The four seasons are caused by the tilt of the Earth's axis and the movement ofthe Earth around the sun. Without the tilt of the axis we would still haveplenty of weather, but the seasons would not occur through mid and northernlatitudes. In equatorial regions, the word season has little meaning. Theclimate remains tropical just about all of the time.Twice each year, the sun is directly overhead at the equator. This happens onthe first day of autumn and the first day of spring. This year, the springequinox (meaning equal nights) begins March 20 at 7:21 p.m. EDT. At thatprecise moment, the sun's rays will be directly overhead on the equatorsomewhere out over the Pacific. Beyond that time, the vertical rays of the sunwill migrate northward, reaching the Tropic of Cancer on the first day ofsummer.
Kocet's Corner
A point of interest is that temperature normals only loosely coincide with theseasons. For most of the United States, the coldest quarter of the year is fromearly December through early March, and the warmest quarter of the year is fromthe first week in June to the first week of September.
Across the northern half of the United States and all of Canada, spring takesits old sweet time gaining a foothold. That's because there are still hugevolumes of arctic air that have to be done away with. The sun's rays arepouring in this time of year, but oceans and land masses still retain the coldof winter.
An analogy would be placing an ice cube on the kitchen counter and expecting itto melt instantly. Well obviously, that doesn't happen. Just as it takes quitea bit of time for the ice cube to melt, it takes weeks for the NorthernHemisphere to thaw out.
Story by AccuWeather.com Senior Meteorologist John Kocet.
