Abstract
Abstract. As the first gravity wave (GW) climatology study using nadir-viewing infrared sounders, 50 Atmospheric Infrared Sounder (AIRS) radiance channels are selected to estimate GW variances at pressure levels between 2–100 hPa. The GW variance for each scan in the cross-track direction is derived from radiance perturbations in the scan, independently of adjacent scans along the orbit. Since the scanning swaths are perpendicular to the satellite orbits, which are inclined meridionally at most latitudes, the zonal component of GW propagation can be inferred by differencing the variances derived between the westmost and the eastmost viewing angles. Consistent with previous GW studies using various satellite instruments, monthly mean AIRS variance shows large enhancements over meridionally oriented mountain ranges as well as some islands at winter hemisphere high latitudes. Enhanced wave activities are also found above tropical deep convective regions. GWs prefer to propagate westward above mountain ranges, and eastward above deep convection. AIRS 90 field-of-views (FOVs), ranging from +48° to −48° off nadir, can detect large-amplitude GWs with a phase velocity propagating preferentially at steep angles (e.g., those from orographic and convective sources). The annual cycle dominates the GW variances and the preferred propagation directions for all latitudes. Indication of a weak two-year variation in the tropics is found, which is presumably related to the Quasi-biennial oscillation (QBO). AIRS geometry makes its out-tracks capable of detecting GWs with vertical wavelengths substantially shorter than the thickness of instrument weighting functions. The novel discovery of AIRS capability of observing shallow inertia GWs will expand the potential of satellite GW remote sensing and provide further constraints on the GW drag parameterization schemes in the general circulation models (GCMs).
Highlights
Gravity waves (GWs) are known to play a key role in global climate and weather dynamics by transporting energy and momentum from the lower to the upper atmosphere, transport which is essential for determining the general circulation and temperature structure in the stratosphere and mesosphere
Climatology of the GW variance and zonal preferred propagation direction measured by Aqua-Atmospheric Infrared Sounder (AIRS) are documented
Evidence is found for short horizontal wavelength internal GWs forming dedicated geographical maxima that are closely related to localized sources such as topography and deep convection
Summary
Gravity waves (GWs) are known to play a key role in global climate and weather dynamics by transporting energy and momentum from the lower to the upper atmosphere, transport which is essential for determining the general circulation and temperature structure in the stratosphere and mesosphere (e.g., mesosphere wind reversal, quasi-biennial oscillation, etc.). Different observational instruments can only see partial gravity wave spectra Solving this jigsaw puzzle is underway (e.g., Alexander et al, 2010), the high-frequency portion of the spectrum is invisible to most of the instruments (Wu et al, 2006; Alexander et al, 2010), and the momentum flux associated with these waves remain uncertain. We are missing global information in particular on these shorter horizontal scale waves This presents an important information gap for any effort to constrain gravity wave drag (GWD) in climate models by measurements. AIRS is very sensitive to high-frequency GWs, which are badly constrained in their global distributions by both observations and models. One should keep in mind that GWs in the stratified atmosphere are essentially all internal waves
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