Date of Award

Spring 1-1-2012

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Astrophysical & Planetary Sciences

First Advisor

Fran Bagenal

Second Advisor

Brian Toon

Third Advisor

Bruce M Jakosky

Fourth Advisor

David A Brain

Fifth Advisor

Phil Armitage

Abstract

A new general circulation model for the simulation of the Martian climate is introduced. The model, based on the Community Atmosphere Model (CAM) version 3.1 developed by the National Center for Atmospheric Research (NCAR) is a three dimensional model with full support for multi-processor computing. The model is validated by comparing the simulation results to various spacecraft observations including atmospheric temperature, surface temperature, convective boundary layer depth, water vapor, and cloud opacity. Comparisons of zonal mean atmospheric temperatures are typically within 5 K of observations, and the largest divergences can be accounted for by including the radiative effects of water-ice clouds. Both the pattern and magnitude of the observations for the present-day water vapor and cloud annual cycles have been reproduced in the model.

The model is then used to study a hypothetical ancient Martian climate with a 500 mb CO2 atmosphere, and a solar constant reduced to 75% of the current value. Sensitivity of the climate to the hydrologic cycle is tested assuming various amounts of initial atmospheric water, and cloud parameterizations. The results show that with an initial injection of at least 1000 pr-μm of water vapor, 10 μm cloud particles, and long atmospheric water lifetimes, a stably warm climate can be achieved. In these climates, the globally averaged surface temperature is 265 K, with tropical annual mean temperatures above the freezing temperature of water.

Precipitation rates and patterns in the warm climates are investigated for obliquities ranging between 0° - 65°, and with the presence of oceans, to determine the conditions for river valley formation. Without oceans, significant precipitation at the river valley latitudes only happens at high obliquity, with an initial injection of 50 pr-cm of water into the atmosphere. With oceans, precipitation at river valley latitudes is observed at all obliquities, with local annual precipitation rates above 10 cm per Martian year. The latitudes for peak precipitation depend on obliquity, suggesting that if oceans were present on early Mars, the Noachian river valley should show periodical formation reflecting the obliquity cycle.

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