Plateau Meteorology

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28 December 2008, Volume 27 Issue 6   
  • Analyses on Climatic Features and Water Vapour Transportation of Rainy Center in Southeast Corner of Qinghai-Tibetan Plateau in Spring
  • LU Ya-bin;XIE Ming-en;FAN Bo;SUO Miao-qing
  • 2008 Vol. 27 (6): 1189-1194. 
  • Abstract ( ) PDF (778KB) ( )
  • Rainfall data and NCEP/NCAR data of Yunnan and Tibet were used to indicate the fact of "early rainfall season" rainy center in southeast corner of Qinghai-Tibetan Plateau in spring. The fact revealed that the rainfall season of pluvial center lasted for 9 months, and the rainfall amount in spring flood season took 30%~40% of the annual precipitation, and maximum rainfall mainly happened in spring flood season. Diagnostic analysis of vapour flux of all layers of atmosphere was used to research on the water vapour transportation features of rainy center in southeast corner of Qinghai-Tibetan Plateau. The result indicated that there was a high value center of vapour flux existing along the drainage area of Yaluzangbujiang River which located at the downstream of rainy center in southeast corner of Qinghai-Tibetan Plateau. And in the north of Arabia Sea, at the north of Bay of Bengal and the north of India and Myanmar there was also a high value area of vapour flux. Related analysis indicated that the high value area of vapour flux was corresponded well with rainy centers. The water vapour stream revealed that Yaluzangbujiang River, Bay of Bengal, Arabia Sea and west stream at the front of Southern Trough transported water vapour to rainy center and made the rainy center become the "water vapour sink". The far-way water vapour transportation of Yaluzangbujiang River-Brahmaputra River and Arabia sea was also an important water vapour origin which can't be ignored.
  • Turbulent Characteristics of Atmospheric Boundary Layer under Complex Underlying Using Discrete Orthogonal Wavelet Transform
  • LUO Tao;YUAN Ren-min;WU Xiao-qing;DENG Shu-mei
  • 2008 Vol. 27 (6): 1195-1204. 
  • Abstract ( ) PDF (1392KB) ( )
  • It is well known that wavelet transforms have good time-frequency localization, which makes the transforms be especially suitable for analyzing non-stationary signals, like turbulent signals. In this paper, discrete orthogonal wavelet transform is applied to the 35 m tower measured data, and the isotropy coefficient(ISO) and the wavelet power spectrum are computed using the wavelet coefficients, to study the turbulent characteristics of atmospheric boundary layer over complex underlying. ISO could describe the isotropy characteristic of real atmosphere at different scales well. Based on the distribution of ISO, by a threshold of ISO(here, the threshold is 0.7), we obtained the separation scale of isotropy small eddies(names as ISO0.7). The result shows that the underlying characteristics have a large impact on ISO0.7, when wind blows from different underlyings, the mean ISO0.7 scale varies very obvoius. The result also reveals that the turbulent intensity and stability have some impaction too. The study on wavelet power spectrum shows, the high-frequency segment of wavelet power spectrum has a two-segment tendency beside the frequency fms which corresponds to the separation scale: The segment with frequency higher than fms has a scaling exponent(as)close to-5/3, which means, in this smalleddy frequency range, the turbulence is closely isotropic;and the segment with frequency lower than fms, has a scaling exponent(al)deviating from-5/3, which means, in this frequency range, the turbulence is closely anisotropic. And when wind blows from land and the turbulent intensity is weak, the power spectrum evidently has this two-segment-tendency and the al is very close to-1. So it reveals the impaction of underlying. And the different processes of wind direction change have very different impactions.
  • Study on Coastally Trapped Wave
  • LU Xu;HUANG Wei-jian;ZHANG Ming;HE Xi-yu
  • 2008 Vol. 27 (6): 1211-1217. 
  • Abstract ( ) PDF (487KB) ( )
  • Using the linear shallow water wave equations and supposing that the orographic slope was invariable along the mountain range orientation but was variable across it, the coastally trapped waves was researched in the presence of the bottom topographical gradient. The results show that: When the variation of bottom topography is not significant, the structure of coastally trapped wave can be achieved by the perturbation method and the zeroth order approximation leads to classical Kelvin solution, the first order correction is due to the variations within the Rossby deformation radius. It is noted that the first order approximation to the coastally trapped wave is also non-dispersive. When the gradient of the bottom topography is gentle and the height of topography is not big, the coastally trapped waves show the feature of Kelvin wave, the maximum height of perturbed geopotential is found along the coastal barrier;when the gradient of the bottom topography is so steep and the height of topography is big, it shows the feature of modified Kelvin wave, the maximum height is found a little away from the coastal barrier, along the shore is the low value of perturbed geopotential, beyond the shore is the high value of perturbed geopotential. The higher of the bottom topography and the bigger of the bottom topographical gradient, the fiercer of the disturbance profile.
  • Ensemble Forecast Experiment on Precipitation in Summer by CWRF Numeric Model
  • ZENG Ming-jian;LU Wei-song;LIANG Xin-zhong;WANG Xue-liang
  • 2008 Vol. 27 (6): 1218-1228. 
  • Abstract ( ) PDF (2136KB) ( )
  • Using CWRF numeric model developed by ISWS/UIUC with GFS real forecast data which has 4 times per day and 0.5°×0.5° SST real-time analysis data from NCEP as initial and boundary conditions, adopting 8 group different parameterization schemes from microphysics, cumulus convection, boundary layer and radiation parameterization, an ensemble forecast system which has 32 members was established. Also, the time-variation integration forecast scheme and dynamic weight allocation integration forecast scheme were designed. Based on above forecast system, we experimented on 120 hours real time ensemble forecast. The result showed that CWRF model has good forecast ability for precipitation in China. In short term forecast, the ensemble member is more sensitive to cumulus parameterization. Dynamic weight allocation integration forecast scheme which considered forecast errors can reflect model's forecast capacity in different physical parameterizations, location, and forecast period conditions, on the whole, it has better forecast ability than time-variation integration forecast scheme and any ensemble member.
  • Ensemble Forecasting of a Local Short-Lived Severe Precipitation
  • WANG Chen-xi;YAO Jian-qun
  • 2008 Vol. 27 (6): 1229-1239. 
  • Abstract ( ) PDF (2359KB) ( )
  • Based on the operational ensemble forecast system for Shanghai regional precipitation, the ensemble forecasting of a short-lived severe precipition in Shanghai on 23~24 June 2007 is made. The results show that the precipitation is predicted by the ensemble forecast system, but there is error in predicting the occurring time and location. The ensemble probability forecast is more useful and valuable than the ensemble mean forecast. The effects from the model uncertainty, the initial value uncertainty and the lateral boundary uncertainty on precipitation forecast are different. The effect from the model convective parameterization scheme is very large, which maintains large during the entire model integration. The effect from the model PBL parameterization scheme is small. During the early period of model integration, the effect from the lateral boundary uncertainty is small. Later, the effect becomes larger and larger. After some time, this effect is as large as the effect from the model convective parameterization scheme. During the early period of model integration, the effect from the initial value uncertainty is obvious. Later, this effect becomes smaller and smaller. The ensemble forecast which contains three kinds of uncertainty is better than the ensemble forecast which does not contain the lateral boundary uncertainty. The ensemble forecast which contains the model uncertainty and the lateral boundary uncertainty is better than the ensemble forecast which contains three kinds of uncertainty. In the ensemble forecasting which contains the model uncertainty and the lateral boundary uncertainty, the improving initial value can improve the ensemble forecast of precipitation of low threshold, but it can not improve the ensemble forecast of precipitation of high threshold.
  • Principal Oscillation Pattern of QBO in Summer Precipitation of East China
  • JIA Jian-ying;SUN Zhao-bo
  • 2008 Vol. 27 (6): 1240-1248. 
  • Abstract ( ) PDF (1442KB) ( )
  • Using the mean monthly rainfall data at 160 stations in China and NCEP/NCAR reanalysis mean monthly data, the quasi-biennial oscillation(QBO) in summer rainfall of East China is studied by Principal Oscillation Pattern(POP) and Associated Correlated Pattern(ACP) analyses. The POP analysis shows that the first POP represents 18.2% of the variance of the time series with a period about 4 years. The real part of the first POP is a transitional model with significant increscent amplitude in middle of 1950s and early period of 1990s. The QBO feature of the amplitude is remarkable between the mid-late period of 1980s and middle 1990s. The imaginary part of the first POP is a peak model. The positive value covers the east of South China, Yangtze River valley and Yangtze River-Huaihe valley with a higher value center in Yangtze River-Huaihe valley and a lower value center in middle-west of South China. The amplitude of the peak model has noticeable enhanced in mid-late period of 1990s. The transitional model is correspond to anomaly of west Pacific sea surface temperature(SST) while the peak model is to that of the equator central and east Pacific SST through ACP analysis of SST. The associated correlations of 850 hPa wind, equator zonal wind and meridional wind denote that, when the model of summer rainfall QBO in East China is in the transitional state(negative), the convective is stronger(weaker) over west Pacific and anti-cyclone(cyclone) geneses over the South China Sea, while the model is in the peak state(negative), the equatorial Walk cycle is weaker(stronger) and the location of Hardly cycle is further south(north) with the strengthened(weakened) intensity. Anyway, the SST anomaly in middle and east Pacific has close relationship with summer rainfall QBO propagation in East China by ocean-atmosphere interaction and low-middle-high latitude interaction, and the interaction between Southern and Northern Hemisphere circulation needs more study.
  • Soil Moisture over the West of Northwest China and Its Response to Climate
  • WANG Lei;WEN Jun;WEI Zhi-gang;HU Ze-yong;ZHAO Yi-zhou;WEI Rong-qing
  • 2008 Vol. 27 (6): 1257-1266. 
  • Abstract ( ) PDF (1394KB) ( )
  • The characteristics of gravimetric soil moisture vertical distribution, temporal variation and its response to the local climate changeover the west of Northwest China are analyzed. The results indicate that:(1) Monthly variation of soil moisture could be categorized into steady-going type and fluctuant type. The depth-time plots of soil moisture anomalies, signs of the moisture anomalies tested at most of stations are vertically consistent, signs are the reverse of the upper and lower layers in two stations. Yining, Wulanwusu and Nuomuhong stations reveal high vertical gradients of soil moisture variation, where as high vertical gradients are found in Tulufan stations.(2) Soil has been getting dry at most stations since 1990's, abrupt changes are found in two stations, Tulufan, Wulanwusu. The soil-drying trend is mainly controlled by air temperature. The main reason is that a negative feed back mechanism exists between soil moisture and air temperature.(3) There is response between soil moisture and climate. Negative correlation exists generally between soil moisture and temperature. A little of response is found between soil moisture and precipitation.
  • Analyses on the General Circulation Characteristics of Meiyu over the Changjiang-Huaihe Valley
  • MAO Wen-shu;WANG Qian-qian;LI Guo-ping
  • 2008 Vol. 27 (6): 1267-1275. 
  • Abstract ( ) PDF (1499KB) ( )
  • The Meiyu over the Changjiang-Huaihe valley is the important constituent part of summer rain band in China. Based on the onset date, the end date and the precipitation of Meiyu characteristic data over the Changjiang-Huaihe valley from 1954 to 2001 provided by Jiangsu Meteorological Administration, the general circulation characteristic of the Meiyu is studied. The results show that there are significant difference characters of general atmospheric circulation in the corresponding period between the high Meiyu year and low Meiyu year. The motion of subtropical ridge line at 120°E located between 20°~25°N. The precipitation of Meiyu is marked increasing(decreasing) over the Changjiang-Huaihe region, which is responsible for the south Asia high is weaken(amplification) and intensity of polar vortex, subtropical westerly jet, equatorial easterly jet, intensity of subtropical high, water-vapor transfer of the air current spanning the eqator in the Southern Hemisphere and southwest air flow from the subtropical high westerly, the intensity of convergence over the Changjiang-Huaihe, pumping action in the altitude-low level, ascending motion and convective activity are amplification(weaken), and vice versa.
  • Comparison Experiments of Different Resolutions and Physical Parameterization Schemes in Guizhou Precipitation
  • WU Hong-yu;CHEN Jing
  • 2008 Vol. 27 (6): 1295-1306. 
  • Abstract ( ) PDF (1964KB) ( )
  • The numerical simulation experiments are made with same schemes under three kinds of model horizontal resolutions(20, 15 and 10 km) to simulate the two heavy rainstorm processes of Guizhou using the mesoscale model MM5. The numerical simulation experiments use the cumulus parameterization schemes(KUO, GRELL, KAIN-FRITSCH和BETTS-MILLER, as KU, GR, KF and BM), which is combined with MRF and Blackadar boundary layer's parameterization schemes, to simulate 16precipitation cases in Guizhou flood season. Comparisons among the experiments and analyses the observations indicate that the location of rainfall is sensitive to the parameterization schemes. The higher the model resolution is, the closer the simulations of rainfall distributions to the truth are. The circulation characteristics on four various cumulus parameterization schemes, the simulation results are nearly the same. But the simulated rainfall effects are different: When rainfall is smaller than 50 mm, the predicting effect of GR scheme is better and KF scheme is not better;when rainfall is larger than 50 mm, the predicting effect of BM or KF scheme is better. The predicting differences between MRF or Blackadar boundary layer's parameterization schemes is small. Choosing combinational schemes with BM or KF cumulus parameterization, mixed phase explicit moisture schemes, MRF planetary boundary layer parameterization and cloud radiation parameterization are superior to the others for predicting Guizhou rainstorm.
  • Relationship between Water Vapor Transport over East Asia and Drought and Flood in Summer of Chongqing
  • ZHOU Hao;LIU Xiao-ran;CHENG Bing-yan
  • 2008 Vol. 27 (6): 1324-1332. 
  • Abstract ( ) PDF (2605KB) ( )
  • Using the monthly mean reanalysis data(from 1960 to 2006) of the NCEP/NCAR, the relationship between water vapor transport over East Asia and drought and flood in summer of Chongqing is analyzed. The result shows that the distribution of water vapor over East Asia is obvious different in the abnormal years of Chongqing rainfall in summer(July, August). When the rainfall is excessive in summer(July, August) of Chongqing, the circulation pattern of "two blocking" exists in the middle-high latitudes over Eurasian, which includes two blocking highs over Ural and Okhotsk area, respectively and a trough over Baikal. The positive departure of 500 hPa is over tropic of Pacific. The ridge line location of west Pacific subtropical high is south by south and the intensition is stronger. The middle latitudes area is low pressure area. The cool air enter into the middle latitude of China along the back of Baikal trough and south of Ural blocking, while the warm air enter into China along the southwest of west Pacific subtropical high and India and Bay of Bengal. The cool and warm air join near the basin of Yangtse Rive, which makes the flood over Chongqing city and upper-middle reaches of Yangtse Rive. When the rainfall is deficit, there is the circulation pattern of one trough one ridge. The ridge is over Ural, and the Okhotsk blocking high develops stronger to Baikal lake. There is a stronger high pressure ridge over West Europe. The position of west Pacific subtropical high is north by north and east by east. The main part of west Pacific subtropical high retreats from Chinese mainland. The whole of tropic is negative departure area. Ural makes the south wind controlling the middle-high latitudes of East Asia, which makes the cool air move to the south area difficultly. The warm air enters into China along the south of west Pacific subtropical high. This circulation pattern can't make the cool air and warm air joint over Yangtse Rive, then causes drought over Chongqing area.
  • Preliminary Study on Asymmetric Cause of Formation of Precipitation Associated with Typhoon Haitang
  • YUE Cai-jun;SHOU Shao-wen;ZENG Gang;WANG Yong-qing
  • 2008 Vol. 27 (6): 1333-1342. 
  • Abstract ( ) PDF (1783KB) ( )
  • During the land falling Fujian province of typhoon Haitang(No.5 in 2005) i.e., at 08:00 on 19~20 July 2005(Beijing time), the precipitation associated with the typhoon had significantly south-north asymmetric feature. The analysis of hourly MT1R GMS IR1 cloud image showed that typhoon circulation nephsystem appeared south-north asymmetric distributions. The white cloud area bearing a close relation to precipitation lay primarily in the north of typhoon, however, the nephsystem in the south of typhoon was relatively weak with almost no white cloud area occurrence. Based on the successful simulation from WRF model, the analysis of the simulated relative humidity and vertical ascending motion at 700 hPa indicated that the asymmetric feature of the vertical upward motion was identical to the counterpart of precipitation in such a manner that relative humidity in the south and north of typhoon was almost equal. The further diagnostic results based on the revised wet Qvector(Q*), orographic lifting and surface friction(termed as orographic factors) depicted that both the convergence field of Q*vector divergence and the area of vertical ascending motion forced by orographic factors employed south-north asymmetric features. Synthetic consideration indicated that Q*vector(equal to vertical ascending motion), orographic factors and vertical ascending motion are all the primary dynamical factors contributed to genesis of south-north asymmetric characteristic of precipitation associate with typhoon, however, thermodynamic factor(such as relative humidity) is not important(uniform).
  • Analysis on an Exceptionally Strong Wind Gust Event in Beijing
  • LIAO Xiao-nong;YU Xiao-ding;WANG Ying-chun
  • 2008 Vol. 27 (6): 1350-1362. 
  • Abstract ( ) PDF (2852KB) ( )
  • An exceptionally strong wind gust process with maximum wind speed over 32 m·s-1 appearing in Beijing on June 24, 2006 is analysed. The Doppler weather radar data show that the strong wind gust is caused by a bow echo which is a part of a squall-line. The bow echo comes into being correlates with the rear influx jet which leads to the acceleration of southern part of squell-line and then the squall-line combines with the new-generation cells in front of it. The deep meso-cyclone, the convergence at the low level and the divergence at the upper level play an important role in the development of the strong cell making up of the bow echo. Based on the observation of Doppler weather radar, it could be deduced that the strong surface wind is caused directly by the downburst inside. The microwave radiometerand profiler data are used in the analysis of the environmental condition about the instability and the vertical wind shear in the lower troposphere. The great CAPE, moderate vertical wind shear and the perpendicular wind distribution are favorite to the development of the squall line. The increase of DCAPE and the temperature laps rate in the lower troposphere which is almost equal to the dry-adiabat are both indicate the downburst's coming.
  • Contrast Analyses on Variation Characters of Vertically Integrated Liquid Water Content about Hail Cloud Cell and Thundercloud Cell
  • LIU Zhi-guo;YANG Jian-cai;TAO Jian-hong;FU Zhao;LIANG Hai-he
  • 2008 Vol. 27 (6): 1363-1374. 
  • Abstract ( ) PDF (2277KB) ( )
  • Based on the constant altitude plan data of reflectivity factor of CINRAD which is interpolated with 3D-Barnes scheme, VIL(Vertically Integrated Liquid Water Content, VIL) about cell is calculated with its theoretical model, and the maximum of VIL (VILmax)is identified by use of MAX function.With methods of statistic and piecewise function, the variation character of VILmax and its application to identification of hail cloud is detaily analyzed for 32 severe convective cloud cells on the northeast side of Tibetan Plateau during May~August 2004-2005.Results show that VILmax about severe convective cloud cell during variation process is increasing first and decreasing then, there is unimodal distribution in time series of VILmax, "explosive increasing" and "suddenly decreasing" about VILmax are to differentiate an important characteristic of hail cloud cell and thundercloud."explosive increasing" process of VILmax about hail cloud cell appear twice within four data time intervals before the first hail shooting, with no hail shooting on the surface for the first "explosive increasing" and after the hail shooting 1~2 data time intervals companing with the second "explosive increasing", there is nothe first "explosive increasing" for the second hail shooting of same cell, and the hail shooting on the surface stop with "suddenly decreasing". "Positive(negative) peak" of GVILmax(the rate of change about VILmax)is completely correspond to "explosive increasing and suddenly decreasing" of VILmax about hail cloud cell in time, the identification of hail cloud setted GVILmax is greater workable value in operation.
  • Transport Trajectory Classifying of PM10 in Hefei
  • SHI Chun-e;YAO Ye-qing;ZHANG Ping;QIU Ming-yan
  • 2008 Vol. 27 (6): 1383-1391. 
  • Abstract ( ) PDF (1224KB) ( )
  • Cluster analysis was used to categorize the daily 72 h back trajectories of Hefei in each season during 5-year periods from 2001 to 2005. The relationship between PM10 concentration and transport pattern was studied using the results of cluster analysis, together with the daily measurements of PM10. The results show that the average PM10 concentration within clusters from different directions were different evidently. The highest average PM10 concentration corresponded to the northwesterly trajectories in the seasons except for summer. The relative differences between the cluster-mean PM10 concentration of northwesterly clusters and the seasonal average were 44%, 20% and 31% for spring, autumn and winter, respectively. The highest average PM10 concentration in summer corresponded to northeasterly back trajectories, its relative difference from seasonal average is 20%. The cluster-mean PM10 concentration within the local back trajectories were also higher than the seasonal average in all seasons, and the relative differences from seasonal average were 5%, 16%, 18% and 7% for the four seasons from spring to winter. We obtained six clusters of various back trajectories, which were conducive to the accumulation of pollutants in Hefei. By comparison of the six clusters of trajectory, we concluded that the long range transport of PM10 mainly occurred in the free troposphere, and the regional transport mainly occurred in the boundary layer. More than 50% of the atmospheric pollution events were related with long range transport. The PM10 concentration with the quickly moving air mass were not necessary lower than those with slowly moving air mass.
  • Visibility Trends in Beijing,Tianjin and Hebei Province during 1980-2003
  • FAN Yin-Qi;LI Chun-Qiang
  • 2008 Vol. 27 (6): 1392-1400. 
  • Abstract ( ) PDF (1879KB) ( )
  • The patterns and trends of visibility in Beijing, Tianjin and Hebei Province were presented for the period of 1980-2003 by using two statistical methods: Cumulative percentiles and Ridit analysis. Visibility, relative humidity and other related data from 88 surface weather stations were considered. Visibility data were screened for meteorological effects. The results showed that the visibility has declined in most parts of this region in the past 24 years. The most marked decline of visibility was in summer, and the most outstanding visibility decline was occurred in Cangzhou, Langfang, Tianjin, Hengshui and Handan. After 1995, the poorest visibility was in two areas, one was Shijiazhuang, Xingtai and Handan, the other was Langfang, Tianjing and Cangzhou. There has been an obvious improvement of visibility in Beijing since 1995. From2001 to 2003, the tendency of visibility in most parts of this region was still declined, especially in summer and winter, and the poorest visibility was in the non-urban sites located in the southwest part of Hebei Province near Mountain Taihang. In addition, it was founded that a good correlation was existed between the visibility change trends and the energy consumption and the numbers of automobiles variation tendency at the same time by comparing them.
  • A Preliminary Analysis of AOD's Variation Characteristic in Semi-Arid Region of Chinese Loess Plateau
  • ZHANG Yu-jie;ZHANG Wu;CHEN Yan;CHANG Zhuo-lin;SHI Jin-sen
  • 2008 Vol. 27 (6): 1416-1422. 
  • Abstract ( ) PDF (1052KB) ( )
  • The AOD's variation characteristics in semi-arid region of Chinese Loess Plateau are analyzed by using the observed direct solar radiation data during August 2006 to April 2007 gained by the automatic sun tracking spectrophotometer CE-318 of SACOL. The results show that the AOD spectrum distributions in semi-arid region of Chinese Loess Plateau very nearly follow Angstrom's formula. In visible and near-infrared band AOD decreases while wavelength increases. There are three types of diurnal variations, and they are: Single peak type, steady type and rising type. Diurnal variation characteristics of AODshow that the precipitation has wet removal efficiency for aerosol particles and AOD obviously increases while haze appears. Diurnal average of AOD ranges from 0.1 to 0.4, the frequency of maximum AOD value is the highest at 08~11BST, and the frequency of minimum AOD value is the highest at 12~13BST, 14~17BST. The meteorological condition has obvouisly effect on AOD, under south wind AOD is big but under east wind AOD is small, Comparing with clear condition and haze AOD is obvouis big. For same band, the difference of AOD caused by wind direction is smaller than that caused by haze.

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