An atmospheric wave is a periodic disturbance in the fields of
atmosphericvariables (like surface pressureor geopotential height, temperature, or wind velocity) which may either propagate ("traveling wave") or not ("stationary wave"). Atmospheric waves range in spatialand temporalscale from large-scale planetary waves ( Rossby waves) to minute sound waves. Atmospheric waves with periods which are harmonicsof 1 solar day(e.g. 24 hours, 12 hours, 8 hours... etc) are known as atmospheric tides.
Causes and effects
The mechanism for the forcing of the wave, for example the generation of the initial or prolonged disturbance in the atmospheric variables, can vary. Generally, waves are either excited by
heatingor dynamic effects, for example the obstruction of the flow by mountain ranges like the Rocky Mountainsin the U.S. or the Alpsin Europe. Heating effects can be small-scale (like the generation of gravity waves by convection) or large-scale (the formation of Rossby wavesby the temperature contrasts between continents and oceans in the Northern hemispherewinter).
Atmospheric waves transport
momentum, which is fed back into the background flow as the wave dissipates. This wave forcing of the flow is particularly important in the stratosphere, where this momentum deposition by gravity waves gives rise to sudden stratospheric warmings and the quasi-biennial oscillation.
In the mathematical description of atmospheric waves,
spherical harmonicsare used. When considering a section of a wave along a latitudecircle, this is equivalent to a sinusoidalshape.
Types of waves
Because the propagation of the wave is fundamentally caused by an imbalance of the
forces acting on the air (which is often thought of in terms of air parcels when considering wave motion), the types of waves and their propagation characteristics vary latitudinally, principally because the Coriolis effecton horizontal flow is maximal at the poles and zero at the equator.
The different wave types are:
sound waves (usually eliminated from the atmospheric equations of motiondue to their high frequency)These are longitudinal or compression waves. The sound wave propagates in the atmosphere though a series of compressions and expansions parallel to the direction of propagation.
gravity waves (require stable stratificationof the atmosphere)
* inertio-gravity waves (also include a significant Coriolis effect as opposed to "normal" gravity waves)
Rossby waves (can be seen in the troughs and ridges of 500 hPageopotential caused by midlatitude cyclones and anticyclones)
At the equator, mixed Rossby-gravity and
Kelvin waves can also be observed.
* Holton, James R.: "An Introduction to Dynamic Meteorology", 2004. ISBN 0-12-354015-1
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