QUASI-GEOSTROPHIC FORECASTING AND PHYSICAL PROCESSES OF ICELAND-FAROEFRONTAL VARIABILITY

Using a hydrocast survey of the Iceland-Faroe Front (IFF) from October 1992, quasigeostrophic forecasts are studied to validate their effica cy and to diagnose the physical processes involved in the rapid growth of a cold tongue intrusion. Explorations of 1) the choice of initial objective analysis parameters, 2) the depth of the unknown level of no motion, 3) the effects of surrounding mesoscale activity, 4) variatio ns in the boundary conditions, and 5) simple assimilation of newly acq uired data into the forecasts are carried out. Using a feature validat ion technique, which incorporates a 1) validating hydrocast survey, 2) satellite SST images, and 3) surface drifter observations, mast of th e forecasts are found to perform well in capturing the key events of t he validation strategy, particularly the development of the cold tongu e intrusion (though it tends to develop somewhat more weakly and sligh tly farther downstream than observed). Sharp resolution of frontal str ucture (to capture seed anomalies in the IFF, which later can grow to large amplitude) and smooth representation of far-field boundary condi tions (to eliminate spurious persistent inflow/outflow at the boundari es, which can corrupt developing interior flows) are found to be cruci al in generating good forecasts. An analysis ofthe potential and kinet ic energy equations in the region ofthe developing cold tongue intrusi on reveals a clear signature of baroclinic instability. Topography has little influence on this particular instability event because it tend s to be surface intensified and occurs rapidly over a timescale of 3-5 days.