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28 June 2019, Volume 38 Issue 3   
  • Interannual Anomaly of Cloud Water Content and Its Connection with Water Vapor Transport over the Qinghai-Tibetan Plateau in Summer
  • LIU Juju;YOU Qinglong;WANG Nan
  • 2019 Vol. 38 (3): 449-459.  DOI:10.7522/j.issn.1000-0534.2018.00138
  • Abstract ( ) HTML PDF (18416KB) ( )
  • Based on the ERA-Interim reanalysis data from 1979 to 2016 provided by the European Center for Medium-range Weather Forecast (ECMWF), the cloud water content and its water vapor transport over the Qinghai-Tibetan Plateau (QTP) in summer is analyzed. The results show that the summer cloud water content over the QTP accounts for 48% of the total year, which decreases from southeast to northwest. There are four water vapor channels affecting the cloud water content, which are the Indian Ocean channel, the South China Sea channel, the northern Bay of Bengal and the western Iranian channel (briefly called channel 1, 2, 3, 4 in order), respectively. There are obvious interannual variations of cloud water content and water vapor channel intensities. The interannual variation of cloud water content is in consistent with that of channel 2 and 4. It is shown that both the cloud water content and four channel intensities have increased trends. When the intensity of channel 1 is strong, abnormal water vapor from the northern part of the Indian Ocean and the South China Sea will convergent over the Bay of Bengal and be transported to the QTP, which mainly increases the cloud water content in the northwestern part of the QTP. When the intensity of channel 2 is strong, the anomalous southward flux over the South China Sea and the Indo-China Peninsula and the anomalous southwest flux over the northern Bay of Bengal support more water vapor to the southeastern QTP. The stronger channel 3 intensity indicates more water vapor from westerly and Indian Ocean are transported to the QTP, resulting more cloud water content in the northeastern QTP. When the intensity of channel 4 is strong, the water vapor from the South China Sea to the southern part of the Bay of Bengal is abnormally transported to the QTP, resulting more cloud water content in the central and southeastern TP. In addition, the stronger and southwestward of northwest Pacific subtropical high is consistent with stronger identities of channel 2 and 4, which is conducive to the transportation of water vapor to the QTP.
  • Study on Temporal Spatial Distribution Characteristics of Latent Heat over the Qinghai-Tibetan Plateau
  • CHEN Yue;LI Yueqing;FAN Guangzhou;CHEN Yuhang
  • 2019 Vol. 38 (3): 460-473.  DOI:10.7522/j.issn.1000-0534.2018.00130
  • Abstract ( ) HTML PDF (29009KB) ( )
  • Using monthly mean specific humidity reanalysis data provided by ECMWF (European Centre for Medium-Range Weather Forecasts). We study the spatio-temporal distribution, interannual and interdecadal variation of latent heat from 1979-2015 over Qinghai-Tibetan Plateau (QTP) by using the methods such as annual average analysis of q, climate tendency rate analysis of q at each layer, EOF analysis and so on. The results show that latent heat over QTP decreases from lower layer to upper layer, the amount of latent heat is the most in summer, the second is autumn, distribution characteristics of spring and autumn are similar, and the amount of latent heat is the least in winter. The max values are all located in the southeast and the south side of QTP; Specific humidity increases sharply in summer and the region where specific humidity grow fastest is located in the northeast of QTP. Specific humidity grows slowest in winter and the fastest growing area is also located in the northeast. Generally speaking, there is a positive growth rate of specific humidity over QTP, but the growth rate of specific humidity is negative in the west of QTP and the Yunnan-Guizhou Plateau at lower layers, and that decreases fastest in summer; As for the EOF analysis, the first EOF mode of the four integral layers[from the surface to 500 hPa (the first integral layer), from 500 hPa to 400 hPa (the second integral layer), from 400 hPa to 300 hPa (the third integral layer), from the surface to 300 hPa (the whole integral layer)] generally shows a positive distribution. And the second EOF mode shows a "positive negative" dipole distribution. The third EOF mode of the four integral layers is a "positive-negative-positive" distribution, and the inter-annual variation of all EOF modes are not obvious except the second EOF mode.
  • Analysis on Freezing-thawing Characteristics of Soil in High and Low Snowfall Years in Source Region of the Yellow River
  • YAO Chuang;Lü Shihua;WANG Ting;WANG Junfeng;MA Cuili
  • 2019 Vol. 38 (3): 474-483.  DOI:10.7522/j.issn.1000-0534.2018.00142
  • Abstract ( ) HTML PDF (2559KB) ( )
  • Based on the field observation data in the source region of the Yellow River from October 2011 to December 2017, the characteristics of soil freezing-thawing duration, soil temperature and moisture, surface energy components in high snowfall year and low snowfall year were analyzed in this paper. The results show that the snowy year has higher albedo, lower net radiation, and lower surface heat transfer than the less snowfall year. The time of the snowy year from the heat "source" to the heat "sink" is later than the less snowfall year. Snow accumulation can reduce the radiant energy absorbed by the soil, reduce the sensible heat transfer on the surface, increase the surface latent heat transport during the frozen period and the thawing period of the soil, reduce the heat transfer from the soil to the atmosphere during the frozen period, and reduce the heat transfer from the atmosphere to the soil during the thawing period. The snow cover has a cooling effect in the freezing period, which makes the soil freeze earlier in the snowy years and the soil temperature is lower in the same period. It has the function of heat preservation in the frozen period, which makes the soil temperature higher in the snowy years. In the thawing period, it has the effect of heat preservation ("cooling"), which makes the ablation later and the soil temperature is low in the same period. During the whole freezing-thawing period, the shallow soil moisture in the snowy year is higher than that in the less snowy year, indicating that the snow has a moisturizing effect on the shallow soil. Snow accumulation makes the soil to start freeze earlier and the start of ablation later, which can extend the number of days that the soil is completely frozen.
  • The Characteristics of the Water Vapor Transport and Associated Sources under Abnormal Precipitation Conditions in the Source Region of the Yellow River Using FLEXPART
  • ZHU Li;LIU Rong;WANG Xin;WANG Zuoliang;WEN Jun;ZHAO Yang;XIE Yan;ZHANG Tangtang
  • 2019 Vol. 38 (3): 484-496.  DOI:10.7522/j.issn.1000-0534.2019.00015
  • Abstract ( ) HTML PDF (19748KB) ( )
  • Based on the precipitation observation data of meteorological stations in the source region of the Yellow River (SRYR) in the past ten years, July is selected as the largest month of precipitation, the maximum positive and negative abnormal year's corresponding to July are 2012 and 2015 respectively. The Lagrange Flexible Particle Dispersion Model (FLEXPART) is driven by NECP reanalysis data to simulate the backward trajectories of target particles in these two months. The characteristics and differences of water vapor transport under abnormal conditions are emphatically analyzed, and the contribution rate of each moisture source to the regional rainfall is calculated quantitatively. The results show that, in July 2012, the moisture transportation to the SRYR is mainly conducted by South Branch which contains two routes entering the SRYR from the southern side of the Qinghai-Tibetan Plateau (QTP):one is the trans-equatorial transport path, that is to say, the Somali jet carries moisture from the Arabian Sea and finally enters the SRYR by way of the Indian Peninsula and Bay of Bengal; the other is that particles carry moisture from the South China Sea and finally enters the SRYR by way of the Sichuan Basin. On the contrary, the North Branch which means moisture enters the SRYR from the Western or northern side of the QTP plays a dominant role in July 2015, including two typical paths as well:one is that the Easterly jet carries the moisture from the South China Sea and finally enters the SRYR by the Bay of Bengal and Indian Peninsula; the other is that the Westerly Jet carries moisture from the northern Africa or eastern European Plain and finally enters the SRYR, via Central Asia. The characteristics of specific humidity variation during the movement of particles show that the southern foot of the Himalayas, the Sichuan Basin, the Bay of Bengal and the northern Tibetan Plateau are potential moisture sources for precipitation in the SRYR. Moreover, the estimation of moisture sources contributions to the precipitation in SRYR shows that:the arid and semi-arid grassland areas on the northern side of the TP are main sources of precipitation for the SRYR in July of dry year. The contribution rate is 52.9%, which is much higher than the other four potential moisture sources. While the contributions of the three main sources in the wet year are far less significant than those in the dry year. No matter what type of precipitation, the southwestern QTP and the northern side of the QTP provide the main external water vapor for the main precipitation in the SRYR.
  • The Bulk Transfer Coefficient and Characteristics of Surface Heat Source on Alpine Grassland at Naqu
  • ZHENG Huixuan;HU Zeyong;SUN Genhou;XIE Zhipeng;YAN Xiaoqiang;WANG Yidan;FU Chunwei
  • 2019 Vol. 38 (3): 497-506.  DOI:10.7522/j.issn.1000-0534.2019.00024
  • Abstract ( ) HTML PDF (1014KB) ( )
  • Based on the data from the Naqu Station of Plateau Climate and Environment in the Northern Qinghai-Tibetan Plateau, this paper investigates the relative humidity close to the underlying surface and the bulk transfer coefficient over the underlying surface of typical alpine grassland in the Naqu area of the Qinghai-Tibetan Plateau. On this basis, using the conventional observation data from the Naqu Weather Station of the China Meteorological Administration from 1980 to 2016 to calculate and analyze the characteristics of surface fluxes over alpine grassland in Qinghai-Tibetan Plateau. The results suggest that:(1) The monthly average of the relative humidity close to the underlying surface at Naqu Station is between 33% and 62%, the highest is in September, and the lowest is in February, the monthly mean bulk transfer coefficient for heat CH at Naqu Station vary from 1.6×10-3 to 2.7×10-3, and the monthly mean bulk transfer coefficient for vapor Cλ at Naqu Station vary from 1.0×10-3 to 2.0×10-3. (2) The surface fluxes at Naqu area from 1980 to 2016 are calculated, the annually averaged sensible heat fluxes H showed a weakening trend, while the latent heat fluxes showed an increasing trend, which led to the inconspicuous trend of surface heat source. In stages, the mutation of sensible heat fluxes occurred in 2004, the trend before and after the turning point was firstly weakened and then increased, the latent heat fluxes decreased significantly from 1994 to 2005, which led to a significant reduction in surface heat source from 1995 to 2005. (3) The seasonal variation of latent heat fluxes at Naqu Station is more obvious than the change in sensible heat fluxes, the seasonal variation of the surface heat source is more dependent on the seasonal variation of latent heat fluxes.
  • Observations of Soil Thermal Properties in a Typical Mesa over Chinese Loess Plateau
  • MA Xin;ZHANG Tangtang;CHEN Jinlei
  • 2019 Vol. 38 (3): 507-517.  DOI:10.7522/j.issn.1000-0534.2018.00158
  • Abstract ( ) HTML PDF (2189KB) ( )
  • The temporal variation of soil thermal properties and the response to precipitation in a typical cropland are analyzed during a period from July 2014 to January 2015 over Loess Plateau. The flat and relatively wide loess area is the simplest underlying surface of the Loess Plateau. It is important to understand the land-atmosphere interactions over the loess area and then further promote the study to other underlying surfaces over the Loess Plateau. The underlying surface of the Pingliang Land Surface Process and Severe Weather Research Station, Chinese Academy of Sciences is typical loess area which offered meteorological and land surface observation data to many researches. This study cannot represent the whole loess plateau but can provide reference to understand the water and heat exchange process on land surface. The results are as follows:(1) In addition to 10 cm, the soil thermal diffusivity decreasing in summer, almost keeping stabilization in autumn and increasing in winter, while soil temperature shows a downward trend in this duration. Linear growth is not found between the soil thermal diffusivity and soil depth, although the soil thermal diffusivity at 100 cm depth is always higher than that one at 40 cm depth in the total study period. (2) The soil thermal properties at 5 cm and 10 cm layers are varied significantly and the daily variation amplitude of soil thermal properties at 40 cm and 100 cm gradually decrease. Influenced by the fluctuation of soil water content, soil thermal properties at 10 cm fluctuated the most among four layers. (3) The soil thermal properties at 5 cm change significantly with precipitation. The soil volumetric heat capacity and thermal conductivity change inconsistently when soil water content is high will lead to a decrease of soil thermal diffusivity, and the soil volumetric heat capacity and thermal conductivity increase with the increase of soil water content. There is a positive relationship between the soil volumetric heat capacity and thermal conductivity. Precipitation mainly affects the soil thermal properties through changes in soil water content.
  • Discussion on the Characteristics of Plateau Monsoon and Its Relationship with East Asian Summer Monsoon
  • WANG Yidan;HU Zeyong;SUN Genhou;XIE Zhipeng;YAN Xiaoqiang;ZHENG Huixuan;FU Chunwei
  • 2019 Vol. 38 (3): 518-527.  DOI:10.7522/j.issn.1000-0534.2019.00025
  • Abstract ( ) HTML PDF (18504KB) ( )
  • This paper uses ERA-Interim's geopotential height field, temperature field and wind field reanalysis data to calculate the Dynamic Plateau Monsoon Index (DPMI) from 1988 to 2017, and analyzed the spatial distribution of the plateau monsoon. The relationship between characteristics and time evolution, combined with the East Asian Summer Monsoon Index (EASMI), explores the relationship between the plateau monsoon and the East Asian monsoon. The results show that:(1) The plateau summer monsoon began to form in April, and the warm low value system was formed on the plateau. In June, the warm low-pressure system center formed and reached the strongest. At this time, the plateau summer wind intensity also reached the maximum; the warm closed low pressure in October The system moves to the northeast and the intensity decreases and exits. The plateau summer monsoon ends. (2) DPMI and EASMI have obvious interannual variation characteristics, and the intensity of the plateau summer monsoon and the East Asian summer monsoon is consistent in the key years. (3) The geopotential height field of the mid-latitude area affected by the East Asian monsoon and the geopotential height field of the Qinghai-Tibet Plateau are in the same positive correlation area, and the correlation coefficient between DPMI and EASMI in the first two months is the largest, indicating that the plateau summer monsoon pair The East Asian summer monsoon has certain indications. (4) The East Asian summer monsoon circulation is affected by the change of the plateau temperature field. The low-pressure system of the plateau summer monsoon is closely related to the plateau temperature field.
  • Comparison of Circulation Characteristics between Two Typical Dry Years in Flood Period over Eastern Yunnan-Guizhou
  • CHI Zaixiang;HU Yuewen;XIA Yang;HU Zuheng;DU Zhengjing;YAN Rui
  • 2019 Vol. 38 (3): 528-538.  DOI:10.7522/j.issn.1000-0534.2018.00161
  • Abstract ( ) HTML PDF (17224KB) ( )
  • Based on the daily precipitation and temperature data in 2011 and 2013 of 84 meteorological stations in the eastern Yunnan-Guizhou, reanalysis data of NCEP/NCAR and the formula of accumulated temperature drying degree. The basic characteristics and the abnormal circulation of drought disaster in the eastern Yunnan-Guizhou of flood season (April to Sepetember) in 2011 (La Nina) and 2013 (neutral) were analyzed. The results show that the flood season rainfall in 2011 is less than the 2013 with the characteristics of inhomogeneous space-time distribution. The rainfall of April to May, July to Sepetember make an important contribution to the drought in 2011 and July to August in 2013 by comparison, as well as, the index of accumulated temperature drying degree reflects the degree of drought of 2011 and 2013 well. The South Asia High was abnormal stronger, larger area, east ridge point are East is the Common ground of 2011 and 2013, but the intensity and area of Western Pacific Subtropical High in 2011 is stronger than the 2013 which is the important reason that drought in 2011 more severe than 2013. The low layer moisture transport of the bay of Bengal, South China Sea and the Western Pacific were weak than usual is the main reason of scarce precipitation in 2011 and 2013 in the eastern Yunnan-Guizhou precipitation less the main reason, and there is a good corresponding relationship between the precipitation and the water divergence center in the eastern Yunnan-Guizhou. The water vapor transport on 700 hPa play a decisive role in the flood season drought of 2011 and 2013, and the divergence is stronger in 2011 than 2013 which case the severer drought in 2011. The apparent moisture content revealed that the drought in 2011 is more serious than that in 2013. In addition, the 500 hPa circulation field and 700 hPa water vapor transport field have some reference value for the long time forecast of drought and flood in the eastern Yunnan-Guizhou.
  • Analysis of Atmospheric Temperature and Humidity Profiles within Precipitation Cloud in Lhasa Measured by TRMM PR and IGRA
  • WANG Mengxiao;WANG Rrui;FU Yunfei
  • 2019 Vol. 38 (3): 539-551.  DOI:10.7522/j.issn.1000-0534.2019.00011
  • Abstract ( ) HTML PDF (11974KB) ( )
  • The atmospheric temperature and humidity profiles of precipitation cloud reflects the structure characteristics of precipitation cloud. In order to reveal the profiles inside the precipitation clouds of Lhasa in Qinghai-Tibet Plateau, the multi-year merging data of the precipitation profiles derived from the Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) and the temperature and humidity profiles issued by the Integrated Global Radiosonde Archive (IGRA) are analyzed. The results show that the precipitation echo reflectivity factor is distributed between 17 and 45 dBz, most of which is less than 26 dBz. The echo height of the storm top reaches 17 km, presenting a 'thin and tall' appearance, corresponding to wetness but unsaturation in the lower atmosphere. However, the difference between the temperature and dew-point temperature within such precipitating clouds is smaller than its climatic value. The echo shape of deep precipitation system also presents "thin and tall" appearance. According to the nonlinear variation of rain rate with height within deep precipitating system, its vertical structure can be divided into three layers. While the vertical structure of shallow precipitating system presents one layer, that is, the slope of rain rate varies logarithmically linearly with height, and the maximum average rain rate (0.7 mm·h-1) appears on the ground. The lapse of dew-point temperature is different in deep precipitation system and shallow precipitation system above and below the height of 400 hPa (7.5 km). The altitude of the melting layer in the precipitation system is about 6.3 km, but no brightness band is detected by PR. The statistical results also show that the atmospheric precipitable precipitation is 20.89 mm·d-1 in Lhasa sounding station and its vicinity, the conversion rate of precipitation system is about 27.0%. Probably, the conversion rate of deep precipitation system is 2.9 times higher than that of shallow precipitation system. Besides, The CAPE of the deep precipitation system and the shallow precipitation system are 1941.7 J·kg-1 and 1451.8 J·kg-1, respectively.
  • Precipitation Characteristics of Southwest Vortex in Sichuan Basin from May to October in 2004—2017
  • HAN Linjun;BAI Aijuan
  • 2019 Vol. 38 (3): 552-562.  DOI:10.7522/j.issn.1000-0534.2018.00100
  • Abstract ( ) HTML PDF (20604KB) ( )
  • Based on the CFS reanalysis data with spatial resolution of 0.5×0.5 degrees, we conduct a census of the Southwest Vortex from May to October in 2004—2017 after making a quality test to CFS and TMPA V7 data. According to the precipitation distribution shown by TMPA V7 data, we classified Southwest Vortex. The frequency of the precipitation in different directions is counted, and the precipitation characteristics of the four most types are analyzed, including the range of rainstorm and the intensity of precipitation. The circulation differences as well as precipitation formation mechanism of the four representative cases are analyzed. The results show that, there is a consistently growth in the amount of Southwest Vortex through these summer half years. Moreover, the southwest vortex precipitation frequently occurred in the northeast, east, southeast and central parts of the southwest vortex successively in the summer half year. Analysis of four kinds of frequent frequency southwest vortex precipitation characteristics. It is found that precipitation in central section has the largest average range of rainstorm and the strongest precipitation intensity, followed by precipitation in southeast part of southwest vortex, east part and northeast part successively. Through the analysis of circulation situation on representative case, we found that, both in the type of central part and northeast part precipitation, cold and warm currents meet in the northern part of the basin. The difference is that central part precipitation occurs when there is a wider range of cold air intrusion at the low level and the southwest airflow is stronger compared with the type of northeast part precipitation. These two branches form a circular flow field in the basin which is different from confrontation state happened in the type of northeast part precipitation. The type of east and southeast part precipitation happens when there is no cold air invasion. The last one happens when the southwest current turn westward in front of Daba Mountains. However, the former one happens when the current flows eastward compared with type of southeast part precipitation and finally flows across Daba Mountains. The formation mechanism of four kinds of Southwest Vortex is analyzed. It is found that there is a significant vertical circulation in Southwest Vortex. The circulation circle is usually composed of an ascending airflow near the southwest vortex and a downdraft of the north side. The precipitation area is usually corresponding to the position of the circulation circle.
  • Application of Assimilation of Doppler Radar Data on Heavy Rain Simulating Test in Fujian
  • JIANG Zongxiao;SHEN Yongsheng;JIANG Yongcheng;ZENG Xiaomei;LIAO Yanzhen;WANG Tie
  • 2019 Vol. 38 (3): 563-572.  DOI:10.7522/j.issn.1000-0534.2018.00155
  • Abstract ( ) HTML PDF (14299KB) ( )
  • The mesoscale model WRFV3.5 was used to compare the result of different cumulus convectional and microphysical parameterization schemes on rainstorm simulating over Fujian area, and do simulated test on heavy rain by assimilating Doppler radar data in Fujian. The result indicated that the microphysical parameterization of WSM5 along with BMJ cumulus convectional parameterization had relatively well matched with observed strong precipitation, the TS score of this group were 0.29 both in downfall and rainstorm simulating. The Doppler radar data directly assimilated into the mesoscale model, which focused on the rainstorm period of typhoon, applied by the Three Dimensional Variation Assimilation System (3DVAR). The simulated effect was better with Doppler than assimilation of surface observed data. Furthermore, the radar reflectively data assimilation, which made the rainstorm area adjust to the south, was favored to precipitation area simulations (the TS score increased by 0.12), while only assimilated radial velocity of Doppler data could be advantaged to rainfall strength simulations (the TS score increased by 0.13). The result of assimilation with both reflectively and radial velocity data showed minimum deviation compared to observation (the TS score increased by 0.16). In addition, the result also showed interval time of assimilation had obvious influenced on simulated effects, and three or six hour of assimilated interval time was the best experiment in case simulations.
  • Climatic Characteristics of Regional Persistent Heavy Rain and Heavy Rainfall Pattern over Hunan
  • DAI Zejun;CAI Ronghui;PENG Lili;BAI Feng;ZHANG Chao
  • 2019 Vol. 38 (3): 573-582.  DOI:10.7522/j.issn.1000-0534.2018.00094
  • Abstract ( ) HTML PDF (12886KB) ( )
  • The frequency of extreme heavy precipitation events over Hunan is increasing under the background of global warming. Based on the daily precipitation data collected from 88 stations over Hunan and NCEP reanalysis data during 1961-2016, the climate characteristics of regional persistent heavy rain and heavy rainfall pattern over Hunan were analyzed by using the abrupt change analysis, clustering analysis, composite analysis and so on. The results shows that the regional persistent heavy rain during the past 56-year over Hunan has occurred annual average 2 times, and the maximum number of consecutive days is 5. The percent of regional persistent heavy rain is 73% and 0% in summer and winter, and is 16%, 38%, 20% and 14% in May, June, July and August respectively. Annual regional persistent heavy rain process times changed from 1.4 in 1961-1992 to 2.8 in 1993-2016, and 1993 is the mutational year. The regional persistent heavy rain mainly occurred more than 0.9 times a year over the north of central Hunan, and the frequency of regional persistent heavy rain over north of central Hunan was significantly more than that over southern Hunan. The regional persistent heavy rain intensity averaged over Hunan is 82.5 mm·d-1, which is 7.7 mm·d-1 bigger than that of non-sustained regional heavy rain, and the stations of regional heavy rain intensity greater than 85 mm·d-1 are mainly distributed over northwest and southeast Hunan. The heavy rainfall can be divided into four spatial distribution pattern:northwestern, north-central, south-central and southeastern type, and the percent of the four heavy rainfall pattern days to the total heavy rainfall days is 25.6%, 30.1%, 21% and 18.4%, respectively. The precipitation intensity of the northwestern type and southeastern type was higher than that of the north-central type and south-central type, and the heavy rainfall area of the former two types was more concentrated. The location and direction of synthesis wind field shear and large value area of water vapor convergence on 925 hPa are basically consistent with the strong precipitation area of four heavy rainfall pattern over Hunan, which has a good indication for prediction about the heavy rainfall area over Hunan.
  • Response of Extreme Hydrological Events to Extreme Climate in the Shule River Basin
  • CHENG Yufei;CHENG Wenju;HU Xiangquan;ZHAO Jinyan
  • 2019 Vol. 38 (3): 583-592.  DOI:10.7522/j.issn.1000-0534.2019.00027
  • Abstract ( ) HTML PDF (3790KB) ( )
  • In order to clarify the response of extreme hydrological events to extreme weather events in the Shule River Basin, the daily value data of temperature, precipitation and evaporation in the Shule River Basin and its surrounding meteorological stations, such as Tuole, Dunhuang, Guazhou, Yumen, Jiuquan and Mazongshan, are selected, the daily runoff data of the Changmabao Hydrological Station is also selected. Through the methods of trend analysis, moving average and principal component analysis, this study analyzed the extreme climate indices, the interannual variation law of extreme hydrological events and the factors affecting extreme hydrological events in Shule River Basin, and clarified the annual distribution characteristics of extreme floods in the basin. The results show that the interannual temperature rises in the Shule River Basin is obvious, the precipitation fluctuations change, there is no obvious increasing trend, and the evaporation shows a downward trend. The extreme temperature indices indicating high temperature showed a significant upward trend, and the extreme temperature indices indicating low temperature showed a significant downward trend, indicating that the temperature in Shule River Basin increased significantly. The extreme precipitation indices showed an significant increase. The extreme flood events and frequency in this basin showed an upward trend, while the extreme dry events and frequency showed a downward trend. Extreme flood events are mainly controlled by extreme precipitation events, especially the total amount of extreme precipitation. Extreme high temperature events also affect the increase of the total amount of extreme flood, while extreme dry events are mainly controlled by extreme low temperature events. In addition, the occurrence time of the largest peak flow in 2000-2016 has advanced from August to July.
  • Numerical Simulation of the Impact of Ice Nucleus Spectra on Microphysical Process and Electrification in Thunderstorms
  • WANG Mengyi;TAN Yongbo;SHI Zheng;LIU Jun;YU Mengying;ZHENG Tianxue
  • 2019 Vol. 38 (3): 593-603.  DOI:10.7522/j.issn.1000-0534.2019.00013
  • Abstract ( ) HTML PDF (9934KB) ( )
  • In this paper, we discuss the effect of three different ice nucleus spectral environments on the microphysical, electrification, and charge structure of thunderstorm clouds, using the existing two-dimensional(2-D) cumulus model. Simulation results show that:(1) Different ice nucleus spectral environments have a great influence on the content and distribution of ice-phase particlesin thunderstorm clouds. The larger the vertical temperature zone of the ice nucleusspectral, the wider the distribution of the ice phase particles produced. In the case of a large concentration of ice nucleus, the content of ice crystals and graupel particles is high, more small ice crystals appear in the zone of higher elevations; (2) The number of ice nucleus in high-temperature region has a significant affects the updrafts velocity. More ice nucleus in the high-temperature region leads to more latent heat released by the ice phase particles during the development of the microphysical process, resulting in intensive updrafts and vigorous convection development; (3) In the case of ice nucleusspectral environment with high ice crystal concentration in the low-temperature region, The non-inductive electric rate and inductive electric rate are high in thunderstorm clouds, resulting in increased charge. In the spectral environment with high ice nucleus in high temperature regions, a large number of ice crystals and graupel gain positive charge to form a sub-positive charge zone, and the charge structure exhibits tripolarity; while in a high-temperature zone, the spectrum environment with less ice nuclei and less hydrometeors particles participate in electrification, Dipolar charge structures are easily formed.
  • Spatiotemporal Distribution Characteristics of MαCS in Summer of Tianshan Mountains
  • LI Jiangang;JIANG Cailian;ZHANG Yunhui;YANG Lianmei;SUN Mingjing
  • 2019 Vol. 38 (3): 604-616.  DOI:10.7522/j.issn.1000-0534.2018.00151
  • Abstract ( ) HTML PDF (17128KB) ( )
  • The spatiotemporal distribution characteristics of Meso-α scale Convective System (MαCS) were analyzed in the summer of 2010-2014 in the Tianshan Mountains and their sides area by use of conventional observation and FY-2E satellite data, the characteristic of cloud image and environmental conditions from typical process was further discussed. The results showed that:(1) MαCS appeared frequently in June with the occurrence of majority of oval MαCS. The initiation and maximization period of MαCS was focused on afternoon and latter half of the night, and it terminated during the first half of the night, the peak time in three periods lagged sequentially about 2 h; the daily variation of circular MαCS and oval MαCS can be described with single-peak and multi-peak changes respectively. The life cycle of MαCS centered on 3~6 h, the frequency distributed widely in June, and intensively from July to August; the most oval MαCS sustained longer than that of circular MαCS. Extended time in stage of formation and dissipation of circular MαCS and oval MαCS respectively was displayed. (2) MαCS generated mostly in hillside plains or shallow areas in the Western Tianshan and inner Tianshan Mountains, and over the main part of central, Southeast and northeast Tianshan Mountains until it reached maximum extent, terminated in Yili Valley plains and on both sides of eastern Tianshan Mountain area at last. The long axis of cold cloud cover in the maturation period of MαCS concentrated mostly on the range between 500 km and 800 km; the area of cloud top decreased with the frequency of MαCS. Circular MαCS moved slowly while developing, and speeded up after the maximization, oval MαCS moved slowly from beginning to end instead. The TBBmin of MαCS cloud cluster showed unimodal and approximately normal distribution. The TBB average gradient in circular MαCS was greater than that in oval MαCS. (3) MαCS in Tianshan Mountains was formed mainly by the merging of more local meso-β scale convective bubble in large-area stratus cloud. The MαCS occurs easily in the pumping area of jet belt in high level and the convergence ascending area in front of trough in the middle-low level, abundant water vapor carried by the southwest and northwest airflow in the middle-low level gathers up under the background of the unstable stratification of the atmosphere and the continuous accumulation of unstable energy, which promotes the continuous development of MαCS.
  • Research on Cloud Characteristics based on FY-2F Satellite Data in Xinjiang Region
  • LI Shuai;HOU Xiaogang;CUI Yu;LIANG Fengchao;XU Zhide
  • 2019 Vol. 38 (3): 617-624.  DOI:10.7522/j.issn.1000-0534.2018.00101
  • Abstract ( ) HTML PDF (17604KB) ( )
  • Cloud is the most important regulator of the radiation budget in the land-atmosphere system. Studying the characteristics of cloud is of great significance for understanding the complex interactions between clouds, radiation and climate. And cloud is an important parameter for the artificial-increasing water, it is also very important for the ability of judging precipitation. At present, cloud remote sensing research usually bases on the products of CloudSat, ISCCP, Aqua and so on, but there are few applications of Fengyun satellite cloud products. In particular, even fewer applications in the Xinjiang region. By utilizing FY-2F/CTA, FY-2F/CLC hour products from January to December in 2014, based on the mean synthesis method, we monitored and analyzed the cloud characteristics in Xinjiang region. The result showed that:(1) the average annual total cloud cover in Xinjiang was 37.7%, among them, Altai mountain cloud resources were the most abundant, followed by the Kunlun Mountains, Junggar Basin, Tianshan Mountains, and Tarim Basin is the most scarce, the average annual total cloud covers of above area were 45.7%, 40.0%, 38.2%, 37.9% and 26.1%. The values of each area were focused on 40%~50%, 30%~50%, 30%~40%, 30%~40% and 20%~30% respectively, and the proportions within above interval were 50%, 95%, 50%, 95% and 85%. The cloud resources of north Tianshan region(including Tianshan Mountains) in winter and spring was more abundant, and that of south Tianshan region was more abundant in spring; The total cloud cover in Xinjiang was less during the day and relatively more at night, But it was in contrast in Tarim Basin. (2) The total cloud cover in the north of Tianshan Mountains was high in north and east, low in south and west, and it was in contrast in south region of Tianshan Mountains. (3) Three Xinjiang major mountainous areas mainly were covered by high-level cloud, rain clouds, or volume clouds. Kunlun mountain area was with more dense clouds, Junggar Basin and Tarim Basin were mainly with layered clouds and high cumulus cloud. The spatial and temporal distribution of clouds in the Xinjiang region, especially the three mountainous areas, had a certain regional and stability, which was conducive to artificial rainfall.
  • Contrast Experiment of Different Coordinate Remapping Schemes in Radar Velocity Data Assimilation
  • MU Xiyu;XU Qi;PAN Yujie;SUN Shiwei;LI Xin;HUANG Anning
  • 2019 Vol. 38 (3): 625-635.  DOI:10.7522/j.issn.1000-0534.2019.00012
  • Abstract ( ) HTML PDF (36454KB) ( )
  • Two interpolation schemes of radial velocity data in radar data assimilation are compared and analyzed through the high-precision numerical analysis and forecasting system jointly developed by Jiangsu Meteorological Bureau and Center for Analysis and Prediction of Storms. In Grid-scheme, the radar radial velocity data is interpolated from the polar coordinates to the three-dimensional model Grid by least squares method. In Tilt-scheme, the radar radial velocity data is only interpolated to the horizontal Grid through the bilinear interpolation in the horizontal direction but is not interpolated in the vertical direction, retained in the radial coordinates of the radar. In both schemes, radar reflectivity data is interpolated into the three-dimensional model Grid. The Grid-scheme results in smoothing of low-level data, and the Tilt-scheme retains more characteristics of radar observations. In this paper, the assimilation results of the two schemes are compared and analyzed through the cases of tornado, gust and heavy rain in Meiyu front. In the tornado case, the Grid-scheme obtained a part of larger assimilation wind field, while the Tilt-scheme result clearly showed the echo of tornado and the fine structure of the vortex. In the gust case, the maximum wind speed difference obtained by the two schemes is 3 m·s-1. The Tilt-scheme result was closer to the maximum wind speed observation and the distribution of the assimilated high wind speed region is more in line with the observation. In the Meiyu case, the Grid-scheme failed to reflect the high wind speed regions in the northeast and southwest regions. The horizontal high wind speed region obtained by the Tilt-scheme was obviously better than the Grid-scheme. At the lower altitude near the radar, the observations are dense, and the Tilt-scheme is better able to reflect the real atmospheric state. However, because of the lack of other observations for verification, the effects of the two schemes need to be compared by using numerical prediction or other methods.
  • Data Quality Analysis and Control Method of X-band Dual Polarization Radar
  • WANG Chao;WU Chong;LIU Liping
  • 2019 Vol. 38 (3): 636-649.  DOI:10.7522/j.issn.1000-0534.2018.00096
  • Abstract ( ) HTML PDF (33580KB) ( )
  • The Bureau of Meteorology in Beijing and Foshan began constructing an X-band dual-polarization radar networks to enhance their ability to elaborate nowcasting. However, in the following two years of flood season observation, it is found that there are still a series of problems in X-band dual-polarization radar, and its data quality that could be improved largely. The article uses the characteristics of polarization parameters that uniformed in nature and slowly changed with time and space in the process of weak rainfall and selects the observation data of weak precipitation process in Beijing and Foshan. Through the method of accumulating in radial or azimuth by taking a long-term observation, this paper analyzes the accuracy of polarization parameter measurement that affected by the ground, lightning rod, rotation and pitching joints and puts forward to the corresponding quality control method. The following conclusions are drawn:(1) different reflectivity factor (ZDR), correction coefficient (ρhv) and differential propagation phase (ΦDP) are more sensitive to the ground objects than horizontal polarization reflectivity factor (Z), where ρhv is less than 0.85, ZDR lower than -1 dB, and a threshold of 0.9 is set according to the difference of ρHV between rainfall and ground objects. The ρhv can be accumulated for a long time to identify the echo of ground object effectively. (2) The azimuth and amplitude of each lightning rod's influence on the dual polarization parameters are approximately the same. In the ±15° azimuth range centered on the lightning rod, the ZDR increases by approximately 0.4 dB to 1.5 dB, the ρhv lowers to 0.01 or less, and the Z decreases by nearly 1 to 2 dBZ, and in which these parameters will reach the extremum. Through the statistical correction based on the above azimuth, the effect of lightning protection on dual polarization parameters can be better removed. (3) The abnormality of the rotary joints will cause the ZDR to change unevenly in the horizontal direction, while the exception of pitching joint will cause the ZDR to have a large gap between the high and low elevation angles. The ZDR variation curve of the elevation angle of each layer will be obtained through the accumulation of the ZDR along the azimuth for a period of time, which can achieve ZDR error calibration. Through the test, the quality control method proposed in this paper can effectively improve the data quality of X-band dual-polarization radar and provides support for its further promotion in operation.
  • Characteristics of Carbon Flux in Sandy Grassland Ecosystem under Natural Restoration in Horqin Sandy Land
  • CHEN Yinping;NIU Yayi;LI Wei;LI Yuqiang;GONG Xiangwen;WANG Xuyang
  • 2019 Vol. 38 (3): 650-659.  DOI:10.7522/j.issn.1000-0534.2018.00133
  • Abstract ( ) HTML PDF (1273KB) ( )
  • The characteristics of net ecosystem CO2 exchange (NEE) at different time scales were investigated in sandy grassland ecosystem under natural restoration in Horqin Sandy Land, based on the year-round (1 January 2017~31 December 2017) eddy covariance system. The results showed that:1) The monthly mean diurnal variation of NEE changed apparently with a single peak curve; there were obvious absorption peaks during the growing season (from May to September) while obvious release peaks during the non-growing season (from October to April). At the seasonal scale, the absorption peak and the release peak appeared alternately; the growing season was a carbon sink (with a net CO2 absorption of 202.11 g·m-2), whereas a carbon source for non-growing season (with a net CO2 release of 298.13 g·m-2). The annual carbon budget of the sandy grassland ecosystem showed a carbon source, with a net CO2 release of 96.02 g·m-2·a-1. 2) The NEE was significantly (P < 0.01) negatively linearly related to the temperature (both air and soil temperatures) during the growing season, but on the contrary during the non-growing season. However, the NEE was significantly (P < 0.01) positively linearly related to the soil water content during both the growing and non-growing seasons. The temperature and soil water content had significant synergistic effect on NEE.
  • Global Spatial and Temporal Distribution of Aerosol Optical Depth for Different Kinds of Aerosols
  • ZHANG Zhijuan;CHEN Bin;JIA Rui;YI Yuhong
  • 2019 Vol. 38 (3): 660-672.  DOI:10.7522/j.issn.1000-0534.2019.00002
  • Abstract ( ) HTML PDF (16426KB) ( )
  • The spatial and temporal distribution of aerosol optical thickness for sulfate, black carbon, organic carbon, sea salt, dust, and total aerosols from 1980 to 2017 was analyzed using MERRA-2; six typical regions were selected to study the contribution of each type of aerosol to total aerosol optical depth. The results show that five types of aerosols are unevenly distributed globally and have seasonal variations; the global total aerosol optical thickness is the largest in summer (0.137), followed by spring (0.130), and the smallest in winter (0.118); in the six typical regions, the largest aerosol optical depth is in North Africa whose value is 0.43, followed by the eastern part of China, which is 0.41; the dominant types of aerosols in each region are different, in North America, Eastern China and Central India, sulfate is the dominant aerosol type with the contribution of 66%, 63% and 42% to total AOD, respectively, in the Indian Ocean, South Africa and North Africa, sea salt, organic carbon and dust are the main types of aerosols, respectively, with the contribution of 65%, 51% and 82%, respectively. There is a clear growth trend for black carbon, sulfate and total aerosols in Eastern China and central India and the linear trend 0.007 a-1 and 0.0056 a-1 for total aerosol optical depth in Eastern China and central India, respectively, but after 2010 there is a significant decline in Eastern China.