Polar regions experience a radiation deficit . The midlatitudes are a region of active heat transport, out of the tropics to higher latitudes. It is this differential radiational heating that powers our atmosphere, causing it to remain in ceaseless fluid motion, attempting to re-balance the radiational imbalance. Least annual variation in equatorial latitudes, due to constant day lengths and high sun angles. Radiational and temperature contrasts between tropics and poles are pronounced in the winter.
Contrast mean temps in south Florida with Wisconsin.
Strong latitudinal temperature gradient in winter . In summer, radiational and temperature contrasts between tropics and poles diminish. Temps in Florida and Wisconsin fairly similar. Weak latitudinal temperature gradient in summer . Note general shifts in temperature belts with changing seasons on January vs. July mean temperature maps.