Some new and interesting current meter observations have recently been reported by Scott and Csanady [1976]. One of their results is the finding of a linear relationship between longshore wind stress and currents observed 2 m above the bottom. Using a frictional model, they are able to draw inferences about the longshore slope of sea level in the absence of wind. The purpose of the present note is to expand on their interpretation of the longshore slope and to offer some cautionary remarks concerning the comparison with geodetic leveling.The model of Scott and Csanady (their equation (3a)) becomes rwx/p = rt2b + gh ( O •'/ O x )where the x direction is along the coast, rw is the wind stress, and r is a resistance coefficient; the other symbols have traditional meanings. By careful analysis and prudent averaging they arrive at their Figure 8, which allows them to determine a value of 0.158 cm/s for r and an intercept of 0.46 cm"/s" for the wind stress (divided by p) when the longshore current goes to zero, 2 m above the bottom. From the intercept, Scott and Csanady calculate a longshore slope of the sea surface of 1.4 X 10-*, or about 7 cm in 500 km. They conclude that sea level falls about 7 cm from Boston, Massachusetts, to Atlantic City, New Jersey. Such slopes of sea level, on the coastal side, are found with every known current; they are consistent with the observed density distributions and are dynamically in balance with the slope of the sea surface across the coastal flows as the currents change latitude. These effects have been discussed elsewhere [Sturges, 1974].The density distribution off the northeastern coast of the United States suggests that sea level slopes down from north to south about 10 cm along the 2000-m isobath, relative to the 2000-dbar surface, from Cape Cod to the Chesapeake Bay. The data of Scott and Csanady gave much the same longshore slope close to shore, suggesting that the longshore gradient changes little with distance from the shore, at least out to the 2000-m isobath. One interesting and perhaps surprising aspect of this resultis to see how the longshore sea level slope changes with season. Figure ! shows the annual trend of sea level at Boston and Atlantic City. The means between the two curves have been offset by 7 cm in the sense suggested by Scott and Csanady, which is in reasonable agreement with the value obtained from the large-scale density field just offshore discussed above [see Sturges, 1974, Figure 1]. It appears that the longshore slope is a minimum in the fall of the year when the longshore wind stress is also a minimum. The yearly average winds are out of the west southwest; the longshore stress is approximately 0.5 dyn cm" [Hellerman, 1967]. In the summer they are lighter and Copyright ¸ 1977 by the American Geophysical Union. Paper number 6C0919. more variable; in September they are weak and shift around from SSW to the north or northeast [Marine Climatic Atlas, 1956]. Whether this change in longshore slope is associated with a change in the mean flow field is a...

Six mechanisms have so far been proposed to explain Langmuir circulations and their associated wind streaks. One mechanism involving shearing instability and two requiring the action of a surface film are supported by the greatest amount of evidence. Studies at Lake Ccorgc, New York, suggest that more than one mechanism may operate at one location.A particular mechanism may operate at a specific site because of typical conditions at that site, but a different mechanism may be more important at another site. Plots of thermal structure in the near-surface layer of Lake George and measurements of vertical current velocities suggest that Langmuir circulations are the most important mixing process in the epilimnia of lakes.

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Time series of wind, current, nutrients, chlorophyll, and zooplankton are used to examine the effect of storm events on the food chain dynamics of the New York Bjght. Storms cause dilution of phytoplankton concentration in the vertical plane, but lead to aggregation of chlorophyll in the horizontal field. Nutrients are made available with onshore flow in response to wind events favorable for upwelling.A series of nutrient budgets suggest that storm-induced mixing and upwelling of nitrate may satisfy at least 33% of the productivity demand of this system. Examples of the biological response to storms are drawn from 20 cruises during January, March, April-May, and August-September 1974, 1975, 1976 under mixed and stratified conditions of the water column. The interaction of storms and seasonal stratification suggests predictable structure and frequency of chlorophyll distribution across the shelf which mav influence both the survival strategies of herbivores and the loci of energy transfer to the rest of the food chain.

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