The North Atlantic Subtropical Surface Salinity Maximum as Observed by Aquarius Frederick Bingham...
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![Page 1: The North Atlantic Subtropical Surface Salinity Maximum as Observed by Aquarius Frederick Bingham UNC Wilmington Collaborators: Julius Busecke, Arnold.](https://reader035.fdocuments.us/reader035/viewer/2022070414/5697c0141a28abf838ccd2cb/html5/thumbnails/1.jpg)
The North Atlantic Subtropical Surface Salinity Maximum as
Observed by Aquarius
Frederick BinghamUNC Wilmington
Collaborators: Julius Busecke,Arnold Gordon and Claudia Giulivi (LDEO), Zhijin Li (JPL)
Also thanks to J. D’Addezio!Work funded by NASA
Journal of Geophysical Research Oceans doi:10.1002/2014JC009825
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The SPURS Experiment
Surface salinity maximum and formation site of subtropical underwater (STUW)
O’Connor et al., (2005)
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Formation of STUW
Gordon and Giulivi, 2014
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Mean SSS in SPURS region from Aquarius
Aquarius L2 V3.0 data averaged into 0.5° along-track bins. Aug. 2011 – Sept. 2013
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Seasonal SSS in SPURS Region
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Harmonic Analysis of SSS
Amplitude Phase
~5 cm/s
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Seasonal migration of maximum SSS
Change in maximum SSS
E-P for SPURS Region from ERAI (blue)
S0(E-P)/h for the SPURS region (green)
Courtesy: J. D’Addezio
Surface area of SSS>37.4
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Along-track variability
Probability of finding fronts
Along-track standard deviation
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SSS change (2013-2012)-(2012-2011)
psu
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Mean (1993-2013) current speed (cm/s) from OSCAR
SSS-max
Mean E (red), P (blue), E-P (green) and moisture flux divergence (black)
Observed E-P plus observed surface current gives SSS change of ~0.6 between 15 and 25°N vs. observed of about 1.5*
*D’Addezio and Bingham, 2014. Data are from ERAI, averaged over 1979-2013
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The SSS-max as a negative feedback loop
Higher surface salinity in SSS-max
-> higher salinity subducted STUW
-> greater stratification between surface and STUW
-> decreased detrainment of freshwater from the surface as it flows poleward
-> decreased surface salinity in SSS-max
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ITCZ
SSS M
ax
Seasonal migration and modulation
Subduction/detrainment
Ekman Transport / Convergence
Trade Winds
Evaporation
Density frontandintrusion
Interior Flow
Rainfall 30N10N
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Motion of Barycenter of SSS-max
Latitude Longitude
Position
SPURS Central Mooring
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South Pacific SSS-max
Interannual longitude
Seasonal longitude
South Pacific SSS-max has similar seasonality to N. Atlantic, but with larger amplitude
South Pacific SSS-max position is correlated with ENSO. What about the N. Atlantic?
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Summary
• Documented mean structure and variability of the SSS-max using Aquarius data
• The SSS-max has low variability and a small seasonal cycle
• Parts of the SPURS region have gotten fresher at a rate of ~0.2-0.3 psu/yr
• Propagation of seasonal phase is consistent with northward transport by Ekman flow and the classic view of SSS-max formation
• The SSS-max shows evidence of frontal structures and fresh intrusions, either advective or from rainfall
• There was a rapid decrease in SSS in the second half of 2012 and a decrease in surface area covered by the SSS-max, possibly related to low E-P (heavy seasonal rainfall)
• Future work will gain insight from comparison with other ocean basins and by elucidating the links between the SSS-max areas and global phenomena such as ENSO and the NAO
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A Subtropical North Atlantic Regional Atmospheric Moisture Budget*
E-P (mm/day) plus Ekman TransportMean E (red), P (blue), E-P (green) and moisture flux divergence (black)
*D’Addezio and Bingham, 2014. Data are from ERAI, averaged over 1979-2013
Observed E-P plus Ekman transport gives SSS change of ~0.6 between 15 and 25°N vs. observed of about 1.5