Analysis and interpretation of airglow and radar observations of quasi-monochromatic gravity waves in the upper mesosphere and lower thermosphere over Adelaide, Australia (35°S, 138°E)
✍ Scribed by R.L. Walterscheid; J.H. Hecht; R.a. Vincent; I.m. Reid; J. Woithe; M.P. Hickey
- Publisher
- Elsevier Science
- Year
- 1999
- Tongue
- English
- Weight
- 910 KB
- Volume
- 61
- Category
- Article
- ISSN
- 1364-6826
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✦ Synopsis
Observations of wave!driven ~uctuations in emissions from the OH Meinel "OHM# and O 1 Atmospheric band were made with a narrow!band airglow imager located at Adelaide\ Australia "24S\ 027E# during the period April 0884 to January 0885[ Simultaneous wind measurements in the 79Ð099 km region were made with a co!located MF radar[ The directionality of quasi!monochromatic "QM# waves in the mesopause region is found to be highly anisotropic\ especially during the solstices[ During the summer\ small!scale QM waves in the airglow are predominately poleward propagating\ while during winter they are predominately equatorward[ The directionality inferred from a Stokes analysis applied to the radar data also indicates a strong NÐS anisotropy in summer and winter\ but whether propagation is from the north or south cannot be determined from the analysis[ The directionality of the total wave _eld "which contains incoherent as well as coherent features# derived from a spectral analysis of the images shows a strong EÐW component\ whereas\ an EÐW component is essentially absent for QM waves[ The prevalence of QM waves is also strongly seasonally dependent[ The prevalence is greatest in the summer and the least in winter and correlates with the height of the mesopause^whether it is above or below the airglow layers[ The height of the mesopause is signi_cant because for nominal thermal structures it is associated with a steep gradient in the Brunt!Va Ãisa Ãla à frequency that causes the base of a lower thermospheric thermal duct to be located in the vicinity of the mesopause[ We interpret the QM waves as waves trapped in the lower thermosphere thermal duct or between the ground and the layer of evanescence above the duct[ Zonal winds can deplete the thermal duct by limiting access to the duct or by negating the thermal trapping[ Radar measurements of the prevailing zonal wind are consistent with depletion of zonally propagating waves[ During winter\ meridional winds in the upper mesophere and lower thermosphere are weak and have no signi_cant e}ect on meridionally propagating waves[ However\ during summer the winds in the duct region can signi_cantly enhance ducting of southward propagating waves[ The observed directionality of the waves can be explained in terms of the prevailing wind at mesopause altitudes and the seasonal variation of distant sources[ Þ 0888 Elsevier Science Ltd[ All rights reserved[