Extratropical forcing of temperature change in tropical tropopause layer of January 2009

Thermodynamic changes in the tropical tropopause layer are investigated in the major stratospheric sudden warming event starting on about 16 January 2009. At the same time, the temperature in the tropical upper stratosphere starts to descend and then cold anomaly propagates downward, while the tropics between 150 and 100 hPa starts to cool from 18 January, prior to 70-hPa temperature drop. We performed thermodynamical and dynamical analyses with ERA-Interim data. It is found that on 18 January tropical ascent dominantly contributes to cool the tropics between 150 and 100 hPa. After that, convergence of the vertical eddy heat flux, which is closely tied with the convection structure, gradually decreases the temperature in the tropical uppermost troposphere. Eliassen-Palm flux and 3-dimensional wave activity flux show on around 18 January waves propagate from Alaska to the tropics of eastern South America and eastern Africa at 100 hPa and dissipate there. In addition, these waves are cogenetic with the planetary waves causing the SSW event. Vertical flow estimated by the external forcings reveals the wave dissipation drives the tropical ascent between 150 and 100 hPa.