On Mars, why are the seasons "strongly amplified" in the southern hemisphere and masked in the northern hemisphere?

In the Darian calendar entry on Wikipedia we read (emphasis mine):

The Martian year is treated as beginning near the equinox marking spring in the northern hemisphere of the planet. Mars currently has an axial inclination similar to that of the Earth, so the Martian seasons are perceptible, though the greater eccentricity of Mars' orbit about the Sun compared with that of the Earth means that their significance is strongly amplified in the southern hemisphere and masked in the northern hemisphere.

While I see that due the high eccentricity of Mars, it makes the seasons to have far-from-equal length (At Earth this is the case as well - though not significant), but I don't see why the seasons significance should be "strongly amplified" in the southern hemisphere. If the southern hemisphere has a longer (say) Winter, so the northern hemisphere will have a longer Summer. How does this kind of symmetry fail.

Edit: I think I have found a possible solution: probably around the time of South hemisphere Summer, Mars is closer to the Sun. Though if it so, the South Summer is shorter in time.

• Solstices and equinoxes of Mars and Earth Mar 27 at 18:25
• The amount of insolation during the shorter northern summer is greater than that during the longer southern summer. The "distance-squared" portion of that calculation is the variable that has the largest effect. Mar 28 at 15:11

2 Answers

Your solution is correct. Mars has a perihelion that is, coincidentally, quite close to the southern Hemisphere summer solstice. Perihelion is actually about one (Earth) month before the solstice. The last Perihelion was on the third of August 2020 and the last southern summer solstice was on the second of September.

The intensity of sunlight is therefore significantly stronger during the southern hemisphere summer.

This chart, from "Solar Radiation Incident on Mars and the Outer Planets: Latitudinal, Seasonal, and Atmospheric Effects" shows that during the Northern summer, no part of the planet receives more than 400 cal/cm²/day, and mid-latitudes receive about 350. Whereas at Southern solstice, much of the Southern hemisphere receives more than 500 cal/cm²/day

• Earth also has perihelion close to the northern winter / southern summer solstice (it's in the first week of January), and this causes a similar phenomenon. But the effect is much less pronounced on Earth because of Earth's lower eccentricity (~0.017 vs. ~0.093 for Mars, which causes a 6.5% difference in solar radiation intensity at perihelion vs. aphelion on Earth, and 30% for Mars). I think that explains the wording of the Wikipedia quote. Either there was more context there that got edited out, or the context was in someone's head but never made it to the page. Mar 27 at 16:04
• (1 cal/cm²)/(1sol) is 0.47 W/m², so 500 cal/cm²/day is around 235 W/m². Mar 28 at 12:46
• @hobbs: Earth also has a lot more ocean in the Southern Hemisphere, which mitigates the effects of the eccentricity as far as surface temperatures go (since the oceans can absorb the extra solar radiation without heating up as much.) Mar 28 at 13:00
• @MichaelSeifert Also, here in the Southern hemisphere, we have a large cold reservoir in the form of the circumpolar current (and the Antarctic ice sheet). Mar 28 at 15:34

Apart from the eccentricity you pointed out that has a role in a difference in the weather, one more factors that plays a role is the difference in the terrain and topology between the hemisphere. This is known as Martian dichotomy. The two hemispheres' geography differ in elevation by 1 to 3 km. The average thickness of the Martian crust is 45 km, with 32 km in the northern lowlands region, and 58 km in the southern highlands. The northern highlands is relatively flat while southern highlands has most of the impact craters.

What role does Martian dichotomy play on the weather?

1. Dust storms: Southern hemisphere receive frequent dust storms than the northern hemisphere.
2. Hadley circulation: The atmospheric circulation is asymmetric across hemisphere where Southern hemisphere's weather being the most volatile and difference in ice content at the polar caps (the south polar cap is much smaller than the one in the north)
3. Equinox precession: This results in southern hemisphere receiving more sunlight in summer and less in winter than the Northern. Their summer and winters are far longer than what we have on Earth.