Abstract. We investigate stratospheric gravity wave observations by the
Atmospheric InfraRed Sounder (AIRS) aboard NASA's Aqua satellite and
the High Resolution Dynamics Limb Sounder (HIRDLS) aboard NASA's
Aura satellite. AIRS operational temperature retrievals are
typically not used for studies of gravity waves, because their vertical and
horizontal resolution is rather limited. This study uses data of a
high-resolution retrieval which provides stratospheric temperature
profiles for each individual satellite footprint. Therefore the
horizontal sampling of the high-resolution retrieval is 9 times
better than that of the operational retrieval. HIRDLS provides 2-D
spectral information of observed gravity waves in terms of
along-track and vertical wavelengths. AIRS as a nadir sounder is
more sensitive to short-horizontal-wavelength gravity waves, and
HIRDLS as a limb sounder is more sensitive to short-vertical-wavelength
gravity waves. Therefore HIRDLS is ideally suited to
complement AIRS observations. A calculated momentum flux factor
indicates that the waves seen by AIRS contribute significantly to
momentum flux, even if the AIRS temperature variance may be small
compared to HIRDLS. The stratospheric wave structures observed by
AIRS and HIRDLS often agree very well. Case studies of a mountain
wave event and a non-orographic wave event demonstrate that the
observed phase structures of AIRS and HIRDLS are also similar. AIRS has a
coarser vertical resolution, which results in an attenuation of the
amplitude and coarser vertical wavelengths than for
HIRDLS. However, AIRS has a much higher horizontal resolution, and
the propagation direction of the waves can be clearly identified in
geographical maps. The horizontal orientation of the phase fronts
can be deduced from AIRS 3-D temperature fields. This is a
restricting factor for gravity wave analyses of limb
measurements. Additionally, temperature variances with respect to
stratospheric gravity wave activity are compared on a statistical
basis. The complete HIRDLS measurement period from January 2005 to
March 2008 is covered. The seasonal and latitudinal distributions of
gravity wave activity as observed by AIRS and HIRDLS agree well. A
strong annual cycle at mid- and high latitudes is found in time
series of gravity wave variances at 42 km, which has its maxima during
wintertime and its minima during summertime. The variability is largest during
austral wintertime at 60∘ S. Variations in the zonal winds at 2.5 hPa are associated
with large variability in gravity wave variances. Altogether,
gravity wave variances of AIRS and HIRDLS are complementary to each other. Large parts of the gravity wave
spectrum are covered by joint observations. This opens up
fascinating vistas for future gravity wave research.
Numerical Simulations of a Gravity Wave Event over CCOPE. Part I: The Role of Geostrophic Adjustment in Mesoscale Jetlet Formation
