53 Hadley Cell Regimes in an Idealized GCM for a Broad Range of Astronomical and Atmospheric Parameters

Monday, 26 June 2017
Salon A-E (Marriott Portland Downtown Waterfront)
Alexander Paterson, University of Exeter, Exeter, United Kingdom; and G. K. Vallis

We use a novel method to construct a seasonally varying radiative-convective equilibrium temperature field that may be used to force an idealized dry aquaplanet GCM through Newtonian relaxation. Our method allows for flexible changes in both general orbital parameters as well as the surface heat capacity, lapse rate and optical depth. A temperature field is derived from an astronomical determination of insolation, which is used with analytic expressions for surface radiative equilibrium and tropopause height to calculate temperature. A surface energy balance is used to add some damping to the seasonal temperature changes. These modifications result in a flexible semi-analytic method to calculate the temperature field used for Newtonian relaxation.

We use our model to study the Hadley and Ferrel cells while varying obliquity, heat capacity, tropopause height, and rotation rate. Our results indicate that the tropopause height and the strength of the winter Hadley cell have a relationship which transitions from an increase in cell strength with tropopause height to a slight decrease in strength as the tropopause height is increased past 1.5 times that of an Earth-like atmosphere. This transition is not observed in the equinoctial Hadley cells, which show a steady increase in strength with tropopause height. We will discuss reasons for these differences, and explore the dynamical structure of the circulation for variations in heat capacity and orbital parameters.

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