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Long‐Term Trends in Tropical (10°N–15°N) Middle Atmosphere (40–110 km) CO 2 Cooling
Author(s) -
Ramesh K.,
Sridharan S.
Publication year - 2018
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1029/2017ja025060
Subject(s) - thermosphere , atmospheric sciences , atmosphere (unit) , depth sounding , mesosphere , stratosphere , climatology , quasi biennial oscillation , ozone , environmental science , oscillation (cell signaling) , atmospheric temperature , ionosphere , physics , chemistry , geology , meteorology , biochemistry , astronomy , oceanography
Long‐term trends in middle atmosphere (~40–100 km; here extended up to 110 km), 15 μm carbon dioxide (CO 2 ) cooling rates, and their responses to solar cycle (SC), quasi‐biennial oscillation, and El Niño‐Southern Oscillation are investigated over Indian tropical region (10°N–15°N) using TIMED‐SABER (Thermosphere Ionosphere Mesosphere Energetics and Dynamics‐Sounding of the Atmosphere using Broadband Emission Radiometry) observations during 2002–2015 (23–24 SCs). The CO 2 cooling directly depends on temperature so that higher temperature causes more infrared emission from CO 2 at 15 μm band and thus provides larger CO 2 cooling. The 15 μm CO 2 cooling trends are relatively smaller below ~70–80 km, and their amplitude increases above this height. The trends are positive between ~40 and ~62 km peaking at ~47 km (0.06 ± 0.014 K/day/decade) and negative at ~63–74 and ~79–84 km. Further the positive trends increase sharply above ~84 km at the rate of ~0.1–3.0 K/day/decade between 85 and 110 km. The CO 2 cooling response to SC, El Niño‐Southern Oscillation, and quasi‐biennial oscillation is smaller below ~70–75 and stronger above this height. The 15 μm CO 2 heating exhibits semiannual variation with ~0.1–0.8 K/day during equinoxes between ~70 and 77 km. In addition, the increase in CO 2 cooling significantly influences the background temperature and thereby ozone concentration, neutral number density and layer thickness (width) in the stratosphere and mesosphere.