The Martian Atmosphere in Late 2003 to Early 2004: Observations, Predictions, and Analyses II
Presiding: P Withers, Boston University; M D Smith, NASA Goddard Space Flight Center
P24A-01 INVITED 15:30h
Predicting the Mars Atmosphere for MER EDL
As the two Mars Exploration Rovers (MER) approached Mars, Mars Global Surveyor (MGS) detected a regional dust storm. The storm developed as a local storm descending the Chryse storm track but instead of dying out near the equator, it crossed over the Meridiani landing site into the southern hemisphere and started growing. It eventually became a planet encircling storm, with a global impact on atmospheric temperatures. The storm peaked (in terms of dust loading) around December 18th. While the storm was already decaying, it was still expected to change the atmosphere from baseline "clear" atmosphere used for planning Entry Descent and Landing (EDL). To help insure the successful landing, an attempt was made to model and then predict the atmosphere as the dust from the storm (and associated warming) cleared. Two types of data analyses were performed. The first was to rapidly look at MGS-TES daily global maps and MOC weekly reports. This gave a good qualitative assessment of the activity and help give a global view of the activity. The daily global atmospheric temperature maps from TES were particularly useful in showing where there were atmospheric changes but little measurable dust. The second analysis was to use vertical temperature profiles retrieved from the TES data. An effort was made to minimize the turnaround on the analysis and a 3 day latency was achieved. The retrieved profiles from the orbit nearest to the landing site were averaged over a ~ 10 degree latitude bin. They were then incorporated into an engineering model based on the one described in Golombek et al. [2003]. This is an interpolation scheme/Monte-Carlo distribution generator and not an actual dynamical model. It basically uses the TES data as a mean and applies a variability. For Spirit, there was no attempt to make predictions (the storm was too close to landing), so the most recent profiles were just used as a best guess. This turned out to be adequate, resulting in the final model being within ~ 1 σ of preliminary estimates from the accelerometers. For Opportunity, a series of predictions for the landing day conditions were made. The basic approach was to assume that the dust storm would decay back to seasonal conditions in an exponential fashion (based on other recorded storms). Thus an exponential curve in time was fit to the TES profiles on each pressure surface independently. The value of the fit at the landing date was then used for a prediction. Due to the MGS orbital mechanics, the actual latitude of the measurements varied daily (but remained within +/- 20 degrees of the landing site). The data did, unfortunately for predictions, show a latitudinal trend. To the east of the Meridiani Planum site, there was little geographic variations while to the west, temperatures decreased slowly away from the site. Due to the coverage and temporal variability as the storm decayed, the magnitude of this trend was difficult to estimate. Given the paucity of data and the uncertainty included explicitly in the model, this trend was not explicitly modeled for MER EDL purposes. There was some change in the predictions with time over the four weeks they were made, but much less than in the atmosphere itself. Thus the predictions served their purpose of allowing the engineers to design for the encountered atmosphere instead of trying to track the changes as they occurred. The ultimate validation of the modeling approach was that both rovers landed successfully.
P24A-02 15:45h
Atmospheric Profiles from Spirit and Opportunity
Spirit and Opportunity each carried two 3-axis accelerometers and two 3-axis gyroscopes to trigger events, such as parachute deployment, during atmospheric entry. These instruments were designed and operated for engineering and operational purposes; they were not science instruments. However, their measurements can be used to derive vertical profiles of atmospheric density, pressure, and temperature. These are the first entry profiles obtained simultaneously with remote sensing measurements, from MGS TES in this case, of the same atmospheric properties, which enables independent testing of the accuracy of this measurement technique. I will discuss the positive and negative features of these instruments, the quality and availability of their datasets, preliminary atmospheric results, and the prospects for wider use of these results.
P24A-03 INVITED 16:00h
Spacecraft Observations of Atmospheric Temperature and Aerosol Optical Depth Near the Time of the MER Landings
Continued atmospheric monitoring by the Mars Global Surveyor TES and Mars Odyssey THEMIS instruments provided daily maps of the regional to global scale variation of atmospheric temperature and aerosol optical depth before, during, and after the time of the two Mars Exploration Rover (MER) landings in January 2005. After landing, the MER Mini-TES instrument provided additional complementary information about the late-summer atmospheric state at the Gusev Crater and Meridiani Planum landing sites. Orbital observations taken before the MER landings documented the initiation, growth, and decay of a large regional dust storm in mid-December 2004, just weeks before the MER Spirit landing. This dust storm caused an increase in atmospheric temperature above nominal seasonal values, and left relatively dusty conditions for the rovers after landing. Atmospheric entry parameters such as the height at which to open the parachute were adjusted considering the daily TES updates in the days before both MER landings. Here we present observations of atmospheric temperatures and aerosol optical depth by TES and THEMIS in the time period near the MER landings. We compare the TES and THEMIS observations against the values predicted from climatology and the observations taken after landing by the MER Mini-TES.
P24A-04 INVITED 16:15h
The Local and Regional Meteorology of the MERs' Environment as Simulated by a Mesoscale Model
The Mars Regional Atmospheric Modeling System (MRAMS) was used to assess local atmospheric hazards during the MER landing site selection process, and, later used to plan for entry, descent, and landing (EDL) at Meridian Plenum and Gusev Crater. A comparison of MRAMS predictions to observed and inferred conditions during EDL and subsequent surface operations is presented. Data to properly validate the model is lackcing. However, qualitatively, the MRAMS predictions are shown to be accurate, including the identification of a superadiabatic and turbulent boundary layer observed by Mini-TES, and low-level wind shear at Gusev Crater, particularly over the rims, as inferred by EDL descent data. A high dust loading scenario, although anticipated as a possibility, was not modeled due primarily to computing resource limitations. However, a regional dust storm just prior to arrival at Mars sent visible dust opacities to near unity at each of the landing sites. Results of MRAMS simulations at these higher opacities conducted post-landing are presented and compared to the previous lower dust loading results and to observations. Finally, follow-up MRAMS simulations that look at the seasonality of local circulations and their relationship to aeolian features observed in Gusev Crater are presented.
http://boulder.swri.edu/~rafkin
P24A-05 16:30h
FFSM Analyses of MGS TES Atmospheric Data: The MER Mission Period
The MER Landers touched down on Mars in the late northern winter season of the third MGS mapping year, at areocentric longitude dates of 328 and 339 degrees. The Mars atmosphere was highly active dynamically at this time, with strong transient eddy activity present in the northern hemisphere and substantial regional dust storm activity occuring in both hemispheres shortly before the landings took place. Fast Fourier Synoptic Mapping (FFSM) analyses of the MGS TES atmospheric data permit these fields to be mapped synoptically (two maps per sol), utilizing the full space-time resolution of the data without any averaging or smoothing of the data. We have made use of FFSM analyses to examine the TES atmospheric observations for the late 2003-2004 time period, and the results of these studies will be presented and discussed. The atmospheric state during this period will be placed in the context of previous and following seasonal periods, and will be compared with the same seasonal period in the prior two MGS mapping years.
P24A-06 16:45h
The Simulation of Transient Eddies and Frontal Systems in the Martian Atmosphere
The initiation and evolution of a number of regional scale dust storms has been documented in detail with MOC imagery and with TES temperature and dust opacity observations. These storms are evidently associated with traveling waves embedded in the strong westerly jet that is present in the northern hemisphere in the fall, winter and spring seasons. The most prominent storms occurred in the low topography regions (Acidalia, Arcadia and Utopia) within two seasonal windows (Ls=200-240 and Ls =305-340) before and after northern winter solstice. In particular, a large regional storm was observed in early December 2003 (Ls=309). This storm originated in the northern hemisphere and moved southward to the equator in the longitude sector east of Tharsis in the same fashion as storms in preceding years. Upon reaching low latitudes, this dust storm rapidly intensified and spread, yielding the highest dust optical depths at low to mid southern latitudes. It appears that these flushing storms are present in most Mars years and significantly contribute to the seasonally-varying envelope of background dust opacity and global mean temperature. We will present a study of the climatology of traveling baroclinic wave behavior present in annual cycle simulations of the martian atmosphere using the GFDL Mars general circulation model (MGCM). In general, we find that zonal waves 2 and 3 are favored in the NH fall and late winter seasons, as observed, and that these waves are modulated by topography to favor storm development in the low elevation regions. We will also show high-resolution simulations with surface stress dependent interactive dust lifting that provide insight into the storm intensification stage as dust is transported southward in these basins. The inclusion of predicted water ice clouds provides an additional means of comparing the simulated circulations with observed dust and water ice cloud morphologies.
http://www.gfdl.noaa.gov/~rjw