Christopher S. Meinen

Interannual Variability in Warm Water Volume Transports in the Equatorial Pacific during 1993–99*

Abstract Previous studies have indicated that the volume of warm water (WWV) in the equatorial Pacific is intrinsically related to the dynamics of the El Nino–Southern Oscillation (ENSO) cycle. A gridded subsurface temperature dataset, which incorporates temperature measurements from expendable bathythermograph profiles as well as measurements from the moorings in the Tropical Atmosphere and Ocean Array, was used along with historical hydrography to quantify the variability of the WWV (with temperatures greater than 20°C) within the region 8°S–8°N, 156°E–95°W during 1993–99. These data were also used to estimate geostrophic transports of warm water relative to a level of no motion at 1000 dbar (1 dbar = 104 Pa). Ekman transports were estimated using wind data from gridded observations, assimilating model output, and satellite scatterometer measurements. The results indicate that the buildup of WWV between the weak 1994–95 El Nino event and the onset of the strong 1997–98 El Nino event resulted primarily f...

Interannual variations in the Atlantic meridional overturning circulation and its relationship with the net northward heat transport in the South Atlantic

[1] Variability of the Atlantic Meridional Overturning Circulation (AMOC) and its effect on the net northward heat transport (NHT) in the South Atlantic are examined using a trans-basin expendable bathythermograph (XBT) high-density line at 35S (AX18). The time-mean AMOC is 17.9 ± 2.2 Sv during 2002–2007. Although the geostrophic transport dominates the time-mean AMOC, both geostrophic and Ekman transports are important in explaining the AMOC variability. The contributions of geostrophic and Ekman transports to the AMOC show annual cycles, but they are out ofphase,resultinginweakseasonalvariabilityoftheAMOC. The NHT variability is significantly correlated with the AMOC, where a 1 Sv increase in the AMOC would yield a 0.05 ± 0.01 PW increase in the NHT. Partition of transport into the western and eastern boundaries and interior suggests that, to quantify changes in the AMOC and NHT, it is critical to monitor all three regions. Citation: Dong, S., S. Garzoli, M.Baringer,C.Meinen,andG.Goni(2009),Interannualvariations intheAtlanticmeridionaloverturningcirculationanditsrelationship with the net northward heat transport in the South Atlantic, Geophys. Res. Lett., 36, L20606, doi:10.1029/2009GL039356.

Structure of the North Atlantic current in stream-coordinates and the circulation in the Newfoundland basin

Accurate knowledge of the absolute North Atlantic Current (NAC) transport has been limited in the past by the di

Observed Interannual Variability of the Florida Current: Wind Forcing and the North Atlantic Oscillation

culty of obtaining absolute velocity measurements. For this study, historical hydrography was combined with time series of round trip travel time from inverted echo sounders, bottom pressure sensor measurements, and measured velocities from deep current meters, via aGravest Empirical Modea tech- nique, to yield time series of temperature and absolute velocity sections. These sections were used to determine the mean NAC stream-coordinates structure of temperature and absolute velocity for the period from August 1993 to February 1995. This structure is narrower and stronger than the corresponding Eulerian average, with peak speeds greater than 80 cm s and bottom velocities exceeding 10 cm s. The calculated mean NAC transport was 131

Vertical Velocities and Transports in the Equatorial Pacific during 1993–99*

14 (10 m s); temporal variations resulted in a4 110 m s standard deviation. The stream-coordinates estimate of mean absolute transport was found to be about 10% smaller than the corresponding Eulerian mean transport of 14610 m s as a result of partially summing the north and south transports within the Mann Eddy, a large semi-permanent anticyclonic eddy normally located just o!shore of the NAC. Most transport sections across the NAC in this region include the northward transport of the inshore side of the Mann Eddy because it is di

Absolutely referenced geostrophic velocity and transport on a section across the North Atlantic Current

cult to discriminate between the two #ows. Historical estimates place the Mann Eddy absolute transport around 50}6010 m s; thus, the transport crossing this transect that can be identied with the NAC is about 9010 m s. The barotropic component of the transport (dened as the bottom velocity multiplied by the water depth) is found to contribute at least 30% of the total absolute transport, depending on the choice of baroclinic reference level. Because a time series of transport measurements was made in this study, the accuracy of the mean transport estimate is better than previous estimates, which have all been based on snapshot measurements. From a combination of these measurements with other published measurements, a scheme for the overall circulation and transport in the Newfoundland Basin is suggested. 2001 Elsevier Science Ltd. All rights reserved.

Calibrating Inverted Echo Sounders Equipped with Pressure Sensors

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 278N 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 winddriven circulation.The estimated lag times are at least 2 times faster than those predictedby 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 lowfrequency 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 208 and 308N 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.

Further evidence that the sound-speed algorithm of Del Grosso is more accurate than that of Chen and Millero

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...

Seasonal variations in the South Atlantic Meridional Overturning Circulation from observations and numerical models

A transect of CTD proles crossing the North Atlantic Current (NAC) along WOCE line ACM6 near 42.53N during August 1}7, 1993, provides geostrophic shear velocity proles, which were absolutely referenced using simultaneous POGO transport #oat measurements and velocity measurements from a ship-mounted acoustic doppler current proler (ADCP). The NAC absolute transport was 112

Meridional Extent and Interannual Variability of the Pacific Ocean Tropical-Subtropical Warm Water Exchange

23]106 m3 s~1, which includes a portion of the transport of the Mann Eddy, a large permanent anticyclonic eddy commonly adjacent to the NAC. The NAC transport estimated relative to a level of no motion at the bottom would have underestimated the true total absolute transport by 20%. A surprisingly large 58]106 m3 s~1 #owed southward just inshore of the NAC. This #ow, centered near 1500 dbars about 200 km o!shore of the shelf-break, was fairly barotropic with a peak velocity of greater than 20 cm s~1, and the water mass characteristics were of Labrador Sea Water. These absolute transport observations suggest southward recirculation inshore of the NAC at 42.53N and a stronger NAC than has previously been observed. ( 1999 Elsevier Science Ltd. All rights reserved.