Seasonal Temperature Cycle
The seasonal cycle in the atmosphere is driven by the fact that the Earth’s axis is not at right angles to the sun (it is actually 23° away from perpendicular). This means that, at different times of year, different latitudes get the most incoming solar radiation. At the equinoxes, the sun is overhead at the equator, at the June solstice, the sun is over the Tropic of Cancer and at the December solstice, it is over the Tropic of Capricorn. This means that, in June, July and August (northern hemisphere summer), the northern hemisphere is warmer than the southern hemisphere. Similarly in December, January and February, the southern hemisphere is warmer. These months are not symmetrical about the solstice (for example, we do not talk about the November, December, January season) because the climate system tends to lag the sun, as it takes a while to heat up or cool down.