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James J. Singer

Abstract

Recent studies in the Gulf of Mexico have generated datasets that permit comparisons of CTD data with electronically digitized T-7 XBT data. This paper presents the results of two such comparisons involving the use of the BathySystems SA-810 and the Sippican Mk-9 digitizers and makes a further comparison with the findings of other investigators. A single, general, linear depth adjustment and an alternate third-order polynomial adjustment to the Sippican drop-rate equation are determined for the combined XBT dataset for application at depths greater than 100 meters. At shallower depths, the standard Sippican equation alone is applied. It is noted that the slope of the calculated linear adjustment is nearly identical to that calculated by Heinmiller et al. for the lower part of the water column (below 325 m) in the Sargasso Sea. The alternate polynomial adjustment was found to agree within 4.5% (1.1 meters) of the depth adjustment at 750 meters calculated by Hanawa and Yoritaka for data collected in the northwestern part of the North Pacific subtropical gyre off Japan.

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C. E. Knowles
and
J. J. Singer

Abstract

During the period 20 June-2 July 1973, hydrographic data were collected at Oregon Inlet, N. C. An examination of the water temperature time-history record at three stations in and near the inlet show 1) that in two periods with predominately southerly winds, the temperature fluctuated in the range from 13.7° to 27.5°C with an apparent tidal periodicity; 2) that for nearly 48 h between these two periods and with northeasterly winds, a nearly constant temperature of 22.0° to 22.5°C was maintained in spite of normal tidal fluctuations; and 3) this constant temperature period is bracketed by two 24 h transitional periods that are initiated almost coincidently with wind directional changes. It appears that the sequence and relationship of these wind and water temperature data may be explained by and provide additional evidence and documentation of wind-induced upwelling along the northeastern North Carolina coast previously reported by Wells and Gray (1960), Carter, Pritchard and Carpenter (1966) and Boicourt (1973). Indeed, an important conclusion that can be drawn from this sequence and relationship of data is that temperature, salinity and current velocity records in and near a barrier island inlet can furnish much information about the exchange and mixing processes on the adjacent continental shelf, especially when there are large differences in temperature and salinity between the sound and shelf waters.

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James T. Moore
,
Fred H. Glass
,
Charles E. Graves
,
Scott M. Rochette
, and
Marc J. Singer

Abstract

Twenty-one warm-season heavy-rainfall events in the central United States produced by mesoscale convective systems (MCSs) that developed above and north of a surface boundary are examined to define the environmental conditions and physical processes associated with these phenomena. Storm-relative composites of numerous kinematic and thermodynamic fields are computed by centering on the heavy-rain-producing region of the parent elevated MCS. Results reveal that the heavy-rain region of elevated MCSs is located on average about 160 km north of a quasi-stationary frontal zone, in a region of low-level moisture convergence that is elongated westward on the cool side of the boundary. The MCS is located within the left-exit region of a south-southwesterly low-level jet (LLJ) and the right-entrance region of an upper-level jet positioned well north of the MCS site. The LLJ is directed toward a divergence maximum at 250 hPa that is coincident with the MCS site. Near-surface winds are light and from the southeast within a boundary layer that is statically stable and cool. Winds veer considerably with height (about 140°) from 850 to 250 hPa, a layer associated with warm-air advection. The MCS is located in a maximum of positive equivalent potential temperature θ e advection, moisture convergence, and positive thermal advection at 850 hPa. Composite fields at 500 hPa show that the MCS forms in a region of weak anticyclonic curvature in the height field with marginal positive vorticity advection. Even though surface-based stability fields indicate stable low-level air, there is a layer of convectively unstable air with maximum-θ e CAPE values of more than 1000 J kg−1 in the vicinity of the MCS site and higher values upstream. Maximum-θ e convective inhibition (CIN) values over the MCS centroid site are small (less than 40 J kg−1) while to the south convection is limited by large values of CIN (greater than 60 J kg−1). Surface-to-500-hPa composite average relative humidity values are about 70%, and composite precipitable water values average about 3.18 cm (1.25 in.). The representativeness of the composite analysis is also examined. Last, a schematic conceptual model based upon the composite fields is presented that depicts the typical environment favorable for the development of elevated thunderstorms that lead to heavy rainfall.

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