Rotational and spin-orbit distributions of NO observed by MIPAS/ENVISAT during the solar storm of October/November 2003

Aurorally enhanced 5.3 μm emission from nitric oxide was observed by the MIPAS instrument on board the ENVISAT satellite during the solar storm of October/November 2003. Spectral modeling of the NO(Δν = 1) fundamental band emissions was performed in order to determine the NO rotational and spin-orbit distributions. In the thermosphere, NO(ν = 1) is produced by collisional excitation of NO(ν = 0) by O atoms and also by the chemical reactions of N(4S) and N(2D) atoms with O2. There are no measurements of the nascent spin-orbit distribution of NO produced by the reaction of N atoms with O2. Auroral activity leads to increased production of N(4S) and N(2D) atoms, resulting in enhanced chemical formation of NO. In the MIPAS data taken during the solar storm, strong NO signal levels and increased rotational temperatures indicated high levels of auroral activity. A comparison of the data from October/November 2003 with data taken during a quiescent period in June 2003 showed that NO(ν = 1) produced by N + O2 has a hotter spin-orbit distribution than NO(ν = 1) produced by O atom collisional excitation. The results imply that the spin-orbit ratio may be useful for identifying different sources of NO in the thermosphere. In addition, the NO(ν = 1) spin-orbit distributions were found not to be in local thermodynamic equilibrium (non-LTE) for both quiescent and auroral conditions. The non-LTE effects must be taken into account in order to accurately retrieve atmospheric NO concentrations from 5.3 μm emissions. Copyright 2005 by the American Geophysical Union.