PWS Field Experiment Overview
The Alaska Ocean Observing System (AOOS) and the Oil Spill Recovery Institute
(OSRI) are sponsoring a field experiment between April and August of 2009 to evaluate
regional forecast models for wind, waves and ocean circulation in Prince William Sound.
This field experiment will be preceded in the summer of 2008 by a re-run or hindcast
using 2004 observational data to compare historical and current model forecast skill.
Details of the 2004 field experiment can be found at:
http://ak.aoos.org/pws/lagrangian_2004.html. In the spring of 2009 there will be a desktop experimental model run utilizing real-time data streams from operational PWS
observational platforms. The objective of these experiments is to quantitatively evaluate
the performance of forecast models in Prince William Sound including the WRF
atmospheric and ROMS ocean circulation models, the SWAN wave model, and the
SAROPS search and rescue trajectory model.
Model performance evaluations will be based on comparisons with 1) observational data
collected during a four week field experiment in 2009, and 2) model performance during
the 2004 experiment. The overarching questions are 1) How well are the models able to
predict atmospheric and oceanic water properties, wave conditions, and circulation
patterns in different areas of PWS?; 2) Has the circulation model forecast skill for the
central basin improved from those in 2004?; and 3) What is the cost/benefit of the AOOS
for weather and ocean forecasting?
AOOS is now providing access to real-time and historical observational data for PWS
from one data portal (http://www.aoos.org). These data are available to the developers of
atmospheric and ocean circulation models, and a wave model, to facilitate assimilation
and validation. During the 2009 field experiment, drifting buoys will be repeatedly
deployed, retrieved, and redeployed during a two to four week period. There will be an
emphasis on model validation of surface and deeper currents in the central basin, so the
majority of drifter deployments will occur within the field of view of an existing HF
radar surface current mapping system. Additional deployments may occur around the
perimeter of the Sound to validate the velocity of surface currents forced predominantly
by fresh water runoff and track the fate of Lagrangian drifters that mimic Coast Guard
Search and Rescue targets as well as oil spill trajectories. The experiment will provide
the opportunity for individuals and institutions to test new sensors, platforms, and
evaluate models.
Field Sampling Work Plan
General description
The focus area of the field program will be a circle with a 20 km radius centered at 60°
35’ N, 146° 56’ W (Fig. 1). This places the field program in the same location as was
used in the 2004 lagrangian field experiment (Cox, 2005). It is north of Hinchinbrook
Entrance in the central portion of Prince William Sound where the 2004 field experiment
was conducted (Cox, 2005). The bathymetry is characterized by a relatively wide and
deep (400 m) deep trench that runs north-south (Fig. 2). Hinchinbrook Entrance is the
major connection to the Gulf of Alaska and Copper River water is sometimes observed
flowing in the Entrance. North of the area glacial melting and rainfall contribute to a
freshened surface water layer that flows southward on the western side of PWS.
During the 2004 experiment a cyclonic circulation was observed in the central basin.
Surface drifters tended to remain in the circulation for two to three days and then move
out of the central basin. This typically occurred when the drifter was on the northern or
western side of the cyclonic circulation. Drifters drogued at 10 m remained in the area
following a cyclonic path for a much longer period of time.
The main vessel traffic is expected to be tankers transiting to and from the Valdez oil
terminal; the ferry connecting Whittier, Valdez, and Cordova; and fishing vessels
transiting between fishing areas near hatcheries in western and northern PWS and the
larger communities.
A cell phone tower is located at Naked Island, which allows for communication between
shore and the field and possible to transfer data while in the field.
Fig. 1. The main study region is denoted by the solid red circle. The dotted circles are
locations where short experiments may be conducted.
Fig. 2. Bathymetry of PWS is shown. Each color change is represents 100 m of depth.
The intensive field observation period will occur between July 19 and August 3. A
general timeline follows.
Timeline
Nearshore moorings deployed
Entrance moorings deployed
HF – radar deployed
Clean nearshore moorings
Jul 19-20
ships load, deploy glider, and initial CTD surveys
Jul 21-25
Central Sound drifter deployment
Jul 26-28
Short experiments and possible day in Cordova
July 29-Aug 2 Central Sound drifter deployment
Aug 3
Ships unload
HF – radar removed
Sept 30
Entrance moorings turn around
Nearshore moorings recovered
Mar 30
Two vessels are expected to be used. One larger vessel will support hydrographic
surveys, autonomous underwater vehicles, biological sampling if the latter program is
funded, and as a hotel ship during the exercise. A smaller boat will be used to deploy and
retrieve drifters. The larger boat will load the morning of July 19th in Cordova and depart
mid-day to conduct initial hydrographic surveys. The smaller boat will load and depart
on the 20th in preparation for drifter deployments early on the 21st. Both boats will
anchor at Naked Island during the experiment to reduce travel time to the study site (It
may be possible for the smaller vessel to return to Cordova on a daily basis.)
The expectation is that two people plus the captain of the small boat will conduct the
drifter collection and redeployment. One person will be needed to collect hydrographic
measurements along with two people for AUV operations. These people will be
stationed on the larger vessel.