Spectral variability of gravity-wave kinetic and potential energy at 69° N: a seven-year lidar study

Abstract

We present the first multi-year study of gravity-wave (GW) kinetic Ekin and potential Epot energy spectra in the polar middle atmosphere, based on simultaneous temperature and horizontal-wind measurements by the Doppler Rayleigh–Mie–Raman lidar at the ALOMAR observatory (69° N, 16° E). The analysed 7 year dataset (2017–2023) comprises 61 soundings, each longer than 12 h, totalling 2036 h of observations between 35–60 km. Our results reveal a strong winter-summer contrast that depends on both frequency and vertical wavenumber: winter spectra exhibit significantly higher energies and greater variability, particularly at long periods, while summer spectra are marked by a distinct near-inertial peak, most pronounced in Ekin. We further reveal that the ratio of kinetic to potential energy depends systematically on frequency and vertical wavelength, with near-inertial, short-vertical-scale waves channelling a disproportionate share of energy into kinetic form, indicating that the two-dimensional GW spectrum cannot be treated as fully separable. Frequency spectra also show, for the first time, broken power laws at 35–40 km, merging into a single flatter power law with increasing altitude. These findings provide new constraints on the spectral energy budget at high latitudes in the middle atmosphere and deliver essential benchmarks for validating and improving GW parameterisations in climate and numerical weather prediction models.