Gravity wave responses throughout the lower and middle atmosphere to airflow over the southern Andes and the Antarctic peninsula: A natural laboratory for assessing responses to complex terrain, coupling to higher altitudes, and evaluation of OGWD parameterizations

Numerous data suggest that the southern Andes and the Antarctic Peninsula are major sources of orographic gravity waves (OGWs) and that these waves penetrate to, and may have significant influences extending into, the mesosphere and possibly the lower thermosphere. Strong climatological tropospheric winds and the roughly north-south alignment of orographic features at latitudes of ~30 to 70oS ensure strong OGW forcing. Indeed, responses in the stratosphere to GW sources in this region appear to be the largest of any site on Earth. Strong climatological wintertime mean winds and semidiurnal tidal structures in the mesosphere and lower thermosphere (MLT) appear to also provide periodic propagation channels for OGWs to higher altitudes. Thus, this region represents a natural laboratory for assessing and quantifying these dynamics through comprehensive and correlative measurement capabilities and numerical modeling. We anticipate that such efforts would contribute dramatically to

1) quantifying OGW forcing, structure, and variability in the troposphere and lower stratosphere (TLS);

2) defining sensitivity of OGW responses to upstream conditions in the TLS;

3) quantifying OGW propagation and momentum transport into the upper stratosphere and MLT, and the impacts on mean and tidal structures and the residual circulation at these altitudes; and

4) comprehensive evaluation of OGW drag parameterization schemes.

These objectives are expected to be addressed through merging of comprehensive measurements and advanced modeling capabilities. Ground-based and airborne measurements would assess TLS and MLT mean, tidal, and OGW structures over the full range of latitudes. A suite of numerical modeling capabilities ranging from linear and high-resolution nonlinear simulations over complex terrain to nested mesoscale and high-resolution global models would permit detailed comparisons with observations, a singular vector evaluation of sensitivity to upstream influences and initial conditions, assessments of the effects of OGW instability dynamics on momentum transport and spectral evolution, and the impacts of these dynamics on the circulation, structure, and variability of the MLT. Testing of OGW drag parameterizations in the global model would be enabled by comprehensive observations, well-defined OGW forcing conditions, and high-resolution models of local terrain responses. Internal funding for this program has already been committed by the Naval Research Laboratory, and we anticipate a proposal for an extensive field program and related modeling activities to NSF later this year, with an airborne program anticipated to employ the NSF/NCAR HAIPER in 2011 or 2012.