Gravity wave intensity and momentum fluxes in the mesosphere over Shigaraki, Japan (35°N, 136°E) during 1986-1997

Abstract

Abstract. Averaged seasonal variations of wind perturbation intensities and vertical¯ux of horizontal momentum produced by internal gravity waves (IGWs) with periods 0.2±1 h and 1±6 h are studied at the altitudes 65±80 km using the MU radar measurement data from the middle and upper atmosphere during 1986±1997 at Shigaraki, Japan (35 N, 136 E). IGW intensity has maxima in winter and summer, winter values having substantial interannual variations. Mean wave momentum¯ux is directed to the west in winter and to the east in summer, opposite to the mean wind in the middle atmosphere. Major IGW momentum uxes come to the mesosphere over Shigaraki from the Paci®c direction in winter and continental Asia in summer.

Interpretation of the mesospheric and lower thermospheric mean winds observed by MF radar at about 30°N with the 2D-SOCRATES model

“…The dominant feature of the momentum flux divergence shown in Fig. 3(a) is westward in winter and eastward in summer, which is consistent with the study of internal gravity wave (IGW) momentum flux directions by the MU radar (Tsuda et al, 1990;Nakamura et al, 1996;Gavrilov et al, 2000). Fig.…”

Summer sudden Na number density enhancements measured with the ALOMAR Weber Na Lidar

“…This upwelling is related to a modification of the mean zonal circulation due to gravity wave breaking and the resulting momentum flux divergence (e.g. Lindzen, 1981;Gavrilov et al, 2000;Fritts et al, 2002).…”

Lidar observations of middle atmospheric gravity wave activity over a low-latitude site (Gadanki, 13.5° N, 79.2° E)

“…These waves, having their source at lower heights, propagate upwards and deposit energy through wave breaking and dissipation processes in the mesosphere, thereby significantly altering its thermal structure and wind pattern (Booker and Bretherton, 1967;Lindzen, 1973;Dunkerton, 1982;McIntyre, 1980;Fritts, 1984; Correspondence to: V. Sivakumar (siva@univ-reunion.fr) Rastogi, 1985;Whiteway and Carswell, 1995;Nastrom et al, 1997;Gavrilov et al, 2000;Nastrom and vanZandt, 2001;Fritts and Alexander, 2003). The GW thus have a significant impact on the dynamical processes in the middle atmosphere.…”

“…Using MU radar observations over Shigaraki (35 • N,136 • E), Fritts et al (1990) found that the mean vertical profiles of energy density show with height a decaying trend at low frequencies and a growing trend at higher frequencies. Further, Gavrilov et al (2000) have made a detailed study on GW characteristics and momentum fluxes in the mesosphere and found that at these heights, GW breaking takes place and as a consequence turbulence is generated. Recently, Fritts and Alexanader (2003) have reviewed the gravity wave activity in the middle atmosphere and established that the waves with vertical wavelengths greater than 10 km are generally considered to be important in the middleatmosphere dynamics and such long vertical wavelengths (>10 km) are associated with deep convective heating.…”