Tropical cooling in the case of stratospheric sudden warming in January 2009: focus on the tropical tropopause layer 1Graduate School of Environmental Science, Hokkaido University, Sapporo, Japan
05 Jul 2011
2Morioka Meteorological Observatory, Morioka, Japan
3Faculty of Environmental Earth Science, Hokkaido University, Sapporo, Japan
Received: 06 Jan 2011 – Published in Atmos. Chem. Phys. Discuss.: 21 Jan 2011 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.
Revised: 09 Jun 2011 – Accepted: 18 Jun 2011 – Published: 05 Jul 2011
Citation: Yoshida, K. and Yamazaki, K.: Tropical cooling in the case of stratospheric sudden warming in January 2009: focus on the tropical tropopause layer, Atmos. Chem. Phys., 11, 6325-6336, doi:10.5194/acp-11-6325-2011, 2011.