Vertically Resolved Aerosol Climatology of Mars as Observed by the Mars Global Surveyor Thermal Emission Spectrometer

Dust aerosols have long been recognized as one of the main drivers of the Martian climate due to their impact on radiative balance. Water ice condensate aerosols, in addition to tracing and influencing the water cycle, have recently been recognized as having their own significant impact on radiative balance. (Carbon dioxide condensate ice aerosols are also clearly present, both in the tropical mesosphere and over the winter pole.)

This presentation will focus on the relatively complete vertically resolved water ice and dust aerosol climatology provided by Mars Global Surveyor Thermal Emission Spectrometer (TES) limb-sounding observations. This data set provides a regularly sampled record that covers all seasons in three complete martian years at ~2pm and ~2am local times with 10 km vertical resolution between 10 and 60 km altitudes, and 10 degrees-of-latitude sampling intervals pole-to-pole along the spacecraft orbit track. Since the Mars Reconnaissance Orbiter Mars Climate Sounder (MCS) provides a similar data set, albeit with higher vertical resolution and more frequent sampling (but unfortunately no temporal overlap with TES), we will make comparisons with the MCS data set to illustrate which climatological features are well established and well understood, and which are more mysterious. We will also discuss TES nadir-sounding observations because they establish total column optical depths with greater accuracy.

A binned representation of the TES limb-sounding data set is available in NetCDF format. Important features of the data set include:

– Evidence that dust aerosol is entrained in and advected by the diurnal tides at 30 km altitude and above.

– Two persistent layers of enhanced dust mixing ratio in the tropics, one that is at 20 – 30 km altitudes and was first reported in MCS data, and another at 50 km and above which is marginally detected by TES but appears to be statistically robust

– High altitude water ice condensate aerosols that follow a diurnal pattern that clearly corresponds to the diurnal tide temperature minima.

– Evidence that the aphelion equatorial cloud belt grows more opaque and shifts to lower altitudes at night. In many locations during this season the water ice aerosols contribution to extinction, and hence influence on radiative balance, is significantly larger than that of dust.