Abstract
Abstract. Space-time spectral analysis of satellite data is an important method to derive a synoptic picture of the atmosphere from measurements sampled asynoptically by satellite instruments. In addition, it serves as a powerful tool to identify and separate different wave modes in the atmospheric data. In our work we present space-time spectral analyses of chemical heating rates derived from Scanning Imaging Absorption SpectroMeter for Atmospheric CHartographY (SCIAMACHY) hydroxyl nightglow emission measurements onboard Envisat for the years 2002–2006 at mesopause heights. Since SCIAMACHY nightglow hydroxyl emission measurements are restricted to the ascending (nighttime) part of the satellite orbit, our analysis also includes temperature spectra derived from 15 μm CO2 emissions measured by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument. SABER offers better temporal and spatial coverage (daytime and night-time values of temperature) and a more regular sampling grid. Therefore SABER spectra also contain information about higher frequency waves. Comparison of SCIAMACHY and SABER results shows that SCIAMACHY, in spite of its observational restrictions, provides valuable information on most of the wave modes present in the mesopause region. The main differences between wave spectra obtained from these sensors can be attributed to the differences in their sampling patterns.
Highlights
Planetary scale long-period atmospheric wave modes in the mesosphere/lower thermosphere (MLT) have been reported in the literature for several decades
Because the SABER data are a very comprehensive data set SABER space-time spectra are well suited for a comparison with SCIAMACHY space-time spectra to investigate effects of the different sampling, as well as differences arising from the measurement of different limb emissions (SCIAMACHY: OH layer vs. SABER: optically thin CO2 emissions) which could bring about different observational filters and different responses to atmospheric waves
By comparing “artificial” and original SCIAMACHY spectra with the original SABER spectra we find that part of the differences observed between SCIAMACHY and SABER for the wave modes discussed in Sect. 4 can, be explained by the different sampling patterns
Summary
Planetary scale long-period atmospheric wave modes in the mesosphere/lower thermosphere (MLT) have been reported in the literature for several decades. In the space-time Fourier spectra the different wave modes can be identified by their characteristic frequencies and zonal wavenumbers With these space-time Fourier techniques frequencies of up to 1 cycle/day (periods of about 1 day or longer) can be resolved unambiguously if satellite data are available for both ascending and descending parts of the satellite orbit (Hayashi, 1980; Salby, 1982a,b; Wu et al, 1995). The situation is different if data are available only for the descending or, as is the case for the SCIAMACHY hydroxyl nightglow data, only for the ascending part of the satellite orbit In this case only frequencies of up to 0.5 cycles/day (periods of about 2 days or longer) can be resolved unambiguously
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