Plateau Meteorology

Current Issue

28 June 2013, Volume 32 Issue 3   
  • Impact of Intra-Seasonal Oscillation in Asian Summer Monsoon on Precipitation in Main Rainy Season of Yunnan I: Features and Propagation Processes of Intra-Seasonal Oscillation in Main Rainy Season of Yunnan
  • LI Ting;JU Jian-hua
  • 2013 Vol. 32 (3): 617.  DOI:10.7522/j.issn.1000-0534.2012.00060
  • Abstract ( ) PDF (1176KB) ( )
  • Using the precipitation data at 124 stations of Yunnan  and OLR data from NCAR/NCEP, the activity features and annual differences of Intra-Seasonal Oscillation (ISO) during main rainy season (June-August) in Yunan, and two paths along which tropic Indian ISO propagates to Yunnan and the impact of two Asian Summer Monsoon systems to ISO during main rainy season have been analyzed. The precipitation in main rainy season of Yunnan has prominent negative correlation with OLR averaged in Yunnan region. Summer monsoon ISO in Yunnan which is described as Low Frequency (LF) (30~60 d) OLR shows obvious intra-annual differences. In the stronger ISO  years of main rainy season in Yunnan, LF convection propagates along two paths: One is strong westward propagation from tropic western Pacific ocean or southeastern China, which causing three times active LF convections during  main rainy season of Yunnan; Another is propagation along southwest-northeast direction from tropic Indian ocean along the western bank of Bay of Bengal (BOB), which strengthens LF convection activities during main rainy season in Yunnan when it arrives in Yunnan. Otherwise, in the weak ISO years of main rainy season in Yunnan, just two times weak LF convections happen, which caused by two times weak zonal propagation of LF OLR from southern subtropical region: The first is westward propagation from subtropical western Pacific ocean, and the second is eastward propagation from Northern Arabian Sea. In the stronger ISO years, in developing process of tropic Indian LF convection, it propagates along southwest-northeast directions along the western bank of BOB, and excites the southwest Monsoon in BOB to propagates to Yunnan continually. On the another hand, it propagates eastward from BOB to South China Sea, and excites SCS Summer Monsoon (SCSSM) to propagate to subtropical eastern China and then turn to westward to Yunnan. When passing Yunnan, in northern BOB it meets LF convection that propagates northeastward from western bank of BOB, accomplishing a whole circle of relay propagation along zonal and meridional directions. Therefore, that is the excitation of ISO in tropic Indian to ISO in SCSSM and ISO in BOB southwest monsoon respectively along two paths, causes eastern Asian summer monsoon and southern Asian summer monsoon, these two Asian Monsoon systems impact together to ISO in main rainy season of Yunnan.
  • Impact of Intra-Seasonal Oscillation in Asian Summer Monsoon on Precipitation in Main Rainy Season of Yunnan II: Intra-Seasonal Oscillation Activity Process in Main Rainy Season of Yunnan and Its Response to MJO Activity
  • 2013 Vol. 32 (3): 626.  DOI:10.7522/j.issn.1000-0534.2012.00061
  • Abstract ( ) PDF (984KB) ( )
  • Using OLR and wind reanalysis data from NCEP and precipitation data from APHRO_MA_V1003R1 in Japan, the responding Low Frequency (LF) convection and circulation fields and precipitation anomaly features in ISO active years in main rainy season of Yunnan, and the impact of Intra-Seasonal Oscillation (ISO) in monsoon systems of Bay of Bengal (BOB) and South China Sea (SCS) which excited by tropical Indian Madden and Julian Oscillation(MJO) on Yunnan ISO during main rainy season have been analyzed. The results show that, in ISO active years in main rainy season of Yunnan, LF convection and circulation fields shows negative feature in phase 1~3 and phase 4~6 of Yunnan ISO wave, which caused by eastward and northward propagations of tropical Indian LF convection and westward propagation of subtropical western Pacific LF convection. In developing process of tropical Indian LF, on the one hand, it propagates along western bank of BOB in southwest-northeast directions, which excites Southwest Monsoon ISO of BOB active and to propagate to Yunnan; on the another hand, it propagates eastward from southern BOB to SCS and excites South China Sea Summer Monsoon（SCSSM）ISO active and to propagate northward to sub-tropical eastern China, where ISO turns to propagate westward to Yunnan. When it passes Yunnan and meets LF convection which propagates northeastward along western bank of BOB, a circle of relay propagation along zonal and meridional directions is accomplished. Besides, the precipitation in Yunnan shows positive abnormal in phase 1~3 (in phase 2 it is the most) caused by sub-tropical LF convection propagating westward to Yunnan and BOB LF convection propagating northeastward to Yunnan; and in phase 4~6 the precipitation shows negative abnormal (in phase 5 it is the least) caused by sub-tropical LF convection inhibiting region propagating westward to Yunnan and BOB LF convection inhibiting region propagating northeastward to Yunnan, so precipitation in main rainy season of Yunnan contains smarted response to LF convection. When tropical Indian MJO is strong, its propagation along 2 paths to Yunnan is also strengthens, which causes ISO activities in main rainy season of Yunnan stronger and to produce 3 time of active periods of LF convection. This kind of tropical Indian MJO propagation to Yunnan needs about 30~40 days. Therefore, that's the excitation of tropical Indian MJO to ISO of southwest monsoon of BOB and SCSSM, causes the two Asian monsoon systems of Eastern Asian Summer Monsoon (EASM) and Southern Asian Summer Monsoon (SASM) to impact on Yunnan ISO and precipitation during main rainy season together.
  • Applicability of GLDAS and Climate Change in the Qinghai-Xizang Plateau and Its Surrounding Arid Area
  • 2013 Vol. 32 (3): 635.  DOI:10.7522/j.issn.1000-0534.2013.00054
  • Abstract ( ) PDF (1312KB) ( )
  • Some researches show that the hydrological cycle in the Qinghai-Xizang Plateau and its surrounding arid area is particularly sensitive to global climate change. Due to the observations of evaporation and runoff are sparse,  the hydrological cycle change in the study area is certainly limited. Based on the observation driving data, Global Land Data Assimilation System (GLDAS) represents the regional distribution of surface hydrological cycle element, and also give support to the study of regional scale of hydrological cycle change. Firstly, the four climatic regions are divided the Qinghai-Xizang Plateau and its surrounding arid area, the variation characteristics of temperature and rainfall in each climate zone are analyzed. Then the suitability of temperature and precipitation data of GLDAS four land surface models in 1979-2007 is tested. Lastly the space variation of evaporation and runoff and the change of surface hydrological cycle key elements in different climate zones are discussed. The results show that the average temperature of four climate regions in 2000-2007 and 1979-1994 ranging from 0.65 to 0.97  ℃, and grew obviously. Precipitation changes differently, mean of which in arid and semi-arid area in 2000-2007 is more than 14 mm and 25 mm in 1979-1994. GLDAS temperature and precipitation data have high applicability in the Qinghai-Xizang Plateau and its surrounding arid area in 1979-1994. The root-mean-square error beteen GLDAS temperature data and Chinese surface grid temperature data in extreme arid area is only 0.41 ℃. The differences beteen GLDAS data and APHRODITE precipitation data in four climate region are all less than 0.18 mm·d-1. The water cycle in study area is in dynamic balance during the research period. But the data quality of 2000-2007 has yet to be improved. Runoff and evaporation increasing area grew significantly, and the amplitude have risen sharply, but changing magnitude is uncertain. The change characteristics of hydrological cycle key elements in most areas of Xinjiang Province are consistent with the scientific hypothesis of climatic shift from warm-dry to warm-humid previous proposed. The precipitation of this area is mainly used for evaporation. In the recent years,  the hydrological cycle is strengthened. Multi-year average runoff coefficient are less than 0.2.
  • Study of Characteristic Quantity T* by Large Aperture Scintillometer over Chinese Loess Plateau
  • 2013 Vol. 32 (3): 665-672.  DOI:10.7522/j.issn.1000-0534.2012.00063
  • Abstract ( ) PDF (857KB) ( )
  • Combined with the synchronous data observed by Eddy Covariance system（EC）and gradient tower, the relationship between the characteristic scale of temperature T* and its difference in the process of sensible heat flux measured by Large Aperture Scintillometer（LAS）  and EC and the meteorological elements of surface layer such as wind, potential temperature gradient and stability are analyzed based on the data measured, in the experimental field of  Dingxi  over the Loess Plateau during September 2009. The results show that there is a very good correlation between T*LAS measured by LAS and T*EC measured by EC on the underlying surface over Loess Plateau with the correlation coefficient up to 0.955 and the fitting linear trend coefficient is 1.482. The main wind direction is NNE and SE  in September  after  making a wind statistics, the results show that the correlation coefficient is 0.960 and the fitting linear trend coefficient is 1.349 in NNE wind direction while in SE wind direction the correlation coefficient is 0.968 and the fitting linear trend coefficient is 1.619, which indicates that the wind direction has a significant influence on T*. There is a good linear correlation between potential temperature gradient and T*, but the correlation between T*LAS and potential temperature gradient is better than that between T*EC and potential temperature gradient. The ratio of T* measured by LAS and EC decreases when stability z/L is smaller than 1.5, when stability z/L is greater than 1.5, the ratio of T* tends to increasing along with z/L increasing. The variation range of T*LAS/T*EC gradually becomes smaller along with z/L increasing, and begins to keep the smaller range when z/L increases to 4.
  • Trend and Estimation of Photo-Synthetically Active Radiation at Lhasa Station
  • 2013 Vol. 32 (3): 682-688.  DOI:10.7522/j.issn.1000-0534.2012.00064
  • Abstract ( ) PDF (806KB) ( )
  • The characteristics of photo-synthetically active radiation (Qp) at Lhasa station in the Qinghai-Xizang Plateau were analyzed based on long-term insitu measurements of surface radiation data from Chinese Ecosystem Research Network. The observation data from 2005-2010 are used to investigate the temporal variability of Qp. The results indicate that Qp shows the similar seasonal and diurnal features as those observed for broadband global radiation（Rs）. The annual mean of the daily values of Rs and Qp are 20.2 MJ·m-2 and 37.2 mol·m-2. The high values of Rs and Qp both appeared in June and the low values appeared in January. Their maximum and minimum values are 25.4 MJ·m-2 and 14.0 MJ·m-2， 48.7 mol·m-2 and 25.2 mol·m-2, respectively. The analysis of the hourly values also revealed a diurnal pattern, with higher values around noon and lower values around sunrise and sunset. The Qp fraction （Qp/Rs） ranged from 1.3 mol·MJ-1(in winter)~3.2 mol·MJ-1(in summer) with an annual mean value of 1\^89 mol·MJ-1. The seasonal variation between summer and winter is more obvious. The seasonal Qp/Rs value in winter is 10\^6% lower than that in summer. The hourly values also revealed a diurnal variation with high value around sunrise and sunset, low value around noon. Both Rs and Qp present the trend of diminishing. Then, an all-weather estimation equation was established based on analyzing the temporal variability of Qp and its dependence on the clearness index and solar zenith angle. The relative deviation is about 4\^49%.
  • Evaluation on Nonhydrostatic Three-Dimensional Variational Data Assimilation Scheme of GRAPES-MESO Model
  • 2013 Vol. 32 (3): 689-706.  DOI:10.7522/j.issn.1000-0534.2012.00065
  • Abstract ( ) PDF (2463KB) ( )
  • With the mesoscale operational numerical model GRAPES-MESO V3.0 from  National Meteorological Center of China Meteorological Administration and 12 h T213 forecasts as background field, two numerical experiments with (Exp. 3DVAR) and without (Exp. CNTL) assimilating radio-soundings using the nonhydrostatics GRAPES-3DVAR are conducted  from June to August 2009 to investigate the performance of GRAPES-3DVAR. The statistical verifications of precipitation, geopotential height, temperature, wind and relative humidity and typical weather events are conducted. The results indicate that: (1) The root mean square errors of initial temperature, geopotential height, relative humidity and wind field on 850, 700 and 500 hPa in Exp. 3DVAR are morer than that of in Exp. CNTL, except for 700 hPa relative humidity. Exp. 3DVAR has a significant negative contribution to initial temperature, geopotential height and relative humidity on 500 hPa. And Exp. 3DVAR has an obvious negative contribution to 500 hPa wind forecast with forecasting time going on. (2) As to the area mean of whole model domain, TS scores at different orders in 0～24 h and 12～36 h rainfall forecasts in Exp. 3DVAR are mostly less than that of in Exp. CNTL. (3) The coverage of light rain and moderate rain forecasted by Exp. CNTL are close to the observation, while that of heavy rain, torrential rain, heavy torrential rain are less than that of the observation. Moreover, with the increase of rainfall, the changing small degree of forecast range is more than the observation. The forecast area of rainfall at different orders in Exp. 3DVAR are worse than that of in Exp. CNTL, especially for those above moderate rain. (4) The distribution, evolution and intensity variations of rain region in Exp. CNTL are better than that of Exp. 3DVAR. (5) The daily evolution, peak and valley values of the simulated average rainfall rate in the mid-lower reaches of Yangtze River, South China, North China, Northeast China, east of Southwest China and East China, can be almost simulated in Exp. CNTL, but the average rain rate is weaker than the observation. The forecast of Exp. 3DVAR is similar to that of Exp. CNTL, but the rainfall is weaker than in Exp. CNTL. Accordingly, the difference between Exp. 3DVAR and the observation is increased. (6) Rainfall forecasts in Exp. CNTL and 3DVAR are both in a good consistency with the observation, with the former is a little better than the latter. For rainfall more (lower) than 1.5 mm·d-1, the two experiments tend to forecast more (less) rainfall than the observation, respectively. The forecasts of two experiments are nearly in a same level for rainfall lower than 1.5 mm·d-1. However, Exp. CNTL gives a better forecast than Exp. 3DVAR for rainfall above 1\^5 mm·d-1. (7) In the period of June to August 2009, the daily rain band location and rainfall intensity in Exp. CNTL are well forecasted and nearly close to the observation. This experiment gives a good simulation for the rainfall produced by different weather systems, such as westerly trough, typhoon, low vortex, wind shear and local system. The results of Exp. 3DVAR are roughly similar to that of Exp. CNTL, but its simulated rainfall intensity is generally weaker than that in Exp. CNTL.
  • Case Analysis on Heavy Rainstorm Caused Southwest Vortex under the Influence of Long-Distance Typhoon
  • 2013 Vol. 32 (3): 718-727.  DOI:10.7522/j.issn.1000-0534.2012.00067
  • Abstract ( ) PDF (1638KB) ( )
  • The features of water vapor transport and enthalpy with the influence of the long-distance typhoon were studied based on the observation station data and NCEP/NCAR reanalysis data in Sichuan and Chongqing from 2 to 5 August 2009. The mesoscale characteristics of rainstorm system-southwest vortex affected by  typhoon ‘Swan’ were investigated with 25 points smoothing operator. The results show that the heavy rainstorm is due to favorable atmospheric circulation background. The upper trough moving eastward couples the maintaining southeast vortex system with the influence of  typhoon ‘Swan’ . The long distance in  typhoon ‘Swan’  makes southwest vortex maintaining in Sichuan and Chongqing. The inverted trough of  typhoon ‘Swan’  is significant for warm and humid structures of vortex system. The moisture and energy driven by the typhoon trough easterly flow converge with the warm water vapor transported moisture and energy by southeast warm airflow, which built the moisture and energy channel that transported moisture and energy to low system neighborhood and enhanced accumulation effect in heavy rainstorm area. The accumulated effect contribute to the maintenance of low vortex system physical structure. The easterly airflow at the top of the inverted trough plays a positive role in promoting maintaining of the low vortex system dynamic structure, which enhanced positive vorticity at the middle and low level of vortex system and further promoted the vertical vorticity increasing. The maintained low vortex system leads to the occurrence of prolonged heavy precipitation ultimately.
  • Analysis on Enviroment of Meso-β-Scale System of Continuous Heavy Rainstorm over the Middle Reach of Yangtze River during Meiyu Period in 2010
  • 2013 Vol. 32 (3): 750-761.  DOI:10.7522/j.issn.1000-0534.2012.00070.
  • Abstract ( ) PDF (2091KB) ( )
  • A continuous  rainstorm in the middle reaches of the Yangtze River during 8 to 14 July, 2010 is analyzed using the conventional data, intensive surface and radiosonde observation data, the Black Body Temperature  (TBB) data from infrared satellite, radar echo data and NCEP reanalysis data. The results show that the subtropical high ridge are stably maintained between 23°N and 24°N, 500 hPa  trough over the western Lake Baikal has small fluctuation to mid-latitudes eastward, cold and warm air intersection in  the middle reach of the Yangtze River and low value system on the east side of the Qinghai-Xizang Plateau eastward that provide a favorable environmental conditions for the occurrence and continuance of rainstorm. The diurnal variation of southerly wind during Meiyu period causes the periodicity and diurnal variation characteristics of precipitation. MCSs are the direct influence systems of precipitation. From 8 to 14 July, there are many MCSs corresponding to the mesoscale convergence line,  mesoscale vortex, and convergence zone of airflow confluence center on the ground surface wind flied. Before the heavy precipitation occurred, the atmospheric stratification is potential instability, which provids the instability energy for the precipitation occurrence. Nearly heavy precipitation occurring, the atmospheric stratification appears a deep humid neutral stratification. When the heavy precipitation is about to terminate, the atmospheric stratification is convert to weak stability, and vapor in air column decreases. The above mentioned characteristics of the atmospheric stratification are certainly significant for precipitation prediction. During a continuous rainstorm, the obvious front and strong prefrontal ascending motion are very benefit to the generation and development of mesoscale convective system. The frontogenesis near front has close relationship with the generation and development of heavy precipitation. The calculated result of frontogenesis function shows that the horizontal deformation gives the biggest contribution to frontogenesis.
  • Estimation of Precipitation in Two Climate Change Scenarios in China Using a Statistical Downscaling Approach
  • 2013 Vol. 32 (3): 778-786.  DOI:10.7522/j.issn.1000-0534.2012.00072
  • Abstract ( ) PDF (1292KB) ( )
  • The  monthly rainfall data at 16 stations in China and 500 hPa geopotential height derived from GFDL-CM2.1 model were used to construct a statistical downscaling model. The precipitation China for 2011-2100  are predicted through this downscaling model. The impossible influence of the CO2 concentration variation on the precipitation in the future of China are analyzed. The results show that the precipitation of all regions  and all seasons in China change in SRES A1B and SRES A2. The distribution of precipitation variation in SRES A1B are similar with that in SRES A2. However,  the amplitudes of precipitation variation in SRES A2 are larger than that in SRES A1B, because the CO2 concentration in SRES A2 is higher than that in SRES A1B. The increase of  CO2 concentration is the key factor contributing to the precipitation variation in China. Though the increase of  CO2 concentration could not change the distribution of  precipitation fundamentally,  which intensify the natural variation amplitude of the climatic variables. It is the amplifier of the climatic nature variation. The variation of  precipitation lags  the variation of CO2 concentration about 20～30 years. The higher temperature result from the increase of the CO2 concentration leads to the lift of 500 hPa isobaric layer and the variation of atmospheric circulation, which further exerts impacts on the variation of  precipitation  in the future.
  • Temporal and Spatial Characteristics of August Precipitation in North China and Its Causes in Last 50 Years
  • 2013 Vol. 32 (3): 787-797.  DOI:10.7522/j.issn.1000-0534.2012.00073
  • Abstract ( ) PDF (1581KB) ( )
  • Based on the precipitation data at 53 stations in North China of every August from 1958 to 2007 and monthly average reanalysis data from NCEP/NCAR in the same period, using the EOF and REOF statistical method, Pearson correlation coefficient analysis, statistical test of Mann-Kendall method and wavelet analysis, etc, spatial distribution characteristic of climate anomaly in August of nearly 50 years in North China, evolution of precipitation trend, and comparative analysis of 500 hPa average geopotential height field, 850 hPa vector wind and water vapor flux between more and less rain years,  were analyzed. The results show that: The first three characteristic vector fields of EOF analysis for August precipitation in North China are good enough to reflect the spatial distribution of precipitation anomaly, to be specific, consistent as a whole, disparate into the south and the north, or the east and the west. The former six REOF rotated spatial patterns that the distribution characteristics of August precipitation anomaly in subregions of North China. As to the temporal change trend, August precipitation in North China has a decreasing trend, 1986 is the year of August precipitation in the wet period  transition to the dry period; for the past 10 years August precipitation in North China as compared to the 1950s reduced by nearly a third; the precipitation trends of subregions in nearly 50 years are inconsistent, the southern part of North China does not change significantly, southeast area have humidifying trend, northwest and northeast areas of warming and drying trend are most obvious, to the whole North China in August the climatic change on main contribution. In addition, the western Pacific subtropical high and August precipitation in North China have close relations. When the western Pacific subtropical high intensity on the strong side and the location is shifting northward and westward, is conducive to the formation of the  west low east high' types on 500 hPa, while the lower troposphere, the southerly airstream strong development will be a lot of water vapor transported northward, resulting in above normal precipitation in North China; when the subtropical high intensity on the weak side and the location is shifting eastward, resulting the low precipitation in North China. Furthermore, drought trend in North China mainly due to the 500 hPa circulation around 1986 having significant adjustment and maintain.
  • Analyses on Triggered MCC Evolution Process and Structural Characteristic in a Heavy Rainstorm in Guangxi
  • 2013 Vol. 32 (3): 806-817.  DOI:10.7522/j.issn.1000-0534.2012.00074
  • Abstract ( ) PDF (2144KB) ( )
  • Using the CINRAD-SA Doppler radar data， Micaps conventional weather chart， NCEP data， and FY-2C satellite products， a heavy rainstorm produced by mesoscale convective complex in Guangxi in early June 2010 is analyzed. The results show that:  (1) The predominate influencing system of this case is 850 hPa vortex and shear line, 500 hPa plateau trough and surface stationary front. The stronger energy front, obvious convective unstable stratification on middle and lower levels, and the upper-level θse being downward extension and showing funnel-shaped distribution, and apparent moisture front are the favorable weather model of mesoscale convective system, and high CAPE, lower free convection height, high humidity on lower level, high vertical wind shear are favorable to the occurrence and development of heavy precipitation supercell. (2) The MCS cloud of mesoscale convective system slowly moving southeast from western Guizhou to Hechi and the northwestward MCS cloud in southeastern Guangxi combines  in Central Guangxi to develop the mesoscale convective complex, which slowly moves eastward after the long time stagnation, the southward is the main cloud image characteristics in the heavy rainstorm process. (3) Radar data analysis shows that a wide range of laminated hybrid rainfall echo range is formed in central and western regions of Guangxi during the rainstorm process，  which have a lot of convective storm development on inflow side of strong echo belt, and strong echo belt that is stability and few changes of long-time and post-train are important reason to produce heavy rainfall and strong lightning in the central and western regions of Guangxi. The heavy precipitation supercell storm in Laibin is low-quality mind convective system. At the development stage, the storm shows a supercell storm hook echo structure, and contains a low-level weak echo  and associated front ‘V’ notch echo, and a weak mesoscale cyclone in the corresponding radial velocity image; at the strong phase, the storm is wavy, reflectivity factor from low to high inflow to the lower slope,  being ‘V’ notch echo on the right front and left rear side， the lower inflow side in the front ‘V’ notch echo of the storm, and it is a medium strength and well-developed mesoscale cyclone in the corresponding radial velocity image, being strong sinking inflow in the back of the storm.
  • Analysis on Spatial Structure of Mesoscale Cloud Cluster in Heavy Rainstorm Process off the West Coast Belt of Bohai Sea
  • 2013 Vol. 32 (3): 818-828.  DOI:10.7522/j.issn.1000-0534.2012.00075
  • Abstract ( ) PDF (2213KB) ( )
  • Using the FY-2E satellite and CloudSat, Doppler radar and T639L60 model data, as well as lightning and the synchronous precipitation data, the time and space distributions of the mesoscale cloud clusters are analyzed off  the west coast belt of Bohai Sea during three rainstorm  on July 19, on August 4, and on August 21, 2010. Some conclusions are obtained, for instance, many of meso-β scale and meso-γ scale cloud clusters can be found in infrared image and in water vapor image overlapping with rainfall in 6 h, and they moved along the steering airflow direction at 50~60 km·h-1  on the western edge of the 5 880 dagpm of the subtropical anticyclone，  the temperature of black body is from -96 to -115 ℃ in the rainstorm process. The vortex nephsystem is connected to the mesoscale vortex in the low-level wind field, the banded clouds related to mesoscale shear line in the low layer. The synchronous inversion of radar echo that the alternate change of meso- β scale convective cloud clusters between the strong and weak is from 3 to 6 h. The spatial structure of meso-β scale and meso-γ scale are always changed mutually，  the convergent region of lower-level wind field in specific environments will create new rainstorm clusters. The peak value of lightning frequency and rainfall period is consistent， the merger of medium and small scale rain cluster and low-layer convergence is one of the causes for short-term rainfall.
  • Numerically Test of Influence of Incorporation of TOPMODEL into Land Surface Model SSiB on Hydrological Simulation at Basin Scale
  • 2013 Vol. 32 (3): 829-838.  DOI:10.7522/j.issn.1000-0534.2012.00076
  • Abstract ( ) PDF (1105KB) ( )
  • In order to examine and analyze the effects of integration of land surface model SSiB with TOPMODEL on hydrological simulations, the coupled model (hereinafter SSiBT) which partitions the catchment into saturated and unsaturated zones is used to conduct hydrological simulations at basin scale using data from the Qingyijiang basin. By assessing SSiBT outputs against original SSiB outputs and using observational data sets of daily runoff and water balance of the basin the responses of hydrological simulations to incorporation of TOPMODEL into original SSiB are analyzed and the reasons for such responses are investigated. The study shows that comparing with the results from original SSiB simulations, the coupled model SSiBT predicts more strong vertical changes in soil wetness, higher soil wetness and evaporation and lower total runoff. The study also indicates that original SSiB produces unrealistic partition of runoff between surface runoff and baseflow. When the soil saturated hydraulic conductivity at surface is taken a small value it produces more unrealistic surface runoff and flood discharge while it produces more unrealistic baseflow and much lower flood discharge when the soil saturated hydraulic conductivity at surface is taken a large value. The study also shows that even if the value of soil saturated hydraulic conductivity at surface is so large that there is no overland flow, SSiBT still produces high enough flood runoff during the flood period. Because SSiBT can represent saturated area in the basin resulting from horizontally variations of soil moisture due to topography, it improves simulations of flood runoff during raining season.
  • Analysis on Weakening Process of Convective System Passing over Poyang Lake in Summer
  • 2013 Vol. 32 (3): 865-873.  DOI:10.7522/j.issn.1000-0534.2012.00080
  • Abstract ( ) PDF (1204KB) ( )
  • Using NCEP FNL analysis data and Doppler radar composition reflectivity data of Nanchang, the convection systems passing over Poyang Lake in summer was analyzed. The results show that the convections generated over Mufu Mountains, which is located in northwest Jiangxi, weaken or dissipate during 10:00-16:00 on 23 July 2007 when they pass over Poyang Lake. Based on the double nested WRF V3.2 model, CTR (control experiment which includes Poyang Lake in the second nest) and SES (sensitive experiment which does not include Poyang lake in the second nest) experiments are performed to simulate this process. The simulated results show that CTR experiment could successfully simulate the weakened process of convection activities passing over Poyang Lake. Comparing with the results of CTR experiment, the outgoing long wave radiation (OLR) value simulated by SES experiment is significant larger over Poyang Lake, it means that the Poyang Lake could weaken the convection activities. The difference of surface specific heat capacity between the two experiments results in smaller (larger) sensitive heat flux and latent heat flux in CTR (SES) experiment over Poyang Lake, which brings a significant difference of wind field at low level (950 hPa) between two experiments,  there is an anti-cyclonical circulation of the anomaly wind field (CTR minus SES) over Poyang Lake, the divergence and subsidence processes associated with the anti-cyclonical circulation eventually cause the weakening of convection activities passing over Poyang Lake.
  • Numerical Simulation of the Effect of Microphysical Process of Thunderstorm on Electrical Activity
  • 2013 Vol. 32 (3): 884-893.  DOI:10.7522/j.issn.1000-0534.2012.00082
  • Abstract ( ) PDF (999KB) ( )
  • The one-dimensional time-varying model of thundercloud electrificationhas been used for the simulating two thunderstorm processes using the primarily observations of CCOPE and STEPS, and discussing the effect of pellet flux, surface temperature and reversal temperature on electrical process of thundercloudfrom sensitivity test. In the model, Fletcher and Hallett-Mossop glaciation mechanisms havebeen adoptedas the ice glaciation mechanismof crystal. The numerical simulation results show that, the site of the vertical field extremes in the results simulated by using the radiosonde observation data of CCOPE and STEPS has good consistency with surveyed results, but the simulated extremes are larger thansurveyed extremes. Sensitivity tests results show that,with pellet flux increasing, the time of the first lightning flash will be decreased, the lightning flash frequency will be increased. With the surface temperature increasing, the vertical thickness of negative charge will be decreased, the biggest density of positive and negative chargeswill be increased. When the reversal temperature is lower, the range of negative charge carried by ice crystal is larger. In the model, when the surface temperature is 32 ℃ and the reversal temperature is lower than -26 ℃, there will be a reversed-polarity charge structure in the thundercloud. The model can simulate the charge structure and spatial-temporal distributions of electric fieldintuitively.

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