Letter to the Editor

Persistent circumpolar vortices on the extrasolar giant planet HD 37605 b

¹ Department of Physics, University of California at Santa Cruz, Santa Cruz, CA 95064, USA e-mail: jlangton@ucsc.edu
² UCO/Lick Observatory, Department of Astronomy and Astrophysics, University of California at Santa Cruz, Santa Cruz, CA 95064, USA e-mail: laughlin@ucolick.org

Received: 18 January 2008
Accepted: 25 March 2008

Abstract

Aims. We examine the atmospheric dynamics on the extrasolar gas giant HD 37605 b ( d). As this planet's orbit is highly eccentric (), the intensity of stellar heating varies by a factor of 40 over the course of an orbit. We also consider the effect of cloud formation on the dynamical flows and the temperature evolution resulting from this extremely variable forcing.

Methods. We employ a grid-based two-dimensional compressible hydrodynamics code to model the atmosphere of the extrasolar giant planet HD 37605 b. We use a resolution of 512 longitude gridpoints and 257 latitude gridpoints. The stellar heating is simulated using a one-layer, two-frequency, two-stream approximation to true radiative transfer.

Results. This time-dependent insolation causes the formation of circumpolar vortices near both poles. These vortices appear to be stable over many orbits, and sequester a large volume of cold air, effectively shielding their interiors from the full blast of irradiation at periastron. Evolution of tracers initially placed within these vortices shows the rate of exchange of material between the interior and exterior of these vortices is small: material initially inside the vortex can be expected to remain in the vortex for ~. We note that this result is contingent upon a cloudless atmosphere; the formation of clouds potentially causes a large reduction in both temperature variation and wind speed.