Variation of temperature with latitude at a constant pressure of 400 Pa (4 mbar). One temperature sample is obtained from each retrieved atmospheric profile through interpolation. The black squares show results from a series of radio occultation measurements in January-March 1998. This time period corresponded to early winter in the northern hemisphere (Ls = 264-289 deg). The red triangles show results from a second series of measurements in November-December 1998, during late spring in the northern hemisphere (Ls = 60-78 deg). The horizontal blue line near 60 deg S latitude is the saturation temperature of carbon dioxide at 400 Pa.
In early northern winter/southern summer (black squares), temperature increases steadily with increasing latitude in the southern hemisphere. The highest temperature, near 65 deg S, is 240 K. In late northern spring/southern fall (red triangles), the temperature gradient is reversed. The temperature poleward of 60 deg S is nearly 100 K colder than before and has reached saturation. The atmosphere is condensing into dry ice at the south pole. Note that temperatures at 60 deg N in late northern spring (red triangles) are significantly colder than temperatures at 60 deg S in early southern summer (black squares) due to a 20% increase in the distance from Mars to the Sun.