A global non-hydrostatic model study of a downward coupling through the tropical tropopause layer during a stratospheric sudden warming

N Eguchi,K Kodera,T Nasuno

doi:10.5194/acp-15-297-2015

Abstract

Abstract. The dynamical coupling process between the stratosphere and troposphere in the tropical tropopause layer (TTL) during a~stratospheric sudden warming (SSW) in boreal winter was investigated using simulation data from a global non-hydrostatic model (NICAM) that does not use cumulus parameterization. The model reproduced well the observed tropical tropospheric changes during the SSW, including the enhancement of convective activity following the amplification of planetary waves. Deep convective activity was enhanced in the latitude zone 20–10° S, in particular over the southwest Pacific and southwest Indian Ocean. Although the upwelling in the TTL was correlated with that in the stratosphere, the temperature tendency in the TTL changed little due to a compensation by diabatic heating originating from cloud formation. This result suggests that the stratospheric meridional circulation affects cloud formation in the TTL.

Highlights

There have been many studies on the interaction between the stratosphere and troposphere in the tropical tropopause layer, which is typically located at 14– 19 km altitude or 150–90 hPa (Highwood and Hoskins, 1998; Fueglistaler et al, 2009), with stratospheric water vapour variation on interannual and seasonal timescales being an important topic
The results showed similar effects in the tropics to those seen in observational studies; that is, the tropical convective activity was enhanced zonally, especially in the Southern Hemisphere (SH), and cooling at the tropopause region associated with the stratospheric sudden warming (SSW) event was capable of modulating tropical convective activity
The present study investigates stratospheric dynamical impacts on the tropical tropospheric convection during an SSW event from the view point of thermodynamic balance in the tropical tropopause layer (TTL)

Summary

Introduction

There have been many studies on the interaction between the stratosphere and troposphere in the tropical tropopause layer (hereafter, TTL), which is typically located at 14– 19 km altitude or 150–90 hPa (Highwood and Hoskins, 1998; Fueglistaler et al, 2009), with stratospheric water vapour variation on interannual and seasonal timescales (cf. Randel and Jensen, 2013) being an important topic. We focus on changes in the troposphere, especially in the TTL, during a stratospheric sudden warming (hereafter, SSW) event, which drastically modifies the stratospheric circulation (Brewer–Dobson (BD) circulation) in the space of a week because the tropical convection and the general circulation (the Hadley and Walkerwere cells) rapidly changed during the strong SSW events found by some previous observational studies (e.g. Eguchi and Kodera, 2007, 2010; EK10). Because of the short-duration phenomenon, the impact of SSW on the tropical troposphere can be separated from long-term variability such as the Madden–Julian Oscillation (MJO), El Nino–Southern Oscillation (ENSO) or the Quasi-Biennial Oscillation (QBO). It is still not clear how the connection between the stratosphere and troposphere occurs and how it modulates the convective activity during SSW events

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Conclusion