A hotspot and mechanism of enhanced bottom intrusion on the southern New England shelf

(a), (d): Composite mean bottom currents (black vectors) and salinity (color) for different stages of the bottom intrusion relative to the maximum salinity anomaly at the Block Trough (the rectangular box): 6 days and 2 days prior to the time of maximum anomaly. Spatial mean bottom velocity vector (within the rectangular box) is shown with magnitude amplified by five times for better visualization. Mean wind stress in the region is shown in blue vectors. (b), (e): Same as (a), (d) but for bottom pressure gradient force with magnitude in color and directions in gray vectors. (c), (f): Estimates of the bottom flow using pressure gradient, stress divergence, and acceleration terms within the trough. The light gray dots represent the geostrophic balance, i.e., using the first term to infer bottom flow. The darker gray represents the contribution of the pressure gradient and stress divergence. The black dots represent the consideration of the additional acceleration term, i.e., all three terms below the x-axis. Color-coded Root Mean Square Difference (RMSD) values are shown. Major balance is between pressure gradient, Coriolis, and bottom stress, with pressure gradient being the driving term. Image provided by Ke Chen.