The effect of cloud cover on the Meridional Heat Transport (MHT): lessons from variable rotation experiments

The effect of cloud cover on the Meridional Heat Transport (MHT): lessons from variable rotation... AbstractWe explore the question “what determines the meridional energy transport (MHT)?” by performing a series of rotation-rate experiments with an aquaplanet GCM coupled to a slab ocean. The change of MHT with rotation rate (Ω) falls into two regimes: in a “slow-rotating” regime (Ω < 1/2 modern rotation), MHT decreases with increasing Ω; in a “fast-rotating” regime (Ω ≥ 1/2 modern rotation), MHT is nearly invariant. The two-regime feature of MHT is primarily related to the reduction in tropical clouds and increase in tropical temperature that are associated with the narrowing and weakening of the Hadley Cell with increasing Ω. In the slow-rotating regime, the Hadley Cell contracts and weakens as Ω is increased; the resulting warming causes a local increase in outgoing longwave radiation (OLR) which consequently decreases MHT. In the fast-rotating regime, the Hadley Cell continues to contract as Ω is increased, resulting in a decrease in tropical and subtropical clouds which increases the local absorbed shortwave radiation (ASR) by an amount that almost exactly compensates the local increases in OLR. In the fast-rotating regime, the model heat transport is approximately diffusive, with an effective eddy diffusivity that is consistent with eddy mixing-length theory. The effective eddy diffusivity decreases with increasing Ω. However, this decrease is nearly offset by a strong increase in the meridional gradient of moist static energy and hence results in a near-constancy of MHT. Our results extend previous work on the MHT by highlighting that the spatial patterns of clouds and the factors that influence them are leading controls on MHT. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Climate American Meteorological Society

The effect of cloud cover on the Meridional Heat Transport (MHT): lessons from variable rotation experiments

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Publisher
American Meteorological Society
Copyright
Copyright © American Meteorological Society
ISSN
1520-0442
D.O.I.
10.1175/JCLI-D-16-0745.1
Publisher site
See Article on Publisher Site

Abstract

AbstractWe explore the question “what determines the meridional energy transport (MHT)?” by performing a series of rotation-rate experiments with an aquaplanet GCM coupled to a slab ocean. The change of MHT with rotation rate (Ω) falls into two regimes: in a “slow-rotating” regime (Ω < 1/2 modern rotation), MHT decreases with increasing Ω; in a “fast-rotating” regime (Ω ≥ 1/2 modern rotation), MHT is nearly invariant. The two-regime feature of MHT is primarily related to the reduction in tropical clouds and increase in tropical temperature that are associated with the narrowing and weakening of the Hadley Cell with increasing Ω. In the slow-rotating regime, the Hadley Cell contracts and weakens as Ω is increased; the resulting warming causes a local increase in outgoing longwave radiation (OLR) which consequently decreases MHT. In the fast-rotating regime, the Hadley Cell continues to contract as Ω is increased, resulting in a decrease in tropical and subtropical clouds which increases the local absorbed shortwave radiation (ASR) by an amount that almost exactly compensates the local increases in OLR. In the fast-rotating regime, the model heat transport is approximately diffusive, with an effective eddy diffusivity that is consistent with eddy mixing-length theory. The effective eddy diffusivity decreases with increasing Ω. However, this decrease is nearly offset by a strong increase in the meridional gradient of moist static energy and hence results in a near-constancy of MHT. Our results extend previous work on the MHT by highlighting that the spatial patterns of clouds and the factors that influence them are leading controls on MHT.

Journal

Journal of ClimateAmerican Meteorological Society

Published: Jun 27, 2017

References

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