Self-consistent global transport of metallic ions with WACCM-X

Abstract

Abstract. The NCAR Whole Atmosphere Community Climate Model with thermosphere and ionosphere eXtension (WACCM-X) v2.1 has been extended to include the neutral and ion–molecule chemistry and dynamics of three metals (Mg, Na, and Fe), which are injected into the upper mesosphere–lower thermosphere by meteoric ablation. Here we focus on the self-consistent electrodynamical transport of metallic ions in both the E and F regions. The model with full ion transport significantly improves the simulation of global distribution and seasonal variations of Mg+, although the peak density is slightly lower (about 35 % lower in peak density) compared with the SCIAMACHY measurements. Near the magnetic equator, the diurnal variation in upward and downward transport of Mg+ is generally consistent with the “ionosphere fountain effect”. The thermospheric distribution of Fe is shown to be closely coupled to the transport of Fe+. The effect of ion mass on ion transport is also examined: the lighter ions (Mg+ and Na+) are transported above 150 km more easily than the heavy Fe+. We also examine the impact of the transport of major molecular ions, NO+ and O2+, on the distribution of metallic ions.

Comparison of middle- and low-latitude sodium layer from a ground-based lidar network, the Odin satellite, and WACCM–Na model

“…The equatorial metallic ions are uplifted by V × B forcing and drift down along the magnetic field lines to the subtropical region. The transport of metallic ions is generally consistent with the fountain effect, and the fountain effect is stronger over east Asia (Wu et al, 2021). The metal layer can be influenced by the metallic ions as the major reservoir of the neutrals through the recombination between ions and electrons, though the neutral atoms are not directly transported by the electromagnetic field (Cai et al, 2019a).…”

“…On the other hand, the ground-based lidar measurements are a supplement to satellite data sets when the high-latitude Na layers are not solar-illuminated in winter. The Na column density has a maximum in winter from several local groundbased observations (Gibson and Sandford, 1971;Plane et al, 1999;She et al, 2000;Gardner et al, 2005;Yuan et al, 2012;Li et al, 2018;Andrioli et al, 2020) and global modelling studies of meteoric Na in the MLT (Marsh et al, 2013;Wu et al, 2021). The lower panels during each season depict the northern and southern polar views of the Na column density, and these views make the summer minimum in the high-latitude Na layers clearer.…”

“…More recently, the distribution of Mg + column density simulated by WACCM-X (Wu et al, 2021) shows a stronger convergence along the magnetic equator. The equatorial metallic ions are uplifted by V × B forcing and drift down along the magnetic field lines to the subtropical region.…”

“…A global atmospheric model of the meteoric metals Fe, Na, K, Si, Ca, Al, Mg, and Ni (e.g. Feng et al, 2013;Marsh et al, 2013;Plane et al, 2014;Langowski et al, 2015;Plane et al, 2016Plane et al, , 2018Daly et al, 2020;Plane et al, 2021) has been developed in order to advance understanding the meteor astronomy, atmospheric chemistry, and transport processes that control the different metal layers in the MLT (Feng et al, 2015;Plane et al, 2015;Wu et al, 2019). The model uses a seasonally varying meteoric injection rate of these metals at different latitudes and altitudes.…”

“…The metal layer can be influenced by the metallic ions as the major reservoir of the neutrals through the recombination between ions and electrons, though the neutral atoms are not directly transported by the electromagnetic field (Cai et al, 2019a). The electrodynamical transport of metallic ions has an important impact on the global distribution of metal ions and atoms (Wu et al, 2021). It could explain why WACCM-Na does not capture the large Na observed by the CMP lidars at 10-40 • N.…”