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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 108, NO. D14, 4432, doi:10.1029/2002JD003024, 2003

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

Jan Kazil

Space Research and Planetary Sciences, University of Bern, Bern, Switzerland


Ernest Kopp

Space Research and Planetary Sciences, University of Bern, Bern, Switzerland


Simon Chabrillat

Belgian Institute for Space Aeronomy, Brussels, Belgium


James Bishop

Naval Research Laboratory, Washington, D. C., USA


Abstract

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 α and β 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 α and β fluxes are calculated using geocoronal hydrogen density profiles consistent with the adopted MSIS density distributions.

Received 8 October 2002; accepted 24 April 2003; published 31 July 2003.

Index Terms: 0310 Atmospheric Composition and Structure: Airglow and aurora; 0335 Atmospheric Composition and Structure: Ion chemistry of the atmosphere (2419, 2427); 0340 Atmospheric Composition and Structure: Middle atmosphere—composition and chemistry; 2427 Ionosphere: Ionosphere/atmosphere interactions (0335); 2419 Ionosphere: Ion chemistry and composition (0335).

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Citation: Kazil, J., E. Kopp, S. Chabrillat, and J. Bishop (2003), The University of Bern Atmospheric Ion Model: Time-dependent modeling of the ions in the mesosphere and lower thermosphere, J. Geophys. Res., 108(D14), 4432, doi:10.1029/2002JD003024.