The University of Bern Atmospheric Ion Model: Time‐dependent modeling of the ions in the mesosphere and lower thermosphere

Abstract

[1] In this paper the first time-dependent model of ion chemistry in the mesosphere/lower thermosphere (MLT) region acting within a global, time-dependent, two-dimensional neutral atmosphere model is described. Selected diurnal results are presented for undisturbed solar minimum conditions. The University of Bern Atmospheric Ion Model (UBAIM) is a time-dependent, pseudo-two-dimensional model of the ion chemistry in the Earth atmosphere. It covers latitudes from 85°S to 85°N and (log-pressure) altitudes from 20 to 120 km. On this grid a system of differential equations describing the ion chemistry is integrated numerically until a periodical solution, governed by the diurnal changes in the incident radiation, is reached; this solution constitutes a model for quiet or undisturbed conditions. The basic ion chemistry of the UBAIM contains 311 reactions for 71 charged species. Ionization sources are solar X-ray and EUV radiation, resonantly scattered Lyman a and b photons, and galactic cosmic rays. Densities of main and trace neutral atmospheric constituents are taken from a new version of the bidimensional NCAR model SOCRATES, which has been specifically optimized for mesospheric and lower thermospheric processes with upper boundary conditions set using the empirical MSIS thermosphere model. Direct solar flux inputs are computed by the SOLAR2000 model; scattered Lyman a and b fluxes are calculated using geocoronal hydrogen density profiles consistent with the adopted MSIS density distributions.

Electron density profiles in the quiet lower ionosphere based on the results of modeling and experimental data

“…(Kull et al, 1997;Verronen et al, 2002;Kazil et al, 2003;Enell et al, 2011). The complex models are extremely important for detailed research of ionosphere and magnetosphere physics.…”

D-region electron density and effective recombination coefficients during twilight – experimental data and modelling during solar proton events

“…In our ion-chemical model, complex transformations and formations of different ions which are usually described by large numbers of ion-chemical reactions in detailed schemes (Arnold and Krankowsky, 1971;Arnold, 1980;Ferguson, 1976;Reid, 1977;Chakrabarty et al, 1978;Turunen and Ranta, 1992;Kull et al, 1997;Kazil et al, 2003) are substituted by effective rate coefficients. The latter include the rates of the main ionic transformation processes and contain the dependencies on the neutral temperature and density, humidity and the concentration of the minor neutral species.…”

Influence of water vapour on the height distribution of positive ions, effective recombination coefficient and ionisation balance in the quiet lower ionosphere

“…investigated changes of neutral species during a solar proton event, but did not use any model results to explain his observations. Steady-state, time-dependent and global two-dimensional ion-chemistry models have been presented by Kull et al (1997), Verronen et al (2002Verronen et al ( , 2008Verronen et al ( , 2011, Kazil et al (2003), and Winkler et al (2009). These complex models allow the investigation of the coupling mechanisms between neutral particle chemistry and ion chemistry.…”

“…Model verification is based on the comparison of the modelled electron density profiles with several electron density profiles measured by the European Incoherent Scatter (EIS-CAT) radar during auroral absorption and solar proton events (Vlaskov et al, 1990;Kirkwood et al, 2001;Osepian et al, 2009a) and during rocket flights in the quiet ionosphere at mid-latitudes .…”