Gravity wave momentum flux in the upper mesosphere derived from OH airglow imaging measurements

Shin Suzuki,David C Fritts,Takuji Nakamura,Kazuo Shiokawa,Minoru Kubota,Masaki Tsutsumi,Yuichi Otsuka,Tadahiko Ogawa

doi:10.1186/bf03352703

Abstract

Abstract We report procedures to identify small-scale (20–100 km) atmospheric gravity waves from OH airglow images to estimate momentum fluxes carried by the waves. We also deduce contamination of background continuum emission in OH image, by comparing a simultaneous observation of OH lines measured by the Spectral Airglow Temperature Imager (SATI). We applied the procedures to a one-night dataset obtained at Shigaraki, Japan (34.9°N, 136.1°E) on November 19, 1999. The background wind, which is essential for deriving the intrinsic parameters of gravity waves, was measured by the Middle and Upper Atmosphere (MU) radar. Contamination of background continuum emission with the OH filter was deduced to be 30%. From these procedures, we found that the gravity waves identified in the OH images were mainly propagating southward or southeastward with horizontal wavelengths of 60–90 km and apparent phase speeds of 40–80 m/s. The estimated momentum fluxes on this night was 1–15 m2 s−2, with an average of 4.9 m2 s−2.

Highlights

Atmospheric gravity waves play important roles in both the large- and small-scale dynamics of the mesosphere and lower thermosphere (MLT) through their vertical transport of horizontal momentum (Houghton, 1978; Lindzen, 1981; Vincent, 1984; Fritts and Alexander, 2003)
We present a technique to identify smallscale (20–100 km) gravity waves and to estimate gravity wave momentum fluxes, using one-night OH airglow images obtained at the Shigaraki Middle and Upper Atmosphere (MU) observatory (34.9◦N, 136.1◦E)
Experimental Results We applied the procedures described above to estimate gravity wave momentum fluxes for the one-night dataset obtained at Shigaraki, Japan, on November 19, 1999 (1732– 2029 UT)

Summary

Introduction

Atmospheric gravity waves play important roles in both the large- and small-scale dynamics of the mesosphere and lower thermosphere (MLT) through their vertical transport of horizontal momentum (Houghton, 1978; Lindzen, 1981; Vincent, 1984; Fritts and Alexander, 2003). Wave dissipation causes turbulence and divergence of momentum flux, which leads to local heating, turbulent diffusion, and acceleration of the local mean flow. Tsuda and Murayama (1990) studied mesospheric wind at 60–85 km from 1985 to 1988 with the Middle and Upper Atmosphere (MU) radar at Shigaraki to investigate the acceleration of mean flow by divergence of gravity wave momentum flux. They reported that the meridional momentum flux was very small throughout the year, while the zonal momentum flux was significant and showed a clear seasonal variation with a mean eastward (westward) momentum flux in summer (winter). Typical values of the zonal momentum flux were ∼2 m2 s−2 for wave periods from 5 min to 2 h

Results

Discussion

Conclusion