On the Driving Mechanism of the Annual Cycle of the Florida Current Transport

Czeschel, Lars; Eden, Carsten; Greatbatch, Richard John

doi:10.1175/jpo-d-11-0109.1

Cited by 24 publications

(36 citation statements)

References 43 publications

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“…This implies that T GS responds nearly instantaneously to the interannual fluctuations of alongshore wind forcing, and that remote influences from winds north of the Straits are transmitted rapidly southward by topographic waves. It is worth noting that the generation of interannual T GS by these dynamics is consistent with many previous studies that have attributed seasonal and short‐term variations of T GS to local wind stress forcing and upstream wave propagation [e.g., Anderson and Corry , ; Lee and Williams , ; Schott et al ., ; Czeschel et al ., ].…”

Section: Resultsmentioning

confidence: 99%

Wind-forced interannual variability of the Atlantic Meridional Overturning Circulation at 26.5°N

Zhao

Johns

2014

J. Geophys. Res. Oceans

119

107

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, when the anomalous winddriven Ekman transport also has a significant contribution. The physical mechanisms for the interannual changes of the AMOC are proposed and evaluated in a two-layer model. While the Ekman transport is linked to the North Atlantic Oscillation (NAO), the anomalous geostrophic transport involves the oceanic adjustment to surface wind forcing. In particular, the intensification and weakening of the southward interior geostrophic flow is modulated by the internal Rossby wave adjustment to the surface wind forcing. The Gulf Stream, on the other hand, is controlled by both topographic waves along the US coast and westward propagating planetary waves. Our study suggests that a large part of the observed AMOC interannual variability at 26.5 N can be explained by wind-driven dynamics.

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Section: Resultsmentioning

confidence: 99%

Wind-forced interannual variability of the Atlantic Meridional Overturning Circulation at 26.5°N

Zhao

Johns

2014

J. Geophys. Res. Oceans

119

107

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“…The East Madagascar and Mozambique Ridges may be important by deflecting or dispersing Rossby waves from the interior as they approach the western boundary (Matano et al 2002). Alongshore winds may drive seasonal coastal upwelling/downwelling that could affect transport, as found in the Florida Current (Anderson and Corry 1985;Czeschel et al 2012). Perhaps planetary wave teleconnections to strong monsoon forcing over the northern Indian Ocean and to tropical Pacific trade winds act to modify the annual cycle of the Agulhas Current (Xie et al 2002).…”

Section: May 2015mentioning

confidence: 99%

Capturing the Transport Variability of a Western Boundary Jet: Results from the Agulhas Current Time-Series Experiment (ACT)

Beal

Elipot

Houk

et al. 2015

Journal of Physical Oceanography

126

198

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The volume transport of the Agulhas Current was measured over a 3-yr period by an array of seven current meter moorings and four current-and pressure-recording inverted echo sounders (CPIES) deployed at 348S. CPIES extended the array farther offshore in order to capture, for the first time, the full Agulhas Current during meander events. Transports derived from CPIES are well correlated with overlapping current meter transports (0.89). The Eulerian mean current is 219 km wide and 3000 m deep, with peak surface speeds of 1.8 m s 21 and a weak northward undercurrent on the continental slope below 1200 m. A new algorithm to capture the western boundary jet transport at each time step T is defined as the poleward transport out to the first maximum of the vertically integrated velocity beyond the half-width of the mean jet. The mean transport of the Agulhas Current jet, so defined, is 284 Sverdrups (Sv; 1 Sv [ 10 6 m 3 s 21 ) with a standard error of 2 Sv. Sampling and instrumental errors are explicitly estimated and amount to an additional 9 Sv. A more traditional estimate, based on net transport integrated to a fixed distance offshore T box , gives a mean transport of 277 6 5 Sv. This transport is 10 Sv greater than an equivalent transport at 328S, corresponding to a latitudinal increase equal to that predicted by Sverdrup dynamics. The time series of T and T box show important differences during solitary meander events and at longer time scales. In terms of an annual cycle, the Agulhas Current appears strongest during austral summer, a similar phase to the Gulf Stream and Kuroshio.

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“…The leading theory is that the FC annual cycle is predominantly forced by the along‐channel wind stress in the Florida Straits and by wind stress curl [e.g., Schott et al ., ; DiNezio et al ., ; Rousset and Beal , ]. Modern observations and modeling experiments have revealed the importance of additional processes that can influence the FC seasonal variability, such as the local eddy field [ Frajka‐Williams et al ., ], and baroclinic signals coming from the ocean interior [ Ezer , ; Sturges and Hong , ; Czeschel et al ., ].…”

Section: Introductionmentioning

confidence: 99%

“…One potential source of seasonal variability for the FC transport is semi‐annual/annual first baroclinic Rossby waves observed in the North Atlantic [ Polito and Liu , ; Clément et al ., ]. In fact, modeling studies suggest that baroclinic signals coming from the ocean interior may drive a relevant component of the FC seasonal variability [ Czeschel et al ., ]. Analysis of in situ and satellite altimetry observations suggest that 42% of the MOC variance inferred from geostrophic calculations in the ocean interior at 26.5N can be attributed to first mode variability linked with eddies and Rossby waves at periods of 8–250 days [ Clément et al ., ].…”

Section: Introductionmentioning

confidence: 99%

Remote sources for year‐to‐year changes in the seasonality of the Florida Current transport

2016

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The seasonal variability of the Florida Current (FC) transport is often characterized by the presence of an average annual cycle (8% of the variance) of ∼3 Sv range peaking in boreal summer. However, the seasonality displayed by the FC transport in any individual year may have very distinct characteristics. In this study, the analysis focuses on seasonal changes (73–525 day frequency band) in the FC transport that are associated with a variable annual phase, which is defined as the transient seasonal component (FCt, 27% of the variance). It is shown that the FCt is largely modulated by westward propagating sea height anomaly (SHA) signals that are formed in the eastern North Atlantic 4–7 years earlier than observed at 27°N in the Florida Straits. These westward propagating SHA signals behave approximately like first baroclinic Rossby waves that can modulate changes in the FC seasonal variability upon arrival at the western boundary. The main finding from this study is that changes in coastal sea‐level between 25°N and 42°N linked with westward propagating signals account for at least 50% of the FCt. The integrated changes in the coastal sea‐level between 25°N and 42°N, in turn, drive adjustments in the geostrophic transport of the FC at 27°N. Results reported here provide an explanation for previously reported year‐to‐year changes in the FC seasonality, and suggest that large sea‐level variations along the coast of Florida may be partially predictable, given that these Rossby‐wave‐like signals propagate approximately at fixed rates in the open ocean along 27°N.

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On the Driving Mechanism of the Annual Cycle of the Florida Current Transport

Cited by 24 publications

References 43 publications

Wind-forced interannual variability of the Atlantic Meridional Overturning Circulation at 26.5°N

Wind-forced interannual variability of the Atlantic Meridional Overturning Circulation at 26.5°N

Capturing the Transport Variability of a Western Boundary Jet: Results from the Agulhas Current Time-Series Experiment (ACT)

Remote sources for year‐to‐year changes in the seasonality of the Florida Current transport

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