High Wind Air-Sea Exchanges (HiWASE) - continuous air-sea flux measurements at Station Mike

HiWASE is a UK-SOLAS project which aims to improve the parameterisation of the turbulent air-sea fluxes of CO2, momentum, sensible heat and latent heat, particularly under high wind speed conditions. Although the momentum flux is reasonably well understood there is still debate over the influence of sea-state. The heat fluxes are less well known, with debate about any wind-speed dependence of their transfer coefficients. The CO2 flux is relatively poorly understood, with parameterisations of the gas transfer velocity differing significantly for winds of 7 m/s or more.

In September 2006 NOC staff instrumented the weather ship Polarfront with a range of sensors and systems including the air-sea flux system “AutoFlux”, a directional wave radar and two digital cameras. These complement a range of sensors (including a ship borne wave recorder) which have long been run by the Norwegian Met Office, plus an underway delta pCO2 system run by colleagues at BCCR.

The AutoFlux system includes a Solent R3 sonic anemometer, a MotionPak motion sensor and two Licor-7500 sensors. Each Licor is shrouded in turn for one month at a time and then run without a shroud for the following month. This is done in order to obtain corrections for distortion of the sensor head. The AutoFlux system produces momentum and latent heat fluxes automatically using the inertial dissipation method. Fluxes calculated using the eddy correlation method are currently produced post-cruise. Near real-time (24 hours) summary data are transmitted from the ship via iridium and displayed on a project web page under http://www.noc.soton.ac.uk/ooc/CRUISES/HiWASE/index.php .

The Polarfront occupies Station Mike (66 N 2 E) year round, with only 8 hours in port per month. The instrumentation all operates continually, and will do so at least until the end of the project in late 2009. Continuous operation allows data to be obtained under a wide range of wind speeds and sea states: to date the maximum 15 minute mean wind speed is 25 m/s. Initial results will be presented.