Current Issue

28 February 2019, Volume 38 Issue 1   
  • Analysis of Meso-Small Scale System Characteristics of a Rare Severe Convective Weather in the Northeast Part of Qinghai-Tibetan Plateau
  • ZHU Ping;YU Xiaoding
  • 2019 Vol. 38 (1): 1-13.  DOI:10.7522/j.issn.1000-0534.2018.00070
  • Abstract ( ) HTML PDF (32820KB) ( )
  • A rare severe convective weather process with the large hailstone, local short-time rainstorm, and thunderstorm gale occurred over northeast part of Qinghai-Tibetan Plateau from 17 to 18 August 2016. The genesis and development and propagation mechanism of the meso-small scale convective system, and the atmospheric environment field were all analyzed by using the datum of conventional observation, NCEP reanalysis, himawari-8 satellite, C and X band Doppler radar, etc. And the characteristics between hail echo and rain echo were contrasted too. The results show that:It belonged to the low-level warm advection forcing type because of the obvious lifting northward of Subtropical High over west Pacific. The Water vapor was transported mainly from the South China Sea, and the Bay of Bengal next. The starting and trigger mechanism of sever convection was the weak cold front on surface with a longer life. Convective clouds gradually evolved into mesoscale convection complex (MCC), and the convection propagated toward unstable Atmospheric stratification zone and backward inflow wind of low-level along Huangshui river valley as a whole, and the convective motion dominated by propagation due to the weak inflow wind. The river valley topography was the key to the moving and propagation path of convection. All severe convective cells had comparatively long life cycle, the strong hail cells were similar-supercells and common multi-cells, and the heavy precipitation cells belonged to the multi-cell linear convection. The strong hail cells generally developed stronger and changed more greatly than the heavy precipitation cells, such as the former had stronger echo intensity, higher organization degree, longer life cycle mesocyclone, higher echo top and echo centroid, and most echo parameters had greater changes, especially VIL (vertical integrated liquid water content). In addition, the strong echo pendency located over the weak echo region in the former cells, etc. But before the beginning of severe convection, the VIL almost increased first and then dropped, and the maximum echo intensity exceeded 60 dBZ but changed relatively small both in the hail and precipitation cells. The four positions of thunderstorm gale were generated by the strongly down-divergence flow, that was produced by greater negative buoyancy due to strong temperature-fall period of weak rain of thunder clouds evaporation in thicker dry air level, or the drag of heavy precipitation in linear convection accompanied with dry air entrainment raindrops. The characteristics in radar echo presented the sharp decline of centroid height and mid-altitude radial convergence (MARC).
  • Characteristics of Meridional Circulation Cell on the South Side of Qinghai-Tibetan Plateau and its Effects on Precipitation over the region
  • HU Mengling;YOU Qinglong
  • 2019 Vol. 38 (1): 14-28.  DOI:10.7522/j.issn.1000-0534.2018.00064
  • Abstract ( ) HTML PDF (39295KB) ( )
  • Based on the daily observational precipitation data and ERA-Interim daily reanalysis data from 1979 to 2015, the meridional circulation cell characteristics on the south side of Qinghai-Tibetan Plateau and its effects on precipitation and water vapor transport over the Qinghai-Tibetan Plateau had been investigated. The results are shown as follows:The pre-monsoon circulation, monsoon circulation and Hadley circulation constitute seasonal evolution of meridional circulation cell on the south side of Qinghai-Tibetan Plateau along 80°E-90°E. A decreasing trend is observed with a rate of -0.377 s-1·(10a)-1 in the intensity of pre-monsoon circulation, while an increasing trend is detected with a value of 0.524 m·s-1·(10a)-1 in the intensity of monsoon circulation. There exists the transition of monsoon circulation and Hadley circulation on the south side of Qinghai-Tibetan Plateau along 90°E-105°E. The intensity of monsoon circulation remarkably increases during 1979-2015 with a trend of 0.413 m·s-1· (10a)-1. According to the definition of building and ending time of each meridional circulation cell, the setup of pre-monsoon circulation is delayed and the ending time is advanced and hence the maintaining time of pre-monsoon circulation trends to be shortened. Along the 90°E-105°E, the maintaining time of monsoon circulation shows an increasing trend while the maintaining time of Hadley circulation presents a decreasing trend. When the pre-monsoon circulation becomes stronger, the water vapor in divergence region trends to divergent and the water vapor in convergence region trends to convergent. Moreover, north-east water vapor transport is increased on the southwest Tibetan Plateau and south-west water vapor transport is enhanced on the northwest Qinghai-Tibetan Plateau. The strong summer monsoon circulation is beneficial to northward water vapor transport in the southern Tibetan Plateau and the Bay of Bengal and south-west water vapor transport from the Indian Ocean to the Tibetan Plateau. The precipitation is decreased in the middle and southwest Qinghai-Tibetan Plateau, whereas increases in the southeast and north of the Qinghai-Tibetan Plateau are clear as pre-monsoon circulation is enhanced. When summer monsoon circulation is strengthened, the more/less rainfall occurs in the south/north of Qinghai-Tibetan Plateau.
  • Dynamic and Thermodynamic Effects on Climate Changes over the Qinghai-Tibetan Plateau in Response to Global Warming
  • WANG Yuqi;BAO Yan;NAN Sulan
  • 2019 Vol. 38 (1): 29-41.  DOI:10.7522/j.issn.1000-0534.2018.00066
  • Abstract ( ) HTML PDF (14488KB) ( )
  • Projected climate changes (indicated by P-E) in the Qinghai-Tibetan Plateau (QTP) in 21st century are accessed by 8 coupled climate models from the fifth Phase of the Coupled Model Inter-comparison Project (CMIP5), the possible dynamic and thermodynamic effects of large-scale general circulation on the QTP climate change are investigated based on the moisture budget equation. Results indicated the QTP is projected to be much warmer and wetter than historical period in future, with P-E increased by 17.9% in the wet season of May to September (or vegetation growing season) in the last 20 years of 21st century (from 2080 to 2099) under RCP8.5. Dynamic effects of mean flow change related to poleward expansion of Hadley cell are considered as the dominating factor of projected P-E increase, which contributes to 53% increment of P-E. Thermodynamic effects associated with specific humidity change contribute to 12% P-E increase. In the Three River Source (TRS) region where the most significant greening has been found in the QTP under RCP8.5, the positive feedback of vegetation to future climate change favor the region moisten. The uncertainty in our results highlight the need for understanding the interaction between land surface and regional climate, particularly incorporation more complicated vegetation-climate interactions mechanisms into the models to better quantify the vegetation feedback on climate change.
  • Characteristics and Differences of Temperature Rise between the Qinghai-Tibetan Plateau Region and Northwest Arid Region of China During 1960-2015
  • MA Zhuanzhuan;ZHANG Mingjun;WANG Shengjie;QIU Xue;DU Qinqin;GUO Rong
  • 2019 Vol. 38 (1): 42-54.  DOI:10.7522/j.issn.1000-0534.2018.00074
  • Abstract ( ) HTML PDF (6669KB) ( )
  • The Qinghai-Tibetan Plateau region has long been regarded as the starting area and amplifier for our country and the global climate change, but many studies have shown that the magnitude of climate change in the northwest arid region of China cannot be ignored. Based on this, using the linear trend analysis, the sliding t test, the Mann-Kendall mutation detection and the Sen slope method, the characteristics of temperature on spatial distribution pattern and the multiple-time scale variability are analyzed by the monthly temperature data of 130 meteorological stations in the Qinghai-Tibetan Plateau region and northwest arid region of China during the 1960-2015. The results show that:On the whole, the annual mean temperature change rate of northwest arid region of China[0.32℃·(10a)-1] was higher than Qinghai-Tibetan Plateau region[0.29℃·(10a)-1] during 1960-2015. However, the temperature variations of the Qinghai-Tibetan plateau region and the northwest arid region of China were distinct in different time periods. The annual mean temperature change rate of northwest arid region of China[0.22℃·(10a)-1] was far higher than Qinghai-Tibetan Plateau region[0.14℃·(10a)-1] during the time period of 1960-1997. At the same time, the temperature variation of Qinghai-Tibetan Plateau region had a significant rising trend, at a rate of 0.22℃·(10a)-1 during 1998-2015, and the temperature variation of northwest arid region of China had a slight cooling trend, at a rate of -0.02℃·(10a)-1 during 1998-2015. The regions with temperature rise significantly in the Qinghai-Tibetan Plateau region included the Qaidam basin and the southwestern region of the plateau. The regions with temperature rise significantly in northwest arid region of China included the northern region of Xinjiang and the western region of Inner Mongolia. The interdecadal variation of temperature in the Qinghai-Tibetan Plateau region and northwest arid region of China were characterized by the relatively cold phase during 1960s-1980s, and the relatively warm phase after 1990s. In addition, mutation analysis indicated that the temperature of Qinghai-Tibetan Plateau region and northwest arid region of China began to grow in the same time, but the temperature mutation time of northwest arid region of China was in 1993, and the temperature mutation time of Qinghai-Tibetan Plateau region was in 1994.
  • The Primary Analysis of Wind Field's Influence on Qinghai-Tibetan Plateau Vortex Spinning over Hetao Region, China
  • TU Nini;YU Shuhua;GAO Wenliang
  • 2019 Vol. 38 (1): 66-77.  DOI:10.7522/j.issn.1000-0534.2017.00096
  • Abstract ( ) HTML PDF (39098KB) ( )
  • By using the July and August NCEP/NCAR reanalysis data in 2000, 2002 and 2005, the vorticity budget and middle level wind field of three spinning over Hetao region Plateau Vortexes, with consistent northward moving tropical low vortex, in different active phases were analyzed. Results show that the tropical low vortex's actions will influence the sustained departure Plateau vortexes (SDPVs) environmental fields, which will change the structure of the wind field of the SDPVs and lead to form dissymmetrical wind field structures. The dynamic mechanism of positive vorticity maintenance and development accompanying with spinning SDPVs depend mainly on the contribution of the generating and developing terms of the total positive vorticity changing rate. The contribution mechanism of the vortex to the total positive vorticity changing rate in vortex area of the SDPV is different under low trough, horizontal, and longitudinal shear wind field. The dynamic mechanism of vortex development and maintainence in low trough or transverse shear wind field has close relationship with the convergence stream field's maintainence and development contribution to the positive vorticity changing rate. And the dynamic mechanism of vortex development and maintainence in longitudinal shear wind field has close relationship with the horizental absolute vorticity advection term's contribution to the positive vorticity changing rate, which caused by the south and north wind flow to the vortex east and west region respectively. In the weaker weather system of the shear wind field, The SDPVs tend to move to the center of the total positive vorticity changing rate area.
  • Comparative Analysis of Multi-Source Water Vapor Data in Three River Source and Nearby Areas
  • MA Xueqian;ZHANG Xiaojun;MA Yuyan;CAI Miao;HAN Huibang;KANG Xiaoyan
  • 2019 Vol. 38 (1): 78-87.  DOI:10.7522/j.issn.1000-0534.2018.00073
  • Abstract ( ) HTML PDF (1656KB) ( )
  • The 35-channel microwave radiometer, global navigation satellite system meteorological observations (GNSS/Met), L-band sounding and National Center for Environmental Prediction (NCEP) reanalysis data constructed by enhancement precipitation project of Three Rivers Source were used to continuously monitor and calculated the precipitation water vapor (PWV) in this paper. The differences and influencing factors of multi-source data were compared, grasped and identified the applicability of multi-source data in Three River Source and nearby areas. The results show that GNSS/Met PWV is basically consistent with the reference value, which is not affected by temperature, precipitation, seasons and regions, and the total deviation is 1.45 mm. It can completely represent the water vapor characteristics of Three River Source and nearby areas. The general trend of NCEP PWV is consistent with the reference value, its value is obviously small, only 69% of the reference value, and with the larger deviation of precipitation increases. Temperature, region and season have a significant impact on its value. PWV of microwave radiometer can represent the water vapor characteristics of no or weak precipitation conditions, the value is significantly larger, and affected by the temperature, liquid water content and other factors, the data applicability need a lot of neural network training. The analysis of the ten-day PWV in Three River Source and nearby areas shows that there is little difference in the core area of Three River Source, and it is a trough-type distribution from east to west; the distribution characteristics of nearby areas are very different, with the highest in the east and the lowest in the west. the characteristics closely relate with geographic location, topography, and annual weather processes. These monitoring data analysis and comparative verification have played a fundamental role in the accurate quantitative assessment of cloud water resources in Three River Source and nearby areas. and also played a key role in protecting the ecological environment of the plateau ecology by enhancement precipitation.
  • Evaluation the Applicability of Albedo Products of GLASS, MODIS and GlobAlbedo under the Alpine Meadow over the Qinghai-Tibetan Plateau
  • AN Yingying;MENG Xianhong;ZHAO Lin;LI Zhaoguo;Lü Shihua;MA Yutang
  • 2019 Vol. 38 (1): 88-100.  DOI:10.7522/j.issn.1000-0534.2018.00097
  • Abstract ( ) HTML PDF (12992KB) ( )
  • Surface albedo is a key physical parameter affecting the energy budget and crucial for accurately and quantitatively estimating the energy and water cycle processes on the Tibetan Plateau. Based on the eight years' observations of surface albedo under the alpine meadow over Maqu and Maduo stations in the source region of the Yellow River, the remote sensing products of Global Land Surface Satellite (GLASS), Moderate Resolution Imaging Spectroradiometer (MODIS) and GlobAlbedo were evaluated and analyzed. The results show that the observed albedo of Maqu concentrated in 0.16~0.28 from 2009 to 2016. The GlobAlbedo albedo is greater than the mean observation by 0.048, while the GLASS and MODIS are below the observed value by 0.074 and 0.063, respectively. Relatively, MODIS is closest to the Maqu observation, with RMSE=0.069 and R=0.710.The observed surface albedo at Maduo has a large interannual variation due to the snow effects. GLASS is the highest stability product comparing with the Maduo observation, with RMSE=0.104 and R=0.598. The observed seasonal variation of surface albedo of Maqu is:winter > spring > autumn > summer, with the average of albedo is 0.25, 0.22, 0.19 and 0.18, respectively. The observed annual albedo of Maqu is 0.21; and that of Maduo is 0.25. Seasonal variation in albedo of Maduo is more significant than that of Maqu, which shows the typical "U" structure. The seasonal mean of observation in Maduo station is 0.18 (summer), 0.22 (spring and autumn) and 0.33 (winter). Generally, the consistency of the three surface albedo products with the observations is relatively high in spring and summer, but the increase in the albedo of the three products is earlier than observations in autumn and the albedo is significantly smaller than observations in the late winter or early spring. In addition, for the two sites, the maximum bias between GLASS and MODIS products occur in the autumn and winter, which further demonstrates systematic bias in the snow mapping algorithms of these surface albedo products, and MODIS performs better because of the ability to separate snow from clouds.
  • Reliability of Three Reanalysis Datasets in Simulation of Three Alpine Lakes on the Qinghai-Tibetan Plateau
  • DU Juan;WEN Lijuan;SU Dongsheng
  • 2019 Vol. 38 (1): 101-113.  DOI:10.7522/j.issn.1000-0534.2018.00110
  • Abstract ( ) HTML PDF (13882KB) ( )
  • Lake model is considered as a high-efficiency method to research lake-air interaction. However, few studies focus on reliability of reanalysis data driving model in the lake area on the Qinghai-Tibetan Plateau (QTP). This study explores the applicability of a one-dimensional lake model coupled into WRF at three lakes with different depths, i. e. Nam Co, Bangong Co and Ngoring on the QTP by using the China Meteorological Forcing Dataset (ITPCAS), ERA-Interim reanalysis data, NCEP/NCAR reanalysis data and MODIS LST data. Based on comparing three reanalysis datasets with observational data from weather stations near the lakes during the same period, we evaluate the reliability of reanalysis data in the lake area and further analyze the correction parameters of each reanalysis dataset. The outcomes of the study show that lake model has good ability to simulate the variations of the lake surface temperature on the QTP. Each meteorological element between the stations observation and ITPCAS data is closest among the three reanalysis datasets. The downward longwave radiation and the shortwave radiation of ERA-Interim and the wind speed of NCEP/NCAR are significantly larger, but the downward longwave of NCEP/NCAR is less than the observations. When reanalysis data used to be forcing data of the lake model, the simulation results before and after correction are not obviously different for ITPCAS data. But significantly improved simulation results after full parameters correction for ERA-Interim and NCEP/NCAR. Correcting the downward shortwave radiation only for ERA-Interim data and correcting the air temperature and the downward longwave radiation simultaneously for NECP/NCAR data in areas lacking observational data can improve the simulation of the lake surface temperature.
  • Analysis on the Characteristics of Arctic Sea Ice Movement in Recent 30 Years
  • LI Yujie;GAO Xiaoqing;ZHANG Lujun;GUO Weidong;YANG Liwei
  • 2019 Vol. 38 (1): 114-123.  DOI:10.7522/j.issn.1000-0534.2018.00115
  • Abstract ( ) HTML PDF (12521KB) ( )
  • The distribution and movement of sea ice contains a large amount of information on the coupling of sea and atmosphere. This paper uses the International Arctic Buoy Program (IABP) data and Myocean reanalysis data (ORAP 5.0 series), from 1979 to 2011. The results show that from the comparison between the measured data and the reanalysis data, there is a large deviation between the reanalysis data and the measured data in 1999. After 1999, the trend of the reanalysis data and the trend of the buoy data are similar, because the ORAP 5.0 was adopted in 1999. The new physical model makes the resulting reanalysis data more accurate. From the seasonal distribution of sea ice velocity, the sea ice flow rate is the largest in summer, followed by autumn. From the interannual variation of sea ice flow rate, before 1990, the sea ice flow rate changed year by year, and the sea ice flow rate changed more gradually. After 1990, the sea ice flow rate changed gradually. From the perspective of the sea ice flow rate and the direction of motion, the sea ice flow rate at the Fram Strait is more than 8 cm·s-1. Since the 1990s, the sea ice velocity has gradually changed to a relatively stable state. The reason may be that since the 1990s, the phenomenon of global warming "Hiatus", such as the temperature in the middle and high latitudes of Eurasia and the Atlantic Ocean in North America, has not only "temperature stagnation" but also Significant cooling. There are many MyOcean projects (130 kinds), and different types of reanalysis data are obtained by different ocean models, such as GLYYS2V3, CGLORS, UR025.4, ORAP5.0, MJM105B, etc. These data cover a wide range and the accuracy is very high (such as the sea ice concentration obtained by ORAP5.0 is basically the same as the measured data), so MyOcean data products effectively improve the ability of ocean monitoring and forecasting. This study contributes to the understanding of Arctic marine motion, climate change and marine ecology, and is of great importance to Arctic fisheries and energy development as well as shipping.
  • Statistical Analysis of Summer Heavy Rainfall Events over Jianghuai Region of China
  • LIU Tian;GAO Xiaoqing;TAN Guirong;FAN Yiyuan;HUI Xiaoying
  • 2019 Vol. 38 (1): 136-142.  DOI:10.7522/j.issn.1000-0534.2018.00063
  • Abstract ( ) HTML PDF (11727KB) ( )
  • Based on daily precipitation data from 1980 to 2015 for 632 meteorological observational stations in China, 7 heavy rainfall events in Jianghuai region were selected. The spatial distribution and circulation pattern of these 7 heavy rainfall events in Jianghuai region were calculated using the Empirical Orthogonal Function(EOF) expansion and synthesis. The leading mode of Empirical Orthogonal Function (EOF) (can explain 22.4% of the total variance) manifests when heavy rainfall event occurs in Jianghuai region, precipitations in northern part and in southern part of Jianghuai region show inverse relationship, the precipitation pattern shows "-+-" distribution from north to south over Eastern China. Precipitation anomalies of the second EOF mode (can explain 17.8% of the total variance) shows that when heavy rainfall event occurs in Jianghuai region, precipitation in southeastern part and in central and western parts of Jianghuai region show inverse relationship, the precipitation pattern form north to south over eastern China is "-+"dipole distributions. The 500 hPa mean geopotential height field shows that, circulation feature shows Two-trough and One-ridge from Balkhash Lake to Northeast China in mid-latitude region. Using the principal components of the first EOF mode of the heavy rainfall events in Jianghuai region and the 500 hPa geopotential height field to get correlation coefficients. The result shows that, the contour distribution in the western part of Northeast China and the contour distribution in the eastern part of Inner Mongolia show inverse correlation with the precipitation in Jianghuai region. 850 hPa's wind blows northward over Jianghuai region. In the correlation coefficients field, the v-direction wind field from the southern part of Northeast China to North China shows inverse correlation with the precipitation in Jianghuai region. The result shows that, when the trough in Balkhash Lake and the trough in Northeast China get stronger, north wind over North China assembles with south wind over Jianghuai region. Meanwhile, confluence of cold air and warm air leading to more precipitation over Jianghuai region. Precipitation pattern is of the first EOF mode.
  • Multi-Satellite Observations on the Structure Characteristics of Typhoon Meranti in 2016
  • ZHAO Zhen
  • 2019 Vol. 38 (1): 156-164.  DOI:10.7522/j.issn.1000-0534.2018.00065
  • Abstract ( ) HTML PDF (13546KB) ( )
  • In September 2016, Typhoon Meranti, the strongest recoded tropical cyclone to date 2016 made landfall over the city of Xiamen, China which caused great disaster. A comprehensive examination of Typhoon Meranti (2016) development and evolution processes, precipitation derived from the Integrated Multi-satellitE Retrievals for GPM (IMERG) algorithm and three dimensional structure and characteristics of cloud systems in the typhoon eye and the outer spiral rain bands on the ocean is studied by combination of Himawari-8, CloudSat and Global Precipitation Measurement (GPM) satellite high resolution data. The results reveal that there is a small and clear circular typhoon eye during the super typhoon stage. The distribution of total 24 hour typhoon precipitation exists heterogeneous and asymmetric structure and the maximum precipitation is located near the center of Typhoon Meranti. Measurements form the CloudSat level 2 cloud scenario classification product reveal that the eye wall and spiral cloud bands of Typhoon Meranti appear in the presence of deep convective cloud system and near the cloud top is cirrus and altostratus cloud. Above the 4 km height, there is discontinuous bright band and vigorous cloud system developed upper the bright band from the CloudSat level 2 Geometrical Profile (GEOPRO) product. The CloudSat and GPM satellite onboard radar see very tall convective hot towers at eye wall of Typhoon Meranti. Estimates precipitation from GPM DPR level-2A product indicates a maximum 295 mm·h-1 precipitation rate which is located in the northeastern side of Meranti's eye wall. The vertical profile of radar echo intensity and latent heat from the spectral latent heating algorithm shows asymmetric distribution between eye walls from the GPM satellite. The maximum of 57 dBZ radar echo intensity, 17 km radar echo top and 88 K·h-1 latent heat rate in convective hot towers at eye wall on the right side of the eye is observed by the GPM satellite where warm cloud microphysical processes is dominated in this area.
  • Estimation of Evapotranspiration of Riparian Forests in the Desert Region from Diurnal Fluctuation of Groundwater Levels
  • ZHANG Jingtian;XI Haiyang;WANG Chunlin;LI Peidu
  • 2019 Vol. 38 (1): 179-186.  DOI:10.7522/j.issn.1000-0534.2018.00071
  • Abstract ( ) HTML PDF (4649KB) ( )
  • Evapotranspiration of phreatophytes in the riparian is one of key important component of hydrologic cycle in desert oasis ecosystem. It is also the most dominant driver of groundwater consumption and diurnal fluctuation of groundwater levels. Understandings of the magnitude and variability of the evapotranspiration of phreatophytes in riparian forests are of key important for management of riparian forests. In this paper, the diurnal groundwater level fluctuations method is used to estimate the groundwater evapotranspiration in riparian forests of Ejina oasis. The results show that estimated groundwater evapotranspiration of the populous euphrarica in Qidaoqiao conservation area is consistent with the observed evapotranspiration using Eddy covariance method and with that estimated from the FAO-PM model. The correlation coefficients between estimated evapotranspiration from diurnal groundwater level fluctuations and observed evapotranspiration is strong and significant (p < 0.01). It indicates that estimated groundwater evapotranspiration of the desert riparian forests using the diurnal groundwater level fluctuations is reliable. This method was applied to estimate the evapotranspiration estimations of three different vegetation covers in the study area. When the nocturnal transpiration of populous euphrarica was considered, the ratio of estimated groundwater evapotranspiration to the observed evapotranspiration of populous euphrarica in the Qidaoqiao conservation area increased from 70% to 90% in the growing season of 2015, which indicates that nocturnal transprition is very important for accurate estimation of total evapotranspiration of the phreatophytes in the desert oasis ecosystem.
  • Climatic Factors of Desertification Process in Alpine Meadow
  • ZHANG Yu;ZHANG Kecun;MENG Xianhong;AN Zhishan
  • 2019 Vol. 38 (1): 187-195.  DOI:10.7522/j.issn.1000-0534.2018.00111
  • Abstract ( ) HTML PDF (5453KB) ( )
  • Based on indexes of NDVI and meteorological data in alpine meadow, the main climatic driving factors and mechanism of desertification in alpine meadow were studied. Results indicated as follows:(1) the value of NDVI presents a trend of increasing and then decreasing during 2000-2016, northern and middle of study area is first to decrease and gradually expended to northwest of Sichuan. (2) The air temperature is sustained warming since 1990s, and the upward trend is obvious after 2000.The general tendency of precipitation is decrease and chiefly concentrated in summer with no significant change, sunshine duration showed a downward trend. Annual average wind velocity showed an upward trend since 2000.(3) Air temperature and precipitation are the crucially influencing factors of NDVI, along with time-lapse, the explanatory power of sunshine duration and wind velocity are gradually increased. The interactive q values between two factors are higher than any q value of separated factors, and most of the interactive results belongs to bivariate enhancement or nonlinear enhancement, the interactive effect between each factor has great influence on the desertification process. (4) The gale and sandstorm occurred frequently in Zoige and Maqu, resultant sand transporting direction (RDD) was SSE with low wind energy environment and medium wind direction variability in Maqu during 2014-2016, the proportion of DP at high wind velocity level has increased, and the intensity of sand activity is enhanced from northwest to southeast. Consequently, rising temperature and decreasing precipitation are the dominant factors for meadow desertification, the growth of vegetation is affected by sunshine duration, and the desertification rate and spreading direction are determined by sand activity.
  • Analysis of Temporal and Spatial Evolution Characteristics of Drought Disasters in the Hexi Corridor in Recent 57 Years
  • Wang Chunlin;Si Jianhua;Zhao Chunyan;Li Peidu;Zhang Jingtian
  • 2019 Vol. 38 (1): 196-205.  DOI:10.7522/j.issn.1000-0534.2018.00081
  • Abstract ( ) HTML PDF (1049KB) ( )
  • Drought is one of the most universal meteorological disasters in China. The occurrence of drought will adversely affect agriculture and ecological environment. In the context of global warming, the drought has become a major challenge facing the world. The Hexi Corridor is an important ecological barrier in the northwest of China. Due to its unique geographical and climatic conditions, the Hexi Corridor is a region that drought happens frequently. The frequent occurrence of drought has become an important factor restricting local agricultural and the utilization of water resources. The SPI index can quantify the precipitation deficit for multiple timescales, which can reflect the impacts of drought on different water resources needed by various decision-makers. It has been widely used in practice. Therefore, based on the monthly precipitation data of 15 meteorological stations in Hexi Corridor and its surrounding areas from 1960 to 2016, this paper uses the standardized precipitation index to characterize the annual and seasonal drought grades, analyzing the evolution of drought frequency, the station proportion of drought and drought intensity in Hexi Corridor. Its aim is to reveal the regularity of drought and provide reference for the prevention of drought disaster in Hexi corridor. The results show that:(1) In the past 57 years, the station proportion of drought in annual, spring, summer and winter showed a decreasing trend in Hexi Corridor, the station proportion of drought in autumn showed an insignificant increase. Among them, the biggest drops of the station proportion of drought was in summer. The frequency of large-scale drought in spring and autumn was higher than 29.8%. (2) The drought intensity of the Hexi Corridor showed a decreasing trend at the annual and seasonal scales, among which the drought intensity in summer had the largest decrease. The drought intensity in the study area was dominated by mild drought and moderate drought. (3) The spatial distribution of drought has obvious regional characteristics, among which the drought of Jiuquan and Yumen were frequently. From the linear trend of the SPI index, 66.7% of the stations in the Hexi Corridor showed a decreasing trend on the annual and seasonal scales. The weakening of the drought is conducive to local agricultural and ecological environment. However, the precipitation and temperature in the Qilian Mountains and Hexi Corridor have both increased in the past few decades, this will lead to a greater possibility of local heavy rains and mountain flood disaster in the Hexi Corridor. Therefore, it is necessary to strengthen the defense of rainstorm and flood disasters at the same time of drought resistance.
  • Near-Surface Hourly Atmospheric Driving Data at 0.05°×0.05° based on WRF Model Simulation over 2000-2016 Years for the Heihe River Basin
  • PAN Xiaoduo;MA Hanqing
  • 2019 Vol. 38 (1): 206-216.  DOI:10.7522/j.issn.1000-0534.2018.00062
  • Abstract ( ) HTML PDF (19806KB) ( )
  • The near-surface atmospheric elements including air temperature, pressure, relative humility, wind, precipitation and radiation are called forcing data to drive hydrological, land surface, and ecological models. However, the spatial resolution of general circulation models (GCMs) is too coarse to represent regional climate variations at the regional, basin, and local scale. Weather research and forecasting model (WRF) is a next generation, fully compressible, Euler non-hydrostatic mesoscale forecast model with a run-time hydrostatic option. This model is useful for downscaling weather and climate at the scales from one kilometer to thousands of kilometers, and is useful for deriving meteorological parameters required for hydrological simulation too. The Heihe River Basin (HRB) is the second largest inland river in China. It is located in the middle part of the Hexi Corridor in the arid regions of northwest China and covers an area of approximately 140, 000 km2. The HRB extends from the Qilian Mountain glaciers, passing through alpine meadows and forest areas (precipitation recharge area), through an arid region, In this paper, the near-surface atmospheric forcing data over the Heihe River Basin is introduced, which was produced by using WRF model from 2000 to 2016 at hourly, at 0.05 deg. resolution, including the following variables:2m temperature, surface pressure, 2m specific humidity, downward shortwave radiation, downward longwave radiation, 10m wind field and precipitation. The forcing data was validated against daily data collected at 15 automatic weather stations of Chinese Meteorological Administration (CMA), and hourly data at a few sites of Heihe River eco-hydrological process comprehensive remote sensing observation (WATER and HiWATER). The following conclusions were drawn:2m surface temperature, surface pressure and 2m specific humidity are more reliable, especially the average errors of 2m surface temperature and surface pressure are very small and the correlation coefficients with observations are above 0.96; correlation between downward shortwave radiation and WATER site observation data is more than 0.9 either, and the correlation of downward longwave radiation is 0.6; the error of 10 m wind speed from observational data is large, the correlation is relatively weak. The correlation coefficient between simulated and observed rainfall data at monthly and yearly time scales were up to 0.94 and 0.84, and the correlation coefficient reached 0.53 at daily scale; the correlation between simulated and observed snowfall data at monthly scale reached 0.78, the spatial distribution of snowfall agrees well with the snow fractional coverage rate of MODIS remote sensing product. So WRF model can be used for downscaling analysis in complex and arid terrain of Heihe River Basin, and the simulated data can meet the requirements of watershed scale hydrological modeling and water resources balance.