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.