The Role of Gravity Waves in the Mesosphere Inversion Layers (MILs) over low-latitude (3–15° N) Using SABER Satellite Observations

Abstract. The Mesosphere transitional region over low latitude is a distinct and highly turbulent zone of the atmosphere. A transition MLT region is connected with dynamic processes, particularly gravity waves, as a causative of an inversion phenomenon. MLT inversions have been the subject of numerous investigations, but their formation mechanisms are still poorly understood. In this article, an attempt has been made to investigate the upper and lower inversion phenomena and their causative mechanisms using long-term SABER observations in the height range of 60–100 km during the period of 2005–2020 over a low-latitude region (3–15° N). The results indicate that the frequency of occurrence rate for the upper inversion is below 40 %, whereas for the lower inversion, it is below 20 %, indicating that the upper inversion is dominant over the lower inversion. The upper inversion exists in the height range of 78–91 km with an inversion amplitude of ~20–80 k and a thickness of ~3–12 km, whereas the lower inversion is confined in the height range of 70–80 km with an inversion amplitude of ~10–60 k and a thickness of ~4–10 km. The gravity wave indicator potential energy depicts high energy (below 100 J/kg) in the upper MLT region (90 and 85 km) compared to the lower MLT region (75 and 70 km) with less than 50 J/kg. The stability criteria from Brunt-Vaisala frequency (N²) indicate instability in the upper MLT region (90 and 85 km) with very low values relative to the lower MLT region (75 and 70 km), which supports the higher frequency of upper inversion compared to lower inversion. This result leads us to the conclusion that a high amount of gravity wave potential energy is a consequence of the high instability in the upper inversion relative to the lower inversion.