THE FOUR SEASONS

A SEASON is one of the four periods of the year. Each season--spring, summer, autumn, and winter--lasts about three months and brings changes in temperature, weather, and the length of daylight. During the spring, the days are warm in middle parts of the Northern Hemisphere, the northern half of the Earth. Summer follows with hot days and warm nights. In autumn, the days become cooler, leading to the cold of winter. The four periods are called climatic seasons when based on these temperature and weather changes. In the Southern Hemisphere, the climatic seasons differ by about six months. This hemisphere has summer when the Northern Hemisphere has winter.

SUMMER is the warmest season of the year. The Northern Hemisphere, the northern half of the Earth, has summer weather during late June, July, August, and early September. Summer like days sometimes occur in mid-autumn. In the Southern Hemisphere, summer lasts from late December until early March. The highest summer temperatures usually occur in the middle of a continent. During summer in North America, warm southern winds carry moisture north from the Gulf of Mexico to central and eastern North America. They can bring warm, humid weather to much of the region east of the Rocky Mountains and as far north as Canada. Thunderstorms often develop in and along the northern boundary of this warm, moist air.

AUTUMN is the season between summer and winter. The Northern Hemisphere, the northern half of the Earth, has autumn weather during late September, October, and November. Autumn weather does not last so long in the polar region, where extremely cold winter weather begins earlier. In tropical regions, seasonal changes are not great. The Southern Hemisphere has autumn from March until early June. Many people call this season fall because it is the period of falling leaves. Autumn is also harvest time for many crops. In North America, early autumn days are generally warm and nights are cool. As winter approaches, the air becomes chillier and frost often occurs at night. In much of North America, the end of autumn is marked by the freezing of lakes and streams, southern migration of birds, and prewinter snowstorms. Autumn -- especially September -- is the season when most hurricanes occur. Hurricanes cause great damage along the coasts of the Gulf of Mexico and the western North Atlantic Ocean.

SPRING is the season between winter and summer. The Northern Hemisphere, which consists of the northern half of the Earth, has spring weather during late March, April, May, and early June. In the Southern Hemisphere, spring weather begins about September and ends by early December. Spring weather begins throughout much of North America with the melting of winter snow. In the polar regions, spring weather begins later and does not last as long as it does in the middle parts of the Northern and Southern Hemispheres. Tropical regions do not have great seasonal changes. The number of daylight hours increases during spring, and most spring days have higher temperatures than winter days. Nature awakens in spring, when flowers bloom and hibernating animals leave their winter sleeping places. In many countries, the people have festivals celebrating spring.

WINTER is the coldest season of the year. The Northern Hemisphere, the northern half of the Earth, has winter weather during December, January, February, and early March. In the Southern Hemisphere, winter weather begins in late June and lasts until early September. During winter, the polar regions are especially cold because the sun does not rise there for weeks or months at a time. The lowest winter temperatures usually occur in the middle of all continents. In the Northern Hemisphere, cold, dry air moves south from the North Pole, bringing cold weather. Storms move from west to east along the southern edge of the cold air. In the United States, winter storms produce large snowfalls in some areas. The most snow falls in the western mountains and in much of the northern region east of the Rocky Mountains. Many winter storms bring rain to warmer southern areas.