The Accuracy of Ozone Concentration Derived from the 1.27 μm Dayglow Emission in the Mesosphere and Lower Thermosphere

The daytime ozone concentration in the mesosphere and lower thermosphere has traditionally been derived from the O2(1 Delta) 1.27 μm emissions following the ozone photolysis. Since the lifetime of O2(1 Delta) is relatively long in the upper atmosphere, the O2(1 Delta) may not be in complete photochemical equilibrium and this ozone sensing technique could yield an ozone distribution that has significant sysmatic biases. In this paper, we use a time-dependent one-dimensional photochemical-diffusive-advective model to quantitatively investigate two distinct sources of errors resulting from two approximations in retrieving the daytime ozone based on the 1.27 μm airglow emission by O2(1 Delta) in the mesosphere and lower thermosphere. One is the steady state approximation that could induce errors due to both the rapid changes of the external photolysis rates and the slow radiative/quenching relaxations of O2(1 Delta). The other is the shielding approximation in ozone photolysis calculation where the errors of the upper-layer retrieved ozone are amplified below. The steady state approximation breaks down when the chemical relaxation time is comparable to that of diurnal variations of the photolysis rate and the shielding effect increases rapidly with the increasing slant path near the sunrise/ sunset and at high latitudes. The resulting systematic biases predicted by our model and their spatial and temporal morphology will be compared with those found in ozone concentrations simultaneously derived from the O2(1 Delta) 1.27 μm and O3 9.6 μm emissions taken by the SABER/TIMED instrument. Implications of these biases found in the O2(1Delta)-derived ozone will be discussed.