Terrain-Induced Midtropospheric Frontogenesis and Jet Streak Development During Storm-Fest IOP-17, 8 & 9 March 1992.
Abstract
Diagnostic analysis and numerical modeling studies of STORM-FEST IOP-17 data from 8-9 March 1992 reveal that terrain forced mesoscale secondary circulations play a prominent role in cold front aloft (CFA) formation and in the bifurcation of the polar jet downwind of a barrier. Terrain enhanced adiabatic and diabatic forcing, associated with focused leeside warming to the south and an equatorward surge of cold air from the north, generate mass perturbations that lie within the Rossby radius of deformation. The perturbation results in an imbalance between the mass and momentum field as an increased separation develops between the observed and geostrophic jet max. In order to regain a balance, the divergent part of the wind responds by establishing a thermally-direct circulation within the jet exit region. In response, the `classical jet streak' configuration is distorted as the exit region accelerates downstream. The positive velocity divergence tendency produces a net mass flux divergence throughout the column. In turn, ascent and midtropospheric cooling is observed within the right exit region of the accelerating jet streak. The baroclinic zone associated with the primary trough over the inner-mountain region weakens as cold air is generated downstream of the mountain. The CFA formation is initially dominated by tilting of the vertical temperature gradient and then enhanced by confluence and shear contributions as a `balanced' thermally-indirect circulation is regained. The resulting cooling acts to retard height rises in a region which typically experiences a build up of mass induced by subsiding air. This destabilization acts to promote an environment conducive to severe weather downstream of the mountains.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 09, 1997
- Accession Number
- ADA320416
Entities
People
- Michael E. Adams
Organizations
- Air Force Institute of Technology