NOx production due to energetic particle precipitation in the MLT region: Results from ion chemistry model studies

Production of neutral species such as NOx(N, NO, and NO2) during particle-induced ionization events plays an important role in the chemistry of the mesosphere and lower thermosphere (MLT) region, especially in high latitudes. The effective production rate of NOx is composed of the direct production in reactions associated with the ionization or dissociation process and of indirect production during subsequent ionic reactions and recombination. A state of the art ion chemistry model is used to study the dependence of the effective production rate of NOx on several atmospheric parameters such as density, temperature, and abundance of atmospheric constituents and trace gases. The resulting effective production rates vary significantly, depending on the atmospheric state, and reach values between 1.2 NOx per ion pair in the lower mesosphere and 1.9 NOx per ion pair in the lower thermosphere. In this paper, an alternative approach to obtain realistic NOx production rates without running a full ion chemistry model is discussed; a database setup and readout system is used to replace ion chemistry calculations. It is compared to the full ion chemistry model and to a thermospheric reduced ion chemistry model combined with constant rate estimation below the mesopause. Database readout performs better than the constant estimate at all altitudes, where above 100km reduced ion chemistry better reproduces full ion chemistry, but database readout performs better in terms of numerical cost.