Radiosonde observations of lower atmospheric gravity wave momentum flux spectra at a single mid-latitude station

Abstract

Inertial gravity waves in the troposphere and the lower stratosphere (TLS) were extracted by using the data from Radiosonde observations at a mid-latitude station Miramar Nas (32.87 degrees N, 117.15 degrees W). The momentum flux spectra of gravity wave were calculated. Analysis shows that the momentum flux spectra in the lower atmosphere satisfy the Gaussian distribution. The investigation into Gaussian parameters indicates (1) eastward propagating waves are absorbed by the winter westerly jet and as a result the Gaussian peaks of the westward propagating waves are obviously larger than those of the eastward propagating waves, (2) wave-mean flow interaction and wave-wave interaction are likely to lead to the increase of the spectra width during the process when waves propagate from the troposphere to the stratosphere, (3) the total momentum flux in the lower stratosphere is much smaller than the counterpart in the troposphere, probably because of the absorption and reflection by jet as well as the wave dissipation near the tropopause. Affected by the background wind, the momentum flux spectra exhibit distinctive seasonal variations. Doppler effect profoundly influences the spectra from two aspects. Firstly, Doppler effect will widen the width of the spectra when the background wind is strong. Secondly, Doppler effect would significantly change the intrinsic phase speed at Gaussian center, leading to asymmetric spectra.