Scientists analyzing the climate effects from the 2018 global dust storm on Mars have found that while it did little to change the seasons in the northern hemisphere, it caused winter to end early in southern hemisphere.
The team found that the 2018 storm had profoundly different effects in each hemisphere. At the south pole, where the vortex was almost destroyed, temperatures rose and wind speeds fell dramatically. While the vortex may have already been starting to decay due to the onset of spring, the dust storm appears to have had a decisive effect in ending winter early.
The northern polar vortex, by contrast, remained stable and the onset of autumn followed its usual pattern. However, the normally elliptical northern vortex was changed by the storm to become more symmetrical. The researchers link this to the high dust content in the atmosphere suppressing atmospheric waves caused by the extreme topography in the northern hemisphere, which has volcanoes over twice as tall as Mount Everest and craters as deep as terrestrial mountains.
These differences are likely also related to the eccentricity in the Martian orbit around the Sun, which is greater than that of Earth and actually has a direct effect on its seasons. As noted in this recently published paper about the activity scientists have now documented on the Martian surface in the past decade,
Because perihelion (the closest approach to the Sun) currently occurs [during summer in the south], southern hemisphere seasons are more extreme, with a longer winter and shorter, warmer summer
This difference is probably a major factor explaining the different effects of the global dust storm. It also is probably why the Red Planet’s two polar ice caps are so different.
This difference between the two hemispheres will also likely help drive the intitial human settlement on Mars to the north. Not only does the northern hemisphere have the flat lowland plains, making those first difficult landings easier and safer, it has a more benign climate year round.