Constraining the Parameterization of Polar Inertia Gravity Waves in WACCM with Observations

Abstract:

A discrepancy that has been seen in a number of climate models is that simulated temperatures in the Antarctic lower stratosphere during winter and spring are much lower than observed; this is referred to as the “cold pole” problem. Recent simulations with the NCAR Whole Atmosphere Community Climate Model have shown that polar stratospheric temperatures are much improved by including a parameterization of gravity waves, which have inertial periods, longer horizontal wavelengths and shorter vertical wavelengths than the mesoscale gravity waves already parameterized in this and most other middle atmosphere models. Improvements include a more realistic seasonal development of the ozone hole and somewhat better timing for the winter to summer transition in the zonal winds and Brewer-Dobson Circulation.

Although the availability and quality of observations of gravity waves in the middle atmosphere has been increasing, there are still not sufficient observations to validate the inertial gravity wave morphology and distribution in the model. Here, we use constraints from new analyses of radiosonde observations to provide guidance for the horizontal and vertical wavelengths of the waves, their seasonal variability, and their potential sources such as fronts or flow imbalance. Tighter observational constraints remove an element of arbitrary “tuning” and tie the model simulations of the middle atmosphere more closely to the simulated climate.