Altitude of peak emission of (OI) 5577 Å in the lower thermosphere: Chapman versus Barth mechanisms

Abstract

Heights of peak (OI) 5577 Å emission rates Z C and Z B due to Chapman and Barth mechanisms respectively have been computed for different model atomic oxygen profiles in the lower thermosphere, generated by assigning different values to temperature ( T), mixing factor ( S) and peak atomic oxygen density [O] m. It is found that Z C is only marginally higher than the peak of the [O]profile ( Z m ); the difference being about 0.2 km. On the other hand Z B is always lower than Z m and its variation is relatively more significant. ( Z m − Z B ) may vary between 1.0 km for T = 180 K, S = 0.6 and [ O] m = 1 × 10 11cm −3 to 3.6 km for T = 220 K, S = 0.8 and [ O] m = 1 × 10 12cm −3. It is quantitatively shown that the uncertainties in the laboratory measured rate coefficients can considerably affect the volume emission rate, particularly by the Barth mechanism, whereas the height of maximum emission is insensitive to these uncertainties. It is therefore, concluded that this height difference between Z C , Z m and Z B could be used to resolve the controversy regarding the type of mechanism—that of Chapman or of Barth—which dominates in producing the (OI) 5577 Å in the lower thermosphere.