Geographical distribution and interseasonal variability of tropical deep convection: UARS MLS observations and analyses

Abstract

[1] Tropical deep convection and its dynamical effect on the tropopause and stratosphere are investigated using a suite of data from the Upper Atmospheric Research Satellite (UARS) Microwave Limb Sounder (MLS), including upper tropospheric humidity, cloud radiance, and gravity wave measurements. For this purpose, geographical distributions of temperature, water vapor, and cloudiness in the tropical tropopause layer (TTL) are compared with corresponding maps of gravity wave variance in the stratosphere. In addition, ECMWF global wind divergent and velocity potential fields as well as NOAA outgoing longwave radiation and CMAP rainfall data are analyzed to help pinpoint the locations of deep convection. We found that high-altitude clouds near the bottom of TTL ($147 hPa) are usually surrounded by high-humidity air, and their spatial pattern and seasonal variability are closely associated with regions of vigorous summertime deep convection. Upward propagating gravity waves generated from these convection regions are shifted poleward by prevailing stratospheric winds. We estimate that tropical deep convection lifts $5% of the cloud tops to altitudes above 100 hPa and that most of the extreme deep convection events occur in the Western Pacific and Indian monsoon regions. Lowtemperature regions in the TTL are associated with, but often drift away from, the center of deep convection. Regions of water vapor maxima near the bottom of TTL are located directly above the deep convection centers, but this moisture behavior is somewhat reversed at the top of the TTL. The integrated picture derived from this study implies that convective scale motions could be important in affecting short-term dehydration processes in the TTL. Our results also suggest that the spatial organization and temporal development of tropical convective systems will be better monitored with the follow-on Earth Observing System (EOS) Aura satellite instruments and lead to improved understanding of the complex interaction of tropical convection with largescale dynamic and thermodynamic conditions.

Global distributions of overlapping gravity waves in HIRDLS data

“…This is consistent with previous work, e.g. Jiang et al (2004) and Ern and Preusse (2012). The absolute number of observed Ls waves is not especially low compared to other regions at the same latitude during the other parts of the year (e.g.…”

Global ozone monitoring by occultation of stars: an overview of GOMOS measurements on ENVISAT

“…Various hypothesis for the origin of the observed pattern were discussed (Gurvich et al, 2007) such as the general circulation, forced by solar heating, or a remote consequence of the deep convection. A similar structure was also reported (Jiang et al, 2004) for the temperature variance around 38 km as observed by MLS, suggesting a relation with gravity wave breaking.…”

Satellite observations of middle atmosphere gravity wave absolute momentum flux and of its vertical gradient during recent stratospheric warmings

“…From theoretical considerations, however, refraction of gravity waves into strong wind jets is expected if full 3-D propagation of gravity waves is taken into account (Preusse et al, 2009b;Kalisch et al, 2014). Evidence for this effect from observations has been found, for example, by Jiang et al (2004b), Ern et al (2011 for gravity waves in the summertime subtropics, and by Hindley et al (2015) for mountain waves over South America. First indication of gravity wave meridional propagation for the re-established polar jet during PJO events has been found by Yamashita et al (2013).…”