The wave packets are in general of the ``solibore'' type (Apel et al., 1995), i.e. a group of solitary waves leaving behind a depressed pycnocline which rebounds slowly during a tidal cycle. The number of solitary waves comprising the solibore, measured at mooring A, varies considerably, from a few to more than 20. The packets move at a speed of approximatively 60 cm/s, slowing somewhat as they move onshore. At mooring A, the vertical structure is typical of a mode 1 wave. Both at mooring A and B the stratification slowly recovers after the passage of the bore, taking the most past of the tidal cycle to return to the value it had before the passage of the bore.
At mooring C the wave field is more differentiated, and we can identify two kind of events. The first kind, which was prevalent during the first two weeks of deployment consisted of solibores similar to the ones observed at A. The vertical structure was sometimes a simple mode 1, such as in the event depicted in figure 3. Note that the temperature below 30 m is hardly affected. At other times the vertical structure was more complicate, with evidence of possible temperature inversion, such as the event beginning on yd 223.44 (fig. 4). Also note that in this case the temperature record at 30 m shows considerable more variability. The second kind was more prevalent during the last part of the experiment, and it is also the most intriguing. Fig. 5 shows a typical member of this class. Unlike the other two types, in this case the initial downward displacement is not followed by a distinct train of solitary waves, even in the middle of Stellwagen Basin. The passage of the bore generates extremely high currents near the bottom directed offshore, and, surprisingly, reaches its maximum (in excess of 1 knot) towards the end of the event. At mid depth the current is initially offshore, but reverses halftime during the event. The temperature record shows a similarly remarkable picture. The warming trend spreads towards the bottom. Halftime into the event the first 30 meters of the water column are virtually at the same temperature. Also, unlike the previous cases, in which for the most part the activity is confined to the upper 30 m of the water column, in this case the warming is felt all the way to the bottom, albeit with a delay. During these events, the current flowing offshore exceeds the speed of linear, mode 1, long wavelength waves, which at this depth is of the oder of 40 cm/s, based on the stratification observed. Thus we call these critical bores.
Regardless of the type of bore, the stratification at mooring C recovers more quickly than in the middle of the basin.