If the orbit of the earth were circular, you would expect that both hemispheres would receive the same total, annual insolation on a surface just outside the atmosphere of the earth. Because the orbit is elliptical, and because the earth is a few percent closer to the sun during southern summer (perihelion) than during northern summer (aphelion), without doing the necessary integrals, I would expect that the southern hemisphere gets slightly more insolation when integrated over the year. This wouldn't be enough to make much difference in the weather. The big weather determinent is the ratio ocean to land-mass in each hemisphere, and in the northern hemisphere this ratio is smaller that in the southern hemisphere. I would expect this would lead to more severe swings of weather and temperature conditions in the northern hemisphere because of the larger continents and the large distances between the moderating effects of oceans and the centers of the continental interiors.
It is very complicated, and I am not a meteorologist!
All answers are provided by Dr. Sten Odenwald (Raytheon STX) for the
NASA IMAGE/POETRY project.