An assessment of the global, seasonal, and interannual spacecraft record of martian climate in the thermal infrared
Abstract
A comprehensive inter-comparison of thermal infrared data collected by Mariner 9, Viking, and Mars Global Surveyor (MGS) is presented, with a specific focus on air temperatures, dust opacities, and water ice opacities. Emphasis is placed upon creating a uniform data set so as to most effectively reduce inter-instrument biases and offsets. We show that the globally-averaged martian atmosphere undergoes a repeatable annual cycle of air temperature, closing in northern spring and summer to within a Kelvin. The annual cycle shows a strong asymmetry about the equinoxes, with northern summer showing relatively low temperatures and essentially no short-term (tens of days) variability. Viking and MGS air temperatures are essentially indistinguishable, suggesting that the Viking and MGS eras are characterized by exactly the same climatic state. Southern summer is characterized by strong dust storm activity, with the period around Ls=225 has exhibiting regional or global-scale dust storm events in every year observed by spacecraft. Dust opacity shows a highly repeatable annual cycle, closing to essentially the same values each year in northern spring and summer, with Viking and MGS opacities being very similar. We show that both Viking and MGS data sets have significant and similar polar cap edge dust storm activity. The origins of the various major dust storms can be identified in the thermal infrared data from Viking and MGS, including the "flushing" of dust from the northern autumn baroclinic zone into the southern hemisphere tropics, which has also been identified in visible imaging. Water ice opacities have been retrieved from Viking infrared data for the first time and the tropical cloud belt structure and evolution is essentially the same in each of the multiple years observed by Viking and MGS. Polar hood clouds are observed in the Viking and MGS observations with similar timing and extent.
- Publication:
-
34th COSPAR Scientific Assembly
- Pub Date:
- 2002
- Bibcode:
- 2002cosp...34E2716L