Fluctuation power spectra in the mid stratosphere at increased horizontal resolution

Abstract

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.