As indicated in the figure, the profile was generated from data which were recorded on March 24, 1998. The location of the measurement was 49.3 degrees South latitude and 72.5 degrees East longitude. A glance at the Mars map on the Late Martian Weather! page on this Web site will show that this location is in the deep Hellas impact basin of Mars. The local time of the measurement on Mars was 07:31 p.m. and the martian season at the time and place of the measurement was early summer. The Sun had not yet set at the measurement point, and was approximately 3 degrees above the horizon.

The temperature at the lowest point in the profile, very near the surface of Mars, is -19.7 Celsius degrees, or -3.5 degrees Fahrenheit! Although still cold by Earth standards (especially on a clear summer evening!), this is significantly warmer than the surface temperature in the profiles of January 28 and February 15, 1998. The warmer surface temperature is due to the changes in time of day and also in season from the earlier profiles. There is no hint of a temperature inversion in the figure, and the temperature decreases at an average rate of 2 Celsius degrees per kilometer from the surface to an altitude of 35 kilometers.

There is an uncertainty associated with each of the estimated temperatures which is not shown in the figure because the uncertainty analysis is still underway. Near the surface, the uncertainty (one standard deviation) is approximately 0.5 Celsius degrees while at the highest altitudes the uncertainty is approximately 6 Celsius degrees.

The atmospheric pressure on Mars is very low compared to Earth. Near sea level on Earth the typical pressure is approximately 1000 millibars. The figure shows that the pressure near the surface at the time and place of the measurement was 8.7 millibars, and this at a point which is many kilometers below the martian sea level! At the martian sea level, the pressure was estimated be approximately 5.5 millibars. The sea level pressure is down from the more than 6 millibars recorded in the January 28 profile. This is due largely to the transfer of carbon dioxide from the martian atmosphere to the North martian polar cap which occurs in the cold of winter in the Northern martian hemisphere. The carbon dioxide is recycled from the polar ice cap back into the atmosphere in the North martian spring, causing the global atmospheric pressures to rise on Mars. The cycle then repeats itself in the Southern winter and spring!

The pressure on Mars is very low compared to Earth for two reasons. First, the martian pressure is low because the density of the martian atmosphere is significantly less than Earth's atmosphere. Second, the martian pressure is low because the surface gravity on Mars is only 38% of that on Earth. Pressure is exerted by the weight of an atmospheric column, and the weight decreases if either the density in the column or the gravitational force decreases.

The error analysis is still underway, but it is believed that the uncertainty (one standard deviation) in the estimated pressure near the surface is approximately 0.02 millibars.