Current Issue

28 February 2022, Volume 41 Issue 1   
  • Progress of Recent 60 Years Climate Change and Its Environmental Impacts on the Qinghai-Xizang Plateau
  • Yaoxian YANG, Zeyong HU, Fuquan LU, Ying CAI, Haipeng YU, Ruixia Guo, Chunwei FU, Weiwei FAN, di WU
  • 2022 Vol. 41 (1): 1-10.  DOI:10.7522/j.issn.1000-0534.2021.00117
  • Abstract ( ) PDF (2692KB) ( )
  • The Qinghai-Xizang Plateau is characterized as one of the key areas of global energy and water cycle and is known as Asian water tower.Climate change of the Qinghai-Xizang Plateau has significant impacts on the environmental changes of the its own and surrounding areas.This paper reviews the facts and mechanisms of recent 60 years’ climate change and its associated environmental impacts, emphasizing surface warming, change of surface radiation, precipitation variability among different seasons and regions, change of surface wind speed and surface environment.Changes of skin temperature, surface air temperature and surface wind speed and associated mechanisms during past decade over the Plateau are also analyzed based on reanalysis and site data.Finally, the issues that need to be solved have been sorted out.The conclusions are as follows: (1) The surface warming over Qinghai-Xizang Plateau was earlier and faster than that along the same latitude in Northern Hemisphere.The elevation-dependence warming and increase of clear sky downward longwave radiation caused by Interdecadal atmospheric humidification are the main causes of Qinghai-Xizang Plateau surface warming.However, the variations of surface temperature during past decade are concentrated on inter-annual scale.(2) Due to the continuous rapid warming of the plateau and the anomalies of sea temperature and atmospheric circulation, the precipitation in different regions and seasons presents various variability.(3) Interdecadal shift of surface wind speed is mainly drwen by the meridional difference in warming between the Qinghai-Xizang plateall and the mid-latitude Eurasian Continent and anomalous atmospheric circulation.(4) Environmental changes on the Qinghai-Xizang Plateau are mainly manifested as lake expansion, permafrost degradation, and advance of vegetation rejuvenation; Since the 1990s, glacier in the western Qinghai-Xizang Plateau have been stabilized or even partially recovered, while, glacier in the southeastern Qinghai-Xizang Plateau continue to retreat.The above results are mainly caused by the dipole pattern that precipitation increased and decreased over western and eastern Qinghai-Xizang Plateau, respectively.Meanwhile, the seasonal and intra-seasonal variations of the Summer Monsoon can be reasonable indicators to the vegetation growth and the spatiotemporal variations of vegetation rejuvenation period.(5) The mechanism and numerical simulation of surface temperature and wind speed changes in different seasons and regions need to be further investigated; performance of temperature and precipitation in climate models needs to the improved; high-resolution numerical simulation and data assimilation based on regional models need to be strengthened urgently.

  • Characteristic Analysis of the Spatio-temporal Distribution of Key Variables during the Soil Freeze-thaw Process over the Qinghai-Xizang Plateau
  • Wenhui LIU, Jun WEN, Jinlei CHEN, Zuoliang WANG, Xuancheng LU, Yueyue WU, Yuqin JIANG
  • 2022 Vol. 41 (1): 11-23.  DOI:10.7522/j.issn.1000-0534.2021.00024
  • Abstract ( ) PDF (5257KB) ( )
  • The freeze-thaw process is one of the most prominent features of the land surface process on the Qinghai-Xizang Plateau, and quantifying the variation of the key variables that denote the soil freeze-thaw process has scientific significance for understanding the climate change, hydrological processes and ecosystems of the Qinghai-Tibetan Plateau.By using the ECMWF/ERA5 (European Centre for Medium-Range Weather Forecasts/ERA5) reanalyzed soil temperature, volumetric soil water and air temperature data, the temporal and spatial trends of the start date of soil freezing, the start date of soil thawing and the duration of the soil freezing and their relationships with the air temperature and altitude were investigated by using linear regression, Mann-Kendall test, moving t test and correlation analysis.These results demonstrated that the spatial distribution of soil freeze-thaw process in the Qinghai-Xizang Plateau is characterized by a trend of delaying freeze, advancing thaw and shortening freeze from the northwest to the southeast.The soil freeze-thaw process varied significantly on the Qinghai-Xizang Plateau from 1979 to 2018.The start date of soil freezing was delayed by 14.0 days with a rate of 0.17 d·a-1, and the start date of soil thawing was advanced by 11.0 days with a rate of 0.07 d·a-1, and the duration of the soil freeze was shortened by 25.0 days with a rate of 0.23 d·a-1 over the past 40 years.The overall trend of soil freeze-thaw process is the same in the Qinghai-Xizang Plateau, while the local rate is different.Throughout the period of study, the duration of the soil freeze in the southern and the northern Changtang Plateau is shortened by 47.2 days and 32.9 days.The first date of the soil freeze, the first date of the soil thaw and the duration of the soil freeze are significantly correlated with temperature and altitude.If the air temperature rises by 1.0 ℃, the first date of the soil freeze will be delayed by 5.2 days, and the first date of the soil thaw will be advanced by 4.5 days, so that the duration of the soil freeze will be shortened by 9.8 days.In the high cold Tibetan climatological zone, the first date of the soil freeze will be advanced by 9.1 days, and the first date of the soil thaw will be delayed by 4.9 days, while the duration of the soil freeze will be increased by 13.9 days as the altitude increases by 1000.0 m.

  • Impacts of Spring Soil Moisture Anomalies in Qinghai-Xizang Plateau on the Summer Precipitation Variability in China
  • Xu DING, Xin LAI, Guangzhou FAN
  • 2022 Vol. 41 (1): 24-34.  DOI:10.7522/j.issn.1000-0534.2020.00094
  • Abstract ( ) PDF (6155KB) ( )
  • Using 1979 -2014 Global Land Data Assimilation System-the Community surface parameter data set, China regional daily observation data grid data set (CN05.1) and ERA-interim reanalyze atmospheric circulation data.To study the relationship between the abnormal soil moisture in the Qinghai-Xizang Plateau in May and the surface heat flux in June and the precipitation change in July.The results show that: (1) From 1979 to 2014, the average soil moisture in the 0~10 cm layer area in May was abnormally high years were: 2000, 2001, 2004, 2005, 2006, 2013; the abnormal low years were: 1994, 1995, 1996, 1998, 1999.Soil moisture increased after 2000.Soil moisture increased after 2000.The soil moisture in the higher Tibetan Plateau, the Three Rivers Source Region, and the southern Tibetan valley is significantly higher than in the lower years.The results passed the 90% confidence test.(2) There is a clear correlation between the abnormality of soil moisture in spring and the distribution of summer precipitation in China.When the soil is wet (dry), from high latitude to low latitude, the relevant area is "+ - + -" ("- + - +") banded distribution.(3) The soil is moist in May, and the sensible heat flux in the east and the latent heat flux in the west increase in June.Their combined effect strengthens the convergent circulation of the lower atmosphere and the divergence circulation of the upper layer, so that the East Asia region is controlled by the strong anticyclone circulation above 850 hPa.The 500 hPa and above in the northeast of the plateau is an anticyclone circulation, and the south and west are cyclonic circulations.This circulation field configuration makes the South Asian high pressure move eastward and the Western Pacific subtropical high pressure.(4) In July, the Huanghuai area on the north side of the Pacific High has a vertical upward movement.The warm and moist air flow converges with the dry and cold air flow on the west side of the northeast cold vortex.High-level divergence and low-level convergence are conducive to precipitation in Huanghuai area.The eastern northwestern and northern China regions are controlled by anticyclonic circulation, with strong sinking movement, dry and cold air, and insufficient water vapor transport, which is unfavorable for precipitation.

  • Simulation Analysis of Soil Water and Heat Characteristics in High and Low Snowfall Years on the Qinghai-Xizang Plateau
  • Jiangxin LUO, Shihua LÜ, Cuili MA, Xuewei FANG
  • 2022 Vol. 41 (1): 35-46.  DOI:10.7522/j.issn.1000-0534.2020.00031
  • Abstract ( ) PDF (3680KB) ( )
  • Snow cover and frozen soil on the Qinghai-Xizang Plateau (QXP) play an important role in the global water cycle.In this paper, the Regional Climate Model (RegCM4) coupled with the Community Land Model (CLM4.5) was utilized to conduct regional simulation experiments on the QXP.This was done to explore the mechanism of snow influence on soil water and heat transfer during freezing-thawing periods.Our results showed that RegCM4-CLM4.5 can effectively simulate the characteristics of high and low snowfall years on the QXP, and the center of simulated snow depth was 10~20 cm higher than remote sensing snow depth.The simulation effect of soil temperature was better than that of soil moisture.The correlation coefficient R of simulated soil temperature was 0.95~0.98, and the correlation coefficient R of simulated soil moisture was 0.68~0.89.Comparison of the simulated soil temperature and moisture content of high and low snowfall years on the QXP revealed that the abnormal amount of snowfall had heat preservation and humidification effect on soil.During freezing period, the soil temperature in high snowfall year is higher than that in low snowfall year.During melting period, the soil moisture content in high snowfall year is higher than that in low snowfall year.The frozen soil would also hinder the infiltration of snow melt water, so the difference of soil moisture between the high and low snowfall years was not more than ± 2%.In permafrost area, when there was more snowfall, the freezing depth increased, which was conducive to the development of frozen soil.And in seasonal permafrost area, the increase of snowfall was not conducive to the development of frozen soil.

  • The Characteristics of the Water Vapor Transport under The Condition of Dry and Wet Evolution in the Source Region of the Yellow River
  • Yu LIU, Rong LIU, Xin WANG, Zuoliang WANG, Dayong WANG
  • 2022 Vol. 41 (1): 47-57.  DOI:10.7522/j.issn.1000-0534.2020.00057
  • Abstract ( ) PDF (7207KB) ( )
  • By analyzing Soil Moisture Anomaly Percentage Index (SMAPI) at different soil layers, dry-wet evolution of the source region of the Yellow River (SRYR) during 2008 -2017 are investigated using observations from the Maqu-Ruoergai soil temperature and moisture monitoring network.To diagnose the water vapor transportation path and potential water vapor sources in different processes, the Lagrange Flexible Particle Dispersion Model (FLEXPART), which is driven by reanalysis data (National Centers for Environmental Prediction Final, NECP FNL), are used to simulate the backward trajectories of target particles.The results show that the water vapor transportation path can be divided into three categories: (1) South Branch transportation.The water vapor origins from the Indian Ocean and the Arabian Sea, and finally arrives at the SRYR by way of the Indian Peninsula and Bay of Bengal; (2) East Branch transportation.The water vapor is from the Pacific Ocean and the South China Sea, then passes through the Yangtze River Basin, and finally arrives at the SRYR from eastern and southern flank of the Tibetan Plateau; (3) North Branch transportation.The water vapor is from the Atlantic Ocean, the northern African continent, and the European continent, then arrives at the SRYR from the western or northern side of the Tibetan Plateau by way of the mid-latitude Eurasian continent.Moreover, the North Branch is dominant in dry period, whereas the South and East branches are prominent in wet period.The water vapor sources also show discrepancies for dry and wet periods.The water vapor sources of the Tibetan Plateau are mainly distributed around the Kunlun Mountains during wet period, and are scattered distributed from north to south during transitional period, and are located around the Tianshan during dry period.The intensity of the water vapor sources of the Iranian Plateau, Pamir Plateau, and the Bay of Bengal gradually strengthen from wet to dry period, the intensity of the water vapor sources of the Sichuan Basin-Qinling Mountains and south China enhanced first and then weakened, while the source of Qilian Mountain-Loess Plateau weakened after enhanced.The intensity of water vapor sources over the middle and lower reaches of the Yangtze River and around East China has been weakening from the wet period to the dry period.

  • The Characteristics of Water Vapor Transport Based on Lagrangian Method in the Zoige, Qinghai-Xizang Plateau
  • Yu LIU, Rong LIU, Xin WANG, Zuoliang WANG
  • 2022 Vol. 41 (1): 58-67.  DOI:10.7522/j.issn.1000-0534.2021.00100
  • Abstract ( ) PDF (3977KB) ( )
  • The drought index has always been a practical standard for assessing a specific region's dry and wet state.In order to better understand the spatial distribution pattern of water vapor transport in the Zoige region of the Qinghai-Xizang Plateau under extreme dry and wet conditions, this paper calculates the monthly standardized precipitation evapotranspiration index based on the ground observation data.It extracts the extreme drought and wet conditions in the Zoige region of the Qinghai-Xizang Plateau from 2000 to 2017.The Lagrangian backward trajectory model is used to simulate the water vapor transport path under extreme dry and wet conditions and evaluate the location of potential evapotranspiration water vapor sources and their contributions to the water vapor transport in the study area.The results show that the main water vapor transport path is concentrated in the south branch transport path affected by the southwest monsoon during the wet period.The route originates from the Arabian Sea and the Bay of Bengal and finally arrives at the Zoige from the western and southern flank of the Qinghai-Xizang Plateau.Moreover, the water vapor transport pathway during the drought period is mainly affected by the westerlies.The dominant path starts from North America and the North Atlantic, spreads from west to east, the mid-latitude Eurasian continent, and finally reaches the north of the Qinghai-Xizang Plateau.The main water vapor sources appeared in the Qinghai-Xizang Plateau, Sichuan Basin, Bay of Bengal, Arabian Sea, and other regions.Affected by the water vapor transmission path in different periods, these water vapor sources show different characteristics.In the wet period, the water vapor source is mainly distributed around the south of the Qinghai-Xizang Plateau (the contribution rate is 35.98%).In contrast, the primary water vapor source during the drought period appears in the northern Qinghai-Xizang Plateau (the contribution rate is 28.35%).In addition, the contribution rate of water vapor sources from the Arabian Sea and the Bay of Bengal is higher in the wet period.In contrast, the contribution rate of water vapor in the local Zoige area and Sichuan is higher in the drought period.The analysis results will help to understand the formation mechanism of water vapor during extreme drought and wet states, how the water vapor sources work, and the contribution rate of the water vapor sources.This research can deepen the understanding of the mechanism of drought and flood disasters.

  • Study on Water Vapor Transport Source and Path of Rainstorm in Sanjiangyuan Area
  • Meiyue WANG, Lei WANG, Xiehui LI, Chunyuan WANG, Xiangyue WANG
  • 2022 Vol. 41 (1): 68-78.  DOI:10.7522/j.issn.1000-0534.2020.00097
  • Abstract ( ) PDF (9141KB) ( )
  • Based on the NCAR/NCEP reanalysis data, the weather situation and water vapor transport characteristics of two typical rainstorm weather processes in Sanjiangyuan on July 22-23 ("0722") and August 2-3 ("0802") were analyzed firstly.Then, the WRF model was used to output data for driving the HYSPLIT model to quantitatively analyzing the water vapor transport of the two storms.The results show: (1) The main influence systems of the two rainstorms are the vortex and shear lines formed in the eastern region of Sanjiangyuan and the evolution and advance and retreat of the vortex system has great influence on the intensity and fall area of the rainstorms.(2) The HYSPLIT model uses the high-resolution data output from the WRF model as the initial field and the simulation works well.(3) There are three main moisture transport routes for the “0722” rainstorm: 10 days before the rainstorm, the gas blocks in the northwest path were located in the western region of Xinjiang and entered the Sanjiangyuan via the northern Qinghai-Xizang Plateau, the moisture transport contribution rate is 16%; The air parcels in the southwest path originate from the north of the Bay of Bengal and are transported to Sanjiangyuan through the water vapor transport channel of the Yarlung Zangbo River Grand Canyon, with the water vapor transport contribution rate is 41.5%; Water vapor in the southwest path existed in Guangxi 10 days ago and transported to the rainstorm area through Sichuan and other places, with water vapor transport contribution rate acbeing 42.5%.(4) The water vapor of the "0802" rainstorm is mainly transported to the Sanjiangyuan area via four routes: one route is southwest, and the water vapor of the Bay of Bengal is transported to the rainstorm area through the Yarlung Zangbo River Grand Canyon, the water vapor transport contribution rate is 28%.The remaining three are southeast routes: ten days ago, the main source of water vapor appeared in Guizhou and Hunan and is transported to Sanjiangyuan in the northwest direction, the contribution rate of water vapor transportation of the three routes being 23%, 23% and 26%, respectively.(5) In general, the main water vapors for the two rainstorms come from the southwest and southeast paths.The water vapors in the southwest path come from the Bay of Bengal and are transported to the rainstorm area through the Water vapor transport channel of the Yarlung Zangbo River Grand Canyon.The water vapors along the southeast path are transferred-toward the northwest from Guangdong and Hunan to the rainstorm area.For the rainstorm of "0722", there are also water vapors transport along the northwest path, which has a small contribution rate.

  • A Simulation Study on Soil Parameterization Scheme of Seasonally Frozen Ground Regions based on CLM4.5
  • Chunwei FU, Zeyong HU, Shan LU, Di WU, Weiwei FAN
  • 2022 Vol. 41 (1): 93-106.  DOI:10.7522/j.issn.1000-0534.2021.00050
  • Abstract ( ) PDF (9600KB) ( )
  • In this paper, the field observation data provided by Naqu station of Plateau Climate and Environment in northern Qinghai-Xizang(Tibetan) Plateau, located in the seasonally frozen ground regions, CLM4.5 is used to analyze and evaluate the simulation ability of thermal conductivity parameterization schemes of Luo, Johansen, and C?té as well as virtual temperature parameterization scheme to calculate soil temperature and humidity, providing basis for the future work of selecting the optimal parameters and parameterization schemes to more reasonably simulate the freeze-thaw process of frozen soil on Tibet Plateau.The results suggested that: (1) The soil thermal conductivity of three parameterization schemes was significantly different, of which the C?té scheme had the highest soil thermal conductivity, while the Luo scheme had the lowest.(2) All the three-soil heat conductivity parameterization schemes can reasonably simulate the daily variation trend of soil temperature and humidity.The Johansen scheme can better simulate the annual variation trend of soil temperature, the C?té scheme has a smaller deviation from the observed value in soil temperature simulation, and Luo scheme has a better simulation on soil moisture.(3) After adding the virtual temperature equation and introducing the phase transition efficiency parameter, the negative deviation of the model for soil moisture simulation is reduced.In addition to maintaining good simulation ability of soil temperature, the Y-L scheme can further improve the simulation ability of soil moisture.

  • A Simulation Study on Radiation Budget and Water-Heat Exchange over Alpine Grassland Based on CLM4.5
  • Di WU, Zeyong HU, Chunwei FU, Shujing WANG, Weiwei FAN
  • 2022 Vol. 41 (1): 107-121.  DOI:10.7522/j.issn.1000-0534.2021.00045
  • Abstract ( ) PDF (13036KB) ( )
  • Forced by observations from 1 June to 31 August 2014, which are provided by Naqu station of Plateau Climate and Environment in northern Qinghai-Xizang Plateau, CLM4.5 is used to evaluate the influence on simulated results of both radiation balance and exchange of water-heat after some surface parameters and parameterization schemes including LAI、 vegetation coverage and roughness length have changed.The reason for these changes are also discussed in this article.The results suggested that (1) Compared with the results produced by default scheme Z98, those of schemes named Z12 and B82 perform better in decreasing the positive bias of latent heat fluxes and negative bias of sensible heat fluxes.(2) aerodynamic roughness length calculated by revised Massman model and a method named “Chen” are respectively used to replace the default value, the outcomes produced by CLM approach the observations further.(3)With leaf area index increasing, sensible heat fluxes and reflected radiation and surface long-wave radiation decrease a lot, while latent heat fluxes are on the increase.(4)As the vegetation cover increases, latent fluxes decreases, while sensible heat fluxes and reflected radiation and surface long-wave radiation rise, meanwhile soil temperature and moisture also rise.The aim of this study is to provide a basis for future ambition to simulate the balance of ground surface water and heat over the whole Plateau.

  • The Characteristics of Land‐Atmospheric Water and Heat Exchange during Soil Freezing‐Thawing Process over the Underlying Surface of the Alpine Grassland in the Source Region of the Yellow River
  • Yueyue WU, Jun WEN, Zuoliang WANG, Dongyu JIA, Wenhui LIU, Yuqin JIANG, Xuancheng LU
  • 2022 Vol. 41 (1): 132-142.  DOI:10.7522/j.issn.1000-0534.2021.00014
  • Abstract ( ) PDF (1757KB) ( )
  • The seasonal characteristics of water and heat exchange in the alpine grasslands are significant, and the freezing‐thawing process has an important impact on the land‐atmospheric water and heat exchange.Based on the observation data of the land surface process in the Tangchama small watershed in the source area of the Yellow River from May 2014 to May 2015, this research divides the soil freezing‐thawing process into thawed stage (TT), frozen stage (FF), thawing to freezing (T-F) and freezing to thawing (F-T), and the changes in the different states and period of the net radiation, sensible heat flux, latent heat flux and surface heat flux of the underlying surface of the alpine grassland are analyzed to explore the characteristics of water and heat exchange between the land‐atmosphere in the soil freezing‐thawing process.The results are as follows: (1) The average value of the net radiation flux in the thawed stage is generally greater than that of the other three stages, and the maximum value reaches 203.7 W·m-2.The frozen soil melts in the freezing‐thawing stage, and the soil moisture content gradually increases.The radiation ratio increased significantly during the frozen stage, the net radiation diurnal variation was the largest in the thawed stage, reaching 717.6 W·m-2, and the frozen stage was the smallest, followed by the freezing‐thawing stage.(2) The proportion of sensible heat flux and latent heat flux is different in the thawed and frozen stages.When completely thawed, due to precipitation and soil moisture content, the net radiation is mainly converted into latent heat flux.The maximum diurnal variation of latent heat flux is 193.7 W·m-2, while the sensible heat flux is only about 80.0 W·m-2.The diurnal average of sensible heat and latent heat in the thawing‐freezing phase, the freezing‐thawing period and the frozen period is not much different.The mean latent heat in the three period is 21.9 W·m-2, and the sensible heat is 20.3 W·m-2; The diurnal variation is greater than the latent heat in the three period, the soil suffers a freezing‐thawing cycle, the soil temperature difference is small, and the water content changes, and the net radiation is mainly converted into sensible heat during this period; the diurnal variation of sensible heat was greater than that of latent heat in the three stages.The freezing-thawing cycle occurred in the soil, the difference between ground and air temperature was small, and the moisture content changed.During this period, the net radiation was mainly converted to sensible heat.(3) The soil heat flux is positive (negative) in thawed (frozen) state, indicating that the surface soil absorbs (releases) heat from the atmosphere, and its daily variation range is large (small).The above results show that the state and process of soil freezing and thawing have different characteristics for the water and heat exchange process between the land and atmosphere.

  • Numerical Simulation of Typical Characteristics of Land Surface Water-heat Zxchange over Gyaring Lake and Ngoring Lake in Summer
  • Xianyu YANG, Yaqiong LÜ, Jun WEN, Yaoming MA, Xianhong MENG, Anning HUANG, Hui TIAN, Shaobo ZHANG, Yurun WANG, Lin ZHAO
  • 2022 Vol. 41 (1): 143-152.  DOI:10.7522/j.issn.1000-0534.2020.00090
  • Abstract ( ) PDF (8825KB) ( )
  • To explore the Characteristics of Land Surface Water-heat Zxchange over Gyaring Lake and Ngoring Lake in Summer, the new generation of mesoscale numerical model WRF(Weather Research and Forecasting Model), developed by National Centers for Environmental Prediction(NCEP) and National Center for Atmospheric Research (NCAR) was used to simulate the characteristics of atmospheric boundary layer in Gyaring and Ngoring Lakes area.The results show that the WRF model can preferably simulate the diurnal variation characteristics of 2 m height temperature, sensible heat and latent heat flux.Gyaring and Ngoring Lakes have great cooling (heating) effect to the air above lakes during the day (night), showing obvious cold (warm) lake effect, and producing temperature difference between lakes and land.Such a temperature difference will affect the local wind field.during the day, in the central area of Gyaring and Ngoring Lakes have the strength of 1.0 m·s-1 and 0.5 m·s-1 of downdrafts respectively, and an updraft of 2.5 m·s-1 in intensity appeared over the surrounding area.The effect of Gyaring and Ngoring Lakes on sensible heat and latent heat during the day and night varies greatly.The existence of the two lakes will make the sensible heat and latent heat value of the lake surface lower than the surrounding land during the day, while the effect of the two lakes on sensible heat and latent heat at night is opposite to that of the daytime.For the height of atmospheric boundary layer, the existence of Gyaring and Ngoring Lakes effectively reduces the height of atmospheric boundary layer over the lake area during the day, but the influence of Gyaring and Ngoring Lakes on the height of atmospheric boundary layer is not obvious at night.

  • Characteristics Analysis of the Land-atmospheric Water & Heat Exchanges over the Yarlung Zangbo Grand Canyon Region
  • Qiang ZHANG, Jun WEN, Yueyue WU, Yaling CHEN, Yueqi LI, Zheng LIU
  • 2022 Vol. 41 (1): 153-166.  DOI:10.7522/j.issn.1000-0534.2021.00113
  • Abstract ( ) PDF (6847KB) ( )
  • By using the ECMWF Re-Analyses version5 data, the water vapor transport type over the Yarlung Zangbo Grand Canyon area of southeastern Qinghai-Xizang Plateau(QXP)are categorized, the daily variation characteristics of land-atmospheric water heat exchange fluxes are analyzed at different locations under different water vapor conditions by choosing two observation stations in the Yarlung Zangbo Grand Canyon area, namely, the Pailong Station and the Motuo Station.The results show that: The plateau monsoon period is the period of strong water vapor transport and the warm-wet period in the Yarlung Zangbo Grand Canyon area, while the opposite is true for the Plateau non-Monsoon period.Daily variations of near-surface latent heat fluxes on typical sunny/cloudy days during the Plateau Monsoon/non-Monsoon period are more sensitive and consistent in response to atmospheric water vapor conditions at the Motuo and the Pailong stations.The daily variation of near-surface latent heat flux under strong water vapor conditions is stronger than that under weak water vapor conditions, and the most significant difference in daily variation of near-surface latent heat flux under different water vapor conditions is found at the low altitude and humid Motuo station, where the daily average of near-surface sensible heat flux under strong water vapor conditions (84.05 W·m-2) is about 1.13 times of that under weak water vapor conditions on a typical sunny day during the non-monsoon period on the plateau, and the daily variation can reach 345.37 W·m-2.Different characteristics of near-surface sensible heat fluxes at the two sites in response to different water vapor conditions during the highland monsoon and non-monsoon periods.The daily variation of near-surface sensible heat fluxes at the Pailong and the Motuo stations on typical clear days during the highland monsoon period is stronger under weak water vapor conditions than under strong water vapor conditions.The daily average and variation of near-surface sensible heat flux is most sensitive to the difference of water vapor conditions during the highland monsoon/non-monsoon period at the higher altitude Pailong station, and the daily average and diurnal range of sensible heat flux under weak water vapor conditions (32.71 and 191.1 W·m-2) is about 1.66 and 1.26 times higher than that under strong water vapor conditions under a typical sunny day during the highland monsoon period.The weakening effect of cloud cover and water vapor on solar short-wave radiation is greater than its own greenhouse effect.The daily variations of near-surface sensible heat fluxes at the Motuo and the Pailong stations under weak water vapor conditions on typical cloudy days during the highland monsoon/non-monsoon period are stronger than those under strong water vapor conditions, and the daily average values of near-surface sensible heat fluxes at the Pailong station under weak water vapor conditions on typical cloudy days during the Plateau Monsoon/non-Monsoon period are 35.12 and 14.32 W?m-2 which are 2.59 and 1.27 times higher than those under strong water vapor conditions, respectively.The existence of water vapor transport channels in the Yarlung Zangbo Grand Canyon area, the radiation forcing of atmospheric water vapor has significant effects on the land-atmospheric water & heat exchanges process, the energy parting at the surface is controlled by the land surface property.

  • Analysis on the Temporal and Spatial Evolution Characteristics of Water Vapor Transport and Budget over the Source Region of the Three-River
  • Yaling CHEN, Jun WEN, Rong LIU, Yuqin JIANG, Guoqiang REN, Yueqi LI, Qiang ZHANG, Zheng LIU
  • 2022 Vol. 41 (1): 167-176.  DOI:10.7522/j.issn.1000-0534.2021.00049
  • Abstract ( ) PDF (4556KB) ( )
  • The Source Region of the Three-River (SRTR) lies in the hinterland of the Qinghai-Xizang (Tibetan) Plateau (QXP) and is one of the sensitive regions to climate change in East Asia.It is of great significance to study the distribution, transport, and budget of water vapor for understanding the characteristics of the regional precipitation.This research is based on the ERA5 reanalysis data of the European Centre for Medium-Range Weather Forecasts (ECMWF) from 1980 to 2019, combined with the data of 9 radiosonde stations in the National Meteorological Data Center from 1981 to 2010.The temporal and spatial variation characteristics of water vapor distribution, water vapor transport flux and budget of each boundary over the SRTR and its surrounding areas are analyzed.The results show that there are significant differences in the spatial distribution of water vapor content, which presents a high value region in the southeastern QXP and a low value region in the northwest of the QXP.The distribution and value of water vapor content are different in four seasons, which exhibit the largest in summer, followed by autumn and spring, and the least in winter.The annual cycle of water vapor content manifests the single peak over the SRTR and the Brahmaputra River basin.Water vapor is mainly concentrated in June to August and its maximum appears in July with a value of 41.6 mm.The inter-annual variation shows an increasing trend with a rate of 0.4 mm·(10a)-1.The Arabian Sea and the Bay of Bengal are the main sources of water vapor over the SRTR, followed by the western airflow from the middle latitude and the northwestern airflow.Three kinds of airflows form obvious convergence of water vapor transport flux over the Brahmaputra Grand Canyon.There are seasonal discrepancies in the intensity of water vapor transport.Among the water vapor import boundaries, the western boundary has the largest import (815.3×106 kg·s-1), followed by the southern boundary (724.9×106 kg·s-1) and the seasonal variations of the two boundaries are significant.The northern boundary has less import (317.9×106 kg·s-1), while the eastern boundary is the export boundary of water vapor flux, and the maximum water vapor export is in September with a value of 140.5×106 kg·s-1.The net water vapor import is greater than the export, thus the water vapor flux is in surplus, which is about to affect the variations of precipitation and the regional water cycle over the SRTR.

  • Variation Characteristics of Surface Fluxes on Different Underlying Surfaces and Their Relationship with Precipitation in the Canyon Area of Southeast Tibet
  • Lingzhi WANG, Maoshan LI, Zhao LÜ, Wei FU, Lei SHU, Shucheng YIN
  • 2022 Vol. 41 (1): 177-189.  DOI:10.7522/j.issn.1000-0534.2020.00107
  • Abstract ( ) PDF (6311KB) ( )
  • In this study, variation characteristics of surface fluxes were analyzed by using the eddy covariance observations from four stations of Pailong, Danka, Kabu, and Motuo in the southeastern gorge area of Tibet from November 2018 to October 2019.Pailong Station is located at the entrance of the Canyon in Southeast Tibet, Danka Station is in the middle section, and Kabu Station and Metuo Station are located at the end of the Canyon in Southeast Tibet.Results show that monthly averaged daily latent heat flux is greater than sensible heat flux at night, and it has a single peak during the day.The sensible heat fluxes at Pailong and Danka stations are stronger from November to April and become weaker from May to October.The changing trend of monthly averaged daily sensible heat flux at Kabu station is fluctuating.Sensible heat flux and latent heat flux at Motuo station have the same variation characteristics, with a characteristic of a single peak change.Latent heat fluxes increase first and then decrease at all four stations.Seasonal variations of soil heat flux are obvious, characterizing positive values in spring and summer and negative values in autumn and winter.And the diurnal variation of soil heat flux in Pailong station was the strongest among all stations, and that of Kabu station was the weakest.The diurnal variation intensity of net radiation flux is summer>spring>autumn>winter.The downward and upward longwave radiation fluxes are the largest at Kabu Station and the smallest at Danka Station at the same time they are the largest in summer.The peak of diurnal longwave radiation flux appears later than the shortwave radiation flux.Energy closure rates of Danka, Pailong, Motuo, and Kabu stations are 70.86%, 68.91%, 69.29%, and 67.23%, respectively.In addition, in these four sites the degree of summer closure is high, while the degree of winter closure is low.Latent heat fluxes and soil heat fluxes increase, and sensible heat fluxes decrease as increasing precipitation at the four stations.The sensible heat flux and soil heat flux respond synchronously to precipitation changes, and the changes in latent heat have a significant lag in response to precipitation changes.

  • Study on the Atmospheric Boundary Layer Structure of the Qinghai-Xizang Plateau under the South Branch of the Westerly Wind and the Plateau Monsoon Circulation Field
  • Wei FU, Maoshan LI, Shucheng YIN, Zhao LV, Lingzhi WANG, Lei SHU
  • 2022 Vol. 41 (1): 190-203.  DOI:10.7522/j.issn.1000-0534.2021.00016
  • Abstract ( ) PDF (12636KB) ( )
  • Using the second comprehensive scientific expedition of the Qinghai-Xizang Plateau "Land-Atmosphere Interaction and Climate Effect" three-dimensional comprehensive enhanced observation experiment May, July and October 2019 sounding data at the Mount Everest, Nyingchi, Nagqu, Shiquanhe sites and ERA5 reanalysis data.The characteristics of the atmospheric boundary layer structure of the plateau and its relationship with sensible heat and latent heat flux under the control of different wind fields in the south branch of the westerly wind and the plateau monsoon are discussed.Results show that the height of the atmospheric boundary layer at each station under the westerly south branch wind field is higher than that under the summer monsoon wind field.The height of the convective boundary layers of Mount Everest, Nyingchi, Nagqu and Shiquan River in the southwest wind field are 3250, 2250, 2760 and 3500 m respectively.while the height of the convective boundary layers of Mount Everest, Nyingchi, Nagqu and Shiquan River under the plateau monsoon field are 2000 m, 2100 m, 1650 m and 2000 m.The specific humidity of the surface layer at all site is larger on July than it on other months.The specific humidity of the surface layer in Linzhi area is larger than that of the other three regions, and it reaches 12.88 g·kg-1 at the maximum.The wind direction on Mount Everest over 1200 m is dominated by westerly winds in May and October.The wind direction on Nyingchi above 1500 m is dominated by westerly winds in May and October, and in July, winds above 1200 m is dominated by southerly winds.The wind direction of Shiquan River in May and October is dominated by west-southwest wind, and the wind direction of Shiquan River in July is dominated by west-northwest wind.The high-altitude wind speeds of Mount Everest, Nyingchi and Shiquanhe in May and October are much stronger than those in July.The sensible heat flux at each station under the west wind south branch wind field is dominated, and the latent heat flux at each station under the plateau summer wind field is dominated.

  • Study on the Characteristics of Atmospheric Turbulence Exchange in the Lower Reaches of the Lhasa River in the Eastern Qinghai-Xizang Plateau
  • Bin YANG, Qi YUAN, Changhai TAN, Gong ZHANG, Ning ZHENG, Lianglei GU
  • 2022 Vol. 41 (1): 204-215.  DOI:10.7522/j.issn.1000-0534.2021.00086
  • Abstract ( ) PDF (7150KB) ( )
  • Matter and energy between the land and atmosphere are transported with turbulent movement.Eddy covariance technology is an important way to evaluate atmospheric resources.It plays an important role in turbulence characteristics and accurate flux observation research.In this study, we analyzed the characteristics and similarity of turbulence spectra under different atmosphere conditions in the growing and non-growing seasons using closed-path eddy covariance system of Caigongtang flux station for the underlying surface of the typical grassland in the lower reaches of the Lhasa River in the eastern Qinghai-Xizang Plateau from August to November, 2020.The results showed: (1) During the growing season from August to September, the average daily net ecosystem CO2 exchange (NEE) was -2.3 gC·m-2·d-1, and the average daily ET was 1.8 mm·day-1, During the non-growing season from October to November, the average daily NEE was 1.1 gC·m-2·d-1, and the average daily ET was 0.3 mm·day-1; (2) The normalized spectra of three-dimensional (uv and w) direction of turbulent wind speed and temperature had obvious sub-regions of inertia, the slope of the spectra density curve conformed to the -2/3 law, and the normalized co-spectra of the vertical direction (w) turbulent wind speed and temperature, CO2 and H2O gas concentrations is higher than -4/3 law; (3) The daily variation of atmosphere stability during the growing and non-growing seasons was similar, mainly decreasing with the increase of momentum flux, but the normalized standard deviation ( σ / u *) fitting results of wind speed in each direction were different.During the growing season, σ u / u * σ v / u *, and σ w / u *were 2.84, 2.73, and 1.07, respectively.During the non-growing season, the three increased to 3.23, 3.19, and 1.22, respectively.The increase in normalized standard deviation of horizontal wind speed was obvious during the non-growing season, so the parameterization scheme of the similarity law of turbulent wind speed during the growing and non-growing seasons should be considered separately.The closed-path eddy covariance system can better realize the flux observation in this study area, and this conclusion can provide the basis for the land surface parameterization scheme that considers the similarity of the turbulent wind speed during the growing and non-growing seasons, which helps to observe the atmospheric resources more accurately.

  • Study on Micrometeorological Characteristics of Near Surface Layer in Emeishan Area
  • Na CHANG, Maoshan LI, Lingzhi WANG, Ming GONG, Wei FU, Lei SHU
  • 2022 Vol. 41 (1): 226-240.  DOI:10.7522/j.issn.1000-0534.2021.00111
  • Abstract ( ) PDF (9872KB) ( )
  • The land surface process of the Qinghai-Xizang (Tibet) Plateau has an important impact on China's weather and climate.Mount Emei is in the southeast edge of the Qinghai-Xizang (Tibet) Plateau.It is necessary place for the eastward movement of the plateau system, and the place where the southwest vortex begins to develop.Based on the atmospheric boundary layer gradient tower data, radiation observation data and surface flux data of Emeishan station on the eastern edge of Qinghai-Xizang (Tibet) Plateau from December 2019 to November 2020, this paper uses the eddy correlation method to analyze the changes of surface flux and evapotranspiration near the surface layer in Emeishan area, and estimates the zero plane displacement, aerodynamic roughness, aerothermal roughness Kinetic and thermodynamic parameters such as momentum flux transport coefficient and sensible heat flux transport coefficient.The main conclusions are as follows: The temperature in the canopy is higher than that in the canopy during the day, but the opposite at night.The relative humidity in the canopy is higher than that on the canopy, and the diurnal variation of wind speed near the ground is more obvious in the upper layer than that in the lower layer.The seasonal variation characteristics of near ground temperature, relative humidity and wind speed are obvious.The vertical wind profile has significantly different correlation and inflection point phenomenon in the canopy and above the canopy.The growth rate of wind speed below the inflection point with height is significantly smaller than that above the inflection point.The annual average value of zero plane displacement d is 10.45 m; The annual mean values of aerodynamic roughness Z 0m and thermodynamic roughness roughness Z 0h are 1.65 m and 9.95 m respectively.The annual average values of momentum flux transport coefficient CD and sensible heat flux transport coefficient CH are 1.58×10-2 and 3.79×10-3 respectively.Aerodynamic roughness fluctuates greatly with season, while aerothermodynamic roughness is opposite.The occurrence times and amount of precipitation have obvious seasonal changes.There are more precipitation days and precipitation in July, and the daily change of precipitation is obvious, showing the typical characteristics of night rain in Western Sichuan Basin.The daily variation amplitude of sensible heat flux and latent heat flux is large.The latent heat flux is dominant in summer and sensible heat transport is dominant in winter.The evapotranspiration of each day mainly occurs from 08:00 (Beijing Time the same as after) to 17:00, and reaches the maximum from 11:00 to 14:00, and the seasonal difference is obvious.

  • Characteristics and Possible Causes for Extreme Precipitation in Summer over the Loess Plateau
  • Shan LU, Zeyong HU, Chunwei FU, Weiwei FAN, Di WU
  • 2022 Vol. 41 (1): 241-254.  DOI:10.7522/j.issn.1000-0534.2021.00027
  • Abstract ( ) PDF (14525KB) ( )
  • Using the daily precipitation datasets from 64 meteorological monitoring stations in the Loess Plateau and NCEP/NCAR reanalysis data during the period of 1961 -2016, the spatial-temporal variations of the extreme precipitation were investigated in the Loess Plateau.In addition, the similarities and differences in atmospheric circulation situation corresponding to strong and weak years of extreme precipitation, and in different ages were compared.Results showed that extreme precipitation was the major type in summer in the Loess Plateau, which accounted for about 70% of the total summer precipitation, and presented spatial decreases from east to west of the plateau.Under the background of overall decline of summer precipitation in the Loess Plateau from 1961 to 2016, the proportion of extreme precipitation showed an increasing trend among almost 70% of the stations.Comparison of atmospheric circulation between strong and weak year indicated that when Baikal low strengthened and the subtropical high extended northward in summer, the warm and humid northward air flow from the Northwest Pacific Ocean and South China Sea intensified, leading to the convergence of cold and warm air over the Loess Plateau and consequently more extreme precipitation in summer.In strong extreme precipitation years, there were positive water vapor income anomalies in summer in the Loess Plateau.The positive contribution to water vapor mainly originated from the northern and southern boundaries in June.The water vapor at northern boundary was converted to an output part in July and August, while the water vapor input at the western and southern boundaries increased and more pronounced in August.The more obviously convergence of cold and warm air in summer was detected in strong extreme precipitation years, which was beneficial to the release of unstable energy and the increase of extreme precipitation in study area.Moreover, extreme precipitation in summer was found to have experienced a transition from wet condition to dry condition in the Loess Plateau in the 1980s, and had begun to increase in recent years.Based on the analyses of the characteristics of summer atmospheric circulation in different ages, it can be observed that positive net income of water vapor and obvious convergence of cold and warm air in summer typically resulted in more extreme precipitation in the Loess Plateau in the corresponding year, and vice versa.