Dynamical downscaling simulation of gravity waves generation by tropical cycle

Monday, August 15, 2016

National Center for Atmospheric Research Whole Atmosphere Community Climate Model (WACCM) with ≈0.25 degree horizontal resolution can resolve gravity waves with horizontal scales down to ≈250 km.

Downscaling simulation of gravity waves image
The wavelet transforms of the (a) vertical wind of WRF-25 and (b) vertical wind of high-resolution WACCM at 20◦S at 5 hPa altitude. The dotted line is the location of TC center.

To understand the scale interactions between the gravity waves resolved by WACCM and those with smaller scales, the potential impact on the resolved waves, and dependence of wave characteristics on spatial resolution, high-spatial-resolution Weather Research and Forecasting (WRF) simulations are performed, applying the high-resolution WACCM wind and temperature fields as initial and boundary conditions. Semicircular GWs excited by a tropical cyclone (TC) are found with similar structures and locations in WACCM and WRF with 25 km grid spacing. In this study, the sensitivity of GW structure to the choice of model horizontal resolutions (25 km, 15 km, 10 km, and 4 km) is examined. Although WRF is successful in generating semicircular GWs in each case, the simulation reveals more power at shorter horizontal wavelengths of GWs at finer resolutions. By comparing the GWs from a WRF simulation with explicitly resolved convection (i.e., no convective parameterization) at the same horizontal resolution scale (4 km), we find that the resolved convection, however, play little role in the GWs generated by the TC on the order of 4 km horizontal resolution.

This manuscript was submitted to Journal of Advances in Modeling Earth Systems