Track density function(TDF)was computed for all Western North Pacific tropical cyclones(WNP TCs)tracks from 1950 to 2018,and the TDFs were further investigated using principal component analysis(PCA)to analyze their i...Track density function(TDF)was computed for all Western North Pacific tropical cyclones(WNP TCs)tracks from 1950 to 2018,and the TDFs were further investigated using principal component analysis(PCA)to analyze their inter-annual spatial and temporal variability.Then,the relationships between each empirical orthogonal function(EOF)mode and the typhoon count,typhoon landfall count,track pattern,and the Qinghai-Xizang Plateau snow cover(QXPSC)were examined,and the possible physical mechanisms implied by the statistical relationship were explored.The results show the QXPSC significantly affected the surface-atmosphere heat exchange through snow cover(SC)level,then changed the East Asian summer monsoon regional circulation pattern,influenced the subtropical high-pressure system strength and location,and ultimately affected the WNP TCs track patterns and thus changed their landfall locations.展开更多
Interannual and decadal variations of winter snow cover over the Qinghai-Xizang Plateau (QXP) are analyzed by using monthly mean snow depth data set of 60 stations over QXP for the period of 1958 through 1992. It is f...Interannual and decadal variations of winter snow cover over the Qinghai-Xizang Plateau (QXP) are analyzed by using monthly mean snow depth data set of 60 stations over QXP for the period of 1958 through 1992. It is found that the winter snow cover over QXP bears a pronounced quasi-biennial oscillation, and it underwent an obvious decadal transition from a poor snow cover period to a rich snow cover period in the late 1970’s during the last 40 years. It is shown that the summer rainfall in the eastern China is closely associated with the winter snow cov-er over QXP not only in the interannual variation but also in the decadal variation. A clear relationship ex-ists in the quasi-biennial oscillation between the summer rainfall in the northern part of North China and the southern China and the winter snow cover over QXP. Furthermore, the summer rainfall in the four cli-mate divisions of Qinling-Daba Mountains, the Yangtze-Huaihe River Plain, the upper and lower reaches of the Yangtze River showed a remarkable transition from drought period to rainy period in the end of 1970’s, in good correspondence with the decadal transition of the winter snow cover over QXP. Key words Snow cover over Qinghai-Xizang Plateau - Summer monsoon rainfall in China - Interannual and decadal variations This study was supported by the National Key Programme for Developing Basic Sciences (G 1998040900 Part I).展开更多
The summer snow anomalies over the Tibetan Plateau (TP) and their effects on climate variability are often overlooked,possibly due to the fact that some datasets cannot properly capture summer snow cover over high t...The summer snow anomalies over the Tibetan Plateau (TP) and their effects on climate variability are often overlooked,possibly due to the fact that some datasets cannot properly capture summer snow cover over high terrain.The satellite-derived Equal-Area Scalable Earth grid (EASE-grid) dataset shows that snow still exists in summer in the western part and along the southem flank of the TP.Analysis demonstrates that the summer snow cover area proportion (SCAP) over the TP has a significant positive correlation with simultaneous precipitation over the mei-yu-baiu (MB) region on the interannual time scale.The close relationship between the summer SCAP and summer precipitation over the MB region could not be simply considered as a simultaneous response to the Silk Road pattern and the SST anomalies in the tropical Indian Ocean and tropical central-eastern Pacific.The SCAP anomaly has an independent effect and may directly modulate the land surface heating and,consequently,vertical motion over the western TP,and concurrently induce anomalous vertical motion over the North Indian Ocean via a meridional vertical circulation.Through a zonal vertical circulation over the tropics and a Kelvin wave-type response,anomalous vertical motion over the North Indian Ocean may result in an anomalous high over the western North Pacific and modulate the convective activity in the western Pacific warm pool,which stimulates the East Asia-Pacific (EAP) pattern and eventually affects summer precipitation over the MB region.展开更多
The present reported study investigated the persistence of snow anomalies over the Tibetan Plateau(TP) from the preceding seasons to summer and the relationship between the previous snow cover anomaly and summer preci...The present reported study investigated the persistence of snow anomalies over the Tibetan Plateau(TP) from the preceding seasons to summer and the relationship between the previous snow cover anomaly and summer precipitation over East Asia. The results showed that, relative to other snow indices, such as the station observational snow depth(SOSD) index and the snow water equivalent(SWE) index, the snow cover area proportion(SCAP) index calculated from the SWE and the percentage of visible snow of the Equal-Area Scalable Earth Grids(EASE-grids) dataset has a higher persistence in interannual anomalies, particularly from May to summer. As such, the May SCAP index is significantly related to summer precipitation over the Meiyu-Baiu region. The persistence of the SCAP index can partly explain the season-delayed effect of snow cover over the TP on summer rainfall over the Meiyu-Baiu region besides the contribution of the soil moisture bridge. The preceding SST anomaly in the tropical Indian Ocean and ENSO can persist through the summer and affect the summer precipitation over the Meiyu-Baiu region. However, the May SCAP index is mostly independent of the simultaneous SSTs in the tropical Indian Ocean and the preceding ENSO and may affect the summer precipitation over the Meiyu-Baiu region independent of the effects of the SST anomalies. Therefore, the May SCAP over the TP could be regarded as an important supplementary factor in the forecasting of summer precipitation over the Meiyu-Baiu region.展开更多
The e?ect of anomalous snow cover over the Tibetan Plateau upon the South Asian summer monsoon is investigated by numerical simulations using the NCAR regional climate model (RegCM2) into which gravity wave ...The e?ect of anomalous snow cover over the Tibetan Plateau upon the South Asian summer monsoon is investigated by numerical simulations using the NCAR regional climate model (RegCM2) into which gravity wave drag has been introduced. The simulations adopt relatively realistic snow mass forcings based on Scanning Multi-channel Microwave Radiometer (SMMR) pentad snow depth data. The physical mechanism and spatial structure of the sensitivity of the South Asian early summer monsoon to snow cover anomaly over the Tibetan Plateau are revealed. The main results are summarized as follows. The heavier than normal snow cover over the Plateau can obviously reduce the shortwave radiation absorbed by surface through the albedo e?ect, which is compensated by weaker upward sensible heat ?ux associated with colder surface temperature, whereas the e?ects of snow melting and evaporation are relatively smaller. The anomalies of surface heat ?uxes can last until June and become unobvious in July. The decrease of the Plateau surface temperature caused by heavier snow cover reaches its maximum value from late April to early May. The atmospheric cooling in the mid-upper troposphere over the Plateau and its surrounding areas is most obvious in May and can keep a fairly strong intensity in June. In contrast, there is warming to the south of the Plateau in the mid-lower troposphere from April to June with a maximum value in May. The heavier snow cover over the Plateau can reduce the intensity of the South Asian summer monsoon and rainfall to some extent, but this in?uence is only obvious in early summer and almost disappears in later stages.展开更多
In this paper, a variation series of snow cover and seasonal freeze-thaw layer from 1965 to 2004 on the Tibetan Plateau has been established by using the observation data from meteorological stations. The sliding T-te...In this paper, a variation series of snow cover and seasonal freeze-thaw layer from 1965 to 2004 on the Tibetan Plateau has been established by using the observation data from meteorological stations. The sliding T-test, M-K test and B-G algorithm are used to verify abrupt changes of snow cover and seasonal freeze-thaw layer in the Tibetan plateau. The results show that the snow cover has not undergone an abrupt change, but the seasonal freeze-thaw layer obviously witnessed a rapid degradation in 1987, with the frozen soil depth being reduced by about 15 cm. It is also found that when there ~s less snow in the plateau region, precipitation in South China and Southwest China increases. But when the frozen soil is deep, precipitation in most of China apparently decreases. Both snow cover and seasonal freeze-thaw layer on the plateau can be used to predict the summer precipitation in China. However, if the impacts of snow cover and seasonal freeze-thaw layer are used at the same time, the predictability of summer precipitation can be significantly improved. The significant correlation zone of snow is located in middle reaches of the Yangtze River covering the Hexi Corridor and northeastern Inner Mongolia, and the seasonal freeze-thaw layer exists in Mt. Nanling, northern Shannxi and northwestern part of North China. The significant correlation zone of simultaneous impacts of snow cover and seasonal freeze-thaw layer is larger than that of either snow cover or seasonal freeze-thaw layer. There are three significant correlation zones extending from north to south: the north zone spreads from Mr. Daxinganling to the Hexi Corridor, crossing northern Mt. Taihang and northern Shannxi; the central zone covers middle and lower reaches of the Yangtze River; and the south zone extends from Mt. Wuyi to Yunnan and Guizhou Plateau through Mt. Nanling.展开更多
Because of similar reflective characteristics of snow and cloud, the weather status seriously affects snow monitoring using optical remote sensing data. Cloud amount analysis during 2010 to 2011 snow seasons shows tha...Because of similar reflective characteristics of snow and cloud, the weather status seriously affects snow monitoring using optical remote sensing data. Cloud amount analysis during 2010 to 2011 snow seasons shows that cloud cover is the major limitation for snow cover monitoring using MOD10A1 and MYD10A1. By use of MODIS daily snow cover products and AMSR-E snow wa- ter equivalent products (SWE), several cloud elimination methods were integrated to produce a new daily cloud flee snow cover product, and information of snow depth from 85 climate stations in Tibetan Plateau area (TP) were used to validate the accuracy of the new composite snow cover product. The results indicate that snow classification accuracy of the new daily snow cover product reaches 91.7% when snow depth is over 3 cm. This suggests that the new daily snow cover mapping algorithm is suitable for monitoring snow cover dynamic changes in TP.展开更多
This paper presents an analysis of the mechanisms and impacts of snow cover and frozen soil in the Tibetan Plateau on the sum- mer precipitation in China, using RegCM3 version 3.1 model simulations. Comparisons of sim...This paper presents an analysis of the mechanisms and impacts of snow cover and frozen soil in the Tibetan Plateau on the sum- mer precipitation in China, using RegCM3 version 3.1 model simulations. Comparisons of simulations vs. observations show that RegCM3 well captures these impacts. Results indicate that in a more-snow year with deep frozen soil there will be more precipita- tion in the Yangtze River Basin and central Northwest China, western Inner Mongolia, and Xinjiang, but less precipitation in Northeast China, North China, South China, and most of Southwest China. In a less-snow year with deep frozen soil, however, there will be more precipitation in Northeast China, North China, and southern South China, but less precipitation in the Yangtze River Basin and in northern South China. Such differences may be attributed to different combination patterns of melting snow and thawing frozen soil on the Plateau, which may change soil moisture as well as cause differences in energy absorption in the phase change processes of snow cover and frozen soil. These factors may produce more surface sensible heat in more-snow years when the fi'ozen soil is deep than when the frozen soil is shallow. The higher surface sensible heat may lead to a stronger updraft over the Plateau, eventually contributing to a stronger South Asia High and West Pacific Subtropical High. Due to different values of the wind fields at 850 hPa, a convergence zone will form over the Yangtze River Basin, which may produce more summer pre- cipitation in the basin area but less precipitation in North China and South China. However, because soil moisture depends on ice content, in less-snow years with deep frozen soil, the soil moisture will be higher. The combination of higher frozen soil moisture with latent heat absorption in the phase change process may generate less surface sensible heat and consequently a weaker updraft motion over the Plateau. As a result, both the South Asia High and the West Pacific Subtropical High will be weaker, hence caus- ing more summer precipitation in northern China but less in southem China.展开更多
The calculating schemes of underlying surface processes in the model described by Li et al.(1989) are modified with inclusion of simple land surface processes and oceanic mixed layer processes, then a simulation on th...The calculating schemes of underlying surface processes in the model described by Li et al.(1989) are modified with inclusion of simple land surface processes and oceanic mixed layer processes, then a simulation on the zonal wind along 90°E from the Northern to the Southern Hemisphere with moun- tains is performed.Comparisons of the results and the observations show that the modified model not only has an excellent stability in calculation but also can better display the seasonal change of the wind field,the ability of the present model is improved as compared with that of the previous one. Based on the simulations,the authors investigate the effects of Qinghai-Xizang Plateau snow cover on the formation of South Asian monsoon by thickcning the snow depth and by increasing the snow albedo.The main results arc as follows:The summer meridional circulation over the south of the Plateau and its vicinity is weakeued,and the precipitation reduced.However,over the northern tropics,the circulation is enhanced, and the ecipitation is increased,and the land and the air above it become warmer,the tropical easterly jet is weakened.展开更多
Daily snow depth records at 60 primary dimatc statons over the Tibetan Plateau for the penod 1957-1992 are used as basis for point and areal hme series developmat. A statistical lnodel consistng of a trend plus serial...Daily snow depth records at 60 primary dimatc statons over the Tibetan Plateau for the penod 1957-1992 are used as basis for point and areal hme series developmat. A statistical lnodel consistng of a trend plus serially correated noise is fitted to the data to test for trend in time series of snow cover. Restilts of three trend estimatos based on difference of average, least squares fitting and slope AN (1) process imply that the increase in annual snow depth is a systematic developlnent as evidenced by the presence of a dotenniruStic trend. The spatial pattem of trend estimates convinced that the increase trends are almost onAnpresent over the wtire plateau. Further exandnation of interannual variation of snow cover over the Tiban Plateau and suffoce air tenrperature in winter over the nodriem hemisphere reveals a posihve correlation of +0.21 betWeen the two time series for period of 1957-1992.展开更多
The distribution of winter-spring snow cover over the Tibetan Plateau (TP) and its relationship with summer precipitation in the middle and lower reaches of Yangtze River Valley (MLYRV) during 2003-2013 have been ...The distribution of winter-spring snow cover over the Tibetan Plateau (TP) and its relationship with summer precipitation in the middle and lower reaches of Yangtze River Valley (MLYRV) during 2003-2013 have been investigated with the moderate-resolution imaging spectrometer (MODIS) Terra data (MOD10A2) and precipitation observations. Results show that snow cover percentage (SCP) remains approximately 20% in winter and spring then tails off to below 5% with warmer temperature and snow melt in summer. The lower and highest percentages present a declining tendency while the middle SCP exhibits an opposite variation. The maximum value appears from the middle of October to March and the minimum emerges from July to August. The annual and winter-spring SCPs present a decreasing tendency. Snow cover is mainly situated in the periphery of the plateau and mountainous regions, and less snow in the interior of the plateau, basin and valley areas in view of snow cover frequency (SCF) over the TP. Whatever annual or winter-spring snow cover, they all have remarkable declining tendency during 2003-2013, and annual snow cover presents a decreasing trend in the interior of the TP and increasing trend in the periphery of the TP. Hie multi-year averaged eight-day SCP is negatively related to mean precipitation in the MLYRV. Spring SCP is negatively related to summer precipitation while winter SCP is positively related to summer precipitation in most parts of the MLYRV. Hence, the influence of winter snow cover on precipitation is much more significant than that in spring on the basis of correlation analysis. The oscillation of SCF from southeast to northwest over the TP corresponds well to the beginning,development and cessation of the rain belt in eastern China.展开更多
Using the snow cover fi'action (SNC) output from eight WCRP CMIP3 climate models under SRES A2, A1B, and B1 scenarios, the future trend of SNC over East Asia is analyzed. Results show that SNC is likely to decrease...Using the snow cover fi'action (SNC) output from eight WCRP CMIP3 climate models under SRES A2, A1B, and B1 scenarios, the future trend of SNC over East Asia is analyzed. Results show that SNC is likely to decrease in East Asia, with the fastest decrease in spring, then winter and autumn, and the slowest in summer, In spring and winter the SNC decreases faster in the Qinghai-Xizang Plateau than in northern East Asia, while in autumn there is little difference between them. Among the various scenarios, SRES A2 has the largest decrease trend, then A1B, and B1 has the smallest trend. The decrease in SNC is mainly caused by the changes in surface air temperature and snowfall, which contribute differently to the SNC trends in different regions and seasons.展开更多
基金Supported by the National Natural Science Foundation of China(Nos.42176018,41876010)the Laoshan Laboratory(No.LSKJ202202401)the Graduate Student Fellowship from the China Scholarship Council for Zhaohua WANG(No.201806330006)。
文摘Track density function(TDF)was computed for all Western North Pacific tropical cyclones(WNP TCs)tracks from 1950 to 2018,and the TDFs were further investigated using principal component analysis(PCA)to analyze their inter-annual spatial and temporal variability.Then,the relationships between each empirical orthogonal function(EOF)mode and the typhoon count,typhoon landfall count,track pattern,and the Qinghai-Xizang Plateau snow cover(QXPSC)were examined,and the possible physical mechanisms implied by the statistical relationship were explored.The results show the QXPSC significantly affected the surface-atmosphere heat exchange through snow cover(SC)level,then changed the East Asian summer monsoon regional circulation pattern,influenced the subtropical high-pressure system strength and location,and ultimately affected the WNP TCs track patterns and thus changed their landfall locations.
文摘Interannual and decadal variations of winter snow cover over the Qinghai-Xizang Plateau (QXP) are analyzed by using monthly mean snow depth data set of 60 stations over QXP for the period of 1958 through 1992. It is found that the winter snow cover over QXP bears a pronounced quasi-biennial oscillation, and it underwent an obvious decadal transition from a poor snow cover period to a rich snow cover period in the late 1970’s during the last 40 years. It is shown that the summer rainfall in the eastern China is closely associated with the winter snow cov-er over QXP not only in the interannual variation but also in the decadal variation. A clear relationship ex-ists in the quasi-biennial oscillation between the summer rainfall in the northern part of North China and the southern China and the winter snow cover over QXP. Furthermore, the summer rainfall in the four cli-mate divisions of Qinling-Daba Mountains, the Yangtze-Huaihe River Plain, the upper and lower reaches of the Yangtze River showed a remarkable transition from drought period to rainy period in the end of 1970’s, in good correspondence with the decadal transition of the winter snow cover over QXP. Key words Snow cover over Qinghai-Xizang Plateau - Summer monsoon rainfall in China - Interannual and decadal variations This study was supported by the National Key Programme for Developing Basic Sciences (G 1998040900 Part I).
基金supported by the opening fund from the State Key Laboratory of Cryospheric Sciences, Cold and Arid Regions Environmental and Engineering Research Institute,Chinese Academy of Sciences(SKLCS 08-07)the National Postdoctoral Scientific Foundation (20080440342)
基金the support of the National Natural Science Foundation of China (Grant No. 41271434)the National Key Technologies R&D Program in the 12th Five Year Plan of China (Grant No. 2012BAH32B03)+6 种基金the Hong Kong GRF (Grant No. CUHK 457212)the ITF (Grant No. GHP/002/11GD)the support of the Hong Kong Research Grants Council (Grant No. CUHK 403612)the National Natural Science Foundation of China (Grant Nos. 41275081 and 41228006)the support of the National Natural Science Foundation of China (Grant Nos. 41375090 and 41221064)the Special Project of the National International Science and Technology Cooperation of China (Grant No. 2011DFG23450)the Basic Research Fund of CAMS (Grant No. 2013Z002)
文摘The summer snow anomalies over the Tibetan Plateau (TP) and their effects on climate variability are often overlooked,possibly due to the fact that some datasets cannot properly capture summer snow cover over high terrain.The satellite-derived Equal-Area Scalable Earth grid (EASE-grid) dataset shows that snow still exists in summer in the western part and along the southem flank of the TP.Analysis demonstrates that the summer snow cover area proportion (SCAP) over the TP has a significant positive correlation with simultaneous precipitation over the mei-yu-baiu (MB) region on the interannual time scale.The close relationship between the summer SCAP and summer precipitation over the MB region could not be simply considered as a simultaneous response to the Silk Road pattern and the SST anomalies in the tropical Indian Ocean and tropical central-eastern Pacific.The SCAP anomaly has an independent effect and may directly modulate the land surface heating and,consequently,vertical motion over the western TP,and concurrently induce anomalous vertical motion over the North Indian Ocean via a meridional vertical circulation.Through a zonal vertical circulation over the tropics and a Kelvin wave-type response,anomalous vertical motion over the North Indian Ocean may result in an anomalous high over the western North Pacific and modulate the convective activity in the western Pacific warm pool,which stimulates the East Asia-Pacific (EAP) pattern and eventually affects summer precipitation over the MB region.
基金support of the National Science Foundation of China (Grant Nos. 41271434 and 41375090)the Hong Kong Research Grants Council (Grant No. CUHK403612)the Basic Research Fund of Chinese Academy of Meteorological Sciences (Grant No. 2013Z002)
文摘The present reported study investigated the persistence of snow anomalies over the Tibetan Plateau(TP) from the preceding seasons to summer and the relationship between the previous snow cover anomaly and summer precipitation over East Asia. The results showed that, relative to other snow indices, such as the station observational snow depth(SOSD) index and the snow water equivalent(SWE) index, the snow cover area proportion(SCAP) index calculated from the SWE and the percentage of visible snow of the Equal-Area Scalable Earth Grids(EASE-grids) dataset has a higher persistence in interannual anomalies, particularly from May to summer. As such, the May SCAP index is significantly related to summer precipitation over the Meiyu-Baiu region. The persistence of the SCAP index can partly explain the season-delayed effect of snow cover over the TP on summer rainfall over the Meiyu-Baiu region besides the contribution of the soil moisture bridge. The preceding SST anomaly in the tropical Indian Ocean and ENSO can persist through the summer and affect the summer precipitation over the Meiyu-Baiu region. However, the May SCAP index is mostly independent of the simultaneous SSTs in the tropical Indian Ocean and the preceding ENSO and may affect the summer precipitation over the Meiyu-Baiu region independent of the effects of the SST anomalies. Therefore, the May SCAP over the TP could be regarded as an important supplementary factor in the forecasting of summer precipitation over the Meiyu-Baiu region.
基金the National Natural Science foundation of China(Grant No.40375027) opening item of the Key Laboratory for Mleteorological Disasters and Environmental Change of Nanjing Institute of Mleteorology(No.K2107).
文摘The e?ect of anomalous snow cover over the Tibetan Plateau upon the South Asian summer monsoon is investigated by numerical simulations using the NCAR regional climate model (RegCM2) into which gravity wave drag has been introduced. The simulations adopt relatively realistic snow mass forcings based on Scanning Multi-channel Microwave Radiometer (SMMR) pentad snow depth data. The physical mechanism and spatial structure of the sensitivity of the South Asian early summer monsoon to snow cover anomaly over the Tibetan Plateau are revealed. The main results are summarized as follows. The heavier than normal snow cover over the Plateau can obviously reduce the shortwave radiation absorbed by surface through the albedo e?ect, which is compensated by weaker upward sensible heat ?ux associated with colder surface temperature, whereas the e?ects of snow melting and evaporation are relatively smaller. The anomalies of surface heat ?uxes can last until June and become unobvious in July. The decrease of the Plateau surface temperature caused by heavier snow cover reaches its maximum value from late April to early May. The atmospheric cooling in the mid-upper troposphere over the Plateau and its surrounding areas is most obvious in May and can keep a fairly strong intensity in June. In contrast, there is warming to the south of the Plateau in the mid-lower troposphere from April to June with a maximum value in May. The heavier snow cover over the Plateau can reduce the intensity of the South Asian summer monsoon and rainfall to some extent, but this in?uence is only obvious in early summer and almost disappears in later stages.
基金by the National Key Basic Research Program(2007CB411505)S&T Support Project(2007BAC29B06)National Natural Science Foundation(40705031)
文摘In this paper, a variation series of snow cover and seasonal freeze-thaw layer from 1965 to 2004 on the Tibetan Plateau has been established by using the observation data from meteorological stations. The sliding T-test, M-K test and B-G algorithm are used to verify abrupt changes of snow cover and seasonal freeze-thaw layer in the Tibetan plateau. The results show that the snow cover has not undergone an abrupt change, but the seasonal freeze-thaw layer obviously witnessed a rapid degradation in 1987, with the frozen soil depth being reduced by about 15 cm. It is also found that when there ~s less snow in the plateau region, precipitation in South China and Southwest China increases. But when the frozen soil is deep, precipitation in most of China apparently decreases. Both snow cover and seasonal freeze-thaw layer on the plateau can be used to predict the summer precipitation in China. However, if the impacts of snow cover and seasonal freeze-thaw layer are used at the same time, the predictability of summer precipitation can be significantly improved. The significant correlation zone of snow is located in middle reaches of the Yangtze River covering the Hexi Corridor and northeastern Inner Mongolia, and the seasonal freeze-thaw layer exists in Mt. Nanling, northern Shannxi and northwestern part of North China. The significant correlation zone of simultaneous impacts of snow cover and seasonal freeze-thaw layer is larger than that of either snow cover or seasonal freeze-thaw layer. There are three significant correlation zones extending from north to south: the north zone spreads from Mr. Daxinganling to the Hexi Corridor, crossing northern Mt. Taihang and northern Shannxi; the central zone covers middle and lower reaches of the Yangtze River; and the south zone extends from Mt. Wuyi to Yunnan and Guizhou Plateau through Mt. Nanling.
基金supported by the China State Kay Basic Research Project(2013CBA01802)Chinese National Natural Science Foundation(41101337+2 种基金41001197and 31228021)the Fundamental Research Funds for the Central Universities(lzujbky-2013-103)
文摘Because of similar reflective characteristics of snow and cloud, the weather status seriously affects snow monitoring using optical remote sensing data. Cloud amount analysis during 2010 to 2011 snow seasons shows that cloud cover is the major limitation for snow cover monitoring using MOD10A1 and MYD10A1. By use of MODIS daily snow cover products and AMSR-E snow wa- ter equivalent products (SWE), several cloud elimination methods were integrated to produce a new daily cloud flee snow cover product, and information of snow depth from 85 climate stations in Tibetan Plateau area (TP) were used to validate the accuracy of the new composite snow cover product. The results indicate that snow classification accuracy of the new daily snow cover product reaches 91.7% when snow depth is over 3 cm. This suggests that the new daily snow cover mapping algorithm is suitable for monitoring snow cover dynamic changes in TP.
基金supported by the National Postdoctoral Scientific Foundation(20080440342)the opening fund from the State Key Laboratory of Cryospheric Sciences,Cold and Arid Regions Environmental and Engineering Research Institute,Chinese Academy of Sciences(SKLCS 08-07)
基金supported by the National Key Basic Research Program (No. 2007CB411505)the National Natural Science Foundation (No. 40705031)
文摘This paper presents an analysis of the mechanisms and impacts of snow cover and frozen soil in the Tibetan Plateau on the sum- mer precipitation in China, using RegCM3 version 3.1 model simulations. Comparisons of simulations vs. observations show that RegCM3 well captures these impacts. Results indicate that in a more-snow year with deep frozen soil there will be more precipita- tion in the Yangtze River Basin and central Northwest China, western Inner Mongolia, and Xinjiang, but less precipitation in Northeast China, North China, South China, and most of Southwest China. In a less-snow year with deep frozen soil, however, there will be more precipitation in Northeast China, North China, and southern South China, but less precipitation in the Yangtze River Basin and in northern South China. Such differences may be attributed to different combination patterns of melting snow and thawing frozen soil on the Plateau, which may change soil moisture as well as cause differences in energy absorption in the phase change processes of snow cover and frozen soil. These factors may produce more surface sensible heat in more-snow years when the fi'ozen soil is deep than when the frozen soil is shallow. The higher surface sensible heat may lead to a stronger updraft over the Plateau, eventually contributing to a stronger South Asia High and West Pacific Subtropical High. Due to different values of the wind fields at 850 hPa, a convergence zone will form over the Yangtze River Basin, which may produce more summer pre- cipitation in the basin area but less precipitation in North China and South China. However, because soil moisture depends on ice content, in less-snow years with deep frozen soil, the soil moisture will be higher. The combination of higher frozen soil moisture with latent heat absorption in the phase change process may generate less surface sensible heat and consequently a weaker updraft motion over the Plateau. As a result, both the South Asia High and the West Pacific Subtropical High will be weaker, hence caus- ing more summer precipitation in northern China but less in southem China.
文摘The calculating schemes of underlying surface processes in the model described by Li et al.(1989) are modified with inclusion of simple land surface processes and oceanic mixed layer processes, then a simulation on the zonal wind along 90°E from the Northern to the Southern Hemisphere with moun- tains is performed.Comparisons of the results and the observations show that the modified model not only has an excellent stability in calculation but also can better display the seasonal change of the wind field,the ability of the present model is improved as compared with that of the previous one. Based on the simulations,the authors investigate the effects of Qinghai-Xizang Plateau snow cover on the formation of South Asian monsoon by thickcning the snow depth and by increasing the snow albedo.The main results arc as follows:The summer meridional circulation over the south of the Plateau and its vicinity is weakeued,and the precipitation reduced.However,over the northern tropics,the circulation is enhanced, and the ecipitation is increased,and the land and the air above it become warmer,the tropical easterly jet is weakened.
文摘Daily snow depth records at 60 primary dimatc statons over the Tibetan Plateau for the penod 1957-1992 are used as basis for point and areal hme series developmat. A statistical lnodel consistng of a trend plus serially correated noise is fitted to the data to test for trend in time series of snow cover. Restilts of three trend estimatos based on difference of average, least squares fitting and slope AN (1) process imply that the increase in annual snow depth is a systematic developlnent as evidenced by the presence of a dotenniruStic trend. The spatial pattem of trend estimates convinced that the increase trends are almost onAnpresent over the wtire plateau. Further exandnation of interannual variation of snow cover over the Tiban Plateau and suffoce air tenrperature in winter over the nodriem hemisphere reveals a posihve correlation of +0.21 betWeen the two time series for period of 1957-1992.
基金supported by the National Natural Science Foundation of China(Grant No.41130960)the Project of the China Meteorological Administration(Grant Nos.CCSF201515 and CMAGJ2013M51)
文摘The distribution of winter-spring snow cover over the Tibetan Plateau (TP) and its relationship with summer precipitation in the middle and lower reaches of Yangtze River Valley (MLYRV) during 2003-2013 have been investigated with the moderate-resolution imaging spectrometer (MODIS) Terra data (MOD10A2) and precipitation observations. Results show that snow cover percentage (SCP) remains approximately 20% in winter and spring then tails off to below 5% with warmer temperature and snow melt in summer. The lower and highest percentages present a declining tendency while the middle SCP exhibits an opposite variation. The maximum value appears from the middle of October to March and the minimum emerges from July to August. The annual and winter-spring SCPs present a decreasing tendency. Snow cover is mainly situated in the periphery of the plateau and mountainous regions, and less snow in the interior of the plateau, basin and valley areas in view of snow cover frequency (SCF) over the TP. Whatever annual or winter-spring snow cover, they all have remarkable declining tendency during 2003-2013, and annual snow cover presents a decreasing trend in the interior of the TP and increasing trend in the periphery of the TP. Hie multi-year averaged eight-day SCP is negatively related to mean precipitation in the MLYRV. Spring SCP is negatively related to summer precipitation while winter SCP is positively related to summer precipitation in most parts of the MLYRV. Hence, the influence of winter snow cover on precipitation is much more significant than that in spring on the basis of correlation analysis. The oscillation of SCF from southeast to northwest over the TP corresponds well to the beginning,development and cessation of the rain belt in eastern China.
基金supported by the National Key Science and Technology Program of Ministry of Science and Technology of China (Grant No. 2007BAC03A01)
文摘Using the snow cover fi'action (SNC) output from eight WCRP CMIP3 climate models under SRES A2, A1B, and B1 scenarios, the future trend of SNC over East Asia is analyzed. Results show that SNC is likely to decrease in East Asia, with the fastest decrease in spring, then winter and autumn, and the slowest in summer, In spring and winter the SNC decreases faster in the Qinghai-Xizang Plateau than in northern East Asia, while in autumn there is little difference between them. Among the various scenarios, SRES A2 has the largest decrease trend, then A1B, and B1 has the smallest trend. The decrease in SNC is mainly caused by the changes in surface air temperature and snowfall, which contribute differently to the SNC trends in different regions and seasons.