Spatial and temporal structure of the tertiary ozone maximum in the polar winter mesosphere

Observations from satellites and a ground-based station are combined to construct a global data set for investigating the tertiary ozone maximum in the winter mesosphere for the period August 2004 to June 2017. These give a comprehensive picture of this ozone maximum in latitude, pressure, and time. The location of the tertiary ozone maximum shifts in latitude and pressure with the evolving season; the ozone peak occurs at lower latitude and higher pressure around the winter solstice. Highest average nighttime ozone concentrations and greatest degree of interannual variability are seen in late winter in the Northern Hemisphere (NH). The hemispheric differences and interannual variability in nighttime ozone are related to variations of temperature, H2O, and OH associated with dynamical activity. Elevated stratopause events in the NH winter are associated with transport of air that is depleted in H2O and enhanced in OH; photochemistry then leads to downward displacement of the altitude of maximum ozone and enhancement in the ozone amount. Transport by planetary waves in the NH extends the region of high ozone further from the pole and leads to longitudinal variations. The analysis shows that while the tertiary ozone maximum responds to a particular radiative situation as shown in previous studies, it is also the result of very dry air found in the winter polar mesosphere.