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Line 1: {{Short description\|Periodic disturbance in atmospheres}} [[File:Dust Atmospheric wave Sep 23 2011 1200(UTC).jpg\|~~250px~~thumb\|~~thumbnail~~upright=1.0\|right\|Atmospheric waves, associated with a small dust storm of north ~~eastern~~western Africa on 23 September ~~23,~~ 2011. ]] An '''atmospheric wave''' is a periodic disturbance in the fields of [[atmospheric]] variables (like [[surface pressure]] or [[geopotential height]], [[temperature]], or [[wind velocity]]) which may either propagate (''[[traveling wave]]'') or not (''[[standing wave]]''). Atmospheric waves range in [[Three-dimensional space\|spatial]] and [[Time\|temporal]] scale from large-scale planetary waves ([[Rossby wave]]s) to minute [[sound wave]]s. Atmospheric waves with periods which are [[harmonics]] of 1 [[solar day]] (e.g. 24 hours, 12 hours, 8 hours... etc.) are known as [[atmospheric tide]]s.▼ ▲An '''atmospheric wave''' is a periodic disturbance in the fields of [[atmospheric]] variables (like [[Atmospheric pressure#Surface pressure\|surface pressure]] or [[geopotential height]], [[temperature]], or [[wind velocity]]) which may either propagate (''[[traveling wave]]'') or ~~not~~be stationary (''[[standing wave]]''). Atmospheric waves range in [[Three-dimensional space\|spatial]] and [[Time\|temporal]] scale from large-scale planetary waves ([[Rossby wave]]s) to minute [[sound wave]]s. Atmospheric waves with periods which are [[harmonics]] of 1 [[solar day]] (e.g. 24 hours, 12 hours, 8 hours... etc.) are known as [[atmospheric tide]]s. == 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 [[heating]] or [[Dynamics (mechanics)\|dynamic]] effects, for example the obstruction of the flow by [[mountain ranges]] like the [[Rocky Mountains]] in the [[United States\|U.S.]] or the [[Alps]] in [[Europe]]. Heating effects can be small-scale (like the generation of [[gravity wave]]s by [[convection]]) or large-scale (the formation of [[Rossby waves]] by the temperature contrasts between continents and oceans in the [[Northern hemisphere]] winter). 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 planetary -scale [[Rossby waves]] gives rise to [[sudden stratospheric warming]]s and the deposition by [[gravity waves]] gives rise to the [[quasi-biennial oscillation]]. In the mathematical description of atmospheric waves, [[spherical harmonics]] are used. When considering a section of a wave along a [[latitude]] circle, this is equivalent to a [[sinusoidal]] shape. Spherical harmonics, representing individual Rossby-Haurwitz planetary wave modes, can have any orientation with respect to the axis of rotation of the planet.<ref>{{Cite journal \|last=Longuet-Higgins \|first=M.S. \|date=1964 \|title=Planetary Waves on a Rotating Sphere \|journal=Proc. R. Soc. A \|volume=279 \|pages=446–473}}</ref> Remarkably - while the very existence of these planetary wave modes ''requires'' the rotation of the planet around its polar axis - the phase velocity of the individual wave modes does ''not'' depend on the relative orientation of the spherically harmonic wave mode with respect to the axis of the planet. This can be shown to be a consequence of the underlying (approximate) spherical symmetry of the planet, even though this symmetry is broken by the planet's rotation.<ref>{{Cite journal \|last=Toorn \|first=Ramses van der \|date=2019 \|title=Elementary properties of non-Linear Rossby-Haurwitz planetary waves revisited in terms of the underlying spherical symmetry \|journal=AIMS Mathematics \|language=en \|volume=4 \|issue=2 \|pages=279–298 \|doi=10.3934/math.2019.2.279 \|s2cid=239363997 \|issn=2473-6988\|doi-access=free \|url=https://repository.tudelft.nl/islandora/object/uuid%3Af8e93707-91d3-44ae-aa27-133d59aca842/datastream/OBJ/download }}</ref> ~~In the mathematical description of atmospheric waves, [[spherical harmonics]] are used. When considering a section of a wave along a [[latitude]] circle, this is equivalent to a [[sinusoidal]] shape.~~ == Types of waves == Because the propagation of the wave is fundamentally caused by an imbalance of the [[force]]s acting on the air (which is often thought of in terms of [[air parcel]]s when considering wave motion), the types of waves and their propagation characteristics vary latitudinally, principally because the [[Coriolis effect]] on horizontal flow is maximal at the [[Geographical pole\|pole]]s and zero at the [[equator]]. ~~The~~There ~~different~~are ~~wave~~four different types ~~are~~of waves: * [[sound wave]]s (usually eliminated from the atmospheric [[equations of motion]] due to their high frequency) Line 21 ⟶ 23: At the equator, mixed Rossby-gravity and [[Kelvin wave]]s can also be observed. == See also == * [[Atmospheric thermodynamics]] == References == {{Reflist}} == Further reading == * Holton, James R.: ''An Introduction to Dynamic Meteorology'', 2004. {{ISBN \|0-12-354015-1}} {{Authority control}} [[Category:Atmospheric dynamics\|Wave]]