The variability of stratospheric and mesospheric NO₂ in the polar winter night observed by LIMS

Abstract

The LIMS experiment sounded the upper atmosphere from late October 1978 to late May 1979 and provided vertical profiles of atmospheric temperature, O 3 , H 2 O, HNO 3 , and NO 2 . The data were collected over the latitude range from 64°S to 84°N, both night and day. We have used the technique of radiance averaging before retrieval to measure the altitude distribution of NO 2 over the altitude range from the lower stratosphere into the mesosphere. Observations in the polar winter night region north‐ward of about 70°N reveal NO 2 levels near 175 ppbv at about 70 km, and they show a significant longitudinal variability (factor of 4 to 7). A definite temporal trend exists, showing a buildup of mesospheric and stratospheric NO 2 during the polar night and a subsequent slowing of the increase or decline after sunlight returns, depending on altitude. These results provide further insight regarding the importance of NO 2 conversion to N 2 O 5 in the polar night, and they suggest that downward transport in the mesosphere can be quite localized. The data represent the first experimental evidence that the thermosphere is an NO x source for the mesosphere and stratosphere.