Gravity waves in the stratosphere and troposphere observed by lidar and MST radar

Co-ordinated lidar and MST observations of the stratosphere and troposphere have been made at Aberystwyth (52.4°N, 4.1°W). Density and temperature profiles derived from lidar observations of Rayleigh backscatter above about 21 km have been combined with MST radar measurements of winds to investigate gravity waves at heights between 2 and 50km. The measurements made by each technique reveal that long-period quasi-monochromatic motions frequently dominate the stratospheric gravity-wave field. Characteristic vertical wavelengths range from 1–2 km in the lower stratosphere to some 5–8 km at the greater heights. Vertical wavenumber and frequency spectra are derived for both tropospheric and stratospheric data. Wave energy per unit mass is used as a tracer of wave activity and is combined with vertical wavenumber spectra to investigate wave-field saturation. The significance of measured frequency spectral indices as a function of height is discussed in relation to possible Doppler shifting by the mean wind.