资源环境科技发展态势分析平台

The influence of El Nino/La Nina on the upper-tropospheric circulation pattern, especially on tropical easterly jet stream (TEJ) over the Asian summer monsoon region, has been studied using ECMWF Reanalysis (ERA) Interim Data for a period of 34 years (1980-2013). The TEJ shows distinctive features during El Nino and La Nina events. The intensity of the TEJ increases and it spreads horizontally and vertically during La Nina years, whereas it weakens and shrinks spatially in El Nino years. Walker circulation over the summer monsoon region shows strong easterlies in La Nina events accompanied with vertically enhanced zonal flow. Lower level (approximate to 850hPa) convergence as well as upper level (approximate to 150hPa) divergence is strong in La Nina events and a westward shift of divergence centre is also observed in these years. A strong (weak) anticyclonic flow at upper levels at about 150hPa is prominent during La Nina (El Nino) years over the Tibetan region causing significant inter-annual variability of the TEJ.