Does the northern hemisphere have milder seasons than the southern hemisphere?

Yes. The dominant reason for this is that the severity of the seasons is largely controlled by the amount of insolation, and the portion of the Earth occupied by the ocean. During the summer in the Northern Hemisphere, the Sun reaches its highest point above the horizon so the rays strike the Earth at a steep angle. This is also true of the summer season in the Southern Hemisphere, however, the portion of the Earth's surface occupied by oceans is higher in the Southern Hemisphere so the summer temperatures are somewhat higher on average than in the North. The fact that in the Northern Hemisphere, the Earth is at perihelion ( farthest distance from the Sun) during the summer, while in the Southern Hemisphere it is at aphelion ( closest orbital distance), makes only a 3 percent difference in the average temperature compared to the effect of the solar ray incidence angle and the mitigating effects of the ocean/land ratio.

There is also the well known phenomenon called the Lag of the Seasons, that the highest and coldest temperatures of the summer and winter in the Northern Hemisphere come 4 - 6 weeks after the solstices. This is because the local temperature is determined by the DIFFERENCE between the rate at which the Sun heats the Earth each day, and the rate at which the Earth can radiate this heat back out to space. During the summer, at the solstice, the Earth receives more solar energy than it can radiate in any 24 hour period because the days are long and the nights are short. The average temperature at which a balance between heating in the daytime, and cooling at night can occur continues to increase after the summer solstice and reaches a maximum until about 4-6 weeks later in August. It then begins to decline. Similarly in the winter, the average temperature continues to decrease through the winter solstice, reaching a minimum daily temperature, in the Northern Hemisphere, sometime in February: the dead of winter.


Copyright 1997 Dr. Sten Odenwald
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