Spring (season)
From Wikipedia, the free encyclopedia
|
|
||||||||||||
Spring is one of the four seasons of temperate zones, the transition from winter into summer. Spring is counted as the whole months of March, April, and May in the Northern Hemisphere and September, October, and November in the Southern Hemisphere. In all technicality, spring begins on the Vernal Equinox (March 20th or 21st in the Northern Hemisphere and September 22 or 23 in the Southern) and lasts till Summer Solstice (June 21st or 22nd in the Northern Hemisphere and December 21st or December 22nd in the Southern).
As in summer, the North Pole of the Earth is tilted toward the Sun, and the length of daylight hours increases for the Northern Hemisphere. The hemisphere begins to warm significantly, causing new plant growth to spring forth, giving the season its name (see Effect of sun angle on climate). Snow begins to melt, and rivers and streams swell with runoff and spring rains. Most flowering plants bloom this time of year, in a long succession beginning even when snow is still on the ground, and continuing into early summer. In normally snowless areas, "spring" may begin as early as February during warmer years, with subtropical areas having very subtle differences, and tropical ones none at all. Subarctic areas may not see "spring" at all until May or even June, or December in the outer Antarctic.
Severe weather most often occurs during the spring, when warm air begins to invade from lower latitudes while cold air is still pushing from the polar regions. Flooding is also most common in and near mountainous areas during this time of year due to snowmelt, many times accelerated by warm rains. In the United States, Tornado Alley is most active by far this time of year, especially since the Rocky Mountains prevent the surging hot and cold airmasses from spreading westward and instead force them directly at each other. Besides tornados, supercell thunderstorms can also produce dangerously large hail and very high winds, for which a severe thunderstorm warning or even tornado warning is usually issued. Often, spring storms trigger dozens of warnings, one right after the other, often simultaneously along a line hundreds of miles or kilometers long. Even more so than winter, the jet streams play an important role in severe weather in the springtime.
The hurricane season officially begins in late spring, on May 15 in the northeastern Pacific, and June 1 in the northern Atlantic. Before these dates, hurricanes are almost unheard of and even tropical storms are rare, one of the earliest ever being Tropical Storm Ana in mid-April 2003. Even in June, hurricanes are uncommon.
Springtime is seen as a time of growth, renewal, of new life (both plant and animal) being born, and of the cycle of life once again starting. It is also used more generally as the start of better times, as in Prague Spring.
