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Gravity Waves (GW)

NCAR Experts Directory

Program Leads:
Hanli Liu
Jadwiga Richter

Other Experts:
Vanda Grubišić
Mitch Moncrieff

Gravity Wave Strategic Goals Links:
- Gravity Waves from the Nested Regional Climate Model
- Gravity Wave Forcing and Wind Balance in the Mesosphere and Lower Thermosphere (follows write up listed above)

Potential energy density of gravity waves

What are Gravity Waves?

Gravity waves play a central role in the coupling of the lower and upper atmosphere. They transfer momentum from their lower tropospheric and upper tropospheric and lower stratospheric (UTLS) sources to middle and upper atmospheric regions, e.g., the stratosphere and mesosphere and lower thermosphere (MLT). In these regions, gravity waves break or dissipate, thereby inducing eddy transport of momentum, heat, and atmospheric species. These mesoscale-regional scale processes have global significance because of their accumulative effects from the global distribution of various wave sources. The primary challenges to observational, numerical, and analytical studies are how to better quantify gravity wave excitation as related to various tropospheric processes, the global distribution of the wave sources, their propagation and breaking, and the multiscale interactions involving gravity waves in the UTLS and MLT regions.

Atmospheric gravity waves exist by virtue of the stable density stratification resulting from the atmosphere being acted on by gravity.  Basically, any disturbance to the balanced state results in the propagation of atmospheric gravity waves.  Atmospheric gravity waves occur on a variety of spatial and temporal scales.  Their horizontal wavelengths range from kilometers to thousands of kilometers, and their periods range from the Brunt-Väisäla period (approximately ten minutes) to those of the reciprocal of the Coriolis parameter, which is infinite directly at the Equator and is as short as one-half day at the poles.

Gravity waves can occur at all altitudes in the atmosphere and are important for several reasons.  They can transport energy and momentum from one region of the atmosphere to another.  They can initiate and modulate convection and affect subsequent hydrological processes. They disturb the smooth, balanced state, and hence introduce small-scale structures in physical quantities such as chemical tracers.  The small-scale structures introduced can turn to instabilities that lead to turbulent mixing which is hazardous to aviation. 

Due to their vast spatial and temporal existence, accumulative effects of gravity waves affect the atmospheric dynamics and thermal/compositional structures from mesoscales to global scales. Therefore, understanding gravity wave excitation, propagation, and breaking properties has great implications for both weather and climate applications. The multiscale nature of the gravity waves poses a difficult challenge to the physical understanding and quantification of these waves in both observations and numerical models.

There are two issues that may be thought of as being operationally separate, although of course they are intimately related. These are (a) to better understand gravity waves in the atmosphere and (b) to develop good physically based gravity wave parameterizations for use in atmospheric General Circulation Models (GCMs).