The Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) deployed on board different research aircraft shall provide a detailed picture of the UTLS region. GLORIA uses a two-dimensional detector array for infrared limb-observations. The GLORIA in-flight calibration system consists of two identical large-area high-precision blackbodies, which are independently controlled at two different temperatures. Thermo-Electric Coolers are used to control the temperature of the blackbodies. The system has been comprehensively characterized for its spatially and spectrally resolved radiation properties in terms of radiation temperature traceable to the international temperature scale (ITS-90) at the national metrology institute of Germany (PTB).
Gravity wave variances in CLAES temperature data are isolated by a 0-6 zonal wavenumber Kalman filter. Resulting vertical profiles of temperature residuals are analyzed by a combination of Maximum Entropy Method (MEM) and harmonic analysis for gravity waves (GWs). This is the same method previously employed to study GWs in CRISTA data. We obtain nearly 1.5 years of continuous GW data between 34S and 34N and good coverage at higher latitudes depending on UARS yaw maneuvers. Results are compared to CRISTA data and interpreted for different wave sources. A time series of zonal mean GW variance shows
the seasonal shift of the tropical maximum of GW variance around the equator. Maximum variances are reached 1-2 months after summer solstice, consistent with the shift of the inner tropical convergence zone. Quiet summer and enhanced winter values at mid and high latitudes are due to a combination of wind filtering and wind modulation. Wind filtering occurs when GWs propagate from tropospheric west winds into the lower stratosphere. There prevailing winds reverse from west wind in winter to east wind in summer, thus causing a critical layer for low phase speed GWs during summer. The term wind modulation is used for the Doppler shift of the GW spectrum
by the wind at the observation altitude shifting parts of the GW spectrum in and out the vertical-wavelength visibility limits of the instrument. We find evidence for both processes in the data and indication that GW filtering might be the more important one.
We consider the example of the CRyogenic Infrared Spectrometers and
Telescopes for the Atmosphere (CRISTA) experiment to deduce the sensitivity of an infrared emission limb sounder to gravity waves of different horizontal and vertical wavelength. The sensitivity studies show that gravity waves with horizontal wavelengths of the order of 100-200 km or longer can be detected. The deduced sensitivity factors are validated by comparing CRISTA and data sonde temperature profiles. Analysis of CRISTA temperature data
reveals large gravity wave amplitudes in the stratosphere over southernmost South America. The horizontal structure is compared to
model calculations. Global distributions are discussed with respect to convective sources, wind modulation, and Coriolis force modulation. It is shown that even the very dense spatial sampling of the CRISTA instrument is insufficient to fully resolve the horizontal structure of the waves which are seen in the vertical.
Hence, increased spatial resolution of about 50 X 50 km or better
is required to obtain all information the limb sounding technique is capable to provide.