Nonmigrating tidal impact on the carbon dioxide 15 μm infrared cooling of the lower thermosphere over one solar cycle

Abstract:

We explore the impact of diurnal and semidiurnal solar atmospheric tides that begin near the surface as heat is released by evaporation and condensation on the energy budget of the lower thermosphere: the carbon dioxide (CO₂) infrared cooling of the thermosphere at 15 μm. Cooling rates of CO₂ observed by SABER/TIMED from 2002-2013 are analyzed on two important nonmigrating tides, the DE2 and DE3. Relative amplitudes are on the order of 15-50% with respect to the monthly mean emissions. Seasonal and solar cycle variations are discussed and complemented to Earth’s natural thermostat: the nitric oxide 5.3 μm emissions. Furthermore, photochemical tidal modeling has been done in order to understand the underlying coupling mechanisms responsible for transmitting tidal signal into the CO₂ cooling rates. While the main tidal coupling mechanism is the temperature dependence of the collisional excitation of the CO₂ (01101) fundamental band transition (v=2), there is also evidence for an increasing importance of advection and neutral density variations towards higher altitudes. Our results indicate that the tropospheric tides due to large-scale weather systems are important for modulating the longitudinal and local time structure of the energy budget of Earth’s upper atmosphere.