Current Issue

28 February 2006, Volume 25 Issue 1   
  • Analysis on Dry Intrusion in Heavy Rain and Huang-Hai Cyclone
  • YANG Gui-ming;MAO Dong-yan;YAO Xiu-ping
  • 2006 Vol. 25 (1): 16-28. 
  • Abstract ( ) PDF (2648KB) ( )
  • Using the water vapor (WV) image,isentropic flow,potential vorticity (isentropic potential vorticity,moisture potential vorticity) and θse,a heavy rain process during Meiyu period is analyzed to reveal the effect of dry intrusion on heavy rainfall and Huang-Hai cyclone.The main results are as follows: (1) Dark zone in WV image is a good predictor for heavy rain and extratropical cyclone. (2) The development and change of vertical flow overlapped with relative humidity can clearly reflect the relationship between dry intrusion and heavy rain.It is a good predictor for very short-range forecasting.Dry intrusion triggers the heavy rain and the dry zone above middle-level corresponds well with dark zone in WV image. (3) The airflow on 340K and 330K isentropic surfaces indicates the characteristics of dry intrusion in the middle and top of troposphere and Huang-Hai cyclone,respectively.The jet sliding along the ridge on isentropic surface is consistent with the dark zone in WV image.The big value of IPV relates well with the initiation and development of cyclone.It's distribution provides the features of dry intrusion. (4) The temporal and specialcross-section of MPV1 on isobaric surface can reflect the evolution of dry intrusion.Heavy rain occursin the southern 2-latitude when the area of MPV1 greater than 0.4 PVU extends downwards. (5) Dry intrusion can strengthen the rainfall near the cyclone.It is almost the same time for the happening of the heavy rain and the big value of MPV1.This indicates that the effect of dry intrusion on the heavy rain near and far from cyclone is different.Heavy rain often appear in the area of sharp and dense θse.
  • Structure and Causes of "02.6" Extremely Heavy Rain in the Southern Shaanxi Province
  • BI Bao-gui;BAO Yuan-yuan;LI Ze-chun
  • 2006 Vol. 25 (1): 34-44. 
  • Abstract ( ) PDF (1238KB) ( )
  • Using the NCEP reanalysis data,thermal and dynamical structures of heavy rainstorm in the southern Shaanxi province during 8~9 June 2002 (02.6) are analyzed.Results show that the severe precipitation is closely related to the monsoon burst and the intensification of cross-equatorial flow,which bring plentiful water vapor and meet with cold masses at the eastern of northwest China on 8,June causing extremely heavy rain.There is a vertical secondary circulation crossing lower-lever jet whose ascending branch is at the area of heavy rain.The water vapor comes from southerly and easterly flow which converge at the eastern of northwest China with convergence mainly in lower levels and PBL.The high value of the whole-level apparent heat source <Q1> is near the area of heavy rain in the direction of northeasterly-southwesterly agreeable to shear line very well and the condensation latent heat releasing is main heat source with vertical advection item playing key role in Q1 and Q2.The construction of convection instability and conditional symmetry instability results that there is not only deep thermal instability,but also moisture influx and triggering mechanism of thermal instability causing strong torrential rain.
  • The Effect Urban Heat Island on Change of Regional Mean Temperature in Gansu Province,China
  • BAI Hu-zhi;REN Guo-yu;ZHANG Ai-ying;WANG De-min
  • 2006 Vol. 25 (1): 90-94. 
  • Abstract ( ) PDF (226KB) ( )
  • Using the data of monthly mean temperature at 38 stations in Gansu Province,the effect of increased urban heat island magnitude on the regional annual and seasonal mean temperature series as constructed based on the national basic/reference stations and six urban stationsin 1961-2002 was analyzed.It has been found that the trendsof temperature change as calculated using data from national basic/reference and urban stations are generally larger than that of rural stations.The rural stations consist of six "pure" countryside stations across the province.The contributions of increased urban heat island magnitude to the trendsof regional mean temperature change calculated based on data from national basic/reference stations and six urban stations are estimated as being 18.5%,and 37.6%,respectively.It is also interesting to note that,on the basis of national basic/reference stations records,maximum warming rate of the regional seasonal mean temperature occurred in wintertime,and maximum urban warming rate occurred in wintertime,but the largest relative contribution of increased urban heat island magnitude to theregional warming rate was in springtime.