Long-term study of gravity wave potential energy and OH airglow emissions from 22 years of TIMED/SABER observations

Abstract

Using 22 years (2002–2023) of TIMED/SABER satellite observations, we investigate the long-term coupling between mesospheric hydroxyl (OH) airglow and gravity wave potential energy (Ep). Continuous wavelet transform analysis extracts gravity wave signatures from temperature perturbations, and multiple linear regression decomposes the observed variability into contributions from solar activity, geomagnetic activity, the Quasi-Biennial Oscillation (QBO), and El Niño–Southern Oscillation (ENSO). Three major findings emerge. First, OH emissions and gravity wave Ep are positively coupled, with statistically significant (p<0.05) correlation coefficients of 0.3–0.7 that peak during winter at mid-latitudes. Second, long-term trends reveal contrasting latitudinal patterns: OH trends are negative at mid-latitudes in both hemispheres (-1 to -5×10-10 W m−3 yr−1), consistent with mesospheric cooling, whereas Ep trends are positive at mid-latitudes (up to 5.3×10-2 J kg−1 yr−1), exceeding current model predictions. Both quantities show weaker trends near the equator. Third, a novel decomposition methodology separates temperature-driven chemical responses from non-thermal dynamical effects, revealing that solar forcing operates primarily through thermal mechanisms and accounts for 10 %–15 % of OH variance, while QBO and ENSO influence mesospheric chemistry through dynamical pathways. ENSO drives negative OH responses yet enhances Ep, and QBO responses exhibit opposite patterns between the equator and mid-latitudes. Semi-annual oscillations dominate equatorial variability, while annual oscillations prevail at Southern Hemisphere mid-latitudes.