A climatology of elevated stratopause events in the whole atmosphere community climate model

Abstract

Elevated stratopause (ES) events occurring during Northern Hemisphere winter are identified in four climate simulations of the period 1953–2005 made with the Whole Atmosphere Community Climate Model (WACCM). We find 68 ES events in 212 winters. These events are found in winters when the middle atmosphere is disturbed and there are zonal wind reversals in the stratosphere at high latitudes. These disturbances can be associated with both major and minor stratospheric sudden warming events (SSWs). The ES events occur under conditions where the stratospheric jet, the gravity wave forcing, and the residual circulation remain reversed longer than in those winters where an SSW occurs without an ES. We compare ES events with the type of SSW (vortex splitting and vortex displacement) and find that 68% of ES events form after vortex splitting events. We also present a climatology of ES events based on NASA's Modern‐Era Retrospective Analysis for Research and Applications reanalysis data from 1979 to 2012 and compare it to the model results. WACCM composites of major SSW and ES also show enhanced Eliassen‐Palm flux divergences in the upper mesosphere after the stratospheric warming, immediately before the formation of an ES. However, the formation of an ES in WACCM is due primarily to adiabatic heating from gravity wave‐driven downwelling, which follows the reestablishment of the eastward jet in the upper stratosphere. We find nine winters where an ES forms in the absence of any significant planetary wave activity in the upper mesosphere and illustrate one such event.

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

“…It should be noted that observations at single site locations during specific winters do not always show the MLT westward wind (e.g., Hoffman et al, 2007;Matthias et al, 2013). The westward MLT wind reversal shown in WACCM climatology, however, agrees with climatological observations at 40 • N shown in Yuan et al (2008) and with zonal-mean winds shown in SSW studies using reanalysis data from MERRA (Chandran et al, 2013a) and ECMWF (Salmi et al, 2011). The radar do not usually report winds above 90 km and hence might not detect the westward MLT wind reversal.…”

“…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.…”

“…1 show the T , U and V composites of major SSW events between 1988 and 2010. To detect major SSW events, we have used the algorithm of de la Torre et al (2012) and Chandran et al (2013a). Ten major SSWs between December and February during the period 1988-2010 have been detected using this algorithm.…”

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

“…7), the detection of ES events needs to be performed online. An obvious quantity for the detection would be the stratopause height derived from zonally averaged polar temperatures as suggested by de la Torre et al (2012) and Chandran et al (2013). However, the unequivocal detection of ES events from the polar zonal mean temperature profile suffers from short-term excursions of the stratopause height that result from transient wave forcing.…”

Persistence of upper stratospheric wintertime tracer variability into the Arctic spring and summer

“…These so-called extended SSWs are characterized by elevated stratopauses which reform near and above 80 km Manney et al, 2009). During the recovery phase of these extended events, the anomalous zonal wind flow alters the gravity wave propagation to the mesosphere, thus perturbing the mean meridional circulation and driving a dramatic de-7958 D. E. Siskind et al: Summer stratospheric CH 4 scent of mesospheric air down to the stratosphere (Siskind et al, 2010;Chandran et al, 2013). For example, (Bailey et al, 2014) have shown that mesospheric air enhanced in nitric oxide (NO) and depleted in water vapor (H 2 O) and methane (CH 4 ) can descend from near 90 km in early February down to 40 km by early April.…”