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Control of ITCZ Width by Low‐Level Radiative Heating From Upper‐Level Clouds in Aquaplanet Simulations
Author(s) -
Dixit Vishal,
Geoffroy Olivier,
Sherwood Steven C.
Publication year - 2018
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2018gl078292
Subject(s) - intertropical convergence zone , troposphere , climatology , environmental science , walker circulation , atmospheric sciences , hadley cell , radiative transfer , radiative forcing , geology , meteorology , general circulation model , climate change , precipitation , geography , sea surface temperature , physics , oceanography , quantum mechanics
Atmospheric cloud radiative effects (ACRE) narrow the Intertropical Convergence Zones (ITCZs) in climate models. Some studies have attributed this to the upper tropospheric heating by deep clouds. We report two types of idealized aquaplanet experiments, one where ACRE in specific altitude ranges is removed and another where the ACRE associated with clouds in specific altitude ranges is removed. Lower tropospheric heating due to upper tropospheric clouds in the deep tropics exerts the greatest impact on the ITCZ width and meridional overturning, even though the heating is weaker than in the upper troposphere. It is argued that this is because radiatively driven changes in the shallow circulation drive a feedback via net import of MSE and make the ITCZ more unstable in its core, thereby forcing the ITCZ to contract. The radiative effects of clouds in the subsiding subtropics are found to be of secondary importance in driving the necessary circulation changes.