Global Influences of Mountain Waves in a General Circulation Model

In this work, the global influences of mountain waves (MWs) are studied through a set of sensitivity experiments that alter the amount and vertical distribution of the MW drag deposited by its parameterization. The sensitivity experiments are motivated by a previous result that the conventionally parameterized MW drag in the general circulation model (GCM) used in the MERRA (MERRA-2) reanalysis underrepresented drag by a factor of ~4 (~1.5). Additionally, recent research has suggested that both lateral and vertical dispersion by broad-spectrum, transient MWs, both neglected by conventional instant and monochromatic parameterizations, significantly reduce wave amplitudes and increase the levels at which they break and deposit momentum. To understand the global influences of MWs and implications of these inaccuracies, sensitivity experiments are conducted using the Whole Atmosphere Community Climate Model (WACCM), a deep (z = 150 km) comprehensive general circulation model (GCM) that uses essentially the same parameterization as in MERRA.

The objectives of this study are to document the direct influences of MWs on the general circulation (e.g. zonal winds, residual circulations, polar temperatures) and the indirect influences that occur through interaction with the resolved planetary Rossby waves and the non-orographic gravity wave schemes. This objective is met by conducting climate simulations with and without MW drag. Additionally, the impacts of changing the total MW drag and its vertical distribution, as previously suggested may be needed, are also documented. These sensitivity experiments are compared against the MERRA and MERRA-2 reanalysis datasets to document the tradeoffs of these sensitivity experiments and speculate on how a new MW drag parameterization should behave to improve weather and climate simulations in both the stratosphere and troposphere.