Working Group 4: Geospace Community Modeling

The Whole Atmosphere Community Climate Model with Thermosphere and Ionosphere Extension (WACCM-X) , is a comprehensive numerical model, spanning the range of altitude from the Earth’s surface to the upper thermosphere.  During the past year, scientists at HAO, working with ACOM and CGD, completed version 2.0 of the model, which now contains a fully-interactive ionosphere, including self-consistent electrodynamics and ion transport.  Version 2.0 also includes improvements to upper-atmosphere neutral transport and energetics, electron temperatures, and ion temperatures.

WACCM-X simulation image

WACCM-X simulation of the "April Fools" geomagnetic storm in 2001, showing the global electron column density in units of 1012 cm-2. Note the "tongue of ionization" extending out of both the north and south auroral regions into the dayside low-latitudes, and the highly distorted equatorial ionosphere.

The scientific goals of the model include studying solar impacts on the Earth’s atmosphere, couplings between atmosphere layers through chemical, physical and dynamical processes, and the implications of the coupling for the climate and for the near space environment. The development of the model is inter-divisional collaboration that unifies aspects of upper atmospheric modeling of HAO, the middle atmosphere modeling of ACOM, and the tropospheric modeling of CGD, using the NCAR Community Earth System Model (CESM) as a common numerical framework.

WACCM-X version 2.0, with fully-interactive ionosphere, will be released as part of the new Community Earth System Model, version 2.0, in 2018.  Multi-year runs of WACCM-X, both with free-running climate and with specified dynamics in the lower atmosphere, have been conducted, and are available for analysis by NCAR scientists and external colleagues.  Several large geomagnetic storms have been simulated, including effects auroral activity, flares, and solar energetic particles, as shown in the figure.  Also, the ionospheric consequences of stratospheric warmings, tidal variations, and other atmospheric dynamical effects are being investigated, including by using data assimilation methods to constrain the lower and middle atmosphere.

The new model was presented and discussed at two sessions at the CEDAR summer workshop in June 2017, the Whole Atmosphere Variability session, and the WACCM-X Users Group tutorial session, see:

Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM)

Ionospheric F2-peak electron densities image

An example of comparing TIEGCM run with FFT filter scheme with the run using the ring-average scheme for the 2013 St. Patrick’s geomagnetic storm event, shows ionospheric F2-peak electron densities (~350 km) at middle and high latitudes in the northern hemisphere. In the FFT-TIEGCM outputs (top left) at 2.50 horizontal resolution, the model captures the large-scale structure of plasma transport from the dayside across the polar cap and into the nightside auroral oval by the magnetosphere electric field, but the model results show artificial circles around the geographic pole, which is the result of FFT filtering. The grid discretization effect with a coarse grid resolution of 2.50 is also evident. This effect is also seen in the TIEGCM results of the same grid resolution with the ring-average scheme (top right), although the numerical problem near the pole associated with the FFT filtering does not exist anymore. With the ring-average scheme and high resolutions of 1.250 (bottom left) and 0.6250 (bottom right), the model is able to simulate both the large-scale plasma transport and the fine-scale structures of ionospheric electron density distributions in the polar region, which are consistent with observations.

High-latitude ionosphere and thermosphere are the region where significant energy and momentum input from the solar wind and the magnetosphere occurs. This input is mostly associated with the magnetospheric convection electric field, which drives large-scale transport of ionospheric plasma and causes changes in neutral wind, temperature and composition. The magnetospheric electric field and its associated Joule heating and ion drag to the neutral atmosphere are highly dynamic with different temporal and spatial scales. To accurately simulate the dynamic coupling in geospace and the effects of the solar wind and magnetosphere on the upper atmosphere high-resolution models of the coupled thermosphere and ionosphere system have to be developed to be able to account for the cross-scale coupling within the system. This high-resolution modeling capability, however, is not available until recently because of the difficulty in dealing with neural and plasma transport in the polar region with large plasma drift and wind velocities of hundreds meters per second or more. The currently implemented FFT filter schemes at high latitudes to curb the development of numerical instability when the grid size becomes smaller longitudinally also prevent the models from being easily scaled to high resolution.

HAO scientists and a visiting graduate student from the University of Science and Technology of China and a scientist of the university collaborated to implement a ring-average scheme at the high latitudes in the NCAR’s community model of the upper atmosphere: Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM). This ring-average scheme has the advantage of conserving flow fluxes across the polar cap region over the traditional commonly used FFT scheme and can be easily scaled to different model resolutions but still keeping the high computation efficiency. Upon successfully tested and validated in the TIEGCM, this ring-average scheme is currently in the process of being incorporated into the Whole Atmosphere Community Climate Model with Thermosphere Extension (WACCM-X).