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 E_kin and potential E_pot energy spectra in the polar middle atmosphere based on simultaneous temperature and horizontal-wind measurements by the Doppler Rayleigh-lidar at the ALOMAR observatory (69°N, 16°E). The 7-year data set (2017–2023) comprising 100 soundings, each longer than 12 h, totalling >2700 h of observations with 150 m vertical and 5 min temporal resolution spanning 35–60 km. Overall, winter spectra exhibit significantly higher GW energies and variability than summer: the winter-to-summer amplitude ratio peaks at ≥10 at periods ≥12 h, declining to ∼1.5 above 3 h. This ratio is ∼2.5 in E_pot across all vertical wavelengths, but peaks at ∼4 at 3 km in E_kin and approaches unity at smaller wavelengths. Winter E_kin exhibit a broad enhancement just above the inertial frequency f, whereas summer spectra show a sharp near-inertial peak and a distinct minimum at periods >11 h. E_kin/E_pot shows strong dependence on observed frequency and vertical wavelength, exceeding values of 6 especially near f and short vertical wavelengths (<3 km), hinting at the non-separability of the GW spectrum. Frequency spectra showed -for the first time to be reported- broken power-laws at 35–40 km (more pronounced in summer), gradually merging into a simple power-law with a flatter slope as altitude increased. Our findings are critical for accurate spectral energy budget at high latitudes in the middle atmosphere and provide essential benchmarks to validate GW parameterisations in climate and numerical weather prediction models.