Seasonal variations in the correlation of mesospheric OH temperature and radiance at midlatitudes

摘要

A correlative study of rotational temperatures and radiance of mesospheric hydroxyl (OH) was made using spectrographic measurements from the midlatitude site at Millstone Hill, Massachusetts (42.6°N, 71.5°W). The OH radiance and temperatures were strongly correlated, and the correlation showed a marked seasonal dependence. The dependence was also evident on smaller timescales ranging from days to months. Dynamical effects appeared to dominate the temperature-radiance relationship compared to the photochemistry responsible for the hydroxyl emission rate. The effect was illustrated clearly when the measurements were temporally averaged, hence removing the dynamical influence. A strong summer maximum in OH radiance was observed contrary to a minimum in summer Mass Spectrometer Incoherent Scatter (MSIS) [O]volume mixing ratio values. An increase in mesospheric gravity wave activity during the summer, a feature not observed by the MSIS model, was the likely cause of the summer OH maximum.