North-South Differences

North-South Differences

These four temperature profiles illustrate how the vertical structure of the atmosphere varies with latitude and season. All four profiles extend to the surface, where the variation in pressure is due primarily to topography.

The left-hand panel shows measurements made near northern winter solstice (Ls = 270 deg) at a local time just prior to sunrise. There is a strong temperature inversion in a thin layer adjacent to the ground due to nighttime radiative cooling of the surface. At higher altitudes, the temperature in the summer hemisphere (30 deg S) decreases steadily with increasing altitude at a rate of about 2 K per km. The stucture in the winter hemisphere (25 deg N) is more complex. It includes a deeper temperature inversion extending from the surface to about the 250-Pa pressure level (note that 100 Pascals is equal to 1 millibar). This inversion is produced by the large-scale, cross-equatorial circulation of the atmosphere, which is strongest in this season. The temperature difference between the northern and southern profiles reaches about 20 K at the 400-Pa pressure level. The northern profile also includes temperature oscillations caused by atmospheric waves.

The right-hand panel shows similar measurements made in late northern spring (Ls = 70 deg). The red-dashed curve shows the temperature at which carbon dioxide will condense. No sunlight reaches the south pole in this season. Temperatures at 66 deg S are therefore cold enough, about 140 K, to cause condensation of carbon dioxide at pressures between about 200 and 400 Pa. This produces a "polar hood" cloud composed of dry ice over the south pole, where the seasonal ice cap is forming. The thermal structure in the north is now similar to what was observed previously in the south, though temperatures are somewhat colder due to a 20% increase in the distance from Mars to the Sun.


Last updated: November 17, 1999
Dave Hinson / Joe Twicken