Abstract
Abstract. Temperature changes in the tropics, especially in the tropical tropopause layer, are investigated at the time of a major stratospheric sudden warming (SSW) event that started on about 16 January 2009. During the SSW, the temperature in the tropical upper stratosphere declined and the cold anomaly propagated downward, while the tropics between 150 and 100 hPa started to cool from 18 January, prior to a temperature drop at 70 hPa. We performed thermodynamical and dynamical analyses with ERA-Interim data. During the SSW event, the tropical stratosphere was cooled by upwelling, and the upwelling was induced by wave forcing in the northern extratropical stratosphere. However, the stratospheric wave forcing generated only weak upwelling in the tropics below 100 hPa. During the cooling period at around 18 January, tropical ascent was the main contributor to cooling of the tropics between 150 and 100 hPa. Subsequently, vertical convergence of the vertical heat flux, which is closely tied to the convection structure, resulted in a gradual decrease in temperature within the tropical uppermost troposphere. Waves that had same source region with the upward-propagating waves that caused the SSW event, propagated from Alaska to the tropics of eastern South America and eastern Africa at around 100 hPa, and dissipated in these areas; the associated wave forcing drove the tropical ascent between 150 and 100 hPa.
Highlights
The tropical tropopause layer (TTL; defined here as the tropics between 150 and 70 hPa) is an important region in stratospheric physics and chemistry because of its role as a gateway to the stratosphere
The zonal mean temperature in the TTL is considered to be controlled by wave forcing of the extratropical stratosphere, which is referred to as the “stratospheric pump” (Holton et al, 1995)
Because of the linearity in Eq (15), we can separately estimate the contribution of each external forcing and each forced region to residual mean vertical wind
Summary
The tropical tropopause layer (TTL; defined here as the tropics between 150 and 70 hPa) is an important region in stratospheric physics and chemistry because of its role as a gateway to the stratosphere. The coldness in the TTL, especially in the cold-point tropopause (which is the coldest region in the TTL), controls the large-scale distribution of water vapor in the stratosphere by dehydration of the air entering the stratosphere (Holton and Gettleman, 2001; Hatsushika and Yamazaki, 2003; Fueglistaler et al, 2005). Kerr-Munslow and Norton (2006) suggested that dissipation of quasi-stationary waves in the upper troposphere and lower stratosphere generated by deep convection induces upwelling in the TTL, resulting in a reduction in TTL temperature. Based on this result and model calculations, Norton (2006) reported that seasonally varying tropical Rossby
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