This overview discusses old and new results as to the controversy on the past glacier extension in High Asia, which has been debated for 35 years now. This paper makes an attempt to come closer to a solution. H.v. Wis...This overview discusses old and new results as to the controversy on the past glacier extension in High Asia, which has been debated for 35 years now. This paper makes an attempt to come closer to a solution. H.v. Wissmann's interpretation (1959) of a small-scale glaciation contrasts with M. Kuhle's reconstruction (1974) of a large-scale glaciation with a 2.4 million km2 extended Qinghai-Xizang (Tibetan) inland glaciation and a Himalaya-Karakorum icestream network. Both opinions find support but also contradiction in the International and Chinese literature (Academia Sinica). The solution of this question is of supraregional importance because of the subtropical position of the concerned areas. In case of large albedo-intensive ice surfaces, a global cooling would be the energetical consequence and, furthermore, a breakdown of the summer monsoon. The current and interglacial heat-low above the very effective heating panel of the Qinghai-Xizang (Tibetan) Plateau exceeding 4000 m, which gives rise to this monsoon circulation, would be replaced by the cold-high of an inland ice. In addition, the plate-tectonically created Pleistocene history of the uplift of High Asia — should the occasion arise up to beyond the snowline (ELA) —would attain a paleoclimatically great, perhaps global importance. In case of a heavy superimposed ice load, the question would come up as to the glacio-isostatic interruption of this primary uplift. The production of the loesses sedimentated in NE-China and their very probable glacial genesis as well as an eustatic lowering of the sea-level by 5 to 7 m in the maximum case of glaciation are immediately tied up with the question of glaciation we want to discuss. Not the least, the problems of biotopes of the sanctuary-centres of flora and fauna, i.e., interglacial re-settlement, are also dependent on it. On the basis of this Quaternary- geomorphological-glaciological connection, future contributions are requested on the past glaciation, the current and glacial permafrost table and periglacial development, the history of uplift, and the development of Ice Age lakes and loess, but also on the development of vegetation and fauna in High Asia.展开更多
In coordination with Global Cryosphere Watch （GCW） initiated by World Meteorology Administration （WMO）, a regional ob- servation network is proposed based on existing stations/sites over High Asia and cryospberic ...In coordination with Global Cryosphere Watch （GCW） initiated by World Meteorology Administration （WMO）, a regional ob- servation network is proposed based on existing stations/sites over High Asia and cryospberic elements required by GCW. Thus, High Asian Cryosphere （HAC） network is preliminary designed, composing of seven ＂supersites＂, each containing several refer- ence sites. The network covers major mountain ranges in High Asia, such as East Tianshan, Qilian, Tanggula, Nyainqentanglha, Himalayas as well as the central and eastern Qinghai-Xizang （Tibet） Plateau. Although multiple cryospberic elements were ob- served at the existing HAC network, many others, which are required by Integrated Global Observation System-Cryosphere Theme （IGOS-Cryosphere）, are not yet included. More comprehensive observations are necessary to be included into ＂supersites＂ of HAC, so that the basic requirements for validation of satellite data, assimilation and coupled regional models can be met.展开更多
We analyzed the spatial local accuracy of land cover (LC) datasets for the Qiangtang Plateau,High Asia,incorporating 923 field sampling points and seven LC compilations including the International Geosphere Biosphere ...We analyzed the spatial local accuracy of land cover (LC) datasets for the Qiangtang Plateau,High Asia,incorporating 923 field sampling points and seven LC compilations including the International Geosphere Biosphere Programme Data and Information System (IGBPDIS),Global Land cover mapping at 30 m resolution (GlobeLand30),MODIS Land Cover Type product (MCD12Q1),Climate Change Initiative Land Cover (CCI-LC),Global Land Cover 2000 (GLC2000),University of Maryland (UMD),and GlobCover 2009 (Glob- Cover).We initially compared resultant similarities and differences in both area and spatial patterns and analyzed inherent relationships with data sources.We then applied a geographically weighted regression (GWR) approach to predict local accuracy variation.The results of this study reveal that distinct differences,even inverse time series trends,in LC data between CCI-LC and MCD12Q1 were present between 2001 and 2015,with the exception of category areal discordance between the seven datasets.We also show a series of evident discrepancies amongst the LC datasets sampled here in terms of spatial patterns,that is,high spatial congruence is mainly seen in the homogeneous southeastern region of the study area while a low degree of spatial congruence is widely distributed across heterogeneous northwestern and northeastern regions.The overall combined spatial accuracy of the seven LC datasets considered here is less than 70%,and the GlobeLand30 and CCI-LC datasets exhibit higher local accuracy than their counterparts,yielding maximum overall accuracy (OA) values of 77.39% and 61.43%,respectively.Finally,5.63% of this area is characterized by both high assessment and accuracy (HH) values,mainly located in central and eastern regions of the Qiangtang Plateau,while most low accuracy regions are found in northern,northeastern,and western regions.展开更多
The High Mountain Asia(HMA)is a prominent global mountain system characterized by an average altitude exceeding 4,000 m,intricate topography,and significant spatial variability in climatic conditions.Despite its impor...The High Mountain Asia(HMA)is a prominent global mountain system characterized by an average altitude exceeding 4,000 m,intricate topography,and significant spatial variability in climatic conditions.Despite its importance,there has been a relative paucity of research focusing on the spatiotemporal variations of snow cover,key controlling factors,and variability within HMA sub-basins.This study aims to address this gap by extracting snow cover percentage(SCP)and snow cover days(SCD)data from MOD10A2 snow products,integrating these with precipitation(P)and temperature(T)data from ERA5.Our objective is to analyze the spatiotemporal distribution characteristics of snow cover and to use path analysis to elucidate the key climatic factors and spatial differences influencing snow cover changes.The findings indicate that,on a temporal scale,the overall SCP in HMA exhibited a declining trend from 2001 to 2021.Interannual variations in SCP across HMA sub-basins revealed a decreasing trend in the Pamir(PAM),Western Tibetan Plateau(WTS),Eastern Tibetan Plateau(ETS),Western Kunlun(WKL),Qilian Shan(QLS),and Himalaya(HDS)regions,while an increasing trend was observed in other areas.Spatially,22.97%of the HMA regions experienced an increase in SCD,primarily in the Western Himalaya(WHL),Central Himalaya(CHL),and Southeastern Xizang(SET)regions.Conversely,28.08%of the HMA regions showed a decrease in SCD,predominantly in the Eastern Himalaya(EHL),HDS,and WTS regions.Temperature(T)emerged as the primary influencing factor of SCD change in most HMA sub-basins.However,in the Eastern Kunlun(EKL)and WHL sub-basins,precipitation(P)was identified as the main driver of SCD change,affecting all elevation zones in these regions.Additionally,other climatic conditions can also impact snow cover beyond the primary controlling factor.展开更多
Climate change in High Mountain Asia(HMA)is characterized by elevation dependence,which results in vertical zoning of vegetation distribution.However,few studies have been conducted on the distribution patterns of veg...Climate change in High Mountain Asia(HMA)is characterized by elevation dependence,which results in vertical zoning of vegetation distribution.However,few studies have been conducted on the distribution patterns of vegetation,the response of vegetation to climate change,and the key climatic control factors of vegetation along the elevation gradient in this region.In this study,based on the Normalized Difference Vegetation index(NDVI),we investigated the evolution pattern of vegetation in HMA during 2001-2020 using linear trend and Bayesian Estimator of Abrupt change,Seasonality,and Trend(BEAST)methods.Pearson correlation analysis and partial correlation analysis were used to explore the response relationship between vegetation and climatic factors along the elevation gradient.Path analysis was employed to quantitatively reveal the dominant climatic factors affecting vegetation distribution along the elevation gradient.The results showed that NDVI in HMA increased at a rate of 0.011/10a from 2001 to 2020,and the rate of increase abruptly slowed down after 2017.NDVI showed a fluctuating increase at elevation zones 1-2(<2500 m)and then decreased at elevation zones 3-9(2500-6000 m)with the increase of elevation.NDVI was most sensitive to precipitation and temperature at a 1-month lag.With the increase of elevation,the positive response relationship of NDVI with precipitation gradually weakened,while that of NDVI with temperature was the opposite.The total effect coefficient of precipitation(0.95)on vegetation was larger than that of temperature(0.87),indicating that precipitation is the dominant control factor affecting vegetation growth.Spacially,vegetation growth is jointly influenced by precipitation and temperature,but the influence of precipitation on vegetation growth is dominant at each elevation zone.The results of this study contribute to understanding how the elevation gradient effect influences the response of vegetation to climate change in alpine ecosystems.展开更多
Under the impact of climatic warming, the glaciers in the High Asia in China have been retreating continuously with negative glacial mass balance in recent several decades. The retreat became more intensive in the pas...Under the impact of climatic warming, the glaciers in the High Asia in China have been retreating continuously with negative glacial mass balance in recent several decades. The retreat became more intensive in the past 10 years. The spatial pattern of the glacial retreat in the High Asia in China is that the smallest magnitude of retreat is in the inland of the Tibetan Plateau, the magnitude increases from the inland to the margin of the Tibetan Plateau, and the largest magnitude at the margin of the Tibetan Plateau. The glacial retreat in the High Asia in China has an important impact on the water resource of the arid regions in Northwest China. This study shows that the glacial retreat in the 1990s has caused an increase of 5.5% in river runoff in Northwest China. In the Tarim River basin, the increase of river runoff is higher than 5.5%.展开更多
By use of the NCEP/ NCAR reanalysis data, the seasonal variation of the South Asia high (SAH) is analyzed. The influences of temporal and spatial variations of the middle and upper level atmospheric temperatures, the ...By use of the NCEP/ NCAR reanalysis data, the seasonal variation of the South Asia high (SAH) is analyzed. The influences of temporal and spatial variations of the middle and upper level atmospheric temperatures, the visible heat sources, and the diabatic heating rates in the whole atmospheric column on the seasonal variation of the SAH are discussed. Results show that the SAH has two seasonal balancing modes, one of which is the land high in summer and the other the ocean high in winter. The land high itself can be divided into two patterns as well, that is the Tibetan high and the Iranian high. Heating fields have important impacts on the seasonal variation of the SAH. The SAH is a warm high and its center has the property of heat preference, usually locating over or moving to an area with relatively larger heating rates. The annual cycle of the SAH is mainly controlled by the seasonal process of the latent and sensible heating in South Asia. Strong shortwave radiative heating in the north at high latitudes and over the Tibetan Plateau also has an effects on the northward movement and maintenance of the SAH. The cooling effect of infrared radiation is an important cause in weakening the SAH.展开更多
The tropical Indian Ocean （TIO） is warmer than normal during the summer when or after the El Nio decays. The present study investigates the impact of TIO SST on the South Asian High （SAH） in summer. When the TIO i...The tropical Indian Ocean （TIO） is warmer than normal during the summer when or after the El Nio decays. The present study investigates the impact of TIO SST on the South Asian High （SAH） in summer. When the TIO is warmer, the SAH strengthens and its center shifts southward. It is found that the variations in the SAH cannot be accounted for by the precipitation anomaly. A possible mechanism is proposed to explain the connection between the TIO and SAH： warmer SST in the TIO changes the equivalent potential temperature （EPT） in the atmospheric boundary layer （ABL）, alters the temperature profile of the moist atmosphere, warms the troposphere, which produces significant positive height anomaly over South Asia and modifies the SAH. An atmospheric general circulation model, ECHAM5, which has a reasonable prediction skill in the TIO and South Asia, was selected to test the effects of TIO SST on the SAH. The experiment with idealized heating over the TIO reproduced the response of the SAH to TIO warming. The results suggest that the TIO-induced EPT change in the ABL can account for the variations in the SAH.展开更多
The ability of a climate model to reproduce the climatic characters of the South Asia High （SAH） is assessed by analyzing the 110-yr output of a Flexible Coupled GCM, version 0 （FGCM-0）. Comparing the results of F...The ability of a climate model to reproduce the climatic characters of the South Asia High （SAH） is assessed by analyzing the 110-yr output of a Flexible Coupled GCM, version 0 （FGCM-0）. Comparing the results of FGCM-0 with the NCEP/NCAR reanalysis data, the major findings show that FGCM-0 has better results in simulation of the geopotential height field at 100 hPa, and reproduces fairly the main atmospheric circulation centers. However, there are still some differences in the simulated results compared with the reanalysis data. The coupled model also successfully reproduces the mean seasonal variation of the SAH, that is, it moves from the Pacific Ocean to the Asian continent, remaining over the Tibetan Plateau from winter to summer, and then withdraws from the Tibetan Plateau to the Pacific Ocean from summer to winter. However, such observed relationships between the SAH positions and the summer precipitation patterns cannot be fairly reproduced in the FGCM-0.展开更多
We provide estimates of glacier mass changes in the High Mountain Asia (HMA) area from April2002 to August 2016 by employing a new version of gravity solutions of the Gravity Recovery and ClimateExperiment (GRACE) twi...We provide estimates of glacier mass changes in the High Mountain Asia (HMA) area from April2002 to August 2016 by employing a new version of gravity solutions of the Gravity Recovery and ClimateExperiment (GRACE) twin-satellite mission. We find a total mass loss trend of the HMA glaciers at a rateof –22.17 (±1.96) Gt/a. The largest mass loss rates of –7.02 (±0.94) and –6.73 (±0.78) Gt/a are found forthe glaciers in Nyainqentanglha Mountains and Eastern Himalayas, respectively. Although most glaciers inthe HMA area show a mass loss, we find a small glacier mass gain of 1.19 (±0.55) and 0.77 (±0.37) Gt/a inKarakoram Mountains and Western Kunlun Mountains, respectively. There is also a nearly zero massbalance in Pamirs. Our estimates of glacier mass change trends confirm previous results from the analysisof altimetry data of the ICESat (ICE, Cloud and Land Elevation Satellite) and ASTER (AdvancedSpaceborne Thermal Emission and Reflection Radiometer) DEM (Digital Elevation Model) satellites inmost of the selected glacier areas. However, they largely differ to previous GRACE-based studies which weattribute to our different post-processing techniques of the newer GRACE data. In addition, we explicitlyshow regional mass change features for both the interannual glacier mass changes and the 14-a averagedseasonal glacier mass changes. These changes can be explained in parts by total net precipitation (netsnowfall and net rainfall) and net snowfall, but mostly by total net radiation energy when compared to datafrom the ERA5-Land meteorological reanalysis. Moreover, nearly all the non-trend interannual masschanges and most seasonal mass changes can be explained by the total net radiation energy data. The massloss trends could be partly related to a heat effect due to increased net rainfall in Tianshan Mountains, QilianMountains, Nyainqentanglha Mountains and Eastern Himalayas. Our new results for the glacier mass changein this study could help improve the understanding of glacier variation in the HMA area and contribute tothe study of global change. They could also serve the utilization of water resources there and in neighboringareas.展开更多
In this paper, a close relationship between the intraseasonal variation of subtropical high over East Asia and the convective activities around the South China Sea and the Philippines is analysed from OLR data.This re...In this paper, a close relationship between the intraseasonal variation of subtropical high over East Asia and the convective activities around the South China Sea and the Philippines is analysed from OLR data.This relationship is studied by using the theory of wave propagating in a slowly varying medium and by using a quasi-geoslrophic, linear, spherical model and the IAP-GCM, respectively. The results show that when the SST is warming around the western tropical Pacific or the Philippines, the convective activities are intensified around the Philippines. As a consequence, the subtropical high will be intensified over East Asia. The computed results also show that when the anomaly of convective activities are caused around the Philippines, a teleconnection pattern of circulation anomalies will be caused over South Asia, East Asia and North America.展开更多
Comparisons of the west Pacific subtropical high with the South Asia High are made using the NCEP/NCAR and ECMWF 500 hPa and 100 hPa monthly boreal geopotential height fields for the period 1961-2000. Discrepancies ar...Comparisons of the west Pacific subtropical high with the South Asia High are made using the NCEP/NCAR and ECMWF 500 hPa and 100 hPa monthly boreal geopotential height fields for the period 1961-2000. Discrepancies are found for the time prior to 1980. The west Pacific subtropical high in the NCEP/NCAR data is less intense than in ECMWF data before 1980. The range and strength of the west Pacific subtropical high variation described by the NCEP/NCAR data are larger than those depicted by ECMWF data. The same situation appears in the 100-hPa geopotential field. These discoveries suggest that the interdecadal variation of the two systems as shown by the NCEP/NCAR data may not be true. Besides, the South Asia High center in the NCEP/NCAR data is obviously stronger than in the ECMWF data during the periods 1969, 1979-1991 and 1992-1995. Furthermore, the range is larger from 1992 to 1995.展开更多
High Mountain Asia(HMA) region contains the world’s highest peaks and the largest concentration of glaciers except for the polar regions, making it sensitive to global climate change. In the context of global warming...High Mountain Asia(HMA) region contains the world’s highest peaks and the largest concentration of glaciers except for the polar regions, making it sensitive to global climate change. In the context of global warming, most glaciers in the HMA show various degrees of negative mass balance,while some show positive or near-neutral balance. Many studies have reported that spatial heterogeneity in glacier mass balance is strongly related to a combination of climate parameters. However, this spatial heterogeneity may vary according to the dynamic patterns of climate change at regional or continental scale. The reasons for this may be related to non-climatic factors. To understand the mechanisms by which spatial heterogeneity forms, it is necessary to establish the relationships between glacier mass balance and environmental factors related to topography and morphology. In this study, climate, topography,morphology, and other environmental factors are investigated. Geodetector and linear regression analysis were used to explore the driving factors of spatial variability of glacier mass balance in the HMA by using elevation change data during 2000–2016. The results show that the coverage of supraglacial debris is an essential factor affecting the spatial heterogeneity of glacier mass balance, followed by climatic factors and topographic factors, especially the median elevation and slope in the HMA. There are some differences among mountain regions and the explanatory power of climatic factors on the spatial differentiation of glacier mass balance in each mountain region is weak, indicating that climatic background of each mountain region is similar. Therefore, under similar climatic backgrounds, the median elevation and slope are most correlated with glacier mass balance. The interaction of various factors is enhanced, but no unified interaction factor plays a primary role. Topographic and morphological factors also control the spatial heterogeneity of glacier mass balance by influencing its sensitivity to climate change. In conclusion,geodetector method provides an objective framework for revealing the factors controlling glacier mass balance.展开更多
By analyzing the change of an index for the characteristics of South Asia High and variations of upper-air troughs in 2002–2005,we studied the impact of South Asia high on the beginning and ending of the Mei-yu(i.e.s...By analyzing the change of an index for the characteristics of South Asia High and variations of upper-air troughs in 2002–2005,we studied the impact of South Asia high on the beginning and ending of the Mei-yu(i.e.sustained rain corresponding to the ripening season of plum)in Jiangsu province.Statistic verification is conducted on the relationships between the index and the Mei-yu season in 1991–2005 to examine the impacts of the SAH characteristics index on a rain intensity index of Mei-yu and regional distribution of a characteristics index for different annual patterns of Mei-yu.Historical composite is performed of the 100-hPa circulation field for these patterns using the 100-hPa geopotential height of Northern Hemisphere from 2002 to 2005 and 45-year NCEP reanalysis to study the difference in the circulation for different patterns of Mei-yu.Diagnostic and statistic conclusions,which share much in common,have been obtained as follows.(1)The characteristics preceding to and the advancement/retreat of SAH and the movement of westerly troughs are the factors that influence the onset time of the Mei-yu season;after the Mei-yu onset,the progression/withdrawal of SAH and how farther east it extends are determining how long the Mei-yu lasts and when it ends.(2)During the Mei-yu,the general 100-hPa circulation situation and average characteristics of the SAH are well corresponding to the characteristics of the season and annual patterns of Mei-yu.In addition,the averages of the SAH ridgeline and east-extending index for June,July and the Mei-yu season have some implications to the forecast of the index of Mei-yu intensity.These conclusions can be served as powerful means in determining the starting/ending dates, duration and annual pattern of the Mei-yu season.展开更多
Velocity is an important component of glacier dynamics and directly reflects the response of glaciers to climate change.As a result,an accurate determination of seasonal variation in glacier velocity is very important...Velocity is an important component of glacier dynamics and directly reflects the response of glaciers to climate change.As a result,an accurate determination of seasonal variation in glacier velocity is very important in understanding the annual variation in glacier dynamics.However,few studies of glacier velocity in the High Mountain Asia(HMA)region were done.Along these lines,in this work,based on Sentinel-1 glacier velocity data,the distribution of glacier velocity in the HMA region was plotted and their seasonal variations during 2015-2020 were systematically analysed.The average glacier velocity in the HMA region was 0.053 m/d,and was positively correlated with the glacier area and slope.Glaciers in the Karakoram Mountains had the fastest average flow velocity(0.060 m/d),where the glaciers exhibited the largest average area and average slope.Moreover,glaciers in the GangdisêMountains had the slowest velocity(0.022 m/d)and the smallest average glacier area.The glacier flows were the fastest in spring(0.058 m/d),followed by summer(0.050 m/d),autumn(0.041 m/d),and winter(0.040 m/d).In addition,the glacier flows were the maximum in May,being 1.4 times of the annual average velocity.In some areas,such as the Qilian,Altun,Tibetan Interior,Eastern Kunlun,and Western Kunlun mountains,the peak glacier velocities appeared in June and July.The glacier velocity in the HMA region decreased in midsummer and reached the minimum in December when it was 75%of the annual average.These results highlight the role of meltwater in the seasonal variation in glacier flows in late spring and early summer.The seasonal velocity variation of lake-terminating glaciers was similar to that of land-terminating ones,but the former flowed faster.The velocity difference close to the mass balance line between the lake-and land-terminating glaciers was obviously greater in spring than in other seasons.In summer,the difference between the lake-and land-terminating glaciers at a normalized distance of 0.05-0.40 from the terminus was significantly greater than those of other seasons.The velocity difference between the lake-and land-terminating glaciers is closely related to the variable of ice thickness,and also to the frictional force of the terminal base reduced by proglacial lakes.Thus,it can be concluded that in addition to the variation of the glacier thickness and viscosity,the variation of glacier water input also plays a key role in the seasonal variation of glacier velocity.展开更多
The rapid development of high-speed rail（HSR） is influencing regional development, regional structure, commuting, and regional integration. East Asia is the region with the world＇s first and largest current operati...The rapid development of high-speed rail（HSR） is influencing regional development, regional structure, commuting, and regional integration. East Asia is the region with the world＇s first and largest current operating and planned HSR network. In this paper, we examine the evolutionary mechanism and impacts on the transport circle and accessibility of HSR in East Asia. The results indicate that the HSR network first follows a ＂core-core＂ model and then forms a corridor in Japan, South Korea, and China Taiwan, but then forms a complete network in China Mainland. The current operating HSR lines are mostly distributed in regions with developed economies and dense populations, and more than half of the population and GDP in China can be served by HSR within 1 hour＇s travel time. The planned HSR network will expand to the western region of China and Japan and the southern region of South Korea. The development of the current operating and planned HSR network considerably enlarges the transport circle of core cities, especially cities along trunk HSR lines. This 1 h transport circle of core cities has formed continuous regions in the Yangtze River Delta, the Pearl River Delta, Tokyo, Seoul, and along trunk HSR lines. The HSR network will bring about substantial improvement in accessiblity, but also increase the inequality of nodal accessibility in China Mainland. Spatially, the spatial patterns of the weighted shortest travel time of cities in China Mainland, Japan, and South Korea all present the ＂core-peripheral structure＂, taking Zhengzhou, Tokyo, and Seoul, respectively, as core cities, and cities located along the trunk HSR lines gain large improvement in accessibility.展开更多
The characteristics of the South Asia high (SAH) and subtropical westerly jets in the summer of 2010 and their relationship with the changes in rainband in China were analyzed. As shown by the results, the SAH in the ...The characteristics of the South Asia high (SAH) and subtropical westerly jets in the summer of 2010 and their relationship with the changes in rainband in China were analyzed. As shown by the results, the SAH in the upper troposphere extended northward relatively late in June 2010. Correspondingly, the subtropical westerly jets on the north side of the SAH jumped northward comparatively late, thus delaying the formation of a strong divergence field in the upper air over the Yangtze-Huaihe River valley. This was one of the main causes for the late onset of plum rains in the Yangtze-Huaihe River valley. In July, there was a vertical structure consisting of upper-level divergence and low-level convergence near the subtropical westerly jets on the north side of the SAH and in the air stream dispersal area on the northeast side of the eastward-extending SAH, which was the dynamic mechanism bringing about frequent and extremely heavy rainstorms during the plum rain period in this year. The SAH in the upper troposphere affected the subtropical high in the lower stratosphere, and thereby led to changes in the main rainband location in China.展开更多
High Mountain Asia(HMA),recognized as a third pole,needs regular and intense studies as it is susceptible to climate change.An accurate and high-resolution Digital Elevation Model(DEM)for this region enables us to ana...High Mountain Asia(HMA),recognized as a third pole,needs regular and intense studies as it is susceptible to climate change.An accurate and high-resolution Digital Elevation Model(DEM)for this region enables us to analyze it in a 3D environment and understand its intricate role as the Water Tower of Asia.The science teams of NASA realized an 8-m DEM using satellite stereo imagery for HMA,termed HMA 8-m DEM.In this research,we assessed the vertical accuracy of HMA 8-m DEM using reference elevations from ICESat-2 geolocated photons at three test sites of varied topography and land covers.Inferences were made from statistical quantifiers and elevation profiles.For the world’s highest mountain,Mount Everest,and its surroundings,Root Mean Squared Error(RMSE)and Mean Absolute Error(MAE)resulted in 1.94 m and 1.66 m,respectively;however,a uniform positive bias observed in the elevation profiles indicates the seasonal snow cover change will dent the accurate estimation of the elevation in this sort of test sites.The second test site containing gentle slopes with forest patches has exhibited the Digital Surface Model(DSM)features with RMSE and MAE of 0.58 m and 0.52 m,respectively.The third test site,situated in the Zanda County of the Qinghai-Xizang,is a relatively flat terrain bed,mostly bare earth with sudden river cuts,and has minimal errors with RMSE and MAE of 0.32 m and 0.29 m,respectively,and with a negligible bias.Additionally,in one more test site,the feasibility of detecting the glacial lakes was tested,which resulted in exhibiting a flat surface over the surface of the lakes,indicating the potential of HMA 8-m DEM for deriving the hydrological parameters.The results accrued in this investigation confirm that the HMA 8-m DEM has the best vertical accuracy and should be of high use for analyzing natural hazards and monitoring glacier surfaces.展开更多
NCEP/NCAR data are utilized to analyze an extreme flood year(1998) and an extreme dry year(2006) in the Sichuan-Chongqing region(SCR) and the results are as follows. The positive divergence of South Asia High(SAH) is ...NCEP/NCAR data are utilized to analyze an extreme flood year(1998) and an extreme dry year(2006) in the Sichuan-Chongqing region(SCR) and the results are as follows. The positive divergence of South Asia High(SAH) is stronger in the flood year; the position of the ridge line of SAH is southward compared with the annual average; Western Pacific Subtropical High(WPSH) extends westward and its ridge line is southward. In the drought year, the positive divergence of SAH is weaker, its ridge line is northward, and the position of WPSH is also northward. As shown in the dynamics, in drought(flood) years, negative(positive) vorticity advection in the upper atmosphere can cause the atmosphere to ascend(descend), and anomalous circulation of SAH displays divergence(convergence), and anomalous circulation of the lower atmosphere shows convergence(divergence). Thermal structure of the atmosphere shows that there is warm(cold) temperature advection in the lower atmosphere, and the vertical distribution of diabetic heating causes SAH's local circulation to display convergence(divergence) and affects vertical motion of the lower atmosphere circulation eventually. To some extent, the two extreme years in the SCR is closely related to the vertical motion of atmosphere circulation and the variation of such vertical motion is caused by differences of interactions between SAH and lower atmosphere circulations.展开更多
The NCEP 1°×1°reanalysis of June-to-September dataset between 2002 to 2009 is used in this study to conduct statistical analysis of the relationship between the environmental potential vorticity(PV)on 1...The NCEP 1°×1°reanalysis of June-to-September dataset between 2002 to 2009 is used in this study to conduct statistical analysis of the relationship between the environmental potential vorticity(PV)on 150 hPa located at the south edge of South Asia High(SAH)and TCs making landfall.The results show that 23 of the TCs are affected by the PV on 150 hPa located at the south edge of SAH between 2002 to2009,and three TCs'center pressure decline after the high-value environmental PV moves to the center of the TCs.These three TCs are Senlaku(0216),Bilis(0604)and Linfa(0903).Through diagnostic analysis from the viewpoint of isolines,we determined the relationship between the intensification of these TCs and the PV anomaly at high levels;the isentropic surface is close to the high level’s PV anomaly under the influence of the 150-hPa PV anomaly,leading to the decline of isentropic surfaces on both sides of the PV anomaly.Then the warm core of the middle and high levels of the TC strengthens and PV increases at the middle level,and both of them are beneficial to the reinforcement of the cyclonic vorticity in the low level.As a result,the center pressure of the TC declines.According to Wu’s theory of Slantwise Vorticity Development(SVD),the incline of the isentropic surfaces leads to the development of vertical vorticity,contributing to the vertical motion and the release of the latent heat.Then the warm core of the TC strengthens and the TC strengthens,too.Otherwise,piecewise PV inversion also shows that the high-level PV influences the mid-level more than the low level.展开更多
文摘This overview discusses old and new results as to the controversy on the past glacier extension in High Asia, which has been debated for 35 years now. This paper makes an attempt to come closer to a solution. H.v. Wissmann's interpretation (1959) of a small-scale glaciation contrasts with M. Kuhle's reconstruction (1974) of a large-scale glaciation with a 2.4 million km2 extended Qinghai-Xizang (Tibetan) inland glaciation and a Himalaya-Karakorum icestream network. Both opinions find support but also contradiction in the International and Chinese literature (Academia Sinica). The solution of this question is of supraregional importance because of the subtropical position of the concerned areas. In case of large albedo-intensive ice surfaces, a global cooling would be the energetical consequence and, furthermore, a breakdown of the summer monsoon. The current and interglacial heat-low above the very effective heating panel of the Qinghai-Xizang (Tibetan) Plateau exceeding 4000 m, which gives rise to this monsoon circulation, would be replaced by the cold-high of an inland ice. In addition, the plate-tectonically created Pleistocene history of the uplift of High Asia — should the occasion arise up to beyond the snowline (ELA) —would attain a paleoclimatically great, perhaps global importance. In case of a heavy superimposed ice load, the question would come up as to the glacio-isostatic interruption of this primary uplift. The production of the loesses sedimentated in NE-China and their very probable glacial genesis as well as an eustatic lowering of the sea-level by 5 to 7 m in the maximum case of glaciation are immediately tied up with the question of glaciation we want to discuss. Not the least, the problems of biotopes of the sanctuary-centres of flora and fauna, i.e., interglacial re-settlement, are also dependent on it. On the basis of this Quaternary- geomorphological-glaciological connection, future contributions are requested on the past glaciation, the current and glacial permafrost table and periglacial development, the history of uplift, and the development of Ice Age lakes and loess, but also on the development of vegetation and fauna in High Asia.
基金supported by Chinese 973 Project (2007CB411503)Chinese COPES(GYHY200706005)Hundred Talent Project of Chinese Academy of Sciences
文摘In coordination with Global Cryosphere Watch （GCW） initiated by World Meteorology Administration （WMO）, a regional ob- servation network is proposed based on existing stations/sites over High Asia and cryospberic elements required by GCW. Thus, High Asian Cryosphere （HAC） network is preliminary designed, composing of seven ＂supersites＂, each containing several refer- ence sites. The network covers major mountain ranges in High Asia, such as East Tianshan, Qilian, Tanggula, Nyainqentanglha, Himalayas as well as the central and eastern Qinghai-Xizang （Tibet） Plateau. Although multiple cryospberic elements were ob- served at the existing HAC network, many others, which are required by Integrated Global Observation System-Cryosphere Theme （IGOS-Cryosphere）, are not yet included. More comprehensive observations are necessary to be included into ＂supersites＂ of HAC, so that the basic requirements for validation of satellite data, assimilation and coupled regional models can be met.
基金The Strategic Priority Research Program of the Chinese Academy of Sciences,Nos.XDA20040200,XDB03030500Key Foundation Project of Basic Work of the Ministry of Science and Technology of China,No.2012FY111400National Key Technologies R&D Program,No.2012BC06B00
文摘We analyzed the spatial local accuracy of land cover (LC) datasets for the Qiangtang Plateau,High Asia,incorporating 923 field sampling points and seven LC compilations including the International Geosphere Biosphere Programme Data and Information System (IGBPDIS),Global Land cover mapping at 30 m resolution (GlobeLand30),MODIS Land Cover Type product (MCD12Q1),Climate Change Initiative Land Cover (CCI-LC),Global Land Cover 2000 (GLC2000),University of Maryland (UMD),and GlobCover 2009 (Glob- Cover).We initially compared resultant similarities and differences in both area and spatial patterns and analyzed inherent relationships with data sources.We then applied a geographically weighted regression (GWR) approach to predict local accuracy variation.The results of this study reveal that distinct differences,even inverse time series trends,in LC data between CCI-LC and MCD12Q1 were present between 2001 and 2015,with the exception of category areal discordance between the seven datasets.We also show a series of evident discrepancies amongst the LC datasets sampled here in terms of spatial patterns,that is,high spatial congruence is mainly seen in the homogeneous southeastern region of the study area while a low degree of spatial congruence is widely distributed across heterogeneous northwestern and northeastern regions.The overall combined spatial accuracy of the seven LC datasets considered here is less than 70%,and the GlobeLand30 and CCI-LC datasets exhibit higher local accuracy than their counterparts,yielding maximum overall accuracy (OA) values of 77.39% and 61.43%,respectively.Finally,5.63% of this area is characterized by both high assessment and accuracy (HH) values,mainly located in central and eastern regions of the Qiangtang Plateau,while most low accuracy regions are found in northern,northeastern,and western regions.
基金supported by Tianchi talent project(Granted No.51052401507)。
文摘The High Mountain Asia(HMA)is a prominent global mountain system characterized by an average altitude exceeding 4,000 m,intricate topography,and significant spatial variability in climatic conditions.Despite its importance,there has been a relative paucity of research focusing on the spatiotemporal variations of snow cover,key controlling factors,and variability within HMA sub-basins.This study aims to address this gap by extracting snow cover percentage(SCP)and snow cover days(SCD)data from MOD10A2 snow products,integrating these with precipitation(P)and temperature(T)data from ERA5.Our objective is to analyze the spatiotemporal distribution characteristics of snow cover and to use path analysis to elucidate the key climatic factors and spatial differences influencing snow cover changes.The findings indicate that,on a temporal scale,the overall SCP in HMA exhibited a declining trend from 2001 to 2021.Interannual variations in SCP across HMA sub-basins revealed a decreasing trend in the Pamir(PAM),Western Tibetan Plateau(WTS),Eastern Tibetan Plateau(ETS),Western Kunlun(WKL),Qilian Shan(QLS),and Himalaya(HDS)regions,while an increasing trend was observed in other areas.Spatially,22.97%of the HMA regions experienced an increase in SCD,primarily in the Western Himalaya(WHL),Central Himalaya(CHL),and Southeastern Xizang(SET)regions.Conversely,28.08%of the HMA regions showed a decrease in SCD,predominantly in the Eastern Himalaya(EHL),HDS,and WTS regions.Temperature(T)emerged as the primary influencing factor of SCD change in most HMA sub-basins.However,in the Eastern Kunlun(EKL)and WHL sub-basins,precipitation(P)was identified as the main driver of SCD change,affecting all elevation zones in these regions.Additionally,other climatic conditions can also impact snow cover beyond the primary controlling factor.
基金supported by the Xinjiang Uygur Autonomous Region Major Scientific and Technological Special Project Research and Demonstration on the Development Model of Ecological Agriculture and Efficient Utilization of Soil and Water Resources in Modern Irrigation Areas(2023A02002-1).
文摘Climate change in High Mountain Asia(HMA)is characterized by elevation dependence,which results in vertical zoning of vegetation distribution.However,few studies have been conducted on the distribution patterns of vegetation,the response of vegetation to climate change,and the key climatic control factors of vegetation along the elevation gradient in this region.In this study,based on the Normalized Difference Vegetation index(NDVI),we investigated the evolution pattern of vegetation in HMA during 2001-2020 using linear trend and Bayesian Estimator of Abrupt change,Seasonality,and Trend(BEAST)methods.Pearson correlation analysis and partial correlation analysis were used to explore the response relationship between vegetation and climatic factors along the elevation gradient.Path analysis was employed to quantitatively reveal the dominant climatic factors affecting vegetation distribution along the elevation gradient.The results showed that NDVI in HMA increased at a rate of 0.011/10a from 2001 to 2020,and the rate of increase abruptly slowed down after 2017.NDVI showed a fluctuating increase at elevation zones 1-2(<2500 m)and then decreased at elevation zones 3-9(2500-6000 m)with the increase of elevation.NDVI was most sensitive to precipitation and temperature at a 1-month lag.With the increase of elevation,the positive response relationship of NDVI with precipitation gradually weakened,while that of NDVI with temperature was the opposite.The total effect coefficient of precipitation(0.95)on vegetation was larger than that of temperature(0.87),indicating that precipitation is the dominant control factor affecting vegetation growth.Spacially,vegetation growth is jointly influenced by precipitation and temperature,but the influence of precipitation on vegetation growth is dominant at each elevation zone.The results of this study contribute to understanding how the elevation gradient effect influences the response of vegetation to climate change in alpine ecosystems.
基金supported by the Project of the Chinese Academy of Sciences(Grant No.KZCX3-SW-339)the Innovation Group Found of the National Natural Science Foundation of China(Grant No.40121101)the Project of the Chinese Academy of Sciences(Grant No.KZCX2-SW-118).
文摘Under the impact of climatic warming, the glaciers in the High Asia in China have been retreating continuously with negative glacial mass balance in recent several decades. The retreat became more intensive in the past 10 years. The spatial pattern of the glacial retreat in the High Asia in China is that the smallest magnitude of retreat is in the inland of the Tibetan Plateau, the magnitude increases from the inland to the margin of the Tibetan Plateau, and the largest magnitude at the margin of the Tibetan Plateau. The glacial retreat in the High Asia in China has an important impact on the water resource of the arid regions in Northwest China. This study shows that the glacial retreat in the 1990s has caused an increase of 5.5% in river runoff in Northwest China. In the Tarim River basin, the increase of river runoff is higher than 5.5%.
基金This research was jointly sponsored by "The National Key Programme for Developing Basic Sciences"project (1998040900)Part Ⅰ, and the National Natural Science Foundation of China Project:"Studies on Interaction between the South Asia High and the Asian Monsoon and lts Mechanisms"under Grant No.40175021.
文摘By use of the NCEP/ NCAR reanalysis data, the seasonal variation of the South Asia high (SAH) is analyzed. The influences of temporal and spatial variations of the middle and upper level atmospheric temperatures, the visible heat sources, and the diabatic heating rates in the whole atmospheric column on the seasonal variation of the SAH are discussed. Results show that the SAH has two seasonal balancing modes, one of which is the land high in summer and the other the ocean high in winter. The land high itself can be divided into two patterns as well, that is the Tibetan high and the Iranian high. Heating fields have important impacts on the seasonal variation of the SAH. The SAH is a warm high and its center has the property of heat preference, usually locating over or moving to an area with relatively larger heating rates. The annual cycle of the SAH is mainly controlled by the seasonal process of the latent and sensible heating in South Asia. Strong shortwave radiative heating in the north at high latitudes and over the Tibetan Plateau also has an effects on the northward movement and maintenance of the SAH. The cooling effect of infrared radiation is an important cause in weakening the SAH.
基金supported by the National Key Technology R&D Program 2008BAK50B02CAS Innovation Key Program (Grant No. KZCX2-YW-BR-14)+2 种基金National Basic Research Program of China(2011CB309704)Special Scientific Research Project for Public Interest (Grant No. GYHY201006021)the National Natural Science Foundation of China (Grant Nos.40890155, 40775051, U0733002)
文摘The tropical Indian Ocean （TIO） is warmer than normal during the summer when or after the El Nio decays. The present study investigates the impact of TIO SST on the South Asian High （SAH） in summer. When the TIO is warmer, the SAH strengthens and its center shifts southward. It is found that the variations in the SAH cannot be accounted for by the precipitation anomaly. A possible mechanism is proposed to explain the connection between the TIO and SAH： warmer SST in the TIO changes the equivalent potential temperature （EPT） in the atmospheric boundary layer （ABL）, alters the temperature profile of the moist atmosphere, warms the troposphere, which produces significant positive height anomaly over South Asia and modifies the SAH. An atmospheric general circulation model, ECHAM5, which has a reasonable prediction skill in the TIO and South Asia, was selected to test the effects of TIO SST on the SAH. The experiment with idealized heating over the TIO reproduced the response of the SAH to TIO warming. The results suggest that the TIO-induced EPT change in the ABL can account for the variations in the SAH.
文摘The ability of a climate model to reproduce the climatic characters of the South Asia High （SAH） is assessed by analyzing the 110-yr output of a Flexible Coupled GCM, version 0 （FGCM-0）. Comparing the results of FGCM-0 with the NCEP/NCAR reanalysis data, the major findings show that FGCM-0 has better results in simulation of the geopotential height field at 100 hPa, and reproduces fairly the main atmospheric circulation centers. However, there are still some differences in the simulated results compared with the reanalysis data. The coupled model also successfully reproduces the mean seasonal variation of the SAH, that is, it moves from the Pacific Ocean to the Asian continent, remaining over the Tibetan Plateau from winter to summer, and then withdraws from the Tibetan Plateau to the Pacific Ocean from summer to winter. However, such observed relationships between the SAH positions and the summer precipitation patterns cannot be fairly reproduced in the FGCM-0.
基金This work is funded by the National Key R&D Program of China(2017YFA0603103)the National Natural Science Foundation of China(41974009,42004007)+1 种基金the Key Research Program of Frontier Sciences,Chinese Academy of Sciences(QYZDB-SSW-DQC027,QYZDJ-SSW-DQC042)the open fund of State Key Laboratory of Geodesy and Earth's Dynamics(SKLGED2021-2-6)。
文摘We provide estimates of glacier mass changes in the High Mountain Asia (HMA) area from April2002 to August 2016 by employing a new version of gravity solutions of the Gravity Recovery and ClimateExperiment (GRACE) twin-satellite mission. We find a total mass loss trend of the HMA glaciers at a rateof –22.17 (±1.96) Gt/a. The largest mass loss rates of –7.02 (±0.94) and –6.73 (±0.78) Gt/a are found forthe glaciers in Nyainqentanglha Mountains and Eastern Himalayas, respectively. Although most glaciers inthe HMA area show a mass loss, we find a small glacier mass gain of 1.19 (±0.55) and 0.77 (±0.37) Gt/a inKarakoram Mountains and Western Kunlun Mountains, respectively. There is also a nearly zero massbalance in Pamirs. Our estimates of glacier mass change trends confirm previous results from the analysisof altimetry data of the ICESat (ICE, Cloud and Land Elevation Satellite) and ASTER (AdvancedSpaceborne Thermal Emission and Reflection Radiometer) DEM (Digital Elevation Model) satellites inmost of the selected glacier areas. However, they largely differ to previous GRACE-based studies which weattribute to our different post-processing techniques of the newer GRACE data. In addition, we explicitlyshow regional mass change features for both the interannual glacier mass changes and the 14-a averagedseasonal glacier mass changes. These changes can be explained in parts by total net precipitation (netsnowfall and net rainfall) and net snowfall, but mostly by total net radiation energy when compared to datafrom the ERA5-Land meteorological reanalysis. Moreover, nearly all the non-trend interannual masschanges and most seasonal mass changes can be explained by the total net radiation energy data. The massloss trends could be partly related to a heat effect due to increased net rainfall in Tianshan Mountains, QilianMountains, Nyainqentanglha Mountains and Eastern Himalayas. Our new results for the glacier mass changein this study could help improve the understanding of glacier variation in the HMA area and contribute tothe study of global change. They could also serve the utilization of water resources there and in neighboringareas.
文摘In this paper, a close relationship between the intraseasonal variation of subtropical high over East Asia and the convective activities around the South China Sea and the Philippines is analysed from OLR data.This relationship is studied by using the theory of wave propagating in a slowly varying medium and by using a quasi-geoslrophic, linear, spherical model and the IAP-GCM, respectively. The results show that when the SST is warming around the western tropical Pacific or the Philippines, the convective activities are intensified around the Philippines. As a consequence, the subtropical high will be intensified over East Asia. The computed results also show that when the anomaly of convective activities are caused around the Philippines, a teleconnection pattern of circulation anomalies will be caused over South Asia, East Asia and North America.
基金Key Laboratory on Natural Disasters for Jiangsu Province (KLME050210)
文摘Comparisons of the west Pacific subtropical high with the South Asia High are made using the NCEP/NCAR and ECMWF 500 hPa and 100 hPa monthly boreal geopotential height fields for the period 1961-2000. Discrepancies are found for the time prior to 1980. The west Pacific subtropical high in the NCEP/NCAR data is less intense than in ECMWF data before 1980. The range and strength of the west Pacific subtropical high variation described by the NCEP/NCAR data are larger than those depicted by ECMWF data. The same situation appears in the 100-hPa geopotential field. These discoveries suggest that the interdecadal variation of the two systems as shown by the NCEP/NCAR data may not be true. Besides, the South Asia High center in the NCEP/NCAR data is obviously stronger than in the ECMWF data during the periods 1969, 1979-1991 and 1992-1995. Furthermore, the range is larger from 1992 to 1995.
基金supported by the National Natural Science Foundation of China(42071085,41701087)the Open Project of the State Key Laboratory of Cryospheric Science(SKLCS 2020-10)。
文摘High Mountain Asia(HMA) region contains the world’s highest peaks and the largest concentration of glaciers except for the polar regions, making it sensitive to global climate change. In the context of global warming, most glaciers in the HMA show various degrees of negative mass balance,while some show positive or near-neutral balance. Many studies have reported that spatial heterogeneity in glacier mass balance is strongly related to a combination of climate parameters. However, this spatial heterogeneity may vary according to the dynamic patterns of climate change at regional or continental scale. The reasons for this may be related to non-climatic factors. To understand the mechanisms by which spatial heterogeneity forms, it is necessary to establish the relationships between glacier mass balance and environmental factors related to topography and morphology. In this study, climate, topography,morphology, and other environmental factors are investigated. Geodetector and linear regression analysis were used to explore the driving factors of spatial variability of glacier mass balance in the HMA by using elevation change data during 2000–2016. The results show that the coverage of supraglacial debris is an essential factor affecting the spatial heterogeneity of glacier mass balance, followed by climatic factors and topographic factors, especially the median elevation and slope in the HMA. There are some differences among mountain regions and the explanatory power of climatic factors on the spatial differentiation of glacier mass balance in each mountain region is weak, indicating that climatic background of each mountain region is similar. Therefore, under similar climatic backgrounds, the median elevation and slope are most correlated with glacier mass balance. The interaction of various factors is enhanced, but no unified interaction factor plays a primary role. Topographic and morphological factors also control the spatial heterogeneity of glacier mass balance by influencing its sensitivity to climate change. In conclusion,geodetector method provides an objective framework for revealing the factors controlling glacier mass balance.
基金Special Projects for Forecaster China Meteorological Administration(CMAYBY2011-017)
文摘By analyzing the change of an index for the characteristics of South Asia High and variations of upper-air troughs in 2002–2005,we studied the impact of South Asia high on the beginning and ending of the Mei-yu(i.e.sustained rain corresponding to the ripening season of plum)in Jiangsu province.Statistic verification is conducted on the relationships between the index and the Mei-yu season in 1991–2005 to examine the impacts of the SAH characteristics index on a rain intensity index of Mei-yu and regional distribution of a characteristics index for different annual patterns of Mei-yu.Historical composite is performed of the 100-hPa circulation field for these patterns using the 100-hPa geopotential height of Northern Hemisphere from 2002 to 2005 and 45-year NCEP reanalysis to study the difference in the circulation for different patterns of Mei-yu.Diagnostic and statistic conclusions,which share much in common,have been obtained as follows.(1)The characteristics preceding to and the advancement/retreat of SAH and the movement of westerly troughs are the factors that influence the onset time of the Mei-yu season;after the Mei-yu onset,the progression/withdrawal of SAH and how farther east it extends are determining how long the Mei-yu lasts and when it ends.(2)During the Mei-yu,the general 100-hPa circulation situation and average characteristics of the SAH are well corresponding to the characteristics of the season and annual patterns of Mei-yu.In addition,the averages of the SAH ridgeline and east-extending index for June,July and the Mei-yu season have some implications to the forecast of the index of Mei-yu intensity.These conclusions can be served as powerful means in determining the starting/ending dates, duration and annual pattern of the Mei-yu season.
基金supported by the Major Project on Natural Science Foundation of Universities in Anhui Province(2022AH040111)the National Natural Science Foundation of China(42071085,41701087)。
文摘Velocity is an important component of glacier dynamics and directly reflects the response of glaciers to climate change.As a result,an accurate determination of seasonal variation in glacier velocity is very important in understanding the annual variation in glacier dynamics.However,few studies of glacier velocity in the High Mountain Asia(HMA)region were done.Along these lines,in this work,based on Sentinel-1 glacier velocity data,the distribution of glacier velocity in the HMA region was plotted and their seasonal variations during 2015-2020 were systematically analysed.The average glacier velocity in the HMA region was 0.053 m/d,and was positively correlated with the glacier area and slope.Glaciers in the Karakoram Mountains had the fastest average flow velocity(0.060 m/d),where the glaciers exhibited the largest average area and average slope.Moreover,glaciers in the GangdisêMountains had the slowest velocity(0.022 m/d)and the smallest average glacier area.The glacier flows were the fastest in spring(0.058 m/d),followed by summer(0.050 m/d),autumn(0.041 m/d),and winter(0.040 m/d).In addition,the glacier flows were the maximum in May,being 1.4 times of the annual average velocity.In some areas,such as the Qilian,Altun,Tibetan Interior,Eastern Kunlun,and Western Kunlun mountains,the peak glacier velocities appeared in June and July.The glacier velocity in the HMA region decreased in midsummer and reached the minimum in December when it was 75%of the annual average.These results highlight the role of meltwater in the seasonal variation in glacier flows in late spring and early summer.The seasonal velocity variation of lake-terminating glaciers was similar to that of land-terminating ones,but the former flowed faster.The velocity difference close to the mass balance line between the lake-and land-terminating glaciers was obviously greater in spring than in other seasons.In summer,the difference between the lake-and land-terminating glaciers at a normalized distance of 0.05-0.40 from the terminus was significantly greater than those of other seasons.The velocity difference between the lake-and land-terminating glaciers is closely related to the variable of ice thickness,and also to the frictional force of the terminal base reduced by proglacial lakes.Thus,it can be concluded that in addition to the variation of the glacier thickness and viscosity,the variation of glacier water input also plays a key role in the seasonal variation of glacier velocity.
基金National Natural Science Foundation of China,No.41171107,No.41371143,No.4401121
文摘The rapid development of high-speed rail（HSR） is influencing regional development, regional structure, commuting, and regional integration. East Asia is the region with the world＇s first and largest current operating and planned HSR network. In this paper, we examine the evolutionary mechanism and impacts on the transport circle and accessibility of HSR in East Asia. The results indicate that the HSR network first follows a ＂core-core＂ model and then forms a corridor in Japan, South Korea, and China Taiwan, but then forms a complete network in China Mainland. The current operating HSR lines are mostly distributed in regions with developed economies and dense populations, and more than half of the population and GDP in China can be served by HSR within 1 hour＇s travel time. The planned HSR network will expand to the western region of China and Japan and the southern region of South Korea. The development of the current operating and planned HSR network considerably enlarges the transport circle of core cities, especially cities along trunk HSR lines. This 1 h transport circle of core cities has formed continuous regions in the Yangtze River Delta, the Pearl River Delta, Tokyo, Seoul, and along trunk HSR lines. The HSR network will bring about substantial improvement in accessiblity, but also increase the inequality of nodal accessibility in China Mainland. Spatially, the spatial patterns of the weighted shortest travel time of cities in China Mainland, Japan, and South Korea all present the ＂core-peripheral structure＂, taking Zhengzhou, Tokyo, and Seoul, respectively, as core cities, and cities located along the trunk HSR lines gain large improvement in accessibility.
文摘The characteristics of the South Asia high (SAH) and subtropical westerly jets in the summer of 2010 and their relationship with the changes in rainband in China were analyzed. As shown by the results, the SAH in the upper troposphere extended northward relatively late in June 2010. Correspondingly, the subtropical westerly jets on the north side of the SAH jumped northward comparatively late, thus delaying the formation of a strong divergence field in the upper air over the Yangtze-Huaihe River valley. This was one of the main causes for the late onset of plum rains in the Yangtze-Huaihe River valley. In July, there was a vertical structure consisting of upper-level divergence and low-level convergence near the subtropical westerly jets on the north side of the SAH and in the air stream dispersal area on the northeast side of the eastward-extending SAH, which was the dynamic mechanism bringing about frequent and extremely heavy rainstorms during the plum rain period in this year. The SAH in the upper troposphere affected the subtropical high in the lower stratosphere, and thereby led to changes in the main rainband location in China.
基金The authors gratefully acknowledge the science teams of NASA High Mountain Asia 8-meter DEM and NASA ICESat-2 for providing access to the data.This work was conducted with the infrastructure provided by the National Remote Sensing Centre(NRSC),for which the authors were indebted to the Director,NRSC,Hyderabad.We acknowledge the continued support and scientific insights from Mr.Rakesh Fararoda,Mr.Sagar S Salunkhe,Mr.Hansraj Meena,Mr.Ashish K.Jain and other staff members of Regional Remote Sensing Centre-West,NRSC/ISRO,Jodhpur.The authors want to acknowledge Dr.Kamal Pandey,Scientist,IIRS,Dehradun,for sharing field-level information about the Auli-Joshimath.This research did not receive any specific grant from funding agencies in the public,commercial,or not-for-profit sectors.
文摘High Mountain Asia(HMA),recognized as a third pole,needs regular and intense studies as it is susceptible to climate change.An accurate and high-resolution Digital Elevation Model(DEM)for this region enables us to analyze it in a 3D environment and understand its intricate role as the Water Tower of Asia.The science teams of NASA realized an 8-m DEM using satellite stereo imagery for HMA,termed HMA 8-m DEM.In this research,we assessed the vertical accuracy of HMA 8-m DEM using reference elevations from ICESat-2 geolocated photons at three test sites of varied topography and land covers.Inferences were made from statistical quantifiers and elevation profiles.For the world’s highest mountain,Mount Everest,and its surroundings,Root Mean Squared Error(RMSE)and Mean Absolute Error(MAE)resulted in 1.94 m and 1.66 m,respectively;however,a uniform positive bias observed in the elevation profiles indicates the seasonal snow cover change will dent the accurate estimation of the elevation in this sort of test sites.The second test site containing gentle slopes with forest patches has exhibited the Digital Surface Model(DSM)features with RMSE and MAE of 0.58 m and 0.52 m,respectively.The third test site,situated in the Zanda County of the Qinghai-Xizang,is a relatively flat terrain bed,mostly bare earth with sudden river cuts,and has minimal errors with RMSE and MAE of 0.32 m and 0.29 m,respectively,and with a negligible bias.Additionally,in one more test site,the feasibility of detecting the glacial lakes was tested,which resulted in exhibiting a flat surface over the surface of the lakes,indicating the potential of HMA 8-m DEM for deriving the hydrological parameters.The results accrued in this investigation confirm that the HMA 8-m DEM has the best vertical accuracy and should be of high use for analyzing natural hazards and monitoring glacier surfaces.
基金National Key Basic Research Development Program Project of China(2012CB417202)Key Project of National Natural Science Foundation(91337215)National Natural Science Foundation of China(41275051)
文摘NCEP/NCAR data are utilized to analyze an extreme flood year(1998) and an extreme dry year(2006) in the Sichuan-Chongqing region(SCR) and the results are as follows. The positive divergence of South Asia High(SAH) is stronger in the flood year; the position of the ridge line of SAH is southward compared with the annual average; Western Pacific Subtropical High(WPSH) extends westward and its ridge line is southward. In the drought year, the positive divergence of SAH is weaker, its ridge line is northward, and the position of WPSH is also northward. As shown in the dynamics, in drought(flood) years, negative(positive) vorticity advection in the upper atmosphere can cause the atmosphere to ascend(descend), and anomalous circulation of SAH displays divergence(convergence), and anomalous circulation of the lower atmosphere shows convergence(divergence). Thermal structure of the atmosphere shows that there is warm(cold) temperature advection in the lower atmosphere, and the vertical distribution of diabetic heating causes SAH's local circulation to display convergence(divergence) and affects vertical motion of the lower atmosphere circulation eventually. To some extent, the two extreme years in the SCR is closely related to the vertical motion of atmosphere circulation and the variation of such vertical motion is caused by differences of interactions between SAH and lower atmosphere circulations.
基金National Key Fundamental Research Development Program Planning"973"(2009CB4215032013CB430103)+2 种基金Natural Science Foundation of China(41375058)Construction of Advantageous Disciplines for Higher Education in Jiangsu ProvincePriority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)
文摘The NCEP 1°×1°reanalysis of June-to-September dataset between 2002 to 2009 is used in this study to conduct statistical analysis of the relationship between the environmental potential vorticity(PV)on 150 hPa located at the south edge of South Asia High(SAH)and TCs making landfall.The results show that 23 of the TCs are affected by the PV on 150 hPa located at the south edge of SAH between 2002 to2009,and three TCs'center pressure decline after the high-value environmental PV moves to the center of the TCs.These three TCs are Senlaku(0216),Bilis(0604)and Linfa(0903).Through diagnostic analysis from the viewpoint of isolines,we determined the relationship between the intensification of these TCs and the PV anomaly at high levels;the isentropic surface is close to the high level’s PV anomaly under the influence of the 150-hPa PV anomaly,leading to the decline of isentropic surfaces on both sides of the PV anomaly.Then the warm core of the middle and high levels of the TC strengthens and PV increases at the middle level,and both of them are beneficial to the reinforcement of the cyclonic vorticity in the low level.As a result,the center pressure of the TC declines.According to Wu’s theory of Slantwise Vorticity Development(SVD),the incline of the isentropic surfaces leads to the development of vertical vorticity,contributing to the vertical motion and the release of the latent heat.Then the warm core of the TC strengthens and the TC strengthens,too.Otherwise,piecewise PV inversion also shows that the high-level PV influences the mid-level more than the low level.
