High‐Resolution Analysis of Mesospheric Instabilities on 31 March 2022 at Poker Flat

Atmospheric instabilities that moved against the background mean wind were observed directly on 31 March 2022 from Poker Flat, Alaska using both hydroxyl airglow imaging and sodium resonance LiDAR. These instabilities were extracted from data using a series of Fourier and Morse wavelet transforms to isolate them from background gravity waves (GWs) and therefore minimize contamination. Horizontal wavelength, direction, period, and an estimation of the vertical extent of the unstable layer were measured from ripples in airglow images. Density fluctuations in simultaneous LiDAR data exhibited a similar period and were then used to measure vertical extent and altitudinal location. Together, these observations enabled a set of instabilities to be described in quasi‐3D: horizontal wavelength of 10.6 ± 0.8 km, vertical extent between 1.5–2.5 km, period of about 3 min and traveling 9.0 ± 3.3° north of east. Furthermore, temperature and wind shear profiles derived from LiDAR data showed localized regions where the Richardson number dipped below 0.25, the threshold required for the formation of Kelvin‐Helmholtz instabilities. Gravity waves observed in airglow images propagated 16.9 ± 5.5° west of north with a horizontal wavelength of 34.8 ± 3.3 km and a period of 10 min, and a larger‐scale 2 hr period GW was present in LiDAR data.