WACCM development and extension

Globally averaged number densities of constituents (upper and middle panel) and zonal mean temperature, zonal wind and meridional wind (lower panel) from the ground to the upper thermosphere from a WACCM simulation (January).

High resolution figure

When first proposed, the goal of the Whole Atmosphere Community Climate Model (WACCM) is to develop a model that extend from the Earth surface to the upper thermosphere, and self-consistently resolve the dynamical, chemical, radiative, and electrodynamical processes and the coupling between atmospheric regions. The current standard WACCM version (WACCM3) extends from the surface to the lower thermosphere (~140 km).

We have recently extended WACCM with 1.9x2.5 degrees horizontal resolution to the upper thermosphere at 3.4x10^-7 Pa (the same as the upper boundary of the TIME-GCM, approximately at 500 km). In the process of achieving this upward extension, we have

(1) Implemented modules to resolve the major species diffusion, which becomes increasingly important above 110 km.

(2) Implemented modules and revised the codes to reflect the constituent-dependency of the specific heats, gas constant, and mean molecular weight. They were set to constants in the previous codes.

(3) Revised the treatment of the vertical diffusion equations for minor species and heat conduction equation. The EUV/FUV photochemistry, non-LTE radiative processes, and ion-drag and Joule heating have already been implemented in the WACCM3.

We have made test runs using the extended WACCM, and obtained the wind structure, thermal structure, the vertical profiles of major species (N2, O2, O), oxygen species (O3, O1D, O2_1S, O2_1D), hydrogen species (H, H2O, HO2, OH), nitrogen species (NO, NO2), carbon species (CO, CO2, CH4), ions (O+, O2+, NO+, N+, N2+) and electron density from the ground to the upper thermosphere. Initial comparison shows that these structures in the middle and upper atmosphere are in good agreement with those obtained from TIME-GCM.

We will further validate the WACCM results, including seasonal and annual variation of thermosphere density against TIME-GCM and MSIS. We also plan to implement ambipolar in the WACCM.

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