Temperature, pressure, wind, humidity and precipitation, interact with each other. They influence the atmospheric conditions like the direction and velocity of wind, amount of insolation, cloud-cover and the amount of precipitation. These are known as the elements of both weather and climate.
A year is divided into seasons depending upon variations in atmospheric conditions. They are specified periods in a year which have similar weather conditions.
Four seasons, each of three months duration have been recognized in temperate regions. They are spring, summer, autumn and winter. The rays of the sun are more or less direct on the equator throughout the year. Hence, equatorial regions experience the same temperature all the year round. Therefore, seasons are insignificant on or near the equator. Near the coast, the oceanic influence reduces the seasonal variations. In the polar regions, there are only two seasons i.e. long winter and short summer.
The earth is divided into five thermal zones on the basis of distribution of insolation and temperature. Five thermal zones are torrid zone, north and south temperate zones and north and south frigid zones.
It is the largest of the thermal zones. It covers, almost half the area of the earth’s surface. It is situated between the Tropic of Cancer and Tropic of Capricorn. The sun’s rays are almost vertical throughout the year in this zone. The duration’s of day and night are always equal i.e. 12 hours each on the equator. The range of temperature is lowest at the equator and it increases towards the tropics.
The temperate zones are on either side of the Torrid zone. The North Temperate Zone lies between Tropic of Cancer and Arctic Circle. The South Temperate Zone lies between Tropic of Capricorn and Antarctic Circle. In winter season, the nights are longer and days are shorter and vice versa in summer. The difference between the duration of the day and night increases towards the poles. When it is summer in the northern hemisphere it is winter in the southern hemisphere and vice versa.
Like the temperate zone, frigid zone is also found in both the hemispheres. The North Frigid Zone lies between Arctic Circle and North Pole. The South Frigid Zone lies between Antarctic Circle and South Pole. During winter season, the sun does not rise above the horizon for almost six months. These are the coldest regions of the world. The surface remains permanently frozen under thick snow.