How is weather forecast done?
Forecast systems, particularly those dealing with short-term forecasts, generally use numerical weather prediction methods based on sets of mathematical equations on the behavior of the atmosphere. These equations dealing with various atmospheric phenomena like land/ sea temperature, rain, wind etc. are combined into complex mathematical models. These models receive constant inputs on current weather observations, from which forecast data for future weather is calculated. Although recent advances in satellite and computer technology have helped in significantly improving weather forecasting,our knowledge about the atmosphere is still incomplete and hence 100% accuracy in weather prediction is not possible.
What are the various types of forecasts?
There are four types of weather forecasts. Now-casting is about predicting weather conditions up to 24 hours from the current time. Short range forecasts are valid up to 72 hours ahead while medium range forecasts predict conditions for a period of 4 to 10 days. Monthly and seasonal forecasts like predictions about the arrival of monsoons, come under long range forecasting, that is the prediction of average weather conditions for a minimum of 30 days and up to an entire season.
What causes the monsoon?
Derived from the Arabic word Mausim meaning season, monsoon is the seasonal reversal in wind direction that causes most of the rainfall received in India. Experts believe the monsoon is caused by the annual oscillation of the sun between the tropics of Cancer and Capricorn. The apparent change in the sun's position with reference to the earth changes the position of the 'thermal equator' - the region of maximum heating on the earth's surface. The region around the thermal equator is a low pressure belt that witnesses a continuous rise of moist wind from the sea surface. The oscillating low pressure belt also causes periodic changes in temperature, pressure, wind and so on and builds the monsoon system. There are two types of monsoon that cause rain in India — the southwest monsoon, which covers the entire country, and the northeast monsoon that causes rain in Tamil Nadu and some parts of Kerala.
How is the forecast of the southwest monsoon done?
Long range prediction of the monsoon is based on a statistical method. The method involves identification of predictive signals (predictors) that have been shown to have a stable historical relationship with the 'predict', the monsoon in this case. At present, the IMD uses eight predictors. These include sea surface temperatures of the North Atlantic and equatorial southeast Indian Ocean and Central Pacific Ocean along with land surface temperatures of northwest Europe. The warm water volume of the equatorial Pacific, mean sea level pressure at the North Atlantic and East Asia and the wind in the north central Pacific Ocean are also among them. There are two stages of the monsoon forecast, the first issued in April and an updated forecast done in June.
What is ENSO and how does it affect the Indian monsoon?
El Nino Southern Oscillation refers to anomalously warm or cold sea surface temperatures that develops for long periods of time off the western coast of South America. El Nino or Pacific warm episode represents the warm phase of the oscillation while La Nina represents the cold phase. Although there is no one-to-one correspondence between ENSO and the Indian monsoon, the warm phase of ENSO is generally associated with weaker than normal monsoon and vice versa. Between 1885 and 2007, there were 36 El Nino and 25 La Nina years. In 15 El Nino years, the Indian monsoon was below normal while in 9 La Nina years it was above normal.
Forecast systems, particularly those dealing with short-term forecasts, generally use numerical weather prediction methods based on sets of mathematical equations on the behavior of the atmosphere. These equations dealing with various atmospheric phenomena like land/ sea temperature, rain, wind etc. are combined into complex mathematical models. These models receive constant inputs on current weather observations, from which forecast data for future weather is calculated. Although recent advances in satellite and computer technology have helped in significantly improving weather forecasting,our knowledge about the atmosphere is still incomplete and hence 100% accuracy in weather prediction is not possible.
What are the various types of forecasts?
There are four types of weather forecasts. Now-casting is about predicting weather conditions up to 24 hours from the current time. Short range forecasts are valid up to 72 hours ahead while medium range forecasts predict conditions for a period of 4 to 10 days. Monthly and seasonal forecasts like predictions about the arrival of monsoons, come under long range forecasting, that is the prediction of average weather conditions for a minimum of 30 days and up to an entire season.
What causes the monsoon?
Derived from the Arabic word Mausim meaning season, monsoon is the seasonal reversal in wind direction that causes most of the rainfall received in India. Experts believe the monsoon is caused by the annual oscillation of the sun between the tropics of Cancer and Capricorn. The apparent change in the sun's position with reference to the earth changes the position of the 'thermal equator' - the region of maximum heating on the earth's surface. The region around the thermal equator is a low pressure belt that witnesses a continuous rise of moist wind from the sea surface. The oscillating low pressure belt also causes periodic changes in temperature, pressure, wind and so on and builds the monsoon system. There are two types of monsoon that cause rain in India — the southwest monsoon, which covers the entire country, and the northeast monsoon that causes rain in Tamil Nadu and some parts of Kerala.
How is the forecast of the southwest monsoon done?
Long range prediction of the monsoon is based on a statistical method. The method involves identification of predictive signals (predictors) that have been shown to have a stable historical relationship with the 'predict', the monsoon in this case. At present, the IMD uses eight predictors. These include sea surface temperatures of the North Atlantic and equatorial southeast Indian Ocean and Central Pacific Ocean along with land surface temperatures of northwest Europe. The warm water volume of the equatorial Pacific, mean sea level pressure at the North Atlantic and East Asia and the wind in the north central Pacific Ocean are also among them. There are two stages of the monsoon forecast, the first issued in April and an updated forecast done in June.
What is ENSO and how does it affect the Indian monsoon?
El Nino Southern Oscillation refers to anomalously warm or cold sea surface temperatures that develops for long periods of time off the western coast of South America. El Nino or Pacific warm episode represents the warm phase of the oscillation while La Nina represents the cold phase. Although there is no one-to-one correspondence between ENSO and the Indian monsoon, the warm phase of ENSO is generally associated with weaker than normal monsoon and vice versa. Between 1885 and 2007, there were 36 El Nino and 25 La Nina years. In 15 El Nino years, the Indian monsoon was below normal while in 9 La Nina years it was above normal.
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