Non rotating case, evolution of the first packet

Figure 7 shows the density field every hour during the first tidal cycle At the very beginning, when the flow (from left to right) is subcritical everywhere, the isotherms are slightly displaced upward on the western side. After approximatively 1.5 hours from the onset of the ebb phase the flow becomes supercritical at the crest. The infinitesimal waves that are generated at the crest cannot escape and begin to accumulate, undergoing nonlinear steepening (Hibiya, 1988). The jump that appears over the crest (J1) marks the location of the hydraulic control. Downstream of the control point, where the Froude number is equal to one, a jet develops, similar to the ones observed during downslope wind storms (Smith, 1985). The jet is trapped near the bottom, where it reaches a speed of almost 80 cm/s. The control point is slowly advected downstream, reaching $x=32$ Km at $T=4$. Behind the depression on the lee side of the jump a second depression forms, located at $x=35$ Km at $T=4$ (fig. 7), indicated by the label L1. Shortly after, the jet reaches its maximun downslope extension, below the 60 m isobath. At the same time, a wave is visible, marked A1, traveling upstream. Towards the end of the ebb phase, the jump (J1) begins to move westward (check speed) ($T=6$), followed by the lee wave (L1). Together, they form a 5 Km wide depression, which agrees quite well with the observation of Chereskin (1983). Initially, as the jump passes over the crest, it becomes less steep. The dropping bottom, with the associated increase in wave speed causes the leading edge of the depression to move farther than the trailing edge, widening the depression. It finally becomes a bore as it passes over the western side of the Bank, overtaking the wave A1 around $T=7$ and further steepens before reaching the middle of the Basin ($T=9$), with a downward displacement in excess of 20 m . Behind the jump, the isopycnals remain depressed. Meanwhile, as the flooding tide reaches its maximum intensity over the Bank, a very narrow depression forms on the western side, having a width of about 1 Km, again in agreement with the acoustic images of Chereskin (1983). On the eastern side of the depression a narrow jet along the western flank of the Bank pushes the isopycnals downward, while on the western side water flowing in the opposite direction upwells, creating the bulge marked as B1 at $T=12$. The resulting overturning must have a significant impact on the mixing in the area. Towards the end of the flood phase, a small bore (J2) begins to propagate eastward. By the end of the first tidal cycle, we have thus a bore propagating westward, leaving behind a depressed pycnocline. On the upper western slope of the Bank the pycnocline abrutply rises to form a bulge (B1), followed by a small depression bounded on the eastern side by the estward propagating bore (J2). The propagation of the bore in Stellwagen basin is rather uneventful, until it reaches the 60 m isobath, at which point the isopycnal immediately behind the bore are further depressed, while the velocity near the bottom increases until the flow becomes once again supercritical in the proximity of the bottom, sometimes between ($T=16$ and $T=17$, fig. 8). Since the flow is critical only near the bottom the leading edge of the bore propagates inshore (B1 in the pictures). Behind it, the flow accelerates near the bottom, up to about 60 cm/s, bringing relatively light (and warmer) water at depth. Above the jet, water moves westward, resulting in overturning. Following the leading edge of the bore, a depression forms, moving inshore.