Modelling the seasonal variation of the Florida current
The linear response of a two layer ocean model to a periodic wind stress curl in the presence of bottom topography has been investigated. For periods much less than the time taken for the wind generated baroclinic Rossby waves to pass over the topography (i.e. 'short' periods), the ocean response is primarily that for a homogeneous ocean and thus strongly modified by topography. For periods much longer than this time (i.e. 'long' periods), the Rossby waves compensate for the effect of topography and the non-topographic Sverdrup balance holds. For the Atlantic at 25°N, the long period limit is of the order of years to decades, so at annual period the non-topographic Sverdrup balance is not applicable. Variations in transport can be forced by a wind stress over varying topography, and by the passage of a coastal baroclinic Kelvin wave over varying topography. The relative importance of the above dynamical considerations for the Florida Current can only be determined from a model calculation involving realistic winds, topography and geography. Such a model calculation has been done with observed Bunker wind stress over a two layer ocean. The predicted variation has a Summer maximum and a Fall minimum, in agreement with the measurements of Niiler and Richardson  and more recent STACS data. The one layer model has been forced by monthly means of ATOLL wind stress for the years 1981-1984. The predicted variation was found not to be in agreement with concurrent STACS measurements. A comparison was made between the Bunker winds and the ATOLL winds via various diagnostics. It was found that the meridional component of the wind, which is crucial to the overall Bunker Summer maximum, is of much reduced importance for the ATOLL winds. This could account for the lack of predicted Summer maxima.