Gravity waves are ubiquitous in Earth's atmosphere. They play important roles in the vertical transport of momentum and chemical constituents, and all global climate models now include a parameterization of gravity-wave effects. These parameterizations are, however, poorly constrained by observations, since gravity waves have time and space scales too short to be resolved by the conventional meteorological observing network.
The principal investigators (PIs) will derive global information about gravity wave activity and momentum transport using newly available, high vertical resolution, temperature profiles obtained from the radio occultation of global positioning system (GPS) signals. These data are acquired by two constellations of satellites in low Earth orbit, CHAMP (Challenging Minisatellite Payload) and COSMIC (Constellation Observing System for Meteorology, Ionosphere and Climate), which provide thousands of temperature profiles each day, distributed nearly uniformly over the globe.
Using these global data, the PIs will extract the gravity-wave contribution to the temperature structure by removing those variations that project onto large horizontal spatial scales. The horizontal wavenumbers and propagation directions of gravity waves will be determined from the phase differences between adjacent temperature profiles, and the vertical flux of horizontal momentum due to the wave activity will be estimated - this is the quantity that must be calculated by gravity-wave parameterizations in global models.
The quantity and global coverage of the GPS data will allow the PIs to associate gravity-wave activity with different sources, which include topography, convection, wind shear, synoptic fronts, and geostrophic adjustment. The connections of observed waves to likely sources will be explored using ray-tracing methods. The global data will also permit the structures and variability of large-scale atmospheric waves, such as equatorial Kelvin waves, to be determined with unprecedented accuracy. As data accumulate over time, it will be possible to explore the temporal variability of gravity-wave activity and its associations with variations in the planetary scale circulation of the atmosphere, such as the quasi-biennial oscillation and sudden stratospheric warmings.
Broader impacts of this research are in the importance of better gravity-wave information to the developers of gravity-wave parameterizations for global climate models and for research on wave interactions with high-latitude cirrus clouds.
