HF radar measurements in Liverpool Bay, Irish Sea

A phased array HF radar systems transmitting at 13 MHz with sites at Form by Point, north of the Mersey outflow, and on the North Wales coast near Abergele has been operational since August 2005. Data on a 4 km grid are recorded every 20 minutes, with hourly data telemetered to the Proud man Oceanographic Laboratory by telephone land line. The data are compared with two in situ acoustic Doppler current profilers (ADCPs, measuring both currents and waves) at sites A and B and an in situ wave buoy at site A. A thirty turbine wind farm is in the radar field of view. The semi-diurnal tides are the dominant physical process in Liverpool Bay. There also appears to be a persistent circulation, relating to the density field, with day to day wind driven (surge) currents not as important as in some shelf sea regions. The tidal currents have been compared with results from a 1.8 km grid 3D numerical model. The agreement is good over most of the spatial coverage but in the north-west corner the radar currents, although exhibiting a very well defined tidal signal, are considerably larger than the model currents. Also of note there is significant energy at tidal frequencies (presumably non coherent) in the tidal residual currents, which is also seen in the ADCP records. Tests on the data quality and further comparisons of the HF radar currents and waves with observations and numerical model estimates (including the wind-driven component) were presented. One eventual aim is to test the feasibility of assimilating the current information into the models.