AOFB 1 deployed 24 April 2002, 88.5246 N, 82.7458 W
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Science
Assosciate Research Professor Tim Stanton and his research group have been funded to develop autonomous, ice-deployed drifting buoys capable
of measuring vertical fluxes of momentum, heat and salt in the upper ocean
in Polar regions, through the
National Science Foundation, Office of Polar Programs
"Polar Instrumentation and Technology
Development" program. As the ocean provides a critical "thermal flywheel"
in the Arctic heat balance on seasonal and longer time scales, accurate
measurement of vertical heat fluxes through the upper ocean is critical
in determining the balance between radiative and sensible heat fluxes at
the ice surface, changes in ice cover, thickness and heat content,
and ocean heat content which all interact over seasonal scales to
maintain ice cover in the Arctic. The insulating properties of the
Arctic ice cover largely decouple rapid, strong variations of surface
heat fluxes from the ocean interior. Furthermore, since still water
is also a very good insulator, the vertical transport of heat to and
from the salt stratified ocean interior is determined primarily by the
rate at which the upper ocean is stirred. This stirring occurs when wind
blows over the ice and moves, forming a turbulent boundary layer extending
down from the ice toward the stratified pycnocline, typically at 30m depth.
The flux buoy measures these small net fluxes within the stirred "mixed" layer below
the ice.
While direct measurement of local vertical fluxes has been regarded
as difficult in the ocean, recent advances in high resolution,
low-powered sensor technology, (particularly in current measurement),
and the stable platform provided by the perennial ice pack, provide
a path to measuring long term, unattended vertical fluxes within
the upper ocean. Recent work by the PI in observing ocean fluxes
during ANZFLUX and SHEBA have provided instrumentation and analysis
experience which is being used with these new sensor technologies
to robustly estimate fluxes in a remote instrument, without the
luxury of having access to the raw data streams. The autonomous flux buoy uses
a very low power acoustic travel time
current sensor, a stable conductivity cell and a very high resolution thermistor to measure
velocities, salinity and temperature in the same small volume within the ocean mixed layer.
Correlating fluctuations of
vertical velocity with horizontal velocity fluctuations, temperature fluctuations and
salinity fluctuations provide estimates of the vertical transport of momentum, heat and salt
through the ocean mixed layer (see for example, McPhee and Stanton, Turbulence in the statically unstable oceanic
boundary layer under Arctic leads, Journal of geophysical Research, pp6409-6428,
March 1996).
The primary scientific motivation for the flux buoys is to use them
in conjunction with other autonomous, ocean, ice, and atmospheric
observation systems to provide a means of studying changes in the
Central Arctic Basin environment over long periods. The Long-Term
Observations in Arctic program has yearly installations of
automated instrumented buoys at the North Pole, including PMEL
met buoys, a CREL ice flux buoy, and a JAMSTEC ice/ocean buoy.
This collaboration immediately provides both vital logistics
infrastructure and supporting surface flux and upper ocean
structure measurements to provide a meaningful study of the
heat / ice balance as the buoy cluster drifts through the Arctic Basin.
Credits
Software Development: Jim Stockel and Ric Castillo
Hardware Engineering: Rob Wyland, Jim Lambert
Assembly and Logsitics: Keith Wykoff and Ron Cowen
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