Climatology and characteristics of stratospheric sudden warmings in the Whole Atmosphere Community Climate Model

Abstract

[1] Major stratospheric sudden warmings (SSW) occurring during Northern Hemisphere winter were identified in four runs of the Whole Atmosphere Community Climate Model (WACCM). Their characteristics are compared to those found by other authors using reanalysis data. The comparison shows that the frequency of occurrence of major SSW in the model is very similar to that found in reanalysis data, as is the occurrence of vortex splitting and displacement events. The main difference with respect to observations is that the modeled SSW are relatively longer lasting. WACCM simulates quite accurately some dynamical features associated with major SSW, despite the presence of outlier cases; however, the recently reported relationship between regional blocking and the type of SSW is only partially reproduced by WACCM. In general, the observed climatological and dynamical signatures of displacement SSW tend to be better reproduced by the model than those associated with splitting SSW. We also find that SSW in the model are often associated with an elevated polar cap stratopause, in agreement with recent observations. However, the simulations also show that there is not in general a close correspondence between major SSW and elevated polar cap stratopause events.

A semi-empirical model for mesospheric and stratospheric NO<sub><i>y</i></sub> produced by energetic particle precipitation

“…de la Torre et al (2012) identified ES events by looking at abrupt increases in the polar cap stratopause height, the latter defined as the altitude between 20 and 100 km where temperature maximizes. We have shown, by analyzing temperature and CO from EMAC simulations nudged to ERA-Interim reanalysis data, that the upper stratospheric meridional temperature gradient, expressed as the difference of 0-30 and 70-90 • N temperature averages at 1 hPa, provides a reliable alternative criterion for detection of strong descent episodes.…”

Stratospheric sudden warming effects on winds and temperature in the middle atmosphere at middle and low latitudes: a study using WACCM

“…This approach to determining gravity wave forcing has been used in analysis of both observations and models (Liu et al, 2009;Chandran et al, 2011). WACCM has been previously shown to reproduce both SSW and elevated stratopause events in long-term climatological simulations with occurrence frequencies close to observations (de la Torre et al, 2012;Chandran et al, 2013a) and hence provides a comprehensive tool for studying the latitudinal response in the mid-atmosphere winds and temperatures.…”

The impact of planetary waves on the latitudinal displacement of sudden stratospheric warmings

“…Most of them are based on model simulations, e.g. carried out with the WACCM model (De La Torre et al, 2012;Limpasuvan et al, 2012) or with the Japanese T213L256GCM (Tomikawa et al, 2012). With WACCM, an enhanced effect of SSW on the circulation at latitudes south of 40 • N has been found in connection with splitting events.…”

“…This mid-latitudinal wind reversal in 2010 was also observed in MF radar winds by Chen et al (2012) over Langfang (39 • N,166 • E). Fritz and Soules (1970) were the first who found temperature anomalies in the tropical stratosphere during the SSW of 1970 with the help of global satellite data. More recently observations of stratospheric and mesospheric tropical anomalies during the winter 2004/05 were made by Shepherd et al (2007).…”