Field Measurement Accomplishment
Field measurements were made for two
purposes: 1) mixing and water transport studies (led by
Dr. MacDonald) and 2) model validation (led by Dr. Zhao
with support from Drs. Chen and Cowles). The key finding
of these field works is described as below.
a) September 2004 and April 2005 Surveys
These two surveys were made by Dr. MacDonald
and his students to examine the role of mixing in the
structure and evolution of a buoyant discharge plume.
Major finding from these two field works are described
in two separate manuscripts prepared by MacDonald and
his student. The measurement made in fall 2004 was under
a condition in which buoyancy of the plume was controlled
by temperature and the plume was trapped at the surface.
Field measurements indicate strong mixing across the first
several hundred meters of the near field of the plume,
and suggest that the mixing occurs as a result of bottom
friction focused along the edges of the plume structure.
The plume structure observed is different from conceptual
models of industrial plumes based on previous laboratory
and numerical studies. The results indicate that the existing
discharge structure provides a quick and efficient means
of mixing heat into ambient waters.
An estimation was made on the residence
time of a semi-enclosed estuary with observations of tidal
exchange flow. The result illuminates the issue of bulk
residence time for Mt. Hope Bay. Although the concept
of residence time is simple, an effective estimate of
residence time can be difficult to achieve in practice.
Analysis of tidal flux through the seaward passages of
Mt. Hope Bay provided an estimated residence time, based
strictly on tidal exchange processes, on the order of
2 weeks to a month. A comparison of these values with
appropriate freshwater flushing times suggests that tidal
exchange processes may only be important during low freshwater
b) August 2005 Survey
The field plan was designed by Dr. L.
Zhao with support from Dr. Chen and Dr. Cowles. This was
a multi-institutional cooperative high-resolution sampling
survey with participation of scientists from Woods Hole
Oceanographic Institution (WHOI) and NOAA Northeast Marine
Fisheries Service at Woods Hole. The measurement included
1) ship-mounted ADCP and CTD and 2) satellite-tracking
surface drifters. Dr. MacDonald and his student helped
setting up the CTD/ADCP for this cruse and WHOI and NMFS
provided two surface drifters and Mr. Jim Chruchill at
WHOI participated in the first day survey.
The survey was made on 18-19 August 2005,
a period with the maximum spring tide in the year. On
18 August, the CTD/ADCP measurement was conducted repeatedly
on the ship-track shown in Fig. 19. Two drifters released
at maximum flood tidal current in afternoon near the MHB
Bridge to measure the intensity of tidal flushing and
current separation. The CTD/ADCP data are still undergoing
postprocessing, and drifter trajectories clearly showed
the rapid motions caused by tidal flushing. Two drifters
ended in the upper part of the MHB, which is consistent
with the FVCOM-prediction. Due to the relatively strong
seabreeze from the land, the drifters all