtain the optimal matching monitoring radius of Lightning Location System.Empirical Orthogonal Function （EOF） and 9-point smoothing coefficients were used to analyze the spatial and temporal evolution characteristics in Fujian Province during 1982 -2021 under the optimal matching radius and the factors influencing the activity pattern of thunderstorm days.The results show that： （1） The optimal matching radius between Lightning Location System is 12 km， and the passing rate （failed rate） of the （PMFT） test of 66 stations in the province is 80.30% （19.70%）； （2） The spatial pattern of thunderstorm days in Fujian Province during 1982 -2021 is uneven， which are characterized that thunderstorm activity is stronger in the southwest then east coast， The spatial patterns of the three modes of EOF mainly include "province-wide Province- wide negative phase"， "northeast- southwest Province-wide negative phase"， and "inland coastal Province-wide negative phase".The first mode variance contribution rate is 55%， which can be the major mode， its 9-point smoothed curves and time coefficients characterize the Midwest and South have more lightning activity before 1998 and after 2016， and less lightning activity during 1998 -2016； （3） ENSO has a certain influence on the thunderstorm activity pattern in Fujian Province， and the correlation coefficients of ENSO， El Ni?o， La Ni?a and thunderstorm days in Fujian Province are 43.80%， 55.22% and 14.21% respectively.In summary， the 12 km radius can be used as an effective forecast basis and the optimal matching monitoring radius between manual observation and Lightning Location System leading to solve the problem of continuity of lightning data in Fujian Province.It is important to study the law of lightning activity for improving the ability of lightning disaster prevention.By comparing several kinds of climate events， El Nino has a great influence on the thunderstorm activity pattern in Fujian Province， which is considered as one of the important factors affecting the lightning activity pattern in Fujian Province.

• The Effects of the Tengger Desert Wind and Solar Power Base on Regional Ecological Environment
• Shengjiang PENG, Yuantian XUE, Yalu SUN, Chenlai YANG, Yingqing SU, Meng ZHU
• 2023 Vol. 42 (6): 1615-1624.  DOI:10.7522/j.issn.1000-0534.2023.00078
• Abstract ( ) PDF (5519KB) ( )

• The desert region possesses abundant scenic and thermal resources， yet the causal relationships between the constructed scenery and the heat infrastructure and their impact on the regional ecological environment remain inadequately understood in terms of mechanistic understanding.Conducting research on the ecological environmental impact of regional wind-solar-thermal infrastructure development holds great significance in guiding the advancement of clean energy and promoting socioeconomic growth within the region.This study focuses on the Tengger Desert as its research area.Using the Google Earth Engine cloud platform （GEE） and Landsat 8 remote sensing images obtained in 2000 and 2022， the investigation employs diverse analytical methods such as land use dynamic degree， land use transfer matrix， ecological environment quality index （EEQI）， landscape pattern index， and geographically weighted regression model （GWR） to evaluate the impact of wind-solar-thermal infrastructure development on the regional ecological environment.The findings indicate that： （1） The land use/land cover （LULC） in the sandy area exhibited apparent spatial and temporal heterogeneity， with sandy land， low-coverage grassland， and Gobi being the main land use types.Notably， the proportion of sandy land accounted for 69.10% to 72.72% of the total study area.In terms of the changes in land use types before and after the construction of the wind and solar power base from 2000 to 2022， the regions with substantial alterations were primarily distributed at the southeast and southwest edges of the sandy area.（2） Over the course of the past 22 years， the highest degree of land use dynamics was observed in industrial and mining construction land， with a notable percentage of 0.11%.A significant portion of sandy land has been transformed into industrial and mining construction land， where approximately 80% of this land was designated for wind and solar power base development.Consequently， sandy land has emerged as a pivotal contributor to the expansion of wind-solar-thermal infrastructure.（3） The regions with the highest EEQI values primarily encompass the middle and lower reaches of the Shiyang River， as well as the southwest and southeast edges of the desert.The concentrated area of the wind and solar power base displayed an increase in EEQI ranging from 0.25 to 0.87， denoting a considerable improvement in ecological conditions.（4） The construction of the wind and solar power base results in a reduction in the dispersion degree of landscape elements in the region， an enhancement in the fragmentation degree， and a more complex spatial structure.Additionally， the diversity and heterogeneity of the regional landscape were improved.Moreover， following the construction of the wind and solar power base， there was a consistent increase in the regression coefficient of the sandy area， exceeding 2.5 on average.This improvement contributes to enhancing the regional EEQI and further strengthens the correlation between LULC and ecological conditions.As a result， the beneficial changes in land use that accompany the construction of the wind and solar power base serve to promote the improvement of ecological environment quality and landscape patterns in sandy areas.