A sensitivity study of the middle atmosphere to changes in the parameterized momentum drag of gravity waves

We investigate the sensitivity of some atmospheric diagnostics to a variety of assumptions in the spectral gravity wave parameterization normally used in Whole Atmosphere Community Climate Model, version 3 (WACCM3). WACCM3 uses a Lindzen's type parameterization with waves uniformly distributed from -80 m/s to +80 m/s and a source spectrum defined to produce an acceptable climatology in the reference simulation. The reference simulation is compared to a series of experiments where the source function is altered, the spectral resolution is made not uniform, and the launching level is changed. We also investigate the effect of a source spectrum tied to typical tropospheric sources of gravity waves: convective sources are introduced by using the Beres et al. (2004) scheme; frontal sources are accounted for by using the Charon and Manzini (2002) scheme. Our results show that the middle atmosphere climate can be significantly impacted by changes in the gravity wave parameterization. Typical metrics that are affected include the structure of the stratosphere in the winter hemisphere, the lower stratosphere over Antarctica as it affects ozone chemistry, and the behavior of the summer mesopause. We are also showing that the variability of the mean state is significantly impacted, where variability is measured as standard deviation of meteorological fields, the number of stratospheric sudden warming and their amplitude.