Abstract
A new version of NCAR Whole Atmosphere Community Climate Model with
thermosphere/ionosphere extension (WACCM-X) has been developed. The main
feature of this version is the species-dependent spectral element (SE)
dynamical core, adapted from the standard version for the Community
Atmosphere Model (CAM). The SE is on a quasi-uniform cubed sphere grid,
eliminating the polar singularity and thus enabling simulations at
high-resolutions. Molecular viscosity and diffusion in the horizontal
direction are also included. The Conservative Semi-Lagrangian
Multi-Tracer Transport Scheme (CSLAM) is employed for the species
transport. An efficient regridding scheme based on the Earth System
Modeling Framework (ESMF) is used to map fields between the physics mesh
and geomagnetic grid. Simulations have been performed at coarse
(~200 km and 0.25 scale height) and high
(~25 km and 0.1 scale height) resolutions. The spatial
distribution of the resolved gravity waves from the high-resolution
simulations compare well with available observations in the middle and
upper atmosphere. The forcing by the resolved gravity waves improves the
wind climatology in the mesosphere and lower thermosphere in comparison
to the coarse resolution simulations with parameterized forcing. It also
impacts the thermospheric circulation and compositional structures, as
well as thermospheric variablity. While larger scale waves are dominant
energetically at most latitudes, smaller scale waves contribute
significantly to the total momentum flux, especially at mid-high
latitudes. The waves in the thermosphere are shown to be strongly
modulated by the large-scale wind through Doppler shift and molecular
damping, and they cause large neutral atmosphere and plasma
perturbations.