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The response of the lower stratosphere to zonally symmetric thermal and mechanical forcing

Published version
Peer-reviewed

Repository DOI


Change log

Authors

Hitchcock, P 

Abstract

jats:titleAbstract</jats:title> jats:pThe response of the atmosphere to zonally symmetric applied heating and mechanical forcing is considered, allowing for the fact that the response may include a change in the wave force (or “wave drag”). A scaling argument shows that an applied zonally symmetric heating is effective in driving a steady meridional circulation provided that the wave force (required to satisfy angular momentum constraints) is sufficiently sensitive to changes in the mean flow in the sense that the ratio is large, where K is a measure of the sensitivity of the wave force; α, N, and f are the radiative damping rate, buoyancy frequency, and Coriolis parameter, respectively; and and are the horizontal and vertical length scales of the heating, respectively. Furthermore, in the “narrow heating” regime where this ratio is large, the structure of the meridional circulation response is only weakly dependent on the details of the wave force. The scaling arguments are verified by experiments in a dry dynamical circulation model. Consistent with the scaling prediction, the regime does not apply when the width of the imposed heating is increased. The narrow-heating regime is demonstrated to be relevant to the double peak in tropical lower-stratospheric upwelling considered in a companion paper, supporting the hypothesis that this feature is radiatively driven. Similar arguments are applied to show that a narrow zonally symmetric applied mechanical forcing is primarily balanced by a change in wave force. This provides an explanation for the recently identified compensation between resolved and parameterized waves in driving modeled trends in the Brewer–Dobson circulation.</jats:p>

Description

Keywords

37 Earth Sciences, 3708 Oceanography, 3701 Atmospheric Sciences

Journal Title

Journal of the Atmospheric Sciences

Conference Name

Journal ISSN

0022-4928
1520-0469

Volume Title

Publisher

American Meteorological Society
Sponsorship
European Research Council (267760)
The authors thank Amanda Maycock for help with the radiation code and for helpful discussions. AM and PHi acknowledge funding support from the European Research Council through the ACCI project (grant number 267760) lead by John Pyle. PHi also acknowledges support from an NSERC postdoctoral fellowship. The authors are grateful to Stephan Fueglistaler and Tom Flannaghan for conversations that stimulated some of this work. We also thank Robin Hogan, Alessio Bozzo and Irina Sandu from ECMWF for their help with reproducing the longwave heating rates as well as Ulrike Langematz and Markus Kunze for the ozone climatology. We received detailed and helpful comments from three anonymous reviewers that improved this manuscript.