Alison F. C. Bridger

General circulation model simulations of the Mars Pathfinder atmospheric structure investigation/meteorology data

The NASA Ames Mars General Circulation Model is used to interpret selected results from the Mars Pathfinder atmospheric structure instrument/meteorology (ASI/MET) experiment. The present version of the model has an improved soil thermal model, a new boundary layer scheme, and a correction for non-local thermodynamic equilibrium effects at solar wavelengths. We find good agreement with the ASI/MET entry data if the dust observed at the Pathfinder site is assumed to be distributed throughout the lowest five to six scale heights. This implies that the dust is globally distributed as well. In the lower atmosphere the inversion between 10 and 16 km in Pathfinders entry profile is likely due to thermal emission from a water ice cloud in that region. In the upper atmosphere (above 50 km), dynamical processes, tides in particular, appear to have a cooling effect and may play an important role in driving temperatures toward the CO2 condensation temperature near 80 km. Near-surface air temperatures and wind directions are well simulated by the model by assuming a low surface albedo (0.16) and moderately high soil thermal inertia (336 SI). However, modeled tidal surface pressure amplitudes are about a factor of 2 smaller than observed. This may indicate that the model is not properly simulating interference effects between eastward and westward modes.

Mars-GRAM 2000: A Mars atmospheric model for engineering applications

Abstract This paper presents Mars Global Reference Atmospheric Model 2000 Version (Mars-GRAM 2000) and its new features. All parameterizations for temperature, pressure, density, and winds versus height, latitude, longitude, time of day, and Ls have been replaced by input data tables from NASA Ames Mars General Circulation Model, for the surface through 80-km altitude, and the University of Arizona Mars Thermospheric General Circulation Model for 80 to 170 km. A modified Stewart thermospheric model is still used for higher altitudes and for dependence on solar activity. “Climate factors” to tune for agreement with general circulation model data are no longer needed. Adjustment of exospheric temperature is still an option. Consistent with observations from Mars Global Surveyor, a new longitude-dependent wave model is included, with user input to specify waves having one to three wavelengths around the planet. A simplified perturbation model has been substituted for the earlier one. An input switch allows users to select either East or West longitude positive. The paper includes instructions on obtaining Mars-GRAM source code, data files, and a users guide for running the program. The Mars-GRAM users guide provides sample input and output and gives an example for incorporating Mars-GRAM as an atmospheric subroutine in a trajectory code.

An interpretation of Martian thermospheric waves based on analysis of a general circulation model

Planetary-scale longitudinal variations in density observed by the Mars Global Surveyor accelerometer in the 125 km region can be qualitatively reproduced by the NASA Ames Mars general circulation model in the 80 km altitude region, but only when locations having specific local times are used in the analysis. If the model results are averaged over all local times, the high-altitude longitudinal variations nearly disappear, leaving only a small stationary wave 1 pattern, consistent with theory and previous modeling studies. This analysis suggests that the observed wavelike structures are a result of sampling tidal modes at a limited range of local times, rather than by topographically forced Rossby waves as previously suggested.

The Structure of the Marine inversion Layer off the Central California Coast: Mesoscale Conditions

Abstract Data collected on board an instrumented aircraft during the Marine Atmospheric Boundary Layer Experiments, West Coast (MABLES WC) field study are examined. The data were collected at several levels in the marine and inversion layers approximately 200 km west of the central California coast during August 1978. Composite sounding and cross sections of wind and temperature variables are presented to provide an overview of the mesoscale structure of the offshore marine and inversion layers at the time of MABLES WC. Under typical summertime synoptic conditions, which prevailed early in the study period (three flights examined), a strong inversion is found. Base heights and temperature increases across the inversion base are comparable to values observed in the San Francisco Bay area. The topography of the inversion base shows a slope downward toward the east during all three of these flights and also suggests the presence of convective activity, gravity-wave activity, or both, during two of the three ...

Evaluation of the WOCSS Wind Analysis Scheme for the San Francisco Bay Area

Abstract Applications of the Winds on Critical Streamline Surfaces (WOCSS) model in the San Francisco Bay Area are described. Three case studies, chosen to represent important classes of airflow in the region, were conducted. Two cases involved a prevailing northeasterly flow with or without an inversion, and the third case involved northeasterly flow at the time of the Oakland hills firestorm of 20 October 1991. The dependence of model results (surface winds) on input winds and on the specification of inversion topography is discussed. Dependable results are produced with relatively few well-placed surface observations and with a single sounding. The results suggest that the model is quite suitable for routine, real-time analyses and other practical applications.

New Directions for the AMS Symposium on Education

AFFILIATIONS: Charlevoix—UNAVCO, Boulder, Colorado; PanDya—American Geophysical Union, Washington, D.C.; briDger—San Jose State University, San Jose, California; gill, hamPTon, anD li—The University of Texas at El Paso, El Paso, Texas; herman—Western Illinois University, Macomb, Illinois; Knox—The University of Georgia, Athens, Georgia; sTaniTsKi— NOAA/Climate Program Office, Silver Spring, Maryland CORRESPONDING AUTHOR: Donna Charlevoix, UNAVCO, 6350 Nautilus Dr., Boulder, CO 80301 E-mail: donnac@unavco.org