1. Wind-driven changes of current, temperature, and chlorophyll
inferred from space north of New Guinea
M.-H. Radenac, F. Léger, M. Messié, P. Dutrieux, G. Eldin, C. Menkes
mesotrophic
0,1 mg m-3
oligotrophic
0 mg m-3
Averaged SeaWiFS chlorophyll (Sep – Dec. 2010)

2. cross-track geostrophic current anomaly (Lagerloef et al., 1999)
Data - method
chlorophyll
vent
SeaWiFS, 8 days, 9 km, Sep Dec. 2010
ERS, 7 days, 1°, Aug Dec. 2001
SST
QuikSCAT, 7 days, 0,5°, Aug Nov. 2009
TMI, 7 days, 0,25°, since Dec. 1997
courant
AVHRR – PFV5, nighttime, 4 km
OSCAR, 5 days, 1°
CTOH altimetric tracks, 10 days
cross-track geostrophic current anomaly (Lagerloef et al., 1999) +
Wavelet analysis
Spectra  dominant modes of variability
Band-pass filters  reconstruction of the signal
Intraseasonal 20 – 120 days
Seasonal 150 – 500 days
Interannual > 500 days

3. Chlorophyll response to WWE
The day signals
Sustained intraseasonal activity in summer
Strong relationship between increasing chlorophyll (decreasing SST) and westerly wind in summer
Running correlation of x vs. chl, x vs. SST
Composite maps of chlorophyll and surface currents during WWE
Local upwelling
Surface current convergence
Equatorial extension
Eastward equatorial current
Local upwelling
Equatorial extension
The December 2001 event
West of 146°E
Vertical and biological processses
East of 146°E
Zonal advection
[Chl]/t
u [Chl]/x
v [Chl]/y
u [Chl]/x  v [Chl]/y
December 2001
2°S-0°S

4. x, chl, SST Seasonal variations Along coast Ua 099 023 201
SST chl
Vitiaz Strait
Mamberamo R.
Sepik R.
August February
SST and wind stress
chl and Ua
Austral winter
Austral summer
Trade winds
NW monsoon
NGCC 
NGCC 
Cold water from Solomon Sea
Coastal upwelling
Current convergence near Sepik River

5. Interannual variations
El Niño La Niña
SST and Ua
chl and Ua
SOI, x, SLA
SST, chl Ua
Ua A (160°E, 0°)
El Niño
La Niña
SST  and chl 
SST  and chl 
Same chlorophyll pattern than in summer
Less efficient processes
Upwelling
Same SST pattern than in winter
Penetration of cold and low chlorophyll water from the Solomon Sea
El Niño
more westerlies prior to EN
elevated SLA  shallow nutricline/thermocline
NGCC  in the east (WBC influence)
equatorial influence in the west

6. El Niño upwelling vs. seasonal upwelling
Assuming that vertical advection is the main driver of SST variations
τ ∥ = along shore wind
L = width of the horizontal Ekman layer = 12 km AH = m2 s-1  L = 4-12 km
wupw T stratification
𝜕𝑇 𝜕𝑡 = 𝜏 ∥ 𝜌𝑓𝐿 ∙ 𝜕𝑇 𝜕𝑧
𝐿=𝜋 2 𝐴 𝐻 𝑓
El Niño
Feb.
// (N m-2)
0.01
0.04
wupw (m d-1)
5.7
22.7
T / z (°C m-1)
NO3 / z (mol L-1 m-1)
0.052
0.035
T / t (°C d-1)
0.14
0.31
NO3 / t (mol L-1 d-1)
0.29
0.79
( 2)
( 2.7)
Upwelling inhibition by onshore geostrophic flow
Influence of Ekman pumping

7. current anomaly west of Sepik current anomaly east of Sepik
Summary
wind direction
current anomaly west of Sepik
current anomaly east of Sepik
SST anomaly
chlorophyll anomaly
processes
WWE 
< 0
> 0
UPW
austral summer
austral winter 
CCT
El Niño
≈ 0
UPW & CCT
La Niña
main observations and processes at work at different time scales
UPW = upwelling
CCT = coastal cold tongue