Application of the DSMC Method in Modeling Earth's Rarefied Upper Atmosphere

Abstract:

Improving the accuracy and robustness of simulations of Earth's upper atmosphere is a priority for satellite drag and space weather applications. The Direct Simulation Monte Carlo [DSMC] method is well-suited to modeling the dynamics of such rarefied and non-equilibrium regimes, where continuum techniques break down. Here, we apply DSMC in three-dimensional, transient, and self-consistent neutral density simulations of Earth's rarefied upper atmosphere.

An existing planetary-science code base, established in the modeling of the lunar and Ionian environs, is extended to reflect the physics of Earth's upper atmosphere. Comprehensive atmospheric simulations are computed in parallel on a domain extending from the mid-thermosphere, below the continuum-rarefied transition, through 1000 km altitude. The simulation code includes multi-species neutral- and photo-chemistry, tracking of particle rotational and vibrational states, and non-equilibrium radiation transport. Substantial model development is demonstrated in application to the Earth’s atmosphere, including the incorporation of lower-boundary conditions consistent with the NRLMSISE-00 semi-empirical model, ultraviolet radiation and photo-chemistry rates modeled with reference to space weather indices, and radiative absorption attenuated by integrated column density.

Comparisons with results drawn from existing upper atmospheric models and from indirect satellite mass density measurements are employed in benchmarking model accuracy. Avenues for further development include hybridization with continuum global circulation models in the mid-thermosphere, and the extension of the planetary code's magnetic field and charged-particle models to the Earth case.

Research supported by the Los Alamos Space Weather Summer School, LANL Institutional Computing, and the Institute of Geophysics, Planetary Physics, and Signatures (IGPPS) at LANL.