Hadley Circulations and Penetrative Cumulus Convection

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Abstract
This paper studies how the Hadley circulation is affected by a different treatment of penetrative cumulus convections with the use of the Meteorological Research Institute model (MRI•GCM) under the framework of the Arakawa-Schubert penetrative cumulus parameterization and the aqua planet condition. The present experiments clearly show that a cumulus parameterization adopted in a GCM widely controls low latitude climate.When the occurrence of deep penetrative cumuli is suppressed, precipitation increases at all latitudes with a remarkably concentrated peak at the equator. The Hadley circulation intensifies and shrinks in the latitudinal direction in addition to the decrease of vertical static stability in low latitudes. Similar results are obtained in the experiments with an axially symmetric GCM. Though change of momentum and heat transports by large scale eddies contributes to the shrink of the Hadley circulation, a large scale eddy process is not essential to the circulation's change. The concentrated precipitation around the equator is responsible for the strong Hadley circulation. On the other hand, the narrow Hadley circulation is explained by the change of the mid-latitude precipitation peak.Latitudinal concentration of precipitation around the equator is closely connected with the activity of deep penetrative cumuli. When they are active, they transport water vapor upward from the planetary boundary layer, and the precipitation rate is very close to the local surface evaporation rate. Precipitation is distributed rather broadly in the meridional direction in this case. On the other hand, when deep penetrative cumuli are suppressed, the lower part of the troposphere becomes more humid and the Hadley circulation accumulates water vapor around the equator and maintains a concentrated peak of precipitation there.The suppression of the AS cumuli accompanies the decrease of cumulus friction. The Hadley cell weakens by 15% and shrinks by 2° in the meridional direction through the removal of cumulus friction.