Modeling of Atmospheric Flow Around a Coastal Cape: Lee Side Story

TL;DR

This study uses mesoscale coupled ocean-atmosphere modeling to analyze atmospheric flow around a coastal cape, revealing diurnal cycles, boundary layer dynamics, and terrain effects on wind and pressure patterns.

Contribution

It provides new insights into mesoscale atmospheric dynamics and the influence of coastal topography on wind and pressure features around a cape.

Findings

Orographic wind maximum extends hundreds of kilometers downstream.

Diurnal cycle significantly affects wind and pressure patterns.

Higher terrain increases separation of upwelling front from the coast.

Abstract

The current research focuses on mesoscale dynamics of the atmospheric circulation around an idealized coastal cape representing typical summertime circulation along the northwest coast of the U.S., studied using a mesoscale coupled ocean-atmosphere modeling system. The orographic wind maximum features a strong NW flow extending a few hundred kilometers downstream and seaward of the cape, which closely follows mesoscale orographic low pressure developed in the lee of the cape. Both wind maximum and the lee trough experience a pronounced diurnal cycle, marked by maximum northwest flow and minimum pressure in the local evening hours (its opposite phase during morning hours), and confirmed by observations from limited buoy and coastal stations. Vertical structure of the atmospheric boundary layer over the coastal ocean on the lee side of the cape indicated the downward propagation of potential temperature and wind features during the course of the day, as opposed to the traditional surface-driven development of the atmospheric boundary layer. Momentum analysis showed the local pressure gradients near the surface vary greatly depending on the relative location about the cape. Strong perturbations in relative vorticity downwind of the cape supported the hypothesis that mountain dynamics have a key role in establishing wind regime around the cape. The sensitivity studies indicated the importance of coastal terrain elevation on the formation and the strength of the lee trough and wind maximum. Higher coastal topography was found to cause greater separation of the upwelling front (jet) from the coast downwind of the cape.