Fall AGU Meeting (Dec. 2002) COAST abstracts:

• Allen
  
• Bane et al.
  
• Barth et al.
  
• Carney et al.
  
• Couch et al.
  
• Cowles et al.
  
• Dale et al.
  
• Durski et al.
  
• Egbert et al.
  
• Gan et al.
  
• Hales et al.
  
• Kosro et al.
  
• Kuebel et al.
  
• Kurapov et al.
  
• Perlin et al.
  
• Pierce et al.
  
• Ruttenberg et al.
  
• Samelson
  
• Spitz et al.
  
• Wheeler
  

Abstracts should be cited as:

EOS Trans. AGU, 83 (47),
Fall Meet. Suppl.,
Abstract XXXXX-XX, 2002

OS62A-0239

A Modeling Study of Lagrangian and Eulerian Shelf Flows due to
Periodic Wind Forcing

B T Kuebel, J S Allen, and R M Samelson

The circulation of fluid on the continental shelf is greatly
influenced by the wind stress magnitude and direction. Many shelf
regions experience periods of fluctuating alongshelf winds, causing
shifts between upwelling and downwelling conditions. The upwelling
and downwelling responses are not symmetric. We seek to understand
these asymmetries and their implications on the Eulerian and
Lagrangian flows. We use a two-dimensional (variations across-shelf
and with depth; uniformity alongshelf) primitive equation numerical
model to study shelf flows in the presence of periodic, zero-mean
wind forcing. The model bathymetry and initial stratification is
typical of a broad, shallow shelf during summer.  After an initial,
transient adjustment, the response of the Eulerian fields is nearly
periodic. Despite the symmetric wind stress forcing, there exist both
mean Eulerian and Lagrangian flows. The mean Lagrangian displacement
of parcels on the shelf depends both on their initial location and on
the initial phase of the forcing.  The use of mean parcel positions
during a cycle for calculating displacements helps to remove the
dependence on phase. In an experiment with sinusoidal wind stress
forcing of 1 dyne cm$^{- }^{2}$ maximum amplitude and 6 day period,
the mean Lagrangian displacements were largest in the surface and
bottom boundary layers.  Parcels initialized near the bottom within
50 km of the coast can be displaced to the surface at the coastal
boundary over several periods. Parcels initially in the upper 10m
within 25 km of the coast form large, irregular orbits, yet remain
within this region. Parcels initialized in the middle of the water
column offshore of about 15 km form almost closed orbits after one
period and migrate slowly downward over many periods.  Eulerian mean
velocities, in contrast, have no dependence on initial phase. The
Eulerian across-shelf mean velocity field shows 2 cm s$^{-}^{1}$
onshore flow in the bottom layer from the coast to 30 km offshore and
in the top layer from 10 km to 20 km offshore. Offshore flow of this
magnitude is found both onshore of and below the surface region of
onshore flow.  Corresponding to regions of onshore flow are upward
vertical velocities of 1 {\times} 10$^{- }^{3}$ cm s$^{-}^{1}$
with similar downward velocities in regions of offshore flow.