Reconstructing ocean biogeochemical fields
from simulated Argo float measurements
Ethan Campbell intern
Joe Majkut advisor
Program in Atmospheric and Oceanic Sciences, Princeton University
January 2009
9984 Argo float
profiles!
Argo
the Argo float problem
• 3525 floats = sparse
• Noisy data
– mesoscale eddies + synoptic variability
• Instrument error
Source: NASA Earth Observatory
Argo
the Argo float problem
How accurately can one
reconstruct ocean
biogeochemical fields by
inverting Argo data?
… enter CM2.6
(GFDL’s Climate Model 2.6)
• Coupled
atmosphere,
ocean, sea ice,
and land
• High-resolution
= eddies
Delworth et al. (2012)
Reconstructed fields
(“January 2009”)
CM2.6
Argo
Reconstruction error
Subtropical Front (STF)
Interpolation method
• Inverse distance weighting (IDW) using 3 nearest
neighbors (k = 3) and power value p = 2
– i.e. weights proportional to inverse of distance,
squared
– Gaussian noise added to data points to simulate
instrument inaccuracy
– Exact interpolator (trusts data points)
• Limitations:
–
–
–
–
Land should be an impermeable barrier and isn’t
IDW has no sense of spatial autocorrelation
Restricting search to k = 3 is fast but not ideal
Choosing p = 2 is arbitrary
Correlation metrics
higher density of
floats = less
reconstruction error,
right?
notice the
latitude gradient
Limitations
• CPU- and memory-intensive
• Only one month + surface fields + basic interpolation
• The elephant in the room: Movement of
tracers in CM2.6 is independent of real-world
advection of Argo floats
Real-world relevance
• Where in the world should we add floats to
most improve reconstruction accuracy?
• How robust is the array to the removal of
floats with poor-quality measurements?
• How does float drift correlate with
reconstruction error? (i.e. Iridium vs. ARGOS
floats)
Acknowledgements
• Joe Majkut, my advisor, for supporting me and guiding
my thought process
• Carolina Dufour and Rick Slater for the CM2.6 output
• Bror Jonsson for helping with interpolation methods in
Python
• Chris Ober for his invaluable technical assistance
• Prof. Sarmiento and everyone at AOS and GFDL for giving
me a home away from home this summer!
• Princeton Environmental Institute for their generous
funding
October 4, 2013
Questions?