Space-time analyses, which are sensitive to details of retrieval and gridding processes not seen in zonal and time means, are used to investigate the integrity of version 8 gridded retrieved temperatures from the Improved Stratospheric And Mesospheric Sounder (ISAMS) on the Upper Atmosphere Research Satellite (UARS). This note presents results of such analyses applied to ISAMS tropical data. Comparisons are made with Microwave Limb Sounder (MLS), also on UARS, temperatures.
Prominent zonal wave number 1 features are observed with characteristics similar to those expected for Kelvin waves. Time versus longitude plots reveal quasi-regular eastward phase progression from November 1991 to mid-January 1992. The perturbations extend throughout the upper stratosphere and lower mesosphere (altitudes of 32-64 km), exhibiting peak-to-peak amplitudes of up to 2-3 deg K and periods from approximately 2 weeks in mid-stratosphere to approximately 1 week at higher altitudes. Faster Kelvin waves with periods of 3-5 days are also found in the lower mesosphere. Height versus time plots reveal downward phase and upward group velocities, consistent with forcing from below. Vertical wavelengths are approximately 20 km for the slower mode and about twice this scale for the faster 3-5 day mode. The features are trapped within 10-15 degrees of the equator. Kelvin wave signature in ISAMS and MLS temperatures are compared at 10 and 1 hPa. Good agreement is found, illustrating the internal consistency and ability of both ISAMS and MLS temperature grids to capture relatively small amplitude features with space-time scales of fast, zonally asymmetric equatorial modes.