ROSSBY WAVES
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Subject : Geography
Concept :
- The meandering jet streams are called Rossby Waves.
- Rossby waves are natural phenomenon in the atmosphere and oceans due to rotation of earth.
- In planetary atmospheres, they are due to the variation in the Coriolis effect (When temperature contrast is low, speed of jet stream is low, and Coriolis force is weak leading to meandering) with latitude.
- Rossby waves are formed when polar air moves toward the Equator while tropical air is moving poleward.
- The existence of these waves explains the low-pressure cells (cyclones) and high-pressure cells (anticyclones).
Jet Stream
- The Jet Stream is a geostrophic wind blowing horizontally through the upper layers of the troposphere, generally from west to east, at an altitude of 20,000 – 50,000 feet.
- Jet Streams develop where air masses of differing temperatures meet. So, usually surface temperatures determine where t/he Jet Stream will form.
- Greater the difference in temperature, faster is the wind velocity inside the jet stream.
- Jet Streams extend from 20 degrees latitude to the poles in both hemispheres.
Where does it actually begin?
- Air when warmed in the tropics, around the equator, fuel the Jet Stream as it rises. Hitting the tropopause at about 58,000 feet (the layer of the atmosphere separating the troposphere from the stratosphere), it is drawn toward the colder air at the north and south poles.
Types of Jet Streams
- Sub Tropical Jet Streams are best developed in winter and early spring. Their maximum speed approaches 300 knots which are associated with the merger with polar-front jets. A subsidence motion accompanies subtropical jets and gives rise to predominantly fair weather in areas they pass over. Sometimes they drift northward and merge with a polar-front jet.
- Tropical Easterly Jet Stream occurs near the tropopause over Southeast Asia, India, and Africa during summer. This jet implies a deep layer of warm air to the north of the jet and colder air to the south over the Indian Ocean. The difference in heating and cooling and the ensuing pressure gradient is what drives this jet.
- Polar-Night Jet Stream meanders through the upper stratosphere over the poles. They are present in the convergence zone above the sub polar low pressure belt.