A climatology of the stratopause in WACCM and the zonally asymmetric elevated stratopause

Abstract

A climatology of the stratopause is produced using a 40 year simulation of the Whole Atmosphere Community Climate Model (WACCM). Anomalies in polar winter stratopause temperature and height are interpreted with respect to the location of the polar vortices and anticyclones. The WACCM climatology is compared to an 8 year climatology based on Microwave Limb Sounder (MLS) observations and data from the Goddard Earth Observing System (GEOS) version 5 from August 2004 to July 2012. The WACCM climatology is in excellent agreement with observations, except in the Antarctic vortex where the WACCM stratopause is ~10K warmer and ~5 km higher than observations. WACCM diabatic heating rates support the hypothesis that ageostrophic vertical motions associated with baroclinic planetary waves are responsible for producing Arctic winter temperature anomalies. The area of the winter polar vortices in WACCM at the stratopause is 30% smaller in the NH and 45% smaller in the SH compared to GEOS. The long WACCM record allows us to explore the geographical distribution and temporal evolution of a composite of 15 elevated stratopause (ES) events. This composite is in good agreement with the 2012 ES event observed by MLS, though December ES events in WACCM are not observed by MLS. This is the first work to show that ES events are not zonally symmetric. In the 30 days following ES events, the ES composite shows that the stratopause altitude is highest over the Canadian Arctic, and the highest stratopause temperatures occur 90° to the east over the Norwegian Sea.