Climatology of the Southeastern United States Continental Shelf Waters

Data from 2872 hydrographic stations have been used to determine the oceanographie climatology of the southeastern United States continental shelf waters. The data were sorted by each degree of latitude and by depth into three zones (0–20 m, 21–40 m, 41–60 m). Inner shelf water temperatures were similar to adjacent land air temperatures, while outer shelf temperatures were moderated by the Gulf Stream. Minimum and maximum water temperatures occurred in Georgia and South Carolina inner shelf water. Bottom temperatures were unusually low off Florida in the summer probably because of shelf break upwelling. Surface salinity was lowest adjacent to the rivers and reached minimums in the spring at the time of high runoff. An exception to this occurred in the fall, when strong southward winds apparently advected low salinity coastal water southward and offshore flow was restricted. Heat flux was calculated from changes in monthly mean depth-averaged inner shelf water temperatures. Heating occurred from March through July with maximum rates of 103 W m−2. Cooling occurred from October through February with maximum rates of −90 W m−2. Bulk stratification was estimated from the difference in near-surface and near-bottom monthly mean density. In the spring, stratification increases in inner shelf areas because of decreasing winds and increasing heat flux and runoff. By summer the whole shelf is highly stratified reflecting the contrast between high surface water temperatures and cooler bottom waters. Highest bulk stratification is found over the outer shelf. Stratification decreased with the approach offall with the associated cooling and high winds. Mean flow at midshelf was northward and appears to be produced by an along-shelf slope of sea level of oceanic origin

Grain rotation and lattice deformation during photoinduced chemical reactions revealed by in-situ X-ray nanodiffraction

In-situ X-ray diffraction (XRD) and transmission electron microscopy (TEM) have been used to investigate many physical science phenomena, ranging from phase transitions, chemical reaction and crystal growth to grain boundary dynamics. A major limitation of in-situ XRD and TEM is a compromise that has to be made between spatial and temporal resolution. Here, we report the development of in-situ X-ray nanodiffraction to measure atomic-resolution diffraction patterns from single grains with up to 5 millisecond temporal resolution, and make the first real-time observation of grain rotation and lattice deformation during photoinduced chemical reactions. The grain rotation and lattice deformation associated with the chemical reactions are quantified to be as fast as 3.25 rad./sec. and as large as 0.5 Angstroms, respectively. The ability to measure atomic-resolution diffraction patterns from individual grains with several millisecond temporal resolution is expected to find broad applications in materials science, physics, chemistry, and nanoscience.Comment: 17 pages, 3 figure

Hydrographic Variability of Southeastern United States Shelf and Slope Waters During the Genesis of Atlantic Lows Experiment: Winter 1986

Continental shelf waters are particularly responsive to winter storm events mainly because of their shallow depths. Those of the southeastern United States (the South Atlantic Bight (SAB)) are especially responsive because they are broad and shallow. Also, the Gulf Stream serves as a continual source of warm water at the outer boundary. Thus the SAB receives strong meteorological (wind stress and heat loss) and oceanographic (advective) forcing. During the Genesis of Atlantic Lows Experiment (GALE) the response of shelf waters to winter storm events and Gulf Stream forcing was observed. The mean conditions showed a mixed water column with areas of stratification near the coast and at the shelf break. The nearshore area was stratified only during weak offshore winds, and the shelf break area was stratified during southward winds with accompanying onshore Ekman flow. On the inner shelf, advective buoyancy flux was similar in value to heat flux buoyancy and the buoyancy equivalent of wind mixing. Over the shelf break the advective buoyancy flux was 4 times the other forms of buoyancy flux and controlled the observed potential energy variability. A simple box model heat budget used to separate the effect of Gulf Stream eddies and meanders, and Ekman flow and air‐sea heat exchange on the shelf heat content showed that the observed heat content variability was caused by intrusion of Gulf Stream water. The intrusions may be caused either by onshore Ekman flow during southward winds or Gulf Stream meander events