Horizontal Temperature Variability in the Stratosphere: Global Variations Inferred from Crista Data

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 2 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. 0 260 1 COSPAR. Published by Elsevier Science Ltd. All rights reserved. INTRODUCTION The investigation of horizontal temperature and trace gas fluctuations in the stratosphere is important for two reasons: 1. For validation of satellite experiments one needs to know whether discrepancies in the measured quantities are due to instrumental inaccuracies or atmospheric variability. Hence a statistical description of possible atmospheric variability would be helpful. 2. Quantification of geographical, altitude and time dependencies of such fluctuations allows for the investigation of dynamical processes under certain conditions and on different scales, such as gravity waves (GW), energy or enstrophy cascades. Such processes are often described with the help of power spectral analyses. In practice, such methods put severe demands on datasets. Since high data density and regular spacing are difficult to achieve using satellite data, here another, more robust tool, is presented. Hereby temperature variability is derived from the data without the need to transform them into Fourier space by the use of statistical methods. The properties of this analysis technique are discussed in relation to the two topics mentioned above. INSTRUMENT AND DATA CRISTA (Offermann et al., 1999) measured temperatures and trace gases in the middle (4 14 pm) and far (15 71 pm) infrared by the limb-scanning technique. It was flown on two Space Shuttle missions on a 300 km orbit with 57” inclination during November 3-14, 1994 and August 8-16, 1997. Measurements were taken using four spectrometers and three telescopes simultaneously. In this study, preliminary (Version 1) data of the standard stratospheric mode from the second CRISTA mission (Grossmann, 2000) are used. In this mode the three telescopes covered an altitude regime from about 10 to 55 km with a vertical step width of 2 km. The along-track resolution was nominally about 240 km, the across-track resolution less than 650 km. The latitudinal coverage was f 74”. Precision and accuracy of stratospheric temperature measurements are about the same as those of the first CRISTA mission (Riese et al., 1999), namely 0.35 K and 1 K, respectively. METHODS Three of the four spectrometers were used to derive temperature information from the IR spectral region at 12.63 pm. Thus at every telescope’s footprint one temperature measurement was performed. The analysis