Gravity wave temperature variance calculated using the ray‐based spectral parameterization of convective gravity waves and its comparison with Microwave Limb Sounder observations

Abstract

The ray‐based spectral parameterization of convective gravity wave drag, which explicitly calculates the gravity wave propagation properties, is validated against the Microwave Limb Sounder (MLS) on the Upper Atmosphere Research Satellite (UARS). Offline calculations of the ray‐based parameterization are performed using global reanalysis data and gravity wave temperature variances calculated from the parameterization are compared with those measured from the MLS. The parameterized temperature variances are calculated from gravity wave packets that are visible from the MLS to allow for comparison. The MLS visibility is analytically obtained using the three‐dimensional MLS filter function. Comparisons between the parameterization calculations and MLS measurements show that both the magnitude and spatial distribution of the MLS‐filtered temperature variances in the ray‐based parameterization are in good agreement with observations. However, the MLS‐filtered temperature variances are found to be sensitive to the source‐level wave propagation direction, which, until now, has been regarded as a free parameter in the ray‐based parameterization. This result indicates that the wave propagation direction can be crucial for more realistic parameterization of gravity wave (GW) effects and thus needs to be reasonably determined. Comparisons between the ray‐based parameterization and columnar parameterization, which considers the gravity wave propagation only in the vertical direction, are also made in terms of temperature variance, and both results, after filtered, are similar to MLS observations. However, the magnitude of the unfiltered temperature variance in the equatorial regions with weak MLS visibility is smaller in the ray‐based parameterization than in the columnar parameterization.