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Christopher S. Meinen
,
Michael J. McPhaden
, and
Gregory C. Johnson

Abstract

Geostrophic and Ekman transports calculated from observations of subsurface thermal structure and surface winds are used to determine vertical velocities and transports as a function of time, depth, and longitude in the equatorial Pacific within 5°S–5°N, 165°E–95°W during 1993–99 via a box volume balance. The vertical transports are determined in boxes of 10° of latitude by generally 15° in longitude. The corresponding vertical velocities represent a spatial average over these regions. Both the total vertical velocity and the cross-isopycnal component of the vertical velocity (approximated by the cross-isothermal component) are calculated on seasonal and interannual timescales. For the eastern equatorial Pacific (5°S–5°N, 155°–95°W) the mean vertical transport across 50 m is (24 ± 3) × 106 m3 s−1. Variability in the vertical velocity is large relative to the mean. On interannual timescales this variability is well correlated with the local winds in the western portion of the study area, while the correspondence is weaker in the east where wind variability is much smaller. At seasonal timescales there is good correspondence between the vertical velocity and the local winds throughout the study region. The cross-isothermal vertical velocity is significantly smaller than the total vertical velocity, and the means of both compare well with the few historical estimates available.

Full access
Pedro N. DiNezio
,
Lewis J. Gramer
,
William E. Johns
,
Christopher S. Meinen
, and
Molly O. Baringer

Abstract

The role of wind stress curl (WSC) forcing in the observed interannual variability of the Florida Current (FC) transport is investigated. Evidence is provided for baroclinic adjustment as a physical mechanism linking interannual changes in WSC forcing and changes in the circulation of the North Atlantic subtropical gyre. A continuous monthly time series of FC transport is constructed using daily transports estimated from undersea telephone cables near 27°N in the Straits of Florida. This 25-yr-long time series is linearly regressed against interannual WSC variability derived from the NCEP–NCAR reanalysis. The results indicate that a substantial fraction of the FC transport variability at 3–12-yr periods is explained by low-frequency WSC variations. A lagged regression analysis is performed to explore hypothetical adjustment times of the wind-driven circulation. The estimated lag times are at least 2 times faster than those predicted by linear beta-plane planetary wave theory. Possible reasons for this discrepancy are discussed within the context of recent observational and theoretical developments. The results are then linked with earlier findings of a low-frequency anticorrelation between FC transport and the North Atlantic Oscillation (NAO) index, showing that this relationship could result from the positive (negative) WSC anomalies that develop between 20° and 30°N in the western North Atlantic during high (low) NAO phases. Ultimately, the observed role of wind forcing on the interannual variability of the FC could represent a benchmark for current efforts to monitor and predict the North Atlantic circulation.

Full access
Renellys C. Perez
,
Silvia L. Garzoli
,
Christopher S. Meinen
, and
Ricardo P. Matano

Abstract

Two ocean general circulation models are used to test the ability of geostrophic velocity measurement systems to observe the meridional overturning circulation (MOC) and meridional heat transport (MHT) in the South Atlantic. Model sampling experiments are conducted at five latitudes (between 15° and 34.5°S) spanning the range of extratropical current regimes in the South Atlantic. Two methods of estimating geopotential height anomalies and geostrophic velocities are tested, simulating dynamic height moorings (TS array) and current and pressure recording inverted echo sounders (CPIES) deployed within the models. The TS array accurately reproduces the MOC variability with a slight preference for higher latitudes, while the CPIES array has skill only at higher latitudes resulting from the increased geopotential height anomaly signal. Whether direct model velocities or geostrophic velocities are used, MHT and the MOC are strongly correlated, and successful reconstruction of MHT only occurs when there is skill in the MOC reconstructions. The geopotential height anomaly signal is concentrated near the boundaries along 34.5°S, suggesting that this is an advantageous latitude for deployment of an in situ array. Four reduced arrays that build upon the sites from two existing pilot arrays along 34.5°S were examined. For these realistically sized arrays, the MOC and MHT reconstructions from the TS and CPIES arrays have comparable skill, and an array of approximately 20 instruments can be effectively used to reproduce the temporal evolution and vertical structure of the MOC and MHT.

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Christopher S. Meinen
,
Douglas S. Luther
,
D. Randolph Watts
,
Karen L. Tracey
,
Alan D. Chave
, and
James Richman

Abstract

Profiles of absolute velocity are difficult to obtain in the ocean, especially over long periods of time at the same location. This paper presents a method of estimating full water column absolute horizontal velocity profiles as a function of time by combining historical hydrography with the measurements from two separate instruments, the inverted echo sounder (IES) and the horizontal electric field recorder (HEFR). Hydrography is used to construct temperature, salinity, and specific volume anomaly characteristics as functions of the independent variables pressure and seafloor-to-sea-surface round-trip acoustic travel time (τ). Each IES measured τ is combined with these two-dimensional characteristics to estimate the profile of specific volume anomaly, which then is integrated vertically to obtain profiles of geopotential height anomaly (Δϕ). Profiles of Δϕ from adjacent IES sites are differenced to yield vertical profiles of relative geostrophic velocity. Horizontal electric fields arising from the vertically averaged horizontal water velocity provide the requisite referencing of the IES-derived relative velocities. Comparisons are presented between HEFR+IES absolute velocities in the Southern Ocean near 51°S, 143.5°E and absolute velocities determined via hydrography, acoustic Doppler current profiler, and current meter.

Full access
Gregory C. Johnson
,
Rick Lumpkin
,
Simone R. Alin
,
Dillon J. Amaya
,
Molly O. Baringer
,
Tim Boyer
,
Peter Brandt
,
Brendan R. Carter
,
Ivona Cetinić
,
Don P. Chambers
,
Lijing Cheng
,
Andrew U. Collins
,
Cathy Cosca
,
Ricardo Domingues
,
Shenfu Dong
,
Richard A. Feely
,
Eleanor Frajka-Williams
,
Bryan A. Franz
,
John Gilson
,
Gustavo Goni
,
Benjamin D. Hamlington
,
Josefine Herrford
,
Zeng-Zhen Hu
,
Boyin Huang
,
Masayoshi Ishii
,
Svetlana Jevrejeva
,
John J. Kennedy
,
Marion Kersalé
,
Rachel E. Killick
,
Peter Landschützer
,
Matthias Lankhorst
,
Eric Leuliette
,
Ricardo Locarnini
,
John M. Lyman
,
John J. Marra
,
Christopher S. Meinen
,
Mark A. Merrifield
,
Gary T. Mitchum
,
Ben I. Moat
,
R. Steven Nerem
,
Renellys C. Perez
,
Sarah G. Purkey
,
James Reagan
,
Alejandra Sanchez-Franks
,
Hillary A. Scannell
,
Claudia Schmid
,
Joel P. Scott
,
David A. Siegel
,
David A. Smeed
,
Paul W. Stackhouse
,
William Sweet
,
Philip R. Thompson
,
Joaquin A. Triñanes
,
Denis L. Volkov
,
Rik Wanninkhof
,
Robert A. Weller
,
Caihong Wen
,
Toby K. Westberry
,
Matthew J. Widlansky
,
Anne C. Wilber
,
Lisan Yu
, and
Huai-Min Zhang
Free access
Molly Baringer
,
Mariana B. Bif
,
Tim Boyer
,
Seth M. Bushinsky
,
Brendan R. Carter
,
Ivona Cetinić
,
Don P. Chambers
,
Lijing Cheng
,
Sanai Chiba
,
Minhan Dai
,
Catia M. Domingues
,
Shenfu Dong
,
Andrea J. Fassbender
,
Richard A. Feely
,
Eleanor Frajka-Williams
,
Bryan A. Franz
,
John Gilson
,
Gustavo Goni
,
Benjamin D. Hamlington
,
Zeng-Zhen Hu
,
Boyin Huang
,
Masayoshi Ishii
,
Svetlana Jevrejeva
,
William E. Johns
,
Gregory C. Johnson
,
Kenneth S. Johnson
,
John Kennedy
,
Marion Kersalé
,
Rachel E. Killick
,
Peter Landschützer
,
Matthias Lankhorst
,
Tong Lee
,
Eric Leuliette
,
Feili Li
,
Eric Lindstrom
,
Ricardo Locarnini
,
Susan Lozier
,
John M. Lyman
,
John J. Marra
,
Christopher S. Meinen
,
Mark A. Merrifield
,
Gary T. Mitchum
,
Ben Moat
,
Didier Monselesan
,
R. Steven Nerem
,
Renellys C. Perez
,
Sarah G. Purkey
,
Darren Rayner
,
James Reagan
,
Nicholas Rome
,
Alejandra Sanchez-Franks
,
Claudia Schmid
,
Joel P. Scott
,
Uwe Send
,
David A. Siegel
,
David A. Smeed
,
Sabrina Speich
,
Paul W. Stackhouse Jr.
,
William Sweet
,
Yuichiro Takeshita
,
Philip R. Thompson
,
Joaquin A. Triñanes
,
Martin Visbeck
,
Denis L. Volkov
,
Rik Wanninkhof
,
Robert A. Weller
,
Toby K. Westberry
,
Matthew J. Widlansky
,
Susan E. Wijffels
,
Anne C. Wilber
,
Lisan Yu
,
Weidong Yu
, and
Huai-Min Zhang
Free access