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Weekly Seminar: Fall 2009

Date: October 23

Time: 11:00 AM
Location: Maryland Hall 110
Speaker: Marcello Magaldi
Earth & Planetary Sciences, Johns Hopkins University
Title:"Turbulent coherent structures near coastal capes"

Abstract

Coastal circulation is influenced by the complex shape of the
coastline. In particular, prominent coastline features like headlands
and capes are responsible for the creation of turbulent coherent
structures. Various flow regimes can be observed around coastal capes:
in some cases the structures can merge to form large lee eddies while,
in other cases, they cascade to smaller ones. Understanding under
which conditions different flow regimes appear in the vicinity of
coastal capes is important since they affect the dispersion of
dissolved pollutants, floating organisms, nutrients and sediments.
From a dynamical perspective, the same regimes are also associated
with enhanced mixing, drag and dissipation.

In this talk, idealized and more realistic numerical simulations run
both in barotropically and baroclinically-driven systems are
presented. In the idealized cases, a steady barotropic and geostrophic
current impinges on a triangular cape. It is shown that flow regimes
are dependent on the Burger number and the obstacle slope. The
realistic cases model the effects of wind forcing for the Western
Adriatic Current (WAC) in the Adriatic Sea. The WAC becomes unstable
in the absence of wind as it separates from the coast for the presence
of capes along its path. Downwelling favorable winds narrow and
thicken the coastal buoyant current, suppressing large instabilities.
Upwelling favorable winds enhance mesoscale instabilities via the
opposite mechanism. The impacts of the regimes are quantified in terms
of integral quantities like mixing, current transport and form drag.