Nighttime increase of mesospheric ozone measured with ground-based microwave radiometry

During Feb. and March 1985, ground-based microwave observations of the 142.175-GHz ozone line were made to measure the variations of mesospheric ozone during sunset, throughout the night, and during sunrise. Data was taken from 2 hr before sunset to 2 hr after sunrise. The time resolution was similar to 16 min. Above 50 km, a rapid ozone increase was observed at sunset and a decrease at sunrise. The time required for both changes (10-90%) was similar to 1 hr. Daytime ozone concentrations in the mesosphere were found to be larger after sunrise than before sunset. After the initial sunset rise, the nighttime ozone continued to increase at levels above 60 km, whereas they decreased below this level. The retrieved night-to-day ozone ratio was maximum (4.2) at 70 km, near the top of the measurement range. No diurnal changes were seen below 45 km.