Hadley Circulation Response to Orbital Precession. Part II: Subtropical Continent
The response of the monsoonal and annual-mean Hadley circulation to orbital precession is examined in an idealized atmospheric general circulation model with a simplified representation of land surface processes in subtropical latitudes. When perihelion occurs in the summer of a hemisphere with a subtropical continent, changes in the top-of-atmosphere energy balance, together with a poleward shift of the monsoonal circulation boundary, lead to a strengthening of the monsoonal circulation. Spatial variations in surface heat capacity determine whether radiative perturbations are balanced by energy storage or by atmospheric energy fluxes. Although orbital precession does not affect annual-mean insolation, the annual-mean Hadley circulation does respond to orbital precession because its sensitivity to radiative changes varies over the course of the year: the monsoonal circulation in summer is near the angular momentum-conserving limit and responds directly to radiative changes; whereas in winter, the circulation is affected by the momentum fluxes of extratropical eddies and is less sensitive to radiative changes.
Additional Information© 2013 American Meteorological Society. Received: March 14, 2012; Accepted: July 3, 2012. We thank three anonymous reviewers for their comments. This work was supported by a National Science Foundation Graduate Research Fellowship, a Princeton Center for Theoretical Science Fellowship, and National Science Foundation Grant AGS-1049201. We thank Sonja Graves for providing modifications to the GCM code. The program codes for the simulations, based on the Flexible Modeling System of the Geophysical Fluid Dynamics Laboratory as well as the simulation results themselves, are available from the authors upon request.
Published - jcli-d-12-00149.1.pdf