Mars' Global Sandstorm: Causes and Effects

[Singlau]

Recently I read a book about Mars, and it says that global sandstorm blows from southern hemisphere to northern hemisphere at perihelion. It's because the southern part is more heated at that position and the closer distance to sun gives it a high temperature, thus sublimating large amount CO2 in the southern polar cap. This increase in amount of air blows from southern hemisphere.

Here is my question: why doesn't sandstorm blow in another way at aphelion?

When Mars is farther from sun, its southern hemisphere is farther than northern one, so less heated. More CO2 is deposited back to the southern polar caps. At the sane time, northern ice cap absorb less air back relatively. Why doesn't this difference around the globe create global sandstorm as well?

 

[mfb]

Mars (as every orbiting body) spends more time closer to aphelion, and overall temperatures are lower, so I would expect the processes to be slower there.

Mars doesn't have a global duststorm every orbit, so it could also be some combination of multiple conditions that have to come together.

 

[Singlau]

Thanks!

 

[Janus]

Recently I read a book about Mars, and it says that global sandstorm blows from southern hemisphere to northern hemisphere at perihelion. It's because the southern part is more heated at that position and the closer distance to sun gives it a high temperature, thus sublimating large amount CO2 in the southern polar cap. This increase in amount of air blows from southern hemisphere.

Here is my question: why doesn't sandstorm blow in another way at aphelion?

When Mars is farther from sun, its southern hemisphere is farther than northern one, so less heated. More CO2 is deposited back to the southern polar caps. At the sane time, northern ice cap absorb less air back relatively. Why doesn't this difference around the globe create global sandstorm as well?

There are two effects in play here. there is the axial tilt and the distance towards from the Sun. When Mars is at perihelion, its South pole is pointing more towards the Sun and gets warmer (just like Summers in the Northern hemisphere on Earth are warmer because the North pole is pointing more towards the Sun). It has nothing to to with the Southern hemisphere being closer to the Sun than the northern one, it is the fact that the Sun's rays strike the surface more vertically and the day lit hours are longer. Now add in the fact that Mar's orbit has an eccentricity of over 4 times that of the Earth, so there is a greater difference in Solar radiation at perihelion and you have a lot more heating at this time. At aphelion, the Northern hemisphere is no pointed towards the Sun and has the longer daylight hours, but now Mars is further away from the Sun, so you are not going to get as much heating of the Northern hemisphere during its summer that the Southern one got during its Summer. ( the solar radiation difference varies by ~46%)

 

[Singlau]

Yes, I know that northern hemisphere is not heated that much. But what I'm saying in the first post is that wind is caused by a rapid decrease of air in southern hemisphere, instead of rapid increase of northern ice.

Anyway, now I do understand that the effect on deposition is slower or somehow less rapid than sublimation, which only cause dust storms at perihelion.