Plateau Meteorology

Current Issue

28 April 2016, Volume 35 Issue 2   
  • Analysis on MODIS Albedo Retrieval Quality over the Qinghai-Xizang Plateau
  • CHEN Aijun;LIANG Xuewei;BIAN Lingen;LIU Yujie
  • 2016 Vol. 35 (2): 277-284.  DOI:10.7522/j.issn.1000-0534.2015.00015
  • Abstract ( ) PDF (980KB) ( )
  • For a comprehensive understanding of the retrieval quality of MODIS land surface albedo (LSA) product in the Qinghai-Xizang Plateau, it is statistically analyzed with MCD43B2, the retrieval quality data accompanied with the MODIS LSA, in this paper, and results are as following:(1) the mean retrieval effectiveness (MRE) in each retrieval period is above 80%. The MREs are low in winter and summer, while MREs are high to more than 90% in spring and autumn. (2) Among all LSAs, those with the best quality of full inversions (BQFI) have the highest percentage. The percentages of LSAs with the BQFI in spring and autumn are high and the highest one is nearly up to 80%. Meanwhile, the percentages of LSAs with the BQFI in winter and summer are low and the lowest one is a little more than 50%. (3) The mean percentage for snow-free LSAs is between 70% and 95%, and the snow-free LSAs are mainly those with the BQFI. However, the mean percentage for snow LSAs is about 10%, and the snow LSAs are mainly derived with the magnitude inversion. All above indicate that MODIS LSA product could provide spatio-temporal continuousness, high-accuracy LSA for most area of the Qinghai-Xizang Plateau, but the MREs and the accuracy in winter and summer, as well as the accuracy of the snow LSAs should be further improved in the future.
  • Comparison Analysis of Sensible Heat Fluxes at Two Spatial Scales in Naqu Area
  • SUN Genhou;HU Zeyong;WANG Jiemin;LIU Huolin;XIE Zhipeng;LIN Yun;HUANG Fangfang
  • 2016 Vol. 35 (2): 285-296.  DOI:10.7522/j.issn.1000-0534.2015.00088
  • Abstract ( ) PDF (4631KB) ( )
  • In this study, the comparison analysis on the differences in sensible heat fluxes calculated with eddy covariance (EC) data and large aperture scintillometer (LAS) data of Naqu Station for Plateau Climate and Environment, Chinese Academy of Sciences and the analysis on the possible reasons for such differences are made based on the automatic weather data and the land surface temperature (LST) and normalized differences vegetation index (NDVI) of MODIS. The results show that sensible heat fluxes calculated with LAS data (H_LAS) agree reasonably well with those with EC data (H_EC) both in rain season and dry season. One reason for the differences between H_EC and H_LAS is the differences in their footprints which are caused by wind directions. A detailed analysis of the H_EC and H_LAS changing with net radiation and wind directions in July, 2010 indicates the spatial variability in net radiation in EC and LAS footprint which is created by cloud covers contributes greatly to the differences in the sensible heat fluxes at EC and LAS spatial scales. A statistical relationship between footprint-weighted averages of LST in EC and LAS footprints and their sensible fluxes reveals that high LST leads to large sensible fluxes. A statistical relationship between footprint-weighted averages of NDVI in EC and LAS footprints and the ration of H_EC and H_LAS to net radiations in rain season supported the analysis that the high NDVI leads to the small ratio of sensible heat fluxes to net radiations. The half-hour and monthly-averaged daily variations of sensible heat fluxes at EC and LAS spatial scales demonstrate that surface fluxes in Naqu are influenced by spatial scales, which should be kept in mind when surface fluxes were used to validate fluxes retrieving from remote sensing or from numerical models.
  • Water Vapor Transportation and Its Influences on Precipitation in Summer over Qinghai-Xizang Plateau and Its Surroundings
  • LIN Houbo;YOU Qinglong;JIAO Yang;MIN Jinzhong
  • 2016 Vol. 35 (2): 309-317.  DOI:10.7522/j.issn.1000-0534.2014.00146
  • Abstract ( ) PDF (2804KB) ( )
  • Based on the European Centre for Medium-Range Weather Forecasts (ECMWF) Interim Reanalysis (ERA-Interim hereafter) from 1979 to 2010, the average water vapor transport flux distribution in summer over the Qinghai-Xizang Plateau (QXP hereafter) is calculated and studied. Combined with the high resolution observational data of the daily precipitation over the QXP, four moisture paths influencing the precipitation over the QXP are found, which are defined as the paths of westerly, Arabian Sea, the northern side of Bay of Bengal and South China Sea, respectively. Moreover, the area and function of these paths influencing precipitation process over the QXP have been analyzed and addressed. The results show that the years of both strong (1979, 1984, 1996, 1998, 2002, 2004, 2007) and weak (1994, 2001, 2006) precipitation over the QXP are consistent with the results reflected from path of the northern side of Bay of Bengal. Compared with the rest paths, the influence of the westerly path is weakest, which only has an role in the northwest QXP from Shiquanhe to the south of Tarim Basin; The northern side of Bay of Bengal path has an effect in the central-southeastern QXP;the path of the South China Sea dominates the southeastern and central-south of QXP such as Naqu, Linzhi, Changdu, Yushu and other regions; Arabian Sea path has negative correlations with the rest three paths, especially with the northern side of Bay of Bengal path (R=-0.65, P<0.05). Furthermore, Arabian Sea path indirectly modulates the central-southwestern QXP by adjusting the intensity of both the northern side of Bay of Bengal path and South China Sea path. These results suggest that both the water vapor transport path and pattern of precipitation over the QXP is coherently connected.
  • Diurnal Variation Characteristics of GPS-Retrieved Precipitable Water Vapor over Mid-East Xizang in Summer
  • MA Siqi;ZHOU Shunwu;WANG Shuo;WANG Chuanhui;SUN Jihua
  • 2016 Vol. 35 (2): 318-328.  DOI:10.7522/j.issn.1000-0534.2015.00007
  • Abstract ( ) PDF (1520KB) ( )
  • JICA (Japan International Cooperation Agency) project was carried out from 2005 to 2009 which established 24 ground-based GPS stations over Qinghai-Xizang Plateau and around area. The range of mid-east Xizang includes four GPS stations:Naqu, Dingqing, Linzhi and Longzi. Using GPS-retrieved atmospheric precipitable water vapor (PWV) data of JICA from 2010 to 2013 and the hourly AWS (Automatic Weather Station) precipitation in 2011, on the basic of revealing the diurnal variation, focus on analyzing the diurnal variation characteristics with and without precipitation, as so as the relationship with accumulative precipitation. The results are obtained as follows:(1) The PWV is decreasing while the altitude and latitude increase. And it has obvious diurnal variation over mid-east Xizang. The PWV minimum ordinarily appears at 02:00 (UTC, the same as after) and then increases quickly. The high value can usually last from 08:00 to 19:00. (2) The average and anomaly range of PWV at each station is increasing with the altitude decreasing. And the PWV values in different precipitation events are obviously different. PWV with precipitation would surpass the PWV without 10.2%~31.3%. The difference may get more significant with the altitude increasing. (3) The result of harmonic analysis indicates that the diurnal (24 h) cycle is the main signal of PWV diurnal variation at each station. The signal of semi-diurnal cycle is in different extent and it gets stronger during the day without rain except Linzhi station which has a stronger diurnal cycle. (4) The largest accumulative precipitation occurs at Dingqing station in 2011, and then follows Naqu. The diurnal variation of precipitation has significant characteristic of diurnal cycle at each station. And precipitations often occur after nightfall. The peak of rainfall frequency is usually later than hourly accumulative precipitation. (5) PWV accumulates gradually and decreases rapidly before and after precipitation. The time when PWV begins to rise is generally earlier than hourly accumulative precipitation and rainfall frequency. The precipitation reaches the peak as PWV is still high.
  • Applicability Analysis of MERRA Surface Air Temperature over the Qinghai-Xizang Plateau
  • CHU Duo;YANG Yong;LUOBU Jiancan;BIANBA Ciren
  • 2016 Vol. 35 (2): 337-350.  DOI:10.7522/j.issn.1000-0534.2015.00018
  • Abstract ( ) PDF (2312KB) ( )
  • Atmospheric reanalyses integrate a variety of observing systems with numerical models to produce a temporally and spatially consistent synthesis of data for weather and climate variability studies. Products provided by reanalyises are the objectively analyzed fields over the globe, including regions with minimal observations, and also for fields that are rarely or never observed. In order to evaluate the applicability of MERRA products over the Qinghai-Xizang Plateau (QXP) MERRA reanalysis surface air temperature product T2m with surface observation air temperature from 60 meteorological stations over 30 years from 1981 to 2010 were compared for the seasonal variations and long tern trends of temperature over the QXP. Main results are as follows:(1) MERRA T2m shows very high correlation with observation temperature with a correlation coefficient of 0.76 on average, in which 96.7% of the total stations is significant at the 95% level and 85.0% of the total stations is significant at the 99.9% level. The correlation in winter is better than that in summer. The relatively low correlation coefficients are found at higher latitude regions of northern QXP. (2) MERRA T2m is lower than the in-situ observations in most of stations on the QXP with lower 3.2℃ on average, and is more close to observation temperature in relatively flat terrain and homogeneous surface features in interior and northern region of the QXP while higher bias is found in complex terrain and surface features in the southeastern and southern mountain and river valleys where land-atmosphere interactions strongly affect the physical parameterizations in the numerical models and complex terrain and heterogeneous surface features as well as persistent cloud cover may contribute to these differences. MERRA T2m standard deviation is smaller than observed as well. However, for long term trends the increase in observation temperature (0.525℃·(10a)-1) is well represented by MERRA (0.342℃·(10a)-1) though MERRA underestimates this increasing rate. (3) According to analysis using observation data, it is indicated that the annual mean surface air temperature on the QXP ranges from -5.1℃ to 14.8℃, with 3.6℃ on average. Over the last 30 years from 1981 to 2010, QXP has experienced obvious increase in temperature with 0.525℃·(10a)-1), which obviously higher than 0.29℃·(10a)-1)of China and 0.13℃·(10a)-1) of global warming trends. At seasonal levels, the highest temperature increase occurs in winter with 0.724℃·(10a)-1), followed by spring(0.523℃·(10a)-1) and autumn(0.467℃·(10a)-1), and the lowest increase in temperature is found in summer but it still reaches to 0.389℃·(10a)-1). These 30-year trends of seasonal temperature are well represented by MERRA T2m product although increasing rates are to some extent underestimated. (4) Based on this work and previous comparison study for surface air temperature from NCEP/NCAR, NCEP/DOE and ERA-Interim over the QXP, MERRA T2m has higher correlation with observation compared to these reanalysis products, which means MERRA surface air temperature has some advantage over the QXP compared to other reanalysis data and is one of the better ways to compensate for sparse ground observation network, to implement climate change, energy balance and water cycles related study, and to use initialization fields for regional climate models etc.
  • Seasonal Variation of Radiation and Energy Fluxes over the Rain-Fed Cropland in the Semi-Arid Area of Loess Plateau
  • CHEN Xing;YU Ye;CHEN Jinbei;LI Zhenchao;MA Chenchen;XIE Jin
  • 2016 Vol. 35 (2): 351-362.  DOI:10.7522/j.issn.1000-0534.2015.00004
  • Abstract ( ) PDF (2159KB) ( )
  • It's important to understand the land-atmosphere interactions over the semi-arid area of Loess Plateau, which featured by special climate and unique underlying surfaces. Seasonal variability of precipitation, soil moisture, radiation, albedo and energy fluxes, especially the influence of rain, soil moisture and agricultural production activities to the energy partition, were analyzed systematically, using a full year observations over a rain-fed cropland at the Pingliang Land Surface Process & Severe Weather Research Station. The results showed that the seasonal distribution of precipitation was uneven, gave rise to the significant seasonal differences in soil moisture. Radiative components had seasonal cycles. Shortwave radiation fluctuated with weather conditions, while longwave radiation was less affected. Surface albedo had significant seasonal variations:the maximum midday mean value (0.83) occurred after snow, then dropped to less than 0.2 during crop growth, afterwards, it fluctuated with precipitation after crop harvest. There was a linear relationship between albedo and soil moisture. Turbulent energy fluxes had diurnal cycle and seasonal variations. The partition of energy was largely affected by the changes in precipitation as well as agricultural production activities. The main consumer of the available energy was different among months, monthly mean diurnal cycle of the latent (sensible) heat flux attained maximum in May (April), which was 240.8 (192.5) W·m-2. On an annual scale, the largest consumer of midday net radiation was sensible heat flux, which accounted for about 35% of Rn. While the latent heat flux was about 32% of Rn, which was lower than irrigated croplands. During the rapid growing season of winter wheat (March to May), the average midday LE/Rn was about 34%, which was much lower than irrigated winter wheat agro-ecosystem, indicating that it was water limited in our study site.
  • Climate Characteristics of Surface Heating Fields in Arid Region of Northwest China in Summer
  • WANG Hao;LI Dongliang;WANG Hui
  • 2016 Vol. 35 (2): 363-374.  DOI:10.7522/j.issn.1000-0534.2015.00032
  • Abstract ( ) PDF (3794KB) ( )
  • The monthly surface heating fields in the arid region of Northwest China in summer from 1982 to 2012 were calculated with the satellite remote sensing data of AVHRR/NDVI, MODIS/NDVI and the observed date from 95 meteorological stations in Northwest China. By comparing with 3 sets of reanalysis data, and using mathematical statistics and empirical orthogonal function (EOF) methods, the spatial distributions and temporal variations of the surface heating fields are analyzed. The main conclusions are as follows:(1) The large values of surface heating fields in the arid region of Northwest China in summer are mainly over the Alxa Plateau, Qaidam Basin and regions to its north, eastern Qinghai and east of Hexi Corridor area. (2) The calculated values of surface heating fields are generally smaller than those from three reanalysis data, but all of them have the same magnitude. The ERA-40 reanalysis data and the calculated value of surface heating fields are consistent in both spatial distribution pattern and interannual variations, while the calculated values of surface heating fields give more detailed information of the local climate characteristics. (3) The LV1 of surface heating fields in the arid region of Northwest China in summer have opposite spatial patterns from east to west, and its PC1 displays changing interannual trends of surface heating fields in the arid region of Northwest China in summer around 1995. The LV2 have opposite spatial patterns from northeast to southwest. Furthermore, its PC2 indicates that the surface heating fields in northeastern (southwestern) part of Northwest China increases (decreases) year by year before the mid-1990s, and there is no obvious interannual trends afterwards with a slightly larger (smaller) value. (3) Taking 100°E as the boundary, the surface heating fields in the eastern and western parts of Northwest China vary significantly in terms of intra-annual and interannual variation trends. The intensity of the surface heating fields in eastern regions is stronger than that in western regions. The month of the peak surface heating fields in the east (July) is later than it in the west (June). The summer surface heating fields in western and eastern have opposite interannual variations and the interannual variations of surface heating fields in eastern (western) is dominated by the sensible heat flux (latent heat flux), which varies from weak(strong) to strong (weak) from 1982-1995 and strong (weak) to weak (strong) from 1995-2012.
  • Land Surface Evapotranspiration Estimated based on MODIS Remote Sensing Products over the Semi-Arid Northwest China
  • WANG Lijuan;GUO Ni;YANG Qidong;WANG Jiemin;SHA Sha;HU Die
  • 2016 Vol. 35 (2): 375-384.  DOI:10.7522/j.issn.1000-0534.2014.00158
  • Abstract ( ) PDF (6661KB) ( )
  • Based on the Moderate-Resolution Imaging Spectroradiometer (MODIS) products, the air temperature in the net radiation and evaportranspiration models were instead by the land surface temperature, and the models were modified using the observed data of Semi-Arid Climate and Environment Observatory of Lanzhou University(SACOL). Then the net radiation and evapotranspiration estimated by original and modified models were compared with the observed values in SACOL and Dingxi Arid Meteorology and Ecological Environment Experimental Station (Dingxi station). The results showed that:the MODIS daytime/nighttime land surface temperature was highly correlated with the observed daily maximum\minimum air temperature, and the correlation coefficients were greater than 0.75, therefore the air temperature in the model can be instead by land surface temperature, and using this method all the parameters in the model have specific physical meanings. Compared to the observations, the modified model improved the accuracy of net radiation and evapotranspiration when used the observed data to modify the model. The root mean square errors of the net radiation by modified models reduced to 25.93 W·m-2. The evapotranspiration of SACOL and Dingxi stations estimated by the modified model was closer to the measured data, and the root mean square errors were reduced to 0.81 mm and 0.68 mm, respectively, and the correlation coefficients were greater than 0.6, and all passed the 0.01 level of significance test. Furthermore, the modified model estimated regional evapotranspiration distributions were consistent with the actual land covers of the research area, which implied that the net radiation and evapotranspiration estimated by the modified model was reasonable. Because the modified model only used the remote sensing data without any real-time ground observation, it was a new idea to study the radiation and evapotranspiration in the area where lack of ground measured data.
  • Analysis on Atmosphere Boundary Layer Variation Characteristics and Their Impact Factors in Arid Region and Semi-Arid Region over Northwest China
  • LI Yanying;ZHANG Qiang;ZHANG Aiping;CHEN Ying;YANG Mei
  • 2016 Vol. 35 (2): 385-396.  DOI:10.7522/j.issn.1000-0534.2014.00153
  • Abstract ( ) PDF (2440KB) ( )
  • Using daily sounding data of three stations over northwest China which were Minqin in arid area, Yuzhong in semi-arid region and Pingliang in semi-arid and semi-humid region at 08:00 (Beijing Time, the same as after) and 20:00 from 2006 to 2012, and the ground elements data from 1961 to 2012, the time variation characteristics and influencing factors of troposphere boundary thickness, stable boundary thickness were calculated and comparatively analyzed by potential temperature profile method. The results showed that in the troposphere boundary thickness, Minqin of arid regions was deeper, the thicker layer was above 3300 m appeared from May to June; semi-arid region was more shallow, whose most thick appears from April to June, thickness of Pingliang was above 2700 m, that of Yuzhong was above 2300 m. In the stable boundary layer thickness, Minqin of arid regions was about 500 m, but Yuzhong of semi-arid region was thicker between 1200 m and 1400 m. The boundary layer thickness was most closely to maximum Ts-Ta, showed a significant positive correlation, there was most closely related in Minqin of arid whose coefficient was up to 0.9, and Pingliang of semi-arid area was also closely related to wind speed, the correlation coefficient of troposphere boundary thickness and maximum wind speed in Yuzhong was bigger than 0.8. In recent 50 years, the boundary layer thicknesses of Minqin and Pingliang showed decreasing trends, but that of Yuzhong showed an increasing trend, the reason was although maximum differences between soil temperature and air temperature (Ts-Ta) were all increased linearly in three stations, only wind speed of Yuzhong was increased, and daytime precipitation of Pingliang was decreased obviously. The main factors of affecting boundary layer thickness were maximum Ts-Ta and wind speed, further that of Pingliang was also related to daytime precipitation.
  • Diagnostic Analysis of Precipitation Forecasting from Japan Thin-Grid Model based on MODE
  • XUE Chunfang;PAN Liujie
  • 2016 Vol. 35 (2): 406-418.  DOI:10.7522/j.issn.1000-0534.2015.00010
  • Abstract ( ) PDF (7765KB) ( )
  • Using CMORPH (NOAA Climate Prediction Center Morphing Method) and fusion datas of hourly precipitation from more than 30 thousand automatic stations, based on MODE (Method for Object-Based Diagnostic Evaluation) object matching technology, the forecasting ability of Japan high resolution model of 34 precipitation cases in China from 2012 to 2013 was studied and compared with the traditional TS and ETS skill scores. The result shows that:first, the model can generally forecast the rainfall, but the number and characteristics of objects significant differences in different convolution radius. Second, the model gives much forecast of local or weak precipitation cases and limited forecast of regional or heavy precipitation. Third, the model can better tell variation characteristics of the area and the quantity when different convolution radii exist and the rainfall is about 10 mm. The disadvantage of the model is that the fixed threshold is much more centralized and the number of identified cases decrease quickly. If bigger radius are used to convolution, the model can identify the pattern better in heavy rainfall regions. There are possibilities to exist a proper convolution radius to improve total interest in different cases of different magnitude of rainfall. Fourth, the forecasting reward generally is bigger in the low-and mid-latitude areas than in high-latitude regions. However, the model shows no stable abilities to forecast different aspects of the rainfall. Specifically speaking, forecasting rainfall intensity in high-latitudes regions is more reasonable, while in low latitudes forecasting the rainfall area is superior to that in high latitudes regions. Compared with the traditional TS, ETS verification, MODE method is less affected by climate probability, the verify results are more objective and diversity.
  • Frontogenesis Process and Slantwise Vorticity Development of a Rainstorm Process in the Eastern Gansu
  • WANG Fucun;XU Dongbei;YAO Yanfeng;XIU Shaoyu;GUO Pingping;QUE Longkai;HAN Shupu
  • 2016 Vol. 35 (2): 419-431.  DOI:10.7522/j.issn.1000-0534.2014.00127
  • Abstract ( ) PDF (10767KB) ( )
  • By using the data of sounding and surface intensive AWS, the satellite cloud images, the Doppler weather radar and the reanalysis data of ECMWF (ERA-interim) 0.25°×0.25°, the frontogenesis process and slantwise vorticity development of a rainstorm occurred on 20 June 2013 in the eastern Gansu are analyzed. The results show that the strong frontogenesis is caused by interaction among the shear line in lower troposphere, subtropical high, and the cold air in the middle and lower troposphere in the northeastern side of the plateau. The frontogenetical forcing causes rapid development of vertical vorticity and convergence in the shear line, triggering the release of unstable energy to generate strong convection and rainstorm. The rainstorm occurs beneath strong convective cloud of TBB<-52℃. Rain intensity changes from weak to strong with the cold air southward invading and infiltrating in the eastern Gansu, however, that begins to weaken after entering the Sichuan. The height of radar strong echo is below 5 km and 0℃ layer, it has characteristics of low center of mass and high efficiency precipitation echo. The strong echo moving from south to north has the train effect. The intensity changes of frontogenesis, shear line and rainfall are consistent. The frontogenesis function analysis indicated that enhancement stage in the rainstorm, effects of divergence and deformation play the main role and effect of deformation is more obvious, however, effect of tilting term is relatively small. The continuous stage in the rainstorm, effects of divergence and deformation are equal in match or contest of strength, effect of tilting term is frontolysis. Through the complete form of vertical vorticity tendency equation established the direct connection between the vertical vorticity change and frontogenesis, to diagnose the frontogenesis effect on the intensity of the weather system. The frontogenesis tilts the wet isentropic surface and produces significant positive vertical vorticity change in front of the frontal zone, which results in the fast development of shear line.
  • Mesoscale Characteristics of a Rainstorm Process in Inner Mongolia and Its Cause Analysis
  • CHANG Yu;LI Xiujuan;CHEN Chao;MA Suyan;ZHONG Xia;ZHAO Fei;MA Xuefeng
  • 2016 Vol. 35 (2): 432-443.  DOI:10.7522/j.issn.1000-0534.2014.00155
  • Abstract ( ) PDF (17503KB) ( )
  • Using conventional observational data, NCEP 1°×1° reanalysis data, automatic weather station data, FY-2E hourly Temperature of Black Body(TBB) data and Cloud-to-Ground(CG) lightning data, a rainstorm process was analyzed in Inner Mongolia from 14 to 16 July 2013. The results showed:The rainstorm stations about 58% could reach rainstorm magnitude in 2 hours, 3 hours or 6 hours, mesoscale rain cluster and mesoscale rain belt were important feature of rainstorm process. Heavy rainfall was caused by mesoscale convective system(MCS) that generated and vanished in cold front clouds and vortex clouds. When MCS was developing and matured, rain cluster and maximum value of CG density were located the coldest of TBB≤-52℃ where the cold air flowed into. But the region where MCS shifted out existed rain cluster caused by stratiform clouds. When CG density increased, MCS developed and precipitation intensified. When CG density decreased, MCS dissipated and precipitation weakened. The blocking maintenance, the eastward extension of South Asia High and the northward position of the West Pacific Subtropical High provided planetary-scale circulation feature for MCS. The main reason that heavy rainfall concentrated form midnight to dawn was caused by diurnal variation of low-level jet. It was useful for persistent and development of MCS that there were high temperature and high moisture, geopotential instability layer and vertical wind shear in low-level of troposphere. Disturbance mechanism completed by the surface mesoscale ‘people’-shaded shear line advanced development of MCS. MCS occurred in the area of instability on the south side of warm shear line, but an upper-level divergent center and a low-level positive vorticity advection center lagged peak value of heavy rainfall approximately 3~4 hours.
  • Study on Water Vapor and Dry Intrusion in a Heavy Rainfall Event Associated with Typhoon Haiou
  • ZHAO Yu;LI Jing;YANG Chengfang
  • 2016 Vol. 35 (2): 444-459.  DOI:10.7522/j.issn.1000-0534.2015.00061
  • Abstract ( ) PDF (16293KB) ( )
  • A heavy rainfall event that occurred in Shandong Province on 17-19 July 2008 was caused by the interaction between typhoon Haiou and westerly trough. The water vapor and the activities of dry and cold air of this heavy rainfall event were studied by using routine observation, NCEP/NCAR 1°×1° reanalysis and simulated data from the WRF3.2 model. The results show that the water vapor convergence was mainly from the inflow of the southern boundary. The intensification of the inflow of the water vapor from southern boundary primarily contributed to the northward transportation of water vapor from the typhoon. The convergence of water vapor in the west and middle parts of Shandong Province resulted from the vortex in the lower troposphere. The convergence of water vapor in the south-north direction corresponded well with rainfall. Dry and cold air apparently intruded into rainfall area in the process of the rainfall. In the initial phase of the heavy rainfall, dry and cold air in the tropopause first intruded into the rainfall area and induced the acceleration of west wind in the high levels and the enhancement of divergence, which led to the development of upward motion. In the development phase of the heavy rainfall, dry and cold air in the middle troposphere (500 hPa or 600 hPa) intruded into rainfall area with westerly wind from northwest to southeast and met with warm and moist air, resulted in upward motion. In the heavy rainfall period, dry and cold air came not only from northwest in the mid-latitude but also from the high latitudes. Dry intrusion in the higher levels was always ahead of that in the lower levels, which is favorable to the development of potential instability. The activities of dry and cold air as well as warm and moist air intensified frontogenesis in the lower and middle levels in Shandong Province and ageostrophic ascending motion was triggered, which is one of the mechanisms of the intensification of the ascending motion. Convective instability and conditional symmetric instability existed in the heavy rainfall event. Dry intrusion can slant the equivalent potential temperature surface and force warm and moist air to move upward slantwise along front, which is beneficial to the development of conditional symmetric instability.
  • Study on the Space Distribution and Circulation Pattern of Extreme High Temperature over Eastern China in Summer
  • ZHANG Yinghua;LI Yan;LI Deshuai;SHANG Kezheng;ZHENG Fengkui
  • 2016 Vol. 35 (2): 469-483.  DOI:10.7522/j.issn.1000-0534.2014.00159
  • Abstract ( ) PDF (4527KB) ( )
  • Based on the CN05 grid datasets interpolated by the temperature data from 751 observation stations in China from 1961 to 2008, the variation characteristics of extreme high temperature days over eastern China in summer (neh) were firstly studied. Results show a significant increasing trend of neh over the whole eastern China, especially in the northeast China, the eastern and middle part of Inner Mongoli and the Southeast Coast of China, however, the trend is the most insignificant in Jiang-huai and Huang-Huai areas, parts of the area even shows a decreasing trend. The interannual period is mainly between 2.5 and 3 years in the whole eastern China while it is quasi five year in Jiang-huai area. Empirical orthogonal function (EOF) analysis of neh shows a linear trend in the first mode, while a north-south ‘dipole’ pattern appears in Jiang-huai area and northeast China in the second mode, and the ‘dipole’ pattern appears in south China and north China in the third mode, respectively. Composite analysis shows that a positive 500 hPa geopotential height anomaly appears over Jiang-huai area and a negative anomaly appears over northeast China in the positive phase of the second mode, meanwhile, the western Pacific subtropical high (WPSH) is stronger and locates north relative to the climatological average field, the anomalous feature is opposite in the negative phase, respectively. And a positive 500 hPa geopotential height anomaly appears over south China and a negative anomaly appears over north China in the positive phase of the third mode, meanwhile, the WPSH is stronger and locates south, the anomalous feature is opposite in the negative phase too. The partial correlation analysis shows a significant positive correlation between Okhotsk blocking high and neh over northeast China and the Southeast Coast, but shows a significant negative correlation over parts of Huang-huai area; the latitude of the ridge line of WPSH and neh over north China and northeast China shows a significant positive correlation; the intensity of WPSH and neh over Southeast Coast of China also shows a significant positive correlation.
  • Diagnostic Analyses of Characteristics and Causes of Regional and Persistent High Temperature Event in China
  • YANG Hanwei;FENG Guolin
  • 2016 Vol. 35 (2): 484-494.  DOI:10.7522/j.issn.1000-0534.2014.00130
  • Abstract ( ) PDF (4727KB) ( )
  • A persistent large-scale high temperature event occurred in China in the midsummer of 2013 (July and August). Its wide scope of influence, long duration and strong intensity has rarely been seen in history. Brief diagnostic analyses were conducted for the high temperature characteristics of the event, its corresponding atmospheric circulation and possible external forces. The results showed that:(1) The positive phase of Arctic Oscillation (AO) in the middle and high latitude areas of the northern hemisphere provides the circulation background for the occurrence of the persistent high temperature event; the abnormal characteristics which continuously appear in the subtropical high such as overly large area, strong intensity and westward stretching of the western ridge point are the direct factors leading to the occurrence of the persistent high temperature event, while these continuous abnormal characteristics are the results of the comprehensive influence of many factors; the main body of the westerly upper jet belt significantly extends eastward to the central and southern regions of Northern China, being conducive to the stable maintenance of the high temperature. (2) The sea surface temperature (SST) over the same period and early SST play an important role in the occurrence and development of the high temperature event, and this important role is reflected in the fact that the SST anomalies in the western equatorial Pacific Ocean and north of equatorial Indian Ocean during the summer have a certain promoting role in continuing to strengthen the westward extension of the subtropical high, while the consistent warming of the equatorial Indian Ocean SST during the preceding winter is the main precursory signal of the high temperature event. (3) The negative anomaly of Tibetan Plateau snow cover during the preceding winter effectively strengthened factors which had a direct influence on the persistent high temperature event, and it also became another possible precursory signal of the event.
  • Observation Experiment and Simulation Evaluation of Influence of Non-Frozen Water Body on Air Temperature
  • YOU Yuan;GUO Jianxia;CHEN Yi-zhi;SHEN Xuefeng;JIN Lianji;ZHONG Zhuhui
  • 2016 Vol. 35 (2): 495-506.  DOI:10.7522/j.issn.1000-0534.2015.00005
  • Abstract ( ) PDF (11269KB) ( )
  • In order to evaluate how the water body affects the air temperature observing quantitatively, two observing experiments and some numerical simulations were conducted. The results are:(1) The observing experiments indicate that:the air temperature around the water body is increased at night and decreased at daytime. The nearer to the water body, the stronger of the inference is. For the small-scale water body, the scope of the effects is obvious at 200 m at the lee shore in winter, and it seems decrease in spring. While for the large-scale water body, the scope of the effects is obvious about 1km. There are upper bounds of wind speed for the effects at night, 3 m·s-1 to the small water body, 4 m·s-1 to the large one. When wind flow under the bound value, the warming effects are obvious, however, the effects are no show if the wind beyond the bound value. No upper bound appeared during the daytime. (2)Simulations show the same pattern of the effects that the surrounding air of water body is warming at night and cooling at daytime. But the effecting scopes are smaller than the observations. 0.5℃ warm curve is 100 m to the small water body, and 0.2℃ warm curve is 3.7 km to the large water body. (3) The effects of the water body on the surrounding air temperature are sensitive to the background wind speed, initial temperature and weather condition. The intensity and the distance of the effects are larger with the increase of the wind speed limited to the upper bound at night, the temperature at daytime and the decrease of the temperature at night. Different weather conditions, there are different effect of water body on temperature.
  • Cause Analysis of Persistent Heavy Snow Processes in the Northern Xinjiang
  • YANG Lianmei;LIU Wen
  • 2016 Vol. 35 (2): 507-519.  DOI:10.7522/j.issn.1000-0534.2014.00161
  • Abstract ( ) PDF (4944KB) ( )
  • Based on daily precipitation data of 45 meteorological observation stations in Tianshan Mountions and its north to Xinjiang (northern Xinjiang) during 1964-2010 and NCEP/NCAR 2.5°×2.5° daily reanalysis data, the persistent heavy snow process in northern Xinjiang is defined. There were 36 processes from 1964 to 2010, and they can be classified into 4 patterns based on the location of the snowstorm, 25 times in northern Xinjiang, 9 times in north and west of northern Xinjiang, 1 time along the Tianshan Mountains, 1 time in west of northern Xinjiang. The large scale circulation backgrounds, key circulation system configuration and water vapor transport anomalies of processes in northern Xinjiang and in north and west of northern Xinjiang have been analyzed. The results show:(1) Circulation of heavy snow processes in northern Xinjiang can be classified into 3 patterns:the meridional pattern Ⅰ, the meridional pattern Ⅱ and the zonal pattern. The meridional pattern Ⅰ can be classified into 2 patterns:Two polar vortex centers in the Northern Hemisphere with two and three waves in middle high latitudes respectively. The meridional pattern Ⅱ can be classified into 2 patterns:one and two polar vortex centers in the Northern Hemisphere with two waves in middle high latitudes respectively. The zonal pattern:Snowstorms were caused by meeting with wave from frontal zone high latitudes and subtropical front in middle-low latitudes over Xinjiang. (2) Circulation of snow processes in north and west of northern Xinjiang can be classified into 3 patterns:one and two polar vortex centers in the Northern Hemisphere with three waves in middle high latitudes, and the zonal pattern manifested as the West Siberia trough and trough between the Caspian Sea and the Aral Sea jointed together over Xinjiang and caused the snowstorm. (3) These circulation patterns have the same configuration:polar front jet on 300 hPa, strong westerly frontal zone on 500 hPa, low-level westerly jet on 700 hPa, heavy snow area located at the divergence area of wind velocity in the right side of the entrance of polar front jet and the convergence area of wind velocity in the right side of the exit of low-level jet. (4) The water vapor sources are the North Atlantic Ocean and the Barents Sea in high latitudes, the Mediterranean Sea, the Caspian Sea and the Aral Sea in middle latitudes, the Red Sea in low latitudes. Different circulation configurations have different water vapor transports, but mainly from the middle-low latitudes water vapor transport.
  • Study on Circulation Features of Return-Flow and Related Precipitation Types during Cold Seasons in Shandong
  • ZHENG Lina;YANG Chengfang;LIU Chang
  • 2016 Vol. 35 (2): 520-527.  DOI:10.7522/j.issn.1000-0534.2015.00055
  • Abstract ( ) PDF (957KB) ( )
  • Based on sounding and surface observation data of 36 return-flow precipitation cases and precipitation data in Jinan and Qingdao during 2000 to 2013, this paper reveals circulation features, vertial characteristics of temperature and height thickness of return-flow precipitation in Shandong province in winter, and return-flow synoptic situations are typed by warm layer in the middle troposphere and cold layer in lower troposphere. The results show that return-flow situations can be divided into three types of return-flowⅠ, return-flowⅡand thin return-flow, respectively. Thin return-flow is composed of thin cold return-flow and thin warm return-flow warm. To pure snowfall, temperature thresholds in inland are T850≤-4℃, T925≤-2℃, T1000≤0℃ or Tground≤1℃. It is more important that surface temperature is less than 0℃ in coastal areas. Whether in coastal region or inland, rain turns to sleet or snow when temperature indexes show that T850≤-3℃, T925≤-1℃, T1000≤0℃ or Tground≤1℃. Thickness clues are various during the pure snowfall that H850-1000 is from 127 to 130 dagpm and H500-700 is from 252 to 256 dagpm in return-flowⅠand return-flowⅡ. In addition, H925-1000 shows from 61 to 64 dagpm and H500-850 shows from 403 to 413 dagpm in thin cold return-flow air while H700-1000 embodies from 279 to 284 dagpm and H500-700 embodies from 250 to 260 dagpm in thin warm return-flow. When rain turns to snow, H850-1000 marks from 127 to 130 dagpm and H500-700 marks from 252 to 256 dagpm. But phase converted cases of thin return-flow are too little, thinkness indicators need to focus on later.
  • Numerical Simulation of Influence of Relative Growth of Ice and Graupel on Noninductive Electrification
  • LIANG Mengxue;GUO Fengxia;WU Xin;JIANG Tao;SHI Haifeng
  • 2016 Vol. 35 (2): 538-547.  DOI:10.7522/j.issn.1000-0534.2015.00013
  • Abstract ( ) PDF (9545KB) ( )
  • In order to realize the effect of relative growth of ice phase particles in different conditions or different regions on non-inductive electrification process within the thunder cloud, the non-introduction electric parameterization scheme based on S91 laboratory results is introduced into the three-dimensional dynamic-electrification coupled model. Simulated the process of a typical thunderstorm, the generation and consumption process of graupel and ice crystals and the distribution features of the particles with height are analyzed in this paper. The changes in growth situation of water content etc. of graupel particles and ice crystals in the different time of thunder cloud mature period are analyzed, and we compare the noninductive electric charge transfer polarity and magnitude between graupel particles and ice crystals in defferent time with the relative growth status of graupel particles and ice crystals. Analysises of the simulations show that graupel particles and ice crystals grow or consume through different micro physical process, due to different environment conditions of temperature and liquid water. Subtle differences of the temperature or liquid water content condition will affect the relative growth of two types of particles. The relative growth faster particles in two types of ice phase particles charge positively, slower growth particles charge negatively. Relative growth speed determines the polarity and magnitude of two type's ice phase particles taking charge in the process of the inductive electrification.

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