Influence of solar cycle and chemistry on tropical (10°N–15°N) mesopause variabilities

Abstract

Monthly averaged zonal mean temperature and ozone volume mixing ratios obtained from “Sounding of the Atmosphere using Broadband Emission Radiometry” instrument on board “Thermosphere Ionosphere Mesosphere Energetics and Dynamics” satellite for the years 2002–2012 are used to study the seasonal and solar cycle variabilities of tropical (10°N–15°N) mesopause structure. The mesopause temperature and ozone mixing ratios are positively correlated with solar cycle due to changes in CO2 and O, respectively. Although the seasonal variation in mesopause temperatures is quite small, the mesopause altitudes are comparatively higher (~99–100 km) in April and lower (~95 km) in September. The factors controlling the tropical mesopause structure are investigated by taking the mesopause variability for the year 2011 as a case study as it resembles the long‐term mean seasonal variation. It is found that the radiative cooling due to 15 µm CO2 infrared emissions is the only cooling mechanism in the mesopause region. The net heating rates obtained from (i) solar heating by O2 and O3, (ii) chemical heating due to seven major exothermic reactions, (iii) O3 long‐wave radiative heating, and (iv) CO2 cooling are smaller (~20 K/d) in April and larger (~85 K/d) in September at lower thermosphere (~99–101 km). The downward heat conduction from the lower thermosphere forces the mesopause to lower heights in September, although no downward heat conduction is observed in April.

The response of the temperature of cold‐point mesopause to solar activity based on SABER data set

“…The 10.7 cm solar radio flux (F 10.7 ), which varies with solar cycle, is often taken as an index of solar activity [e.g., Gray et al, 2010;Beig, 2011;Ammosova and Ammosov, 2012;Ammosov et al, 2014;Ramesh et al, 2015]. The daily data of F 10.7 adjusted for an arbitrary unit (1 AU) is used to analyze the response of T-CPM to solar activity.…”

“…Forbes et al [] investigated a response of the middle atmosphere at various heights on change of solar activity using SABER temperature data during 2002–2013. Ramesh et al [] studied the solar cycle variabilities of tropical (10°N–15°N) mesopause temperature structure through analyzing SABER observations during 2002–2012. Detailed reviews of this subject were made by Beig et al [] and Beig [].…”

“…Oindrila and Sridharan [2014] investigated the long-term variabilities and trends of middle atmospheric temperature and their responses toward quasi-biennial oscillation, solar cycle, and El Niño-Southern Oscillation, extending 20-100 km altitude and 10-15°N latitude using SABER observations for the years 2002-2012. Forbes et al [2014] investigated a response of the middle atmosphere at various heights on change of solar activity using SABER temperature data during 2002-2013. Ramesh et al [2015 studied the solar cycle variabilities of tropical (10°N-15°N) mesopause temperature structure through analyzing SABER observations during 2002-2012.…”

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

“…However, the mesopause temperature increases linearly, which is less significant. 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, over a long period of time, the CO 2 radiates as much as solar energy (ultraviolet absorbed by O 2 , O 3 , and chemical heating) deposited at a specific altitude. It is well known that the temperature and O 3 vmr follow SC in the mesopause region over tropical latitudes (Ramesh et al, ). In the present study it is shown that the CO 2 cooling responds positively to SC (Figure b) in response to temperature variations in the mesopause region.…”