Planetary Climate Dynamics

Abstract:

Against a backdrop of intensive exploration of the Martian surface environment, intehded to lead to human exploration, some aspects of the modern climate and the meteorology of Mars remain relatively unexplored. In particular, there is a need for detailed measurements of the vertical profiles of atmospheric temperature, water vapor, dust, and condensates to understand the intricately related processes upon which the surface conditions, and those encountered during descent by landers, depend. The most important of these missing data are accurate and extensive temperature measurements with high vertical resolution. The Mars Climate Sounder experiment on the 2005 Mars Reconnaissance Orbiter, described here, is the latest attempt to characterize the Martian atmosphere with the sort of coverage and precision achieved by terrestrial weather satellites. If successful, it is expected to lead to corresponding improvements in our understanding of meteorological phenomena and to enable improved general circulation models of the Martian atmosphere for climate studies on a range of timescales. Copyright 2007 by the American Geophysical Union.

Abstract:

A superrotating atmosphere with equatorial winds of ∼35 m s-1 is simulated using a simplified Venus general circulation model (GCM). The equatorial superrotation in the model atmosphere is maintained by barotropic instabilities in the midlatitude jets which transport angular momentum toward the equator. The midlatitude jets are maintained by the mean meridional circulation, and the momentum transporting waves are qualitatively similar to observed midlatitude waves; an equatorial Kelvin wave is also present in the atmosphere. The GCM is forced by linearized cooling and friction parameterizations, with hyperdiffusion and a polar Fourier filter to maintain numerical stability. Atmospheric superrotation is a robust feature of the model and is spontaneously produced without specific tuning. A strong meridional circulation develops in the form of a single Hadley cell, extending from the equator to the pole in both hemispheres, and from the surface to 50 km altitude. The zonal jets produced by this circulation reach 45 m s-1 at 60 km, with peak winds of 35 m s-1 at the equator. A warm pole and cold collar are also found in the GCM, caused by adiabatic warming in the mean meridional circulation. Wave frequencies and zonal wind speeds are smaller than in observations by cloud tracking but are consistent with a Doppler shifting by wind speeds in the generating region of each wave. Magnitudes of polar temperature anomalies are smaller than the observed features, suggesting dynamical processes alone may not be sufficient to maintain the large observed temperature contrasts at the magnitudes and periods found in this GCM. Copyright 2007 by the American Geophysical Union.