Solar Cycle Modulation of Nighttime Ozone Near the Mesopause as Observed by MLS

Eleven‐year solar cycle variations of nighttime ozone near the secondary ozone maximum layer in the mesosphere are analyzed with Aura Microwave Limb Sounder (MLS) observations since 2004, fully covering solar cycle 24. Produced primarily from the recombination of molecular oxygen (O2) with atomic oxygen (O) transported from the lower thermosphere, the mesospheric nighttime ozone concentration is proportional to atomic oxygen density [O], which itself is modulated by ultraviolet (UV) solar cycle variations. MLS nighttime ozone data and UV data at 240 nm from Solar Radiation and Climate Experiment (SORCE) Solar‐Stellar Irradiance Comparison Experiment (SOLSTICE) show a positive correlation over the solar cycle. Nighttime O3 and nighttime carbon monoxide (CO) distributions are highly correlated with each other with similar seasonal and solar cycle variations, because both [O3] and [CO] depend strongly on UV photolysis and are modulated by Eddy diffusion in this region. Nighttime ozone correlates strongly with temperature, with a generally positive correlation, except at high latitudes during boreal winter. Key Points Solar cycle modulation of nighttime ozone is shown with MLS observation near the mesopause The semi‐annual and solar cycle variations of nighttime ozone is similar to those of nighttime ozone in the mesosphere The nighttime ozone variation in the upper mesosphere and lower thermosphere (UMLT) is largely driven by dynamics via Eddy diffusion