Seasonal sensitivity of the cross-equatorial Hadley cell response to extratropical thermal forcings
Journal
Journal of Climate
Journal Volume
34
Journal Issue
9
Pages
3327-3342
Date Issued
2021
Author(s)
Chung P.-C.
Abstract
This study explores the seasonal sensitivity of tropical circulation responses to an idealized extratropical thermal forcing using the Community Atmosphere Model version 5 coupled to a slab ocean. The thermal heating over the Southern Ocean is held constant, and the tropical responses in each month of the year are investigated. An anomalous cross-equatorial cell and a southward tropical rain belt shift occur every month. The anomalous cross-equatorial cell has a strong influence on the strengths of the Hadley cell and the subtropical jet in the winter hemisphere; in contrast, it has nearly no impact on the Hadley cell and the subtropical jet strengths in the summer hemisphere. The seasonal variation of the anomalous cross-equatorial cell is small (&30% of the annual mean change), and could be understood via the energetic and the sea surface temperature gradient perspectives. Both perspectives point to the seasonality of the anomalous ocean heat uptake within the deep tropics as the key factor explaining the weak seasonality of the anomalous cross-equatorial cell. We propose a hypothesis explaining about 75% of this seasonal variation via the climatological position of the ITCZ relative to the anomalous cross-equatorial cell. The results suggest a modest seasonality in tropical precipitation and circulation responses to extratropical forcing. Also, such seasonality may be partly predicted by the climatological seasonal cycle of the tropical circulations. ? 2021 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).
Subjects
Clouds; Cytology; Oceanography; Surface waters; Tropics; Community atmosphere model; Ocean heat uptake; Sea Surface Temperature gradients; Seasonal variation; Subtropical jet; Thermal forcing; Tropical precipitation; Tropical response; Cells; air-sea interaction; angular momentum; atmospheric forcing; climate change; climatology; extratropical cyclone; Hadley cell; intertropical convergence zone; seasonal variation; teleconnection; Southern Ocean
Other Subjects
Clouds; Cytology; Oceanography; Surface waters; Tropics; Community atmosphere model; Ocean heat uptake; Sea Surface Temperature gradients; Seasonal variation; Subtropical jet; Thermal forcing; Tropical precipitation; Tropical response; Cells; air-sea interaction; angular momentum; atmospheric forcing; climate change; climatology; extratropical cyclone; Hadley cell; intertropical convergence zone; seasonal variation; teleconnection; Southern Ocean
Type
journal article