Evidence for an OH(Upsilon) Excitation Mechanism of CO2 4.3 Micrometers Nighttime Emission from SABER/TIMED Measurements

摘要

The SABER instrument on board the TIMED satellite, successfully launched on 7 December 2001, measures the CO2 4.3-micrometer atmospheric emission at day and night, from the troposphere up to the thermosphere, with a near global latitude coverage and with a very high signal-to-noise ratio. In this paper we analyze the measurements of SABER in channel 7, centered near 4.3 micrometers, taken at night in the upper mesosphere and lower thermosphere under quiet (non-auroral) conditions. The measurements of the 4.3 micrometer radiance in this region are much larger than expected under local thermodynamic equilibrium (LTE) and show a strong correlation with the OH channel signal. SABER data (measuring simultaneously pressure, temperature, CO2 4.3 micrometer emission, and OH(Upsilon) near-IR emission) offer an unprecedented data set for understanding the non-LTE excitation mechanisms in the nighttime mesosphere. We have investigated the SABER 4.3 micrometer radiances with the help of a non-LTE radiative transfer model for CO2 and found that the large radiances can be explained by a fast and efficient energy transfer rate whereby, on average, 2.8- 3 N2(1) vibrational quanta are excited after quenching of one OH(Upsilon) molecule.