Assessment of gravity waves from tropopause to thermosphere and ionosphere in high-resolution WACCM-X simulations

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 solved on a cubed sphere grid, eliminating the polar singularity and 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 is used to map fields between the physics mesh and geomagnetic grid. Simulations have been performed at coarse (similar to 200 km and 0.25 scale height) and high (similar to 25 km and 0.1 scale height) resolutions. Spatial distribution of the resolved gravity waves from the high-resolution simulations compares well with available observations in the middle and upper atmosphere. Analysis of the scale dependence of the gravity wave energy density and momentum flux shows that, 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.