ALBERT

Description: [1]  Production of neutral species such as NO x (N, NO, NO 2 ) during particle induced ionization events plays an important role in the chemistry of the mesosphere and lower thermospere (MLT) region, especially in high latitudes. The effective production rate of NO x 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 NO x 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 NO x per ion pair in the lower mesosphere and up to 1.9 NO x per ion pair in the lower thermosphere. In global chemistry transport models or chemistry climate models that include the thermosphere (as, e.g., WACCM and HAMMONIA), a constant value of 1.25 NO x per ion pair is typically used in the mesosphere and stratosphere, along with a thermospheric ion chemistry solver considering five positive ions and electrons. In this paper, an alternative approach to obtain realistic NO x 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 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 100 km, reduced ion chemistry better reproduces full ion chemistry, but database readout performs better in terms of numerical cost.