Gravity-wave-induced variations in exothermic heating in the low-latitude, equinox mesophere and lower thermosphere region

We investigate gravity-wave-induced variations in exothermic heating in the OH nightglow region at a latitude of 18° in the Northern and Southern Hemispheres during March. An OH nightglow chemistry model with gravity wavefields from a spectral full-wave model is used for the investigation. Our simulation results show that the wave packet induces a large secular increase in the number densities of the minor species involved in the OH chemistry, a 50% increase in O₃, 42% in O, and 29% in OH (v = 8), and the ultimate driver for these increases is the wave-driven downward transport of O. We find that the total exothermic heating rates have increased by ∼44.2% for 18°S and ∼30.9% for 18°N by the end of the simulation time. Also, the peak values of the mean wave-induced total exothermic heating rates are significant, ∼2.0 K d^-1 at the peak altitude of 88 km and ∼2.2 K d^-1 at 89 km for 18S and 18N, respectively. The major reactions contributing to exothermic heating rates are the three-body recombination O + O + M and the H + O₃ reaction. The hemispheric asymmetry in the heating rates is mainly due to the different atmospheric conditions at 18N and 18S since the same wavefields are used in the numerical simulations.