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Controls on the CO2 seasonal cycleSurface pressure measurement performed by the Viking landers show substantial variations in pressure on seasonal timescales that are characterized by two local minima and two local maxima. These variations have widely been attributed to the seasonal condensation and sublimation of CO2 in the two polar regions. It has been somewhat of a surprise that the amplitude of the minimum and maximum that is dominated by the CO2 cycle in the north was much weaker than the corresponding amplitude of the south-dominated extrema. Another surprise was that the seasonal pressure cycle during years 2 and 3 of the Viking mission was so similar to that for year 1, despite the occurrence of two global dust storms during year 1 and none during years 2 and 3. An energy balance model that incorporates dynamical factors from general circulation model (GCM) runs in which the atmospheric dust opacity and seasonal date were systematically varied was used to model the observed seasonal pressure variations. The energy balance takes account of the following processes in determining the rates of CO2 condensation and sublimation at each longitudinal and latitudinal grid point: solar radiation, infrared radiation from the atmosphere and surface, subsurface heat conduction, and atmospheric heat advection. Condensation rates are calculated both at the surface and in the atmosphere. In addition, the energy balance model also incorporates information from the GCM runs on seasonal redistribution of surface pressure across the globe. Estimates of surface temperature of the seasonal CO2 caps were used to define the infrared radiative losses from the seasonal polar caps. The seasonal pressure variations measured at the Viking lander sites were closely reproduced.
Document ID
19940028721
Acquisition Source
Legacy CDMS
Document Type
Conference Paper
Authors
Pollack, J. B. (NASA Ames Research Center Moffett Field, CA, United States)
Forget, F. (NASA Ames Research Center Moffett Field, CA, United States)
Haberle, Robert M. (NASA Ames Research Center Moffett Field, CA, United States)
Schaeffer, J. (NASA Ames Research Center Moffett Field, CA, United States)
Lee, H. (NASA Ames Research Center Moffett Field, CA, United States)
Date Acquired
September 6, 2013
Publication Date
January 1, 1993
Publication Information
Publication: Lunar and Planetary Inst., Mars: Past, Present, and Future. Results from the MSATT Program, Part 1
Subject Category
Lunar And Planetary Exploration
Accession Number
94N33227
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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