Modulation of Nitric Oxide Emissions in the Equatorial Mesosphere and Lower Thermosphere by the Migrating Diurnal Tide

Abstract

Airglow emissions are observed to respond to dynamical processes, like tides in mesosphere and lower thermosphere (MLT). Nitric oxide (NO) 5.3‐ emissions distribute from mesosphere to thermosphere, with one peak near 125 km and another peak near 87 km. The dynamic response of NO volume emission rate (NO VER) to migrating diurnal tide (DW1) in MLT is investigated using Sounding of the Atmosphere using Broadband Emission Radiometry/Thermosphere Ionosphere Mesosphere Energetics and Dynamics and SD‐WACCM‐X data sets. This study focuses on NO VER DW1 between 65 and 100 km over the equator owing to the significant influence of DW1 in this region. The variation of monthly‐mean NO VER DW1 amplitude and phase are similar to temperature DW1, indicating a dynamical modulation by DW1. Especially around 87 km, correlation coefficients between temperature and NO VER reach 0.96 in amplitude and 0.95 in phase. These similarities likely arise because diurnal variation of NO VER excitation mechanisms (earthshine, solar radiation and NO‐atomic oxygen collisions) is largely consistent with diurnal temperature variation. At other altitudes, the consistency weakens. The vertical profiles of both amplitude and phase of NO VER DW1 show seasonal variability. In solstices, phase departs from temperature DW1, with maximum difference occurring ∼80 km (∼). During equinoxes, two distinct vertical phase structures arise: one coincides with temperature DW1 phase structure, while the other deviates distinctly from it. The discrepancy between the two types likely relates to differences in zonal‐mean NO VER intensity and DW1 strength. These results imply that DW1 could largely affect NO emission in MLT, but NO emission cannot fully characterize the dynamical feature of DW1.