The Combined Effects of Gulf Stream–Induced Baroclinicity and Upper-Level Vorticity on U.S. East Coast Extratropical Cyclogenesis

2005 ◽  
Vol 133 (8) ◽  
pp. 2494-2501 ◽  
Author(s):  
Neil A. Jacobs ◽  
Gary M. Lackmann ◽  
Sethu Raman
Keyword(s):  
North Carolina ◽  
Gulf Stream ◽  
Additional Data ◽  
Large Fraction ◽  
Coastal Region ◽  
Western Boundary ◽  
Absolute Vorticity ◽  
Surface Cyclone ◽  
Cape Hatteras ◽  
Upper Level

Abstract The Atlantic Surface Cyclone Intensification Index (ASCII) is a forecast index that quantifies the strength of low-level baroclinicity in the coastal region of the Carolinas. It is based on the gradient between the coldest 24-h average air temperature at Cape Hatteras and Wilmington, North Carolina, and the temperature at the western boundary of the Gulf Stream. The resulting prestorm baroclinic index (PSBI) is used to forecast the probability that a cyclone in the domain will exhibit rapid cyclogenesis. The initial ASCII study covered the years 1982–90. This dataset was recently expanded to cover the years 1991–2002, which doubled the number of cyclone events in the sample. These additional data provide similar position and slope of the linear regression fits to the previous values, and explain as much as 30% of the variance in cyclone deepening rate. Despite operational value, the neglect of upper-tropospheric forcing as a predictor in the original ASCII formulation precludes explanation of a large fraction of the deepening rate variance. Here, a modified index is derived in which an approximate measure of upper-level forcing is included. The 1991–2002 cyclone events were separated into bins of “strongly forced,” “moderately forced,” and “weakly forced” based on the strength of the nearest upstream maximum of 500-mb absolute vorticity associated with the surface low. This separation method reduced the scatter and further isolated the contributions of surface forcing versus upper-level forcing on extratropical cyclogenesis. Results of the combined upper-level index and surface PSBI demonstrate that as much as 74% of the deepening rate variance can be explained for cases with stronger upper-level forcing.

Gulf Stream Marine Hydrokinetic Energy Off Cape Hatteras, North Carolina

2020 ◽  
Vol 54 (6) ◽  
pp. 24-36
Author(s):  
Michael Muglia ◽  
Harvey Seim ◽  
Patterson Taylor
Keyword(s):  
Turbulent Mixing ◽  
Gulf Stream ◽  
Velocity Structure ◽  
Vertical Shear ◽  
Small Scale ◽  
Western Boundary ◽  
Horizontal Shear ◽  
Hydrokinetic Energy ◽  
Cape Hatteras ◽  
Marine Hydrokinetic

AbstractMulti-year measurements of current velocity, salinity, and temperature from fixed and vessel-mounted sensors quantify Gulf Stream (GS) marine hydrokinetic energy (MHK) resource variability and inform development off Cape Hatteras, NC. Vessel transects across the GS demonstrate a jet-like velocity structure with speeds exceeding 2.5 m/s at the surface, persistent horizontal shear throughout the jet, and strongest vertical shears within the cyclonic shear zone. Persistent equatorward flow at the base of the GS associated with the Deep Western Boundary Current (DWBC) produces a local maximum in vertical shear where stratification is weak and is postulated to be a site of strong turbulent mixing. Repeated transects at the same location demonstrate that the velocity structure depends upon whether the GS abuts the shelf slope or is offshore.Currents from a fixed acoustic Doppler current profiler (ADCP) deployed on the shoreward side of the GS exceed 1 m/s 64% of the time 40 m below the surface. The 3.75-year time series of currents from the ADCP mooring document large, roughly weekly variations in downstream and cross-stream speed (−0.5 to 2.5 m/s) and shear (± 0.05 s−1) over the entire water column due to passage of GS meanders and frontal eddies. Current reversals from the mean GS direction occur several times a month, and longer period variations in GS offshore position can result in reduced currents for weeks at a time. Unresolved small-scale shear is postulated to contribute significantly to turbulent mixing.

Different cyclone characteristics along the Gulf Stream and Kuroshio SST front regions

2021 ◽  
Author(s):  
Leonidas Tsopouridis ◽  
Clemens Spensberger ◽  
Thomas Spengler
Keyword(s):  
Gulf Stream ◽  
Kuroshio Extension ◽  
Northwest Pacific ◽  
Western Boundary ◽  
Cold Side ◽  
Sst Front ◽  
The North ◽  
Relative Contribution ◽  
Upper Level ◽  
The Kuroshio

<p>The Northwest Atlantic and the Northwest Pacific are regions of strong temperature gradients and hence favourable locations for wintertime cyclone intensification co‐located with the storm tracks. Although the Gulf Stream and the Kuroshio Extension are both western boundary currents with similar characteristics, the SST gradient is markedly stronger across the Gulf Stream. Further, upper-level flow is stronger and more zonal over the Kuroshio Extension. To estimate the relative contribution of the SST front to the evolution of cyclones and to identify the mechanisms for cyclone intensification in the two regions, we track individual cyclones and categorise them depending on their propagation relative to the SST front. We focus on cyclones staying either on the cold (C1) or warm (C2) side of the SST front, and on cyclones that cross the SST front from the warm to the cold side (C3).  Comparing these categories, we find that low-level baroclinicity, particularly arising from the land–sea contrast, drives the higher intensification of cyclones in C1 and C3 in the Gulf Stream region, with the propagation of those cyclones near the left exit region of the North Atlantic jet contributing to the higher intensification and precipitation. In the Kuroshio region on the other hand, the land–sea contrast plays a less prominent role for the low‐level baroclinicity. Cyclones remaining on the warm side of the Kuroshio SST front (C2), as well as those crossing the SST front from the warm to the cold side (C3) are characterized by higher intensification, associated with a stronger upper-level jet in the Pacific. Comparing the different cyclone categories, there is no direct effect of the SST front on cyclone intensification in both regions. However, the SST front contributes to the climatological low‐level baroclinicity, providing a conducive environment for cyclone intensification for the cyclones crossing the SST front.</p>

Characterization of Patches Along Transects Using High-Resolution 70-kHz Integrated Acoustic Data

1989 ◽  
Vol 46 (12) ◽  
pp. 2056-2064 ◽  
Author(s):  
R. W. Nero ◽  
J. J. Magnuson
Keyword(s):  
North Carolina ◽  
High Resolution ◽  
Gulf Stream ◽  
Window Size ◽  
Recognition Algorithm ◽  
Pass Filter ◽  
Acoustic Data ◽  
Cape Hatteras ◽  
High Pass

A patch recognition algorithm was applied to high-resolution (1 m vertical and 25 m horizontal) daytime sonar date collected from a 20-km-length transect to a depth of 200 m. The transect was oriented perpendicular to the Gulf Stream frontal zone, 105 km east–northeast ENE of Cape Hatteras, North Carolina, on August 8 1985. An adaptive high-pass filter was used to identify patches of high-intensity echo strengths. For a broad based averaging "window size" of 13 m deep by 1.4 km long and an echo strength threshold of 1.4 × integrated echo units patches resemble fine-scale features of the original echogram. A discrimination of patches using sonar statistics from within the patches gave good separation of slope water patches from patches belonging to four other water masses Slope water patches were characteristically small and of low mean scattering. Large but infrequent targets were present In the Gulf Stream, by contrast, patches contained more uniformly distributed targets with a higher mean scattering The observed correlation between echo patches, biological structures, and oceanographic features suggests that the measurement of echo statistics and our patch recognition techniques produce biologically meaningful parameters.

Hydrokinetic Energy Resource Assessment of the Gulf Stream Near Cape Hatteras, North Carolina

2014 ◽  
Author(s):  
Asif Kabir ◽  
Ivan J. Lemongo ◽  
Arturo Fernandez
Keyword(s):  
North Carolina ◽  
Gulf Stream ◽  
Energy Resource ◽  
Resource Assessment ◽  
Ocean Model ◽  
Likelihood Method ◽  
Ocean Current ◽  
Hydrokinetic Energy ◽  
Cape Hatteras ◽  
Promising Source

The Gulf Stream near the coasts of North Carolina is considered a promising source of hydrokinetic energy. A statistical analysis is conducted to assess the energy available for extraction in this region. Weibull distribution is used as the Probability Density Function (PDF) for this purpose. The ocean current velocity data are collected from the ‘HYbrid Coordinate Ocean Model (HYCOM)’. The data are collected at a depth of 20 m from the sea surface which is considered a good position for energy extraction. The Weibull parameters from the analysis are calculated using the maximum likelihood method. The direction of the ocean current was found to be mostly uniform in this region. The theoretical power density of this region was estimated to be more than 275 W/m2 around 70% of the time and exceeded 2000 W/m2 around 10% of the time.

scholarly journals A Laboratory Study of Nonlinear Western Boundary Currents, with Application to the Gulf Stream Separation due to Inertial Overshooting*

2011 ◽  
Vol 41 (11) ◽  
pp. 2063-2079 ◽  
Author(s):  
Stefano Pierini ◽  
Pierpaolo Falco ◽  
Giovanni Zambardino ◽  
Thomas A. McClimans ◽  
Ingrid Ellingsen
Keyword(s):  
Gulf Stream ◽  
Functional Dependence ◽  
Western Boundary ◽  
Western Boundary Currents ◽  
Weakly Nonlinear ◽  
Boundary Currents ◽  
First Case ◽  
Highly Nonlinear ◽  
Cape Hatteras ◽  
Small Change

Abstract Various dynamical aspects of nonlinear western boundary currents (WBCs) have been investigated experimentally through physical modeling in a 5-m-diameter rotating basin. The motion of a piston with a velocity up that can be as low as up = 0.5 mm s−1 induces a horizontally unsheared current of homogeneous water that, flowing over a topographic beta slope, experiences westward intensification. First, the character of WBCs for various degrees of nonlinearity is investigated. By varying up, flows ranging from the highly nonlinear inertial Charney regime down to a weakly nonlinear regime can be simulated. In the first case, the dependence of zonal length scales on up is found to be in agreement with Charney’s theory; for weaker flows, a markedly different functional dependence emerges describing the initial transition toward the linear, viscous case. This provides an unprecedented coverage of nonlinear WBC dependence on an amplitude parameter in terms of experimental data. WBC separation from a wedge-shaped continent past a cape (simulating Cape Hatteras) due to inertial overshooting is then analyzed. By increasing current speed, a critical behavior is identified according to which a very small change of up marks the transition from a WBC that follows the coast past the cape to a WBC (nearly dynamically similar to a full-scale Gulf Stream) that separates from the cape without any substantial deflection, as with the Gulf Stream Extension. The important effect of the deflection angle of the continent is analyzed as well. Finally, the qualitative effect of a sloping sidewall along a straight coast is considered: the deflection of the flow away from the western wall due to the tendency to preserve potential vorticity clearly emerges.

Gulf stream marine hydrokinetic energy resource characterization off Cape Hatteras, North Carolina USA

2016 ◽  
Author(s):  
Ruoying He ◽  
John Bane ◽  
Mike Muglia ◽  
Sara Haines ◽  
Caroline Lowcher ◽  
...  
Keyword(s):  
North Carolina ◽  
Gulf Stream ◽  
Energy Resource ◽  
Hydrokinetic Energy ◽  
Cape Hatteras ◽  
Marine Hydrokinetic

The penetration of Labrador Slope Water to Cape Hatteras and its role in Gulf Stream Dynamics

2020 ◽  
Author(s):  
Adrian New ◽  
David Smeed ◽  
Adam Blaker ◽  
Jenny Mecking
Keyword(s):  
Gulf Stream ◽  
Water Mass ◽  
Gulf Of Maine ◽  
Meridional Overturning Circulation ◽  
Western Boundary ◽  
Boundary Current ◽  
The North ◽  
The Us ◽  
Cape Hatteras ◽  
Northern Side

<p>Labrador Slope Water is known to exist in the Slope Sea off the US eastern shelf as a relatively fresh and cool water mass deriving from the Labrador Current further north, and is present between the upper layer US shelf-derived water masses and the deeper Deep Western Boundary current waters, typically near 400-600m. This LSLW  is investigated in the EN4 database and shown to penetrate as far south as Cape Hatteras (74-75°W), having previously only been described as far west as the Gulf of Maine (66°W). We then examine, using both EN4 and Line W observations, the changes of this water mass between 2005-2008, when the strength of Atlantic Meridional Overturning Circulation (AMOC) measured by the RAPID array at 26°N, was high, and 2009-2015, when the AMOC was low. We show that in the AMOC high period, there was a larger volume of the LSSW present on the northern side of the Gulf Stream system which resulted in an increased meridional slope of the isopycnals near these depths, commensurate with increased geostrophic transport, and also in a more southerly position, of the Gulf Stream after separation at Cape Hatteras. The LSLW could therefore play an important role in decadal timescale variations in the North Atlantic climate system through its impact on the Gulf Stream and AMOC.</p>

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