LONGSHORE CURRENTS AND THE ONSET OF UPWELLING OVER BOTTOM SLOPE.

Abstract

THE EVOLUTION OF LONGSHORE CURRENTS PRODUCED BY UPWELLING ON AN F-PLANE OVER SHELF - LIKE BOTTOM TOPOGRAPHY FOR TIMES LONG COMPARED TO A BAROTROPIC SPIN - UP TIME, BUT SHORT COMPARED TO A DIFFUSION TIME, REVEALS IN A LINEAR, TIME - DEPENDENT, THREE - DIMENSIONAL MODEL THAT: (I) THE TOPOGRAPHIC CONSTRAINTS YIELD A STEADY TOPOGRAPHIC BOUNDARY LAYER ON THESE SHORT TIME SCALES SIMILAR IN STRUCTURE TO THE LAYER FOUND IN AN EARLIER STEADY - STATE MODEL.(II) WITHIN A ROSSBY RADIUS OF DEFORMATION OF THE COAST A SWIFT EQUATORWARD LONGSHORE CURRENT WITH A POLEWARD COUNTERCURRENT IS FORMED.(III) WIND - STRESS FORCING WITH LARGE NORTH - SOUTH SCALES ARE THE MOST EFFICIENT IN DRIVING LONGSHORE CURRENTS, BUT DO NOT EFFECTIVELY PRODUCE INTERNAL KELVIN WAVES, AS DO THE SHORTER LONGSHORE SCALES OF FORCING.(A).