Upper air circulation refers to the movement of air at higher altitudes in the atmosphere, typically flowing in westerly directions at the top of the troposphere. The Jet Stream, a geostrophic wind, is a significant component of upper air circulation. It flows horizontally in the upper layers of the troposphere, primarily from west to east, at altitudes ranging from 20,000 to 50,000 feet. The formation of jet streams occurs when air masses with different temperatures converge.
Facilitates Monsoon Bursts: The Northward movement of the Subtropical Jet Stream (STJ), influenced by upper air circulation, plays a crucial role in triggering the onset of monsoons.
Causes High and Low Pressure Systems: Jet streams exhibit peaks (ridges) and troughs, creating areas of high and low pressure on Earth’s surface. The regions beneath the troughs experience low pressure, while the areas below the ridges have high pressure. This leads to the formation of cyclonic (low pressure) and anti-cyclonic (high pressure) conditions, respectively.
Influences Western Cyclonic Disturbances: During the winter months, the jet stream enters the Indian subcontinent from the west and northwest. Originating over the Mediterranean Sea, it brings western cyclonic disturbances into India.
Steers the Easterly Jet Stream: The jet stream further guides tropical depressions into India, which significantly contribute to the distribution of monsoon rainfall across the subcontinent. Regions along the tracks of these depressions experience the highest rainfall in India.
Noctilucent Clouds: Occasionally, jet streams transport moisture to the stratosphere, leading to the formation of rare noctilucent clouds. These clouds are observed in the night sky, particularly on clear summer nights.
Provides insights into El Niño and La Niña: Jet streams offer valuable information about the occurrence of El Niño and La Niña events.
Hinders Monsoon Winds: In some instances, the position of the upper jet stream above the southern Himalayas during June-July can create anti-cyclonic conditions in northwest India, impeding the progress of monsoon winds.
Accelerates Ozone Depletion: The jet stream can transport ozone-depleting substances from the upper atmosphere to Earth’s atmosphere, contributing to the depletion of the ozone layer.
The impact of jet streams and upper air circulation on India is wide-ranging. Although theories explaining these effects are still evolving, further research is necessary to deepen our understanding of their intricacies.