INFERRING COASTAL UPWELLING DYNAMICS FROM A THERMISTOR ARRAY

Key parameters of coastal upwelling dynamics in the St. Lawrence estua ry are inferred from moored thermistor observations, using a data assi milative technique based on a dynamical model that has terms represent ing upwelling, vertical mixing, and residual heating/advection. The in ferred time series of upwelling velocity, w(t), agrees generally with a time series calculated from a more conventional regression calculati on based on the upwelling term alone. In each case, w (t) is highly co herent with alongshore wind stress, indicating that coastal upwelling dynamics are predominant in this region. We found data assimilation to be superior to the simpler regression technique in two ways. First, t he inferred upwelling time series is more accurate, as gauged by coher ence with wind stress. Second, data assimilation allows the additional inference of other dynamical parameters, such as the vertical diffusi vity. The thermistor array thus indicates that the dynamics of this re gion are largely related to Ekman upwelling, with vertical mixing also being important.