Extracting Synoptic-Scale Diagnostic Information from Mesoscale Models: The Eta Model, Gravity Waves, and Quasigeostrophic Diagnostics

Abstract Fine-mesh models, such as the eta model, are producing increasingly detailed predictions about mesoscale atmospheric motions. Mesoscale systems typically produce stronger vertical motions than do synoptic-scale storms, making it more difficult for forecasters to assess the strength of the latter's dynamics when the signals are overwhelmed by mesoscale processes. This paper describes a method for extracting synoptic-scale information from mesoscale model data. Predicted height fields from the 29-km eta model are investigated to determine the filtering and smoothing requirements necessary to resolve synoptic-scale patterns of vertical motions using quasigeostrophic (QG) diagnostics. The selected late-fall case includes a jet stream that enters the continent over the Pacific Northwest, resulting in orographically induced troughs in the lee of the Cascade Range and Rocky Mountains. Gravity waves are found to emanate from this region in arcs that reach Hudson Bay to the northeast and extend to the Car...