Completed Project: Coupled Boundary Layer – Air Sea Transfer (CBLAST) Experiment

Home More Information Data

Upper Ocean Dynamics and Horizontal Variability
in Low Winds
Pilot 2001-2002

The CBLAST project is funded through the Office of Naval Reasearch

Pilot Program

During July 2001, Dr. Bob Weller, Dr. Mark Pritchard, and the WHOI UOP group participated in the CBLAST-Low pilot experiment south of Martha's Vineyard Island on the New England Shelf. The main stations and positions of moorings are shown in Fig 1.

The aims of the pilot study was to collect and evaluate preliminary hydrographic and meteorological data in the CBLAST-Low study area for provision and improvement of sampling methods, models and protocols prior to the main experiments. Tidal current meter data and sub-surface tide (pressure) gauges were used by Rutgers University in the development of a local tidal/circulation model.

The pilot experiment included the deployment of 2 ASIMET buoys and intensively instrumented sub-surface arrays. The SECNAV buoy deployed at the inshore site provided real time meteorological and hydrographic data via ORBCOM satellite telemetry from its ASIMET system and subsurface arrays via inductive modems and acoustic telemetry. A time series of the meteorological data is shown Fig 2.

The CBLAST buoy sited some 40 km offshore transmitted meteorological data via ARGOS satellite in near real time. An intensively instrumented subsurface array consisting of temperature (1 m vertical resolution), temperature and salinity (4 m vertical resolution) were used to measure scalar properties in the mixed layer. Two ADCPs, one Nortek 2 MHz looking up and a RDI 600 KHZ Workhorse looking down provided velocity data through the entire water column. Data will be assimilated and compared to 1-D model (PWP) results driven by the local meteorological forcing and air-sea flux measurements. The air-sea flux measurements computed using the TOGA-COARE V.2.6b algorithms from the two ASIMET systems will also be compared to Long EZ flux and IR data and other ship borne flux measurements made by AOPE during the pilot study period. Data will also be used to improve local meteorological models currently under development as part of the CBLAST-Low project.

The deployment of a 3-D mooring designed to measure temperature and salinity in 3-D in the upper mixed layer, DRIFTAR experiment and CTD transects both along and across the shelf.

The conceptual image of the 3-D array is shown in Fig 3. Instrumentation of the array consisted of approximately 200 small autonomous, self logging temperature loggers (Onset Tidbits) set at a 5 minute sampling interval and accuracy of 0.1 degrees C. Additional Seabird SBE 37 Microcats and SBE 39s were attached to the array to provide higher frequency (10 second increments) measurements inside the array. A 1 MHz Nortek ADCP (20 m range, 0.2 m bins) provided information on the velocity field directly beneath the array. A photograph of the deployed net grid structure is shown in Fig 4, illustrating the symmetry of the mooring.

Preliminary Analysis

Preliminary analysis of data collected during a 5-day period appears very novel and encouraging. These measurements as far as we are aware, are the first simultaneous 3-D temperature time series measurements made in upper oceans mixed layer. The horizontal lags of the array ranged from about 8 to 200 m and had a vertical depth resolution of 2 m from the surface to 18 m. Fig 5 shows some preliminary results from simple 2-D OA mapping of the temperature anomalies observed in the array. The images indicate there are subtle temperature changes and the presence of evolving and degrading structures within the spatial and temporal constraints of the array. This analysis will eventually be extended to a full 3-D investigation and hopefully provide a unique physical perspective of processes responsible for the development / degradation, stratification / mixing in the upper ocean under low to moderate wind conditions and relatively low wind wave energetics.

CBLAST-LOW Oceanic Investigators

Principle Investigator: Robert A. Weller
Post-Doctoral Investigator: Mark Pritchard

Last updated: April 23, 2008