Climatological And Anomalous Characteristics Of Hadley Cell: Further Investigation And Preliminary Exploration Of Application

This paper demonstrates the rationality of the mass stream function(MSF) for describing Hadley circulation(H.C.).Climate state of two H.C.from ERA-40 and NCEP/NCAR reanalysis dataset are compared.Climate and anomalous state of global H.C.,as well as regional H.C.in the East Asian monsoon region and the East Pacific, and their link with ENSO events and climate anomalies in China are investigated.By the following major conclusions:1) By comparing the vertical air mass flux intensity derived from global (regional) zonally averaged air mass stream function and the actual vertical air mass flux intensity calculated by vertical velocity on the meridian plane,we demonstrated that climatological global(regional) H.C.is the main part of actual vertical transportation on the tropical meridian plane.2) Through comparing the latitudes of minimum variables of climatological OLR with the latitudes of ascending branch center derived from ERA40 data as well as NCEP/NCAR data,it is verified that using ERA40 data for H.C.analysis is more reasonable than NCEP/NCAR data.3) The time-evolving intensity of the ascending branch of global H.C.ψ.has positive relationship with PC1.And their inter-annual variations are significantly positive related to ENSO.During the E1 Nino events,an anomalous meridional circulation is centered in the vicinity of the tropics,which makes the center of the winter hemisphere and the ascending branch more intense and move toward the Tropics.And the anomalous meridional circulation is triggered by the positive anomalous forcing of zonally averaged SST'(φ) profile appeared in the vicinity of the tropics during the E1 Nino events.4) Features of H.C.in the East Asian monsoon region(EA),the East Pacific region(EP) and global differ outstandingly from each other.The active region of H.C. in EA is wider which is basically between 40°S and 40°N.Moreover,it stretches to the north of 60°N in July.And the ascending branch of H.C.is wide and intense in April and July.Comparatively,the active region of H.C.in EP is narrower which is between 20°S and 30°N.The seasonal variation of H.C.in the two regions is different obviously.H.C.has apparent(obscure) seasonal variation in EA(EP).The differences of H.C.in the above regions are related to the thermal contrast of the tropical SST and the land-sea contrast along with the enormous differences of topography. 5) The anomalies of H.C.in the two regions are significantly correlated.During El Nino periods,the intensity of H.C.in EA is weakened while that in EP is strengthened(except in July).This relationship is related to the ENSO events and zonal wind anomalies near the equator.In July,the relationships of anomalous H.C.in EA with that in EP as well as the ENSO events are rather special.6) There are two ascending branches for the EA H.C.in both April and July, which are connected with ITCZ(monsoon trough) and subtropical convergence zone(Mei-yu front) respectively.Therefore anomalous H.C.is closely related with the anomalies of South China Sea monsoon and subtropical monsoon.In spring,the tropical H.C.branch moves northward earlier,the ascending branch in 10～20°N is anomalously strong and the South China Sea monsoon breaks out earlier.In summer, the intense subtropical ascending branch is related with surplus rainfall in the Yangtze-Huaihe River Valley and vice versa.