G. Eidmann

Indications of convectively generated gravity waves in crista temperatures

Abstract During shuttle missions STS-66 (November, 1994) and STS-85 (August, 1997) the CRyogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) acquired temperature data and mixing ratios of, among other trace gases, tropospheric water vapor with very high spatial resolution. Vertical profiles of temperature are analyzed for gravity waves (GW). Enhanced GW activity is found at the equator and in the northern hemispheric subtropics. The patterns of high GW excitation resemble regions of upward tropopause displacement, indicated by high water vapor mixing ratio, suggesting that the waves are generated by deep convection. The observed GWs have non—zero phase speeds with respect to the ground. The horizontal wavelengths of the waves are discussed in conjunction with the wave source.

A detection method for cirrus clouds using CRISTA 1 and 2 measurements

Abstract During both missions of the CRyogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) instrument in November 1994 and August 1997 high reaching tropical clouds at and above the tropopause could be observed. For the cloud detection a simple but effective cloud indicator was developed and tested under different extreme atmospheric conditions. Estimated cloud top heights were used for the computation of cloud occurrence frequencies. The horizontal and vertical distributions are in good agreement with the SAGE II subvisual cirrus cloud climatology. Seasonal variations, strong longitudinal variability and indications of enhanced cloud occurrence frequencies during the El Nino 94 95 and 97 98 events have been detected.

Fluctuation power spectra in the mid stratosphere at increased horizontal resolution

Abstract The second CRISTA IR limb-scanning mission took place from Aug. 8 th to Aug. 16 th 1997. In part of this flight a special measurement mode, the so-called “Staring Mode”, was applied. In this mode CRISTA telescopes and sensors were oriented perpendicular to the flight direction and at approximately fixed tangent heights. A wavelet analysis was performed for the data of two selected regions, one over the tropical and subtropical Eastern Pacific (Region 1) and one over Eastern Asia (Region 2), both at about 29 km altitude. From these data, the first horizontal wavenumber spectra of temperature in the middle stratosphere are derived. The analysis involved three levels of data products: a ) The measured limb radiance difference between the 12.63 and the 12.69 μm IR window, b ) the same radiance difference corrected for tangent height variations, and c ) temperatures computed from b ), based on limb-radiance transport theory and after linear detrending for removing the latitudinal temperature dependence. In region 1, power-law behaviour was found between wavelengths of 256 – 1024 km in all three cases, with the temperature spectrum showing a slope of −2.13 ± 0.80. In region 2, power-law behaviour was also seen but over a wider range of 128 – 4096 km, and with a slope of −1.66 ± 0.36 for the temperature spectrum. These results represent the first calculations of the mid-stratospheric temperature spectrum for such a wide range of horizontal scales. The values obtained for the slopes are discussed and compared to the results of available theories.

Horizontal temperature variability in the stratosphere: global variations inferred from CRISTA data

Abstract In two separate orbital campaigns (November, 1994 and August, 1997), the Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) instrument acquired global stratospheric data of high accuracy and high spatial resolution. The standard limb-scanned CRISTA measurements resolved atmospheric spatial structures with vertical dimensions ≥ 1.5 – 2 km and horizontal dimensions ≥ 100 – 200 km. A fluctuation analysis of horizontal temperature distributions derived from these data is presented. This method is somewhat complementary to conventional power-spectral analysis techniques.