Ecologically Important Reactions and Phenomena in the Mesosphere between the Two Global Ozone Layers

Abstract

Due to their buoyance, methane and water vapor (H2O(g)) ascend into the mesosphere where they are destroyed by chemical reactions or photolysis. In the mesosphere at 81 to 83 km, H2O(g) condenses to ice which then, due to the lack of buoyance, descends to 70 to 75 km where ice sublimates back to H2O(g). A mesospheric minicycle of water forms. In boreal summer evenings the ice layer is visually observable from the ground as noctilucent clouds (NLC). The middle mesospheric ozone maximum (MMM) forms in the wintertime at a height of 70 to 75 km. It is located between the mid-latitudes and somewhat north from the Arctic Circle, and symmetrically in the Southern Hemisphere. In the daytime solar radiation keeps the ozone concentration at a low level. During the civil and nautical twilight the intensity of the sun's rays decrease dramatically. Ozone gains from this decrease most. At high latitudes the solar radiation angle (θs) decreases more slowly than at the mid-latitudes. IR radiation has more time to photoexcite O2(1 Δg) and triplet state ozone (O3*). O2(1 Δg) maintains the ozone concentration and O3* spontaneously provides oxygen atoms. As a result, the amplitude of the MMM layer in terms of ozone concentration increases towards the high latitudes.