Dynamical Adjustment Theory for Boundary Layer Flow in Cold Surges

Abstract

Theoretical responses of boundary layer flow for winter cold surges crossing a coastline are determined. Analytical solutions for linearized equations describing the mixed layer adjustments to impulsive heating and surface drag reduction are obtains Dynamical interpretation contrasts with nonturbulent adjustment processes and nonlinear simulations are made. The response depends upon various physical process length males, two reflecting dynamical adjustments and four reflecting turbulence influences. Upstream wind and inversion strength determine a Froude number Fr which strongly influences the flow, regimes resembling quasi-geostrophic and inertia-gravity behavior (modified by turbulence) are identified. These possess strong two-way coupling between wind and inversion, but primarily a one-way influence between temperature and wind. Surface pressure drops may commence over land (small Fr); their maxima (a few millibars) over the sea are smaller than simple boundary layer warming would imply. Examples show a subsynoptic scale region of coastal subsidence which may extend upwind over land (small Fr) or may be replaced by oscillating reversals over the sea (large Fr). Wind speed adjustments are stronger in large Fr cases. Characteristic wind perturbation scales for land-ocean temperature and drag differences are obtained. Together with the dynamic solutions, they suggest that the change in surface drag may dominate differential heating in altering the flow.