Gravity wave variances and propagation derived from AIRS radiances 1Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
16 Feb 2012
2Naval Research Laboratory, Washington DC 20375, USA
*now at: Goddard Space Flight Center, Greenbelt, MD 20771, USA
Received: 17 November 2010 – Published in Atmos. Chem. Phys. Discuss.: 15 April 2011 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.
Revised: 31 January 2012 – Accepted: 04 February 2012 – Published: 16 February 2012
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).
Citation: Gong, J., Wu, D. L., and Eckermann, S. D.: Gravity wave variances and propagation derived from AIRS radiances, Atmos. Chem. Phys., 12, 1701-1720, doi:10.5194/acp-12-1701-2012, 2012.