Studies of the equatorial box with the UMD ocean model

coriandercultureMechanics

Feb 22, 2014 (3 years and 1 month ago)

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Studies of the equatorial box with
the UMD ocean model

Jim Christian

Fisheries and Oceans Canada

Canadian Centre for Climate Modelling and Analysis

University of Victoria



a brief note on the sea
-
truth
experiment




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EOF’s




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Since 2005 I have been testing diferent
variants of the model against underway
pCO
2

data provided by Dick Feely (NOAA)
and Masao Ishii (JMA)

High friction

Low friction

High friction

Low friction

Climatological forcing

Modified biology

Original biology

W92 gas exchange

Most experiments show a fairly strong correlation over
the full domain because of the mean
spatial

pattern, so I
defined a ‘core ENSO’ region where the correlation of a
climatology run with observed pCO
2

anomalies

would
be ~0 (panel 8)

Time
-
mean section along equator is fairly
good except in experiments 1, 4, and 5



best results with original (Christian et al. 2002) biology +
low friction (Expt 2), or with the modified (Wang et al.
2005) biology + high friction (Expt 3)



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variability

(Expts 1, 5), but applying
neither

generates
too
much

variability, and extreme values that are not observed
(Expt 4)

Therefore I have selected Expts 2 and 3 for analyses of the
equatorial box.

EOF analysis

Q:

what is the correlation between the
mean

concentration of e.g. DIC within the box, and the first
principal component for the whole model domain?

Expt 2

Expt 3

EOF analysis

A:

if we can adequately sample what is
happening in the box we have a pretty good
index of what is happening across the whole
domain

First EOF accounts for around 30
-
40% of total
variance for carbon system variables (DIC, nDIC,
pCO
2
)
and is strongly correlated with ENSO in all
cases

C and N budgets

(for the surface mixed
layer)

For
carbon
, the primary mass balance is between
upwelling

and
meridional advection
, i.e., most of the carbon upwelled within the box
is advected out of the box to the north and south.

Zonal

advection can be convergent or divergent, and is basically a
mirror image of the net gain or loss from upwelling after correcting for
the poleward advection.

The residual ‘excess’ upwelling of C into the box
is ~1.4 Tmol/month and is lost to particle export
(~80%) and CO
2

outgassing (~20%)

For
nitrogen
, the primary mass balance is between
upwelling

and
sedimentation
, and meridional advection is negligible.

Conclusions




the box is a very good proxy for the first (ENSO)
mode of variability over the full domain if the mean
within the box is adequately sampled




most carbon upwelled within the box is advected
poleward and outgasses in the subtropics, whereas
nitrogen is almost entirely removed by sedimentation
within the box




export of C by sedimentation within the box is ~4X
larger than outgassing