The closest distance that a body in Mars orbit comes to Mars, i.e. the periapsis of a body in Mars orbit.
The greatest distance from Mars is known as Apoareion.
Difference of Northern and Southern Climate:
Earth's orbit is nearly circular, so the northern and Southern Hemispheres have summers and winters of nearly identical lengths. However, Mars' orbit is more strongly elliptical. (Earth has an orbital eccentricity of 0.017, where as Mars' eccentricity is 0.093.) The Martian South Pole is pointing towards the Sun at periapsis.
This means that Mars is closest to the Sun in the south hemisphere's summer, and farthest from the Sun in the south hemisphere's winter. Note that when Mars is far from the Sun, it travels slower in its orbit. This makes the southern summers short, and the southern winters long. This results in the Southern Hemisphere having more extreme weather, hotter summers, and much colder winters. The north polar cap gets a frosting of carbon dioxide ice in its winter, but the south polar ice caps build up a thick layer of CO2 ice each winter.
Since the northern hemisphere is generally at lower attitude, the air is thicker there, which further moderates the local temperature swings and provides more radiation protection.
- J.R. Wertz - Orbits and astrodynamics in J.R. Wertz, D.F. Everett & J.J. Puschell eds. Space mission engineering: The new SMAD ISBN 978-1-881883-15-9 p. 202