Weather refers to the state of the atmosphere over an area at any point in time while Climate refers to the sum total of weather conditions and variations over a large area for a long period of time.
- Temperature, pressure, wind, humidity and precipitation, interact with each other.
- It 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.
- The influence of these elements differs from place to place and time to time. It may be restrict to a small area and for a short duration of time.
- This influence is describe as sunny, hot, warm, cold, fine, etc depending upon the dominant element of weather at a place and at a point of time.
- Therefore, weather is the atmospheric condition of a place for a short duration with respect to its one or more elements.
- Two places even a short distance apart may have different kind of weather at one and the same time.
- Season is a period of the year characterize by a particular set of weather conditions resulting from the inclination of the earth’s axis and the revolution of the earth round the sun.
- Four seasons, each of three months duration have been recognize in temperate regions. They are spring, summer, autumn and winter.
- The Indian Meteorological Department has recognized four main seasons.
- They are
- Cold weather season (December to February.)
- Hot weather seasons (March to May)
- Advancing monsoon season or rainy season (June to September.)
- Retreating monsoon season (October to November.)
- 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 average weather conditions, prevalent from one season to another in the course of a year, over a large area is known as climate
- The average of these weather conditions is calculated from the data collected for several years (about 35 years) for a larger area.
- Rajasthan, for example, experiences hot and arid climate, Kerala has tropical rainy climate, Greenland has cold desert climate and the climate of Central Asia is temperate continental.
Factors determining Climate of India:
The factors which determine the climate of a place can be broadly classified into two:
- Factors related to location and relief
- Factors related to air pressure and winds
Factors related to location and relief
- Latitude – The Tropic of Cancer passes through the middle of the country from the Rann of Kachchh in the west to Mizoram in the east.
- Almost half of the country lying south of the Tropic of Cancer lies in the Tropical zone and the northern part of India lies in the sub-tropical and temperate zone.
- The tropical zone is nearer to the equator and therefore experiences high temperatures throughout the year with a small daily and annual range.
- The area north of the tropic of cancer being away from the equator experiences an extreme climate with a high daily and annual range of temperature.
- The Himalayan Mountains – The lofty Himalayan mountains in the north act as an effective climate divide.
- These mountains provide a shield against the cold northern winds which originate near the Arctic Circle and blow across central and eastern Asia.
- It is because of these mountains that this subcontinent experiences comparatively milder winters as compared to Central Asia.
- These mountains also trap the monsoon winds forcing them to shed their moisture within the subcontinent.
- Distribution of land and water – India is surrounded by water bodies on three sides in the south and is girdled by a high and continuous mountain wall in the north.
- Water heats up and cools down quickly as compared to land.
- This differential heating creates different air pressure zones in different seasons in and around the subcontinent.
- This difference in air pressure causes a reversal in the direction of monsoon winds.
- Distance from the sea – The sea exerts a moderate influence on climate.
- As the distance from the sea increases, its moderating influence decreases and such regions have extreme weather conditions.
- This condition is known as continentality i.e, very hot summers and very cold winters.
- Altitude – The places in the mountains are cooler than the places on the plains because with the increase in height temperature decreases.
- Relief – The relief of India also affects the temperature, air pressure, direction and speed of the wind and, the amount and distribution of rainfall.
- The windward sides of Western Ghats and Assam receive high rainfall during June and September whereas the southern plateau remains dry due to its leeward situation along the Western Ghats.
Read more : Climatology