adequacy of the argo array for monitoring water mass ...€¦ · gilbert et al. (2005), limnology...
TRANSCRIPT
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Adequacy of the Argo array for monitoring water mass changes in the
Gulf Stream's northern recirculation gyre Denis Gilbert Institut Maurice-Lamontagne Pêches et Océans Canada Mont-Joli, Québec
Argo Science Workshop 3 Hangzhou, China, March 26, 2009
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OUTLINE
• Argo seen from a coastal perspective • Isopycnal analysis: T-S-O2 fields • Winter mixed layer depth • Dynamic height • Some thoughts on the design of Argo array
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Modified from Shaw et al. (2002, QSR)
Deep ocean climate affects waters far inland
Argo float territory
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Warm-core rings (WCR)
8-day composite satellite imagery of SST on 06/11/1997 (Chauduri et al. 2009, Cont. Shelf Res. 29: 393-406)
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Water properties
on the 27.25 kg/
m3 density surface
Gilbert et al. (2005, L&O, 50: 1654-1666)
T
O2
S
O2 sat.
Historical T-S-O2 data from ISDM and NODC databases (1914-2003)
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Water mass mixing: NACW – LCW
1931-1935 72% LCW, 28% NACW
1980-2003 53% LCW, 47% NACW
Gilbert et al. (2005, L & O, 50: 1654-1666)
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Water mass mixing: LCW – NACW
28%
72%
53% 47%
Labrador Current Water
North Atlantic Central Water
In the 1930s, deep waters (300 m) in the St. Lawrence Estuary were • colder • fresher • more oxygenated
From 1984 to 2008, deep waters (300 m) in the St. Lawrence Estuary were • warmer • saltier • less oxygenated
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Labrador Current Water (LCW) and North Atlantic Central Water (NACW)
147 µM
Gilbert et al. (2005), Limnology and Oceanography, Vol. 50: 1654-1666.
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Slope Water region (depth > 2000 m for Argo)
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Expected number of floats in Slope Water • Slope Water region (d > 2000 m) has an area of
650 000 km2. • For a target float density of one float per 90000
km2 (300 km x 300 km ), we should thus have an average of 7 floats in the Slope Water region.
• Same calculation using a density of 3ºlatitude x 3ºlongitude (85000 km2) gives an average of 8 floats in the Slope Water region.
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Number of Argo floats in Slope Water
Target Argo density is 7.5
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Number of profiles from Argo floats in 2007 1/3° latitude x 1/2° longitude grid is chosen to help "capture" the LCW signature
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Time window for 1/3° latitude x 1/2° longitude • One year of Argo data leaves too many
empty "squares". • Need to focus on multi-year instead of
single-year analyses. • Next slides consider 1998 to 2007 period,
using Argo data only.
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Depth of σθ= 27.25 kg m-3 isopycnal
Gilbert and Nault (2008)
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Temperature on σθ= 27.25 kg m-3
Gilbert and Nault (2008)
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Salinity on σθ= 27.25 kg m-3
Gilbert and Nault (2008)
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Gilbert et Nault, AZMP Bulletin PMZA, 2008
Temperature and salinity anomalies
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Dynamic height anomaly relative to 1000 db
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Some thoughts on the Argo array
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Could CTD sampling on shelf help with DMQC?
Gilbert and Nault (2008)
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Could CTD sampling on shelf help with DMQC?
Gilbert and Nault (2008)
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Winter mixed layer depth
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Proposed changes to Argo design
• Rather than using a uniform 3ºx3º float density coverage, promote finer (coarser) spacing in regions with smaller (larger) spatial correlation scales.
• Improve float density coverage for better monitoring of boundary currents.
• Improve linkages with shelf monitoring programs (CTD shelf transects, gliders…)
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SUMMARY
• At the original Argo design density of one float per 3º, we can expect an average of 7 or 8 floats to be present in the Slope Water region.
• The present Argo design allows the study of climate variability over time scales of pentads (5 years), but is insufficient for studying interannual variability.
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Argo trajectories - Howard Freeland
http://www.pac.dfo-mpo.gc.ca/sci/osap/projects/argo/trajmovies_e.htm