Tidal signatures in temperature data from CRISTA 1 mission

Temperature measurements in the stratosphere and mesosphere were taken duri ng the first Cryogenic Infrared Spectrometers and Telescopes for the Atmosp here (CRISTA 1) mission using CO2 emissions, These measurements range from 13 to close to 100 km, and individual temperature measurements have a preci sion of 1 K. The CRISTA orbit was circular at an inclination of 57 degrees, so local time variations during the 7 day mission were small for a given l atitude and orbit leg. Zonal averages of the data show significant structur e in the vertical and as a function of latitude. Temperature differences be tween the zonal mean data from the ascending and descending portions of the orbit are of the form expected from the diurnal tide. The maximum zonal me an difference is approximate to 20 K and occurs over the equator at an alti tude of 75 km, Zonal variations in the temperature difference indicate that the tidal amplitude is not uniform at all longitudes. At the equator the m aximum amplitude (30 K) appears over the African sector and the minimum (10 K) over the Pacific sector. This variation is most likely a nonmigrating w avenumber 2 diurnal tide although other less plausible possibilities exist. To facilitate comparisons with model results the temperature variations ar e converted to equivalent vertical displacements, assuming the tidal motion s are adiabatic. Such an approach is appropriate in the mesosphere where di urnal variations due to radiative effects are small and reduces the depende nce of the measured temperature amplitude on the background temperature pro file. Equivalent vertical displacements are also calculated using results f rom the global scale wave model. For the most part the model results and ob servations are in excellent qualitative and good quantitative agreement fro m the tropopause to the mesopause. However, the observed vertical wavelengt h is smaller, and its amplitude in terms of equivalent displacement is smal ler in the upper mesosphere than that in the model. The decrease in amplitu de is consistent with that expected from the transition from equinox to sol stice conditions.