The Generation of Propagating Gravity Waves by a Mountain-Plains Solenoid (MPS)

An extraordinarily well-documented mesoscale gravity wave event in Montana is investigated with a mesoscale numerical model. The model and observations both show that a pronounced mountain-plains solenoid (MPS) developed over the Absaroka Mountains due to elevated sensible heating. An eastward-propagating gravity wave was simulated as the strong updraft associated with the MPS impinged upon the stratified shear layer above the well-mixed boundary layer. However, even though a wave duct was present over eastern Montana, this region was apparently too far away from the wave generation region for the waves to be able to "tap" this duct to preserve themselves in the presence of energy dispersion. Explosive convection developed as an eastward propagating cool pool produced by a rainband generated within the lee-side convergence zone merged with a westward-propagating cool pool directly underneath the remnant gravity wave in eastern Montana. The greatly strengthened cool pool resulting from this new convection then generated a bore wave that propagated eastward into North Dakota, but it could not be determined with certainty whether this was the feature seen in the surface microbarographs. This study highlights difficulties encountered in attempting to understand the generation of even very well-observed gravity waves over complex terrain in the presence of convection, and the need for much more detailed observations within the wave generation region.