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An investigation has been carried out to measure mean velocities above a solid block located in a wind tunnel. A Particle Image Velocimetry (PIV) system was used. The purpose of the investigation was to quantify the change in the mean flow speed caused by the bluff body and hence to determine the possible bias in wind speed measurement made from anemometers located above the superstructure of merchant ships. Possible sources of experimental error were investigated and resulted in; a) a blockage ratio correction which varied with position, b) the use of 2-dimensional maps of the free stream flow to obtain reference velocities and c) an estimate of a residual bias of up to 4 % in the PIV wind speed data. The wind speed was accelerated by up to 28 % compared to the free stream (or undistorted) wind speed. Close to the top of the block the wind speed is severely decelerated and the airflow reverses in direction. There was no dependence of either the pattern of the flow or of the magnitude of the wind speed bias on changes in wind directions of up to 30 degrees.

Anemometers on voluntary observing ships (VOS) are usually sited above the bridge in a region where the effects of flow distortion may be large. Until recently it was unclear whether measurements from such anemometers would be biased high or low, and the magnitude of any such bias was not known. This report describes the progress made in determining the effects of flow distortion and hence in predicting the possible bias in such anemometer measurements of the wind speed.

Wind speed measurements obtained from anemometers mounted on ships are prone to systematic errors caused by the distortion of the air flow around the ship's hull and superstructure. This report describes the results of simulations of the air flow around the R.R.S. James Clark Ross made using the Computational Fluid Dynamics (CFD) software VECTIS. The airflow distortion at a number of anemometer sites has been quantified for wind speeds of 5 m/s and 15 m/s blowing a) directly over the bows of the ship, and b) directly over the port beam (90° to port of the bow). The anemometers in this study were located in the bows of the ship and also on the port bridge wing.For bow-on flows the instrument sites in the bows of the ship experienced relatively small flow distortion. At these sites the flow was accelerated by between -1% to 1% and displaced vertically by between 1.7 m and 2.2 m. In contrast, the instrument sites on the port bridge wing experienced a severely distorted flow. The wind speed error varied rapidly from -40% to 20% depending on the exact location of the instrument, and the vertical displacement varied between 5.3 m and 6.3 m.For flows over the port beam the instrument sites in the bows of the ship experienced moderate flow distortion with wind speed errors of 9 % to 13 % and vertical displacements of between 4.8 m and 5.4 m. The instruments sites located on the port bridge wing experienced wind speed errors of -7.1 % to 2.6 %, and vertical displacements of 9.4 m to 10.4 m.

Wind speed measurements obtained from research ships are prone to systematic errors caused by the distortion of the air flow around the ship’s hull and superstructure. In this report the air flow around the RV Ronald H. Brown is simulated at two relative wind directions using Computational Fluid Dynamics (CFD). The airflow distortion at three anemometer sites has been quantified for wind speed of 15 ms-1 blowing a) directly over the bows of the ship, and b) from 30º to port of the bow. All anemometers in this study were located in the bows of the ship and experienced moderate flow distortion, with the wind speed being decelerated by 1% to 4% depending on the instrument location and the wind direction. The flow had been displaced vertically by about 0.7 m for the bow-on flow and by about 0.9 m for the flow from 30º to port.

This report describes RRS James Clark Ross Cruise 44, called CATS-MIAOW (Circulation And Thermohaline Structure - Mixing, Ice And Ocean Weather). It was funded by the UK Natural Environment Research Council as part of its Arctic Ice and Climate Variability (ARCICE) Thematic Research Programme. The cruise supported projects in hydrography, meteorology and geophysics. The cruise divided into two parts, one hydrographic and one meteorological. The hydrographic work comprised sections under ERS-2 satellite overpasses: two long sections with CTD and lowered ADCP, from Norway to Greenland and from Svalbard to Iceland; and a shorter section across northern Denmark Strait, which was repeated. There was also a near-zonal section in Fram Strait. Bottle samples were taken throughout for salinity, dissolved oxygen and SF6.The meteorological work took place in the marginal ice zone (MIZ) during a 10 day period in the middle of the cruise. While in the MIZ atmospheric profiles were obtained using GPS radiosondes and a tethered balloon system. The AUTOFLUX ship mounted surface fluxes system was also used to measure the surface fluxes of heat, momentum and moisture in addition to the usual mean meteorological variables. A suite of short-wave and long-wave sensors were also employed to measure both up- and down-welling radiation. The AUTOFLUX system operated throughout the cruise, providing surface flux and mean meteorological data in support of the hydrographic work.

This report describes the work undertaken on the AutoFlux system by SOC staff on the RRS James Clark Ross during the UK to Falklands passage between 11 September and 17 October 2000. This work coincided with the Atlantic Meridional Transect (AMT) 11 cruise (JR52) which ended on 11 October 2000, and is described elsewhere (Woodward, 2000). The SOC presence on the ship was sponsored by John King (BAS) as part of his Q3 (Antarctic Climate Processes) science program.The aim of the cruise was to test and develop the AutoFlux air-sea interaction system and its associated prototype instrumentation. The system is intended to provide real-time air-sea fluxes of momentum, sensible heat, latent heat and CO2, in addition to the usual mean meteorological parameters. The fluxes are calculated via the ‘inertial dissipation’ method (Yelland et al., 1998), using data from various fast-response instruments. Most of the instruments used in the system have been well proved during SOC research cruises over the last 10 years or more, but the dedicated sonic temperature sensor and the infra-red H2O/CO2 sensor are prototype instruments developed by colleagues involved in the AutoFlux project (MAST project MAS3-CT97-0108). Likewise, the logging and processing system is itself based on software systems which have been developed at SOC/IOS since the 1980s, but many aspects of the system are new and were tested and developed further during the cruise. By the fourth week of the cruise the system was automatically producing hourly direct measurements of the air-sea fluxes and was sending summary messages of the data back to SOC via the ORBCOMM satellite communications system in near real time.