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Kelvin/Rossby
Kelvin Waves
There are two types of Kelvin waves, coastal and equatorial, and they are both gravity driven and non-dispersive. They are often excited by an abrupt change in the overlying wind field, such as the shift in the trade winds at the start of El Niño. Equatorial waves propagate to the east in the northern hemisphere, using the equator as a wave guide. Coastal Kelvin waves propagate around the northern hemisphere oceans in a counterclockwise direction using the coastline as a wave guide. These waves, especially the surface waves are very fast moving, typically with speeds of ~2.8 m/s, or about 250 kilometers in a day. A Kelvin wave would take about 2 months to cross the Pacific from New Guinea to South America.
Rossby Waves
The circulation in the "upper air" (say 700 mbar [or hPa]) upwards, consists of a large circumpolar vortex system -- on this broad flow are superimposed a system of variable, but usually slow-moving long waves, sometimes stationary, or very occasionally retrogressive (i.e. they move east-to-west). Down the scale again, there are a series of short-waves running quickly (circa 15 degrees of longitude per 24 hr: +/- 5 degrees) through the flow, driving, and being in turn modified, by the familiar synoptic scale disturbances in the lower troposphere (i.e. frontal systems), which in turn feed-back energy (in all forms) up the scale to influence the broadscale pattern.
There are two types of Kelvin waves, coastal and equatorial, and they are both gravity driven and non-dispersive. They are often excited by an abrupt change in the overlying wind field, such as the shift in the trade winds at the start of El Niño. Equatorial waves propagate to the east in the northern hemisphere, using the equator as a wave guide. Coastal Kelvin waves propagate around the northern hemisphere oceans in a counterclockwise direction using the coastline as a wave guide. These waves, especially the surface waves are very fast moving, typically with speeds of ~2.8 m/s, or about 250 kilometers in a day. A Kelvin wave would take about 2 months to cross the Pacific from New Guinea to South America.
Rossby Waves
The circulation in the "upper air" (say 700 mbar [or hPa]) upwards, consists of a large circumpolar vortex system -- on this broad flow are superimposed a system of variable, but usually slow-moving long waves, sometimes stationary, or very occasionally retrogressive (i.e. they move east-to-west). Down the scale again, there are a series of short-waves running quickly (circa 15 degrees of longitude per 24 hr: +/- 5 degrees) through the flow, driving, and being in turn modified, by the familiar synoptic scale disturbances in the lower troposphere (i.e. frontal systems), which in turn feed-back energy (in all forms) up the scale to influence the broadscale pattern.
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