Abstract:
The dynamics of the coastal transition zone off Northern California during late May and early June 1987 art
examined through assimilation modeling studies. A regional baroclinic quasi-geostrophic model is driven by the
data through initial and boundary conditions. These initial and boundary conditions are specified by objective
analysis of hydrographic and acoustic Doppler current profiler data. The data assimilation is accomplished
by varying the objective analysis parameters, numerical parameters, and subgrid-scale parameters until the
final solution of the model is in best agreement with the analysis of the data. The solution which best
agrees with the data is regarded as a four dimensional field estimate of the coastal transition zone how. An
aspect of this study that is new to data assimilation modeling of mesoscale eddy fields is the use of acoustic
Doppler current profiler data. These data prove to be very important to accurate description of the oceanic
flow field as indicated by comparison with float trajectories. The complete data seL provides an opportunity
to study the ability of dynamical constraints to improve field estimates when acting upon a subset of the
data (hydrography). Data assimilation modeling generates field estimates that are substantially better than
those based upon the hydrographic data alone as indicated by comparison with the acoustic Doppler current
profiler based analyses. The kinematics and energetics of this constrained (quasi-geostrophic) field estimate
are examined. Despite the relatively small region (108 by 324 km) land short period of the field estimate (21
days), interesting processes are identified. A meandering barotropically unstable part of the jet is identified
using the results of related idealized numerical studies and stability analyses. Similarly, this jet may be
undergoing a simultaneous larger scale mixed instability. Another part of the jet interacts with an eddy and
meanders in a much different manner. Characteristics of the energy balances are identified and compared
with the results of linear analysis and of nonlinear studies utilizing idealized models of the observed jet as
described in this issue by Pierce et al. and Allen et al. respectively.
