[Previous] | [Session 4] | [Next]
R.J. Wilson (NOAA/GFDL), M.I. Richardson (UCLA)
Viking Infrared Thermal Mapper (IRTM) data provide the foundation for much of our current knowledge of the present Martian climate. The IRTM data, which were collected over a period in excess of two Mars years, contain a wealth of information on the spatial and temporal variation of surface and atmospheric temperatures on diurnal to seasonal time scales. The 15 micron channel is of particular interest for atmospheric studies as it was designed to measure brightness temperatures (T15) within a deep layer of atmosphere centered at roughly 0.5 mb (~25 km). Our re-examination of the T15 data suggests that the 15 micron channel was sensitive to surface radiance to an extent that the air temperature measurements are significantly biased. This bias is suggested by the strong correlation between the diurnal variation of tropical surface and T15 temperatures (for non-dust storm conditions). Atmospheric thermal tide modeling provides a basis for distinguishing between the surface and atmospheric contributions to the T15 observations. We use this approach to estimate the surface radiance contribution, which may then be removed from the T15 signal, allowing the atmospheric temperature signal to be recovered. We propose that midday, tropical T15 temperatures 'corrected' in this manner are over 15 K cooler than the IRTM observations. This suggestion is supported by a comparison of IRTM data with Mariner 9 IRIS data. Further, 'correcting' global average IRTM temperatures accounts for the instrumental bias found to exist between simultaneous IRTM and microwave observations. We will present a description of the revised T15 temperatures and discuss aspects of the martian circulation and climate which are highlighted by a consideration of the reprocessed observations.
The author(s) of this abstract have provided an email address for comments about the abstract: rjw@gfdl.gov