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Forcing of the Upper-Tropospheric Monsoon Anticyclones

Forcing of the Upper-Tropospheric Monsoon Anticyclones AbstractDuring the boreal warm season (May–September), the circulation in the upper troposphere and lower stratosphere is dominated by two large anticyclones: the Asian monsoon anticyclone (AMA) and North American monsoon anticyclone (NAMA). The existence of the AMA has long been linked to Asian monsoon precipitation using the Matsuno–Gill framework, but the origin of the NAMA has not been clearly understood. Here the forcing mechanisms of the NAMA are investigated using a simplified dry general circulation model. The simulated anticyclones are in good agreement with observations when the model is forced by a zonally symmetric meridional temperature gradient plus a realistic geographical distribution of heating based on observed tropical and subtropical precipitation in the Northern Hemisphere. Model experiments show that the AMA and NAMA are largely independent of one another, and the NAMA is not a downstream response to the Asian monsoon. The primary forcing of the NAMA is precipitation in the longitude sector between 60° and 120°W, with the largest contribution coming from the subtropical latitudes within that sector. Experiments with idealized regional heating distributions reveal that the extratropical response to tropical and subtropical precipitation depends approximately linearly on the magnitude of the forcing but nonlinearly on its latitude. The AMA is stronger than the NAMA, primarily because precipitation in the subtropics over Asia is much heavier than at similar latitudes in the Western Hemisphere. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of the Atmospheric Sciences American Meteorological Society

Forcing of the Upper-Tropospheric Monsoon Anticyclones

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References (42)

Publisher
American Meteorological Society
Copyright
Copyright © American Meteorological Society
ISSN
1520-0469
eISSN
1520-0469
DOI
10.1175/JAS-D-18-0340.1
Publisher site
See Article on Publisher Site

Abstract

AbstractDuring the boreal warm season (May–September), the circulation in the upper troposphere and lower stratosphere is dominated by two large anticyclones: the Asian monsoon anticyclone (AMA) and North American monsoon anticyclone (NAMA). The existence of the AMA has long been linked to Asian monsoon precipitation using the Matsuno–Gill framework, but the origin of the NAMA has not been clearly understood. Here the forcing mechanisms of the NAMA are investigated using a simplified dry general circulation model. The simulated anticyclones are in good agreement with observations when the model is forced by a zonally symmetric meridional temperature gradient plus a realistic geographical distribution of heating based on observed tropical and subtropical precipitation in the Northern Hemisphere. Model experiments show that the AMA and NAMA are largely independent of one another, and the NAMA is not a downstream response to the Asian monsoon. The primary forcing of the NAMA is precipitation in the longitude sector between 60° and 120°W, with the largest contribution coming from the subtropical latitudes within that sector. Experiments with idealized regional heating distributions reveal that the extratropical response to tropical and subtropical precipitation depends approximately linearly on the magnitude of the forcing but nonlinearly on its latitude. The AMA is stronger than the NAMA, primarily because precipitation in the subtropics over Asia is much heavier than at similar latitudes in the Western Hemisphere.

Journal

Journal of the Atmospheric Sciences – American Meteorological Society

Published: Jul 19, 2019

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