A chemical perspective of day and night tropical (10°N–15°N) mesospheric inversion layers

Abstract

The various occurrence characteristics of day and night tropical (10°N–15°N, 60°E–90°E) mesospheric inversion layers (MILs) are studied by using TIMED Sounding of the Atmosphere using Broadband Emission Radiometry satellite data products of kinetic temperature; volume mixing ratios of O, H, and O3; volume emission rates of O2 (1Δ) and OH (1.6 µm channel), and chemical heating rates due to seven dominant exothermic reactions among H, O, O2, O3, OH, HO2, and CO2 cooling rates for the year 2011. Although both dynamics and chemistry play important roles, the present study mainly focuses on the chemical processes involved in the formation of day and night MILs. It is found that the upper level height of daytime (nighttime) MIL descends (ascends) from ~88 km (~80 km) in winter to ~72 km (~90 km) in summer. The day and night inversion amplitudes are correlated with total chemical heating rates and CO2 cooling rates, and they show semi annual variation with larger (smaller) values during equinoxes (solstices). The daytime (nighttime) inversion layers are predominantly due to the exothermic reaction, R5: O + O + M → O2 + M and R6: O + O2 + M → O3 + M (R3: H + O3 → OH + O2). In addition, the CO2 causes large cooling at the top and small heating at the bottom levels of both day and night MILs. In the absence of dynamical effects, the chemical heating and CO2 cooling jointly contribute for the occurrence of day and night MILs.

Long‐Term Trends in Tropical (10°N–15°N) Middle Atmosphere (40–110 km) CO2 Cooling

“…Here it should be noted that the cooling by O 3 at 9.6 μm emission is an additional cooling mechanism in the stratopause region (Ramesh et al, ; Salby, ). The decreasing temperature causes increasing ozone (rate constant of O + O 2 + M → O 3 + M is inversely dependent on T; Ramesh et al, ) and number density ( ρ ∝ 1/ T ) in the stratopause region. However, in the mesopause region, the increasing temperature leads to slight decreasing ozone vmr and the number density.…”

“…The O vmr increases with height, and its abundance is more prominent above ~80–85 km. Although the CO 2 vmr decreases above 70 km, the increase in CO 2 cooling could be due to (i) increase in energy input at higher heights so there has to be energy loss to balance it out over time; (ii) as the pressure, CO 2 vmr, and its opacity decrease with height, CO 2 becomes more capable of radiating to space; and (iii) the increase in O vmr with height (e.g., Mlynczak et al, ; Ramesh et al, ; Smith et al, ) causes more collisional excitation of CO 2 molecules so that they radiate spontaneously more above 80 km. The positive trend in the stratopause region peaking at ~45 km represents the increasing CO 2 cooling in response to increasing CO 2 vmr quenched by available O at this height level.…”

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

“…In addition, the gravity wave-breaking influence on mesosphere dynamics is an attempt to demonstrate the emergence of the inversion phenomenon over mid and high latitudes (Gan et al, 2012;Walterscheid and Hickey, 2009;Collins et al, 2011;Szewczyk et al, 2013). Observational and modeling approaches have been used to investigate GWs as the causative of inversions Collins et al, 2014;Sridharan et al, 2008;Ramesh and Sridharan, 2012;Ramesh et al, 2013Ramesh et al, , 2014Ramesh et al, , 2017. The effect of gravity waves in the mesosphere inversion based on temperature variability is studied particularly over the mid-and high-latitudes (Singh and Pallamraju, 2018;.…”