Dry Adiabiatic Lapse Rate The eccentricity of the Martian orbit means that the southern autumn and winter are longerthan the northern (194/178 days v 143/156). There is also 40% more solar insolation at perihelion. Therefore the southern hemisphere gets shorter but hotter summers and longer, colder winters. (This situation reverses every 25,000 years due to precession of the Martian poles.) The result of this is that the southern polar cap varies more in size, but although both caps have a seasonal CO 2 ice component of a few cm thickness, only the southern cap has Carbon Dioxide in the residual cap in southern summer. The south polar cap varies more in size. The northern residual cap is about 1000km diameter, mainly H 2 O ice at around -68 degrees C, while the southern residual cap is about 350km diameter and a mixture of water and Carbon Dioxide ice at around -113 degrees C. There is such a fast melting of the southern cap at the onset of summer that global sandstorms are created, fed by torms are created, fed by the temperature gradient from pole to the defrosted and
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