Works
on altimetry in the Solomon Sea (start:29/06/2007)
Lien
sur les sites d'Angélique
Lien sur les sites de Billy:
Plots from ERS winds
Plots from XBT track
Bathymetric maps from Maxsea, details on the Solomon Sea:
Woodlark Island.jpeg
SE_PNG.jpeg
Vitiaz.jpeg
A. Mean Dynamic
Topography
B. Mapped Sea Level Anomalies
C. Processing
of along track data
D. Some plots illustrating
observations in-around the Solomon Sea
E. What to tell
F. EKE
G. EOF Analysis
H. Harmonic Analysis (Annual cycle)
I. Climatologic year
J. Transport
K. Low Frequency
L. Ideas for a
discussion based on the Low frequency signature in the Solomon Sea
A. Mean Dynamic
Topography
1. "Bingham" solution (0.5°x0.5°
grid)
a. unfiltered
solution: Pacific
(30n-30s) ; South Pacific
b. Filtered
solution following Thierry's processing
1. same filtering than for Grace02 (Castruccio) (x=5°, y=1°)
Pacific (30n-30s)
; South Pacific
2. fltx5y1 (x=2.5°,y=.5°): Pacific (30s-30n)
; South Pacific
2. "Maximenko" solution (0.5°x0.5°
grid)
a. unfiltered solution:
i. MDT Pacific
(30n-30s) ; South Pacific
ii. Geostrophic Current
a. Zonal component
(Pacific)
b. Circulation in the
South West Pacific
b. Filtered
solution following Thierry's processing
1. same filtering than for Grace02 (Castruccio) (x=5°, y=1°)
i. MDT: Pacific (30n-30s)
; South Pacific
ii. Geostrophic Current
a. Zonal
component (Pacific)
b. Circulation
in the South West Pacific
TOP
B. Mapped Sea Level Anomalies
time sampling: 7 days
1. unfiltered data: RMS South
West Pacific ; RMS Salomon Sea
a. Seasonal
cycle: RMS
Salomon Sea
2. Filtered data (SBX:5): RMS Salomon Sea
; RMS residual
a. Seasonal
cycle: RMS
Salomon Sea
b.
Interannual: RMS Salomon Sea
TOP
C.
Processing of along track data
C.1 Traitment of altimetric data
Topex/Poseidon along track dataset
has been treated by the CTOH team of Toulouse, with special algorithms
whose aim is to recover good data in the open ocean that would have
been juged erroneous, and to recover data near the coasts.
A post-processing treatment has been applied to flag erroneous left
data. A 4 sigma filter is first applied. Then, data are filtered with a
2 sigma cycle to cycle difference filter. Afterward, data are
"replaced" on a reference track, which is the barycentre of the track
for every cycle.
Another filter is used : the difference of rms between the first point
after or before land and his neighbour is not allowed to rise above 2
cm. This filter is applied several times.
Finally, a point must have a minimum of 200 valid cycles to be valid.
Otherwise, this point can't be used.
Tracks of
interest and
bathymetry
Example of the number of valid cycles and sla variance for a track of
the new product : Track 251
C.2 Comparison of the new product with Aviso and the MSLA gridded data
- Track 23 ; zoom Salomon
a. RMS
;
RMS
Salomon
b. Hovmuller: MSLA
; DEGEO
;
Aviso
- Track 73 ; zoom Salomon
a. RMS ;
RMS Salomon
b. Hovmuller: MSLA
; DEGEO ;
Aviso
- Track 10 ; zoom Salomon
a. RMS ;
RMS Salomon
b. Hovmuller: MSLA
; DEGEO ;
- Track 112 ; zoom Salomon
a. RMS ;
RMS Salomon
b. Hovmuller: MSLA
; DEGEO ;
- Track 149 ; zoom Salomon
a. RMS ;
RMS Salomon
b. Hovmuller: MSLA
; DEGEO ;
Aviso
- Track 162 ; zoom Salomon
a. RMS ;
RMS Salomon
b. Hovmuller: MSLA
; DEGEO ;
- Track 199 ; zoom Salomon
a. RMS ;
RMS Salomon
b. Hovmuller: MSLA
; DEGEO ;
- Track 238 ; zoom Salomon
a. RMS ;
RMS Salomon
b. Hovmuller: MSLA
; DEGEO ;
- Track 86 ; zoom Salomon
a. RMS ;
RMS Salomon
b. Hovmuller: MSLA
; DEGEO ;
- Track 99 ; zoom Salomon
a. RMS ;
RMS Salomon
b. Hovmuller: MSLA
; DEGEO ;
- Track 251 ; zoom Salomon
a. RMS ;
RMS Salomon
b. Hovmuller: MSLA
; DEGEO ;
Aviso
- Track 175
; zoom
Salomon
a. RMS
;
RMS
Salomon
b. Hovmuller: MSLA
; DEGEO
- Track 188
; zoom
Salomon
a. RMS
;
RMS
Salomon
b. Hovmuller: MSLA
; DEGEO
- Track 225
; zoom
Salomon
a. RMS
;
RMS
Salomon
b. Hovmuller: MSLA
; DEGEO
- Track 36
a. RMS ;
b. Hovmuller: MSLA
; DEGEO ;
- Track 123
a. RMS ;
b. Hovmuller: MSLA
; DEGEO ;
- Track 47
a. RMS ;
b. Hovmuller: MSLA
; DEGEO ;
- Track 60
a. RMS ;
b. Hovmuller: MSLA
; DEGEO ;
C.3 Variance along the tracks
Sla rms map after filtering,
using all TP tracks
Sla seasonal
cycle rms map after filtering, using all TP tracks
Sla
interannual variability rms map after filtering plus 3 months
filtering, using all TP tracks
TOP
D. Some
plots illustrating
observations in-around the Solomon Sea
(Most from Billy's website)
NICU.png;
PNGzoom_vectors.png;
vitiaz_sect.png
Boug_Kiri_map_with_adcp.gif;
Boug_Kiri_ug_1000m.gif;
wepocs2_solomon_sea_adcp_ony.gif
poi1map.pdf;
poi1sol.pdf
poi2map.pdf;
poi2wsol.pdf
mw9304_adcp_vectors3.gif
Alex's
page
TOP
E. What to
tell
The Solomon sea is characterized by a complex bathymetry and ocean
dynamic as illustrated on:
Fig.E1.
How altimetry can help to
describe the variability of such dynamics?
- This area exhibits the strongest
variability over the Pacific ocean between 10°N-19°S as shown
from the gridded altimetric product:
Fig.E2: RMS.gif
- The gridded
product, which merged TOPEX/POSEIDON and ERS, has a 1/3°
horizontal resolution, and a 5 day temporal resolution. As shown on the
figure above, the gridded data don't take account of the complex
bathymetry of the Solomon Sea. Therefore, this product could be
irrelevant for our study.
- We decide to use a new processing for
alond track altimetric data. Compared to the classical product, data
are gained near the coast, and more cycles are available. Details on
the processing can be found on the Angelique'web site. Here are the
tracks that have been used:
Fig. E3: tracks of
interest and
bathymetry
Only 10 tracks span the Solomon Sea.
The benefit from this new processing can be
illustrated by comparing the Old (Fig.E4a) with the New (Fig.E4b) Sla
along track 251.
This new Sla data have been validated against tide gauge data available
in our region (look at "Tracks of
interest and
bathymetry" for the location of the tide
gauge). We present the time series of the tide gauge, and of the
nearest altimetric point for the Lombrum, Madang, Rabaul,
Townsville, Honiara sites (faire plots)
- Here is the rms
variability along the tracks:
along track sla rms
(Fig.E5)
The highest variability (15 cm rms) is centered along 8°S and
extends between 11°S-5°S in latitude, and between
150°E-170°E in longitude.
In the Solomon Sea, the eastern part of the basin, along the Solomon
Islands, exhibits higher variability than the western part, alonb
the Papua New Guinea Coast.
Is this difference of variability
representative of different dynamics between the west and the east into
the Solomon Sea?
The western part of the basin is characterized by Western Boundary
Currents, the NGCUC flowing northward below the NGCC; whereas the
eastern part is characterized by complex recirculation.
East of the Solomon Islands, the highest variability are not against
the coast but a few degrees to the east. Qiu and Chen (2004) have
studied the seasonal cycle in this area, and have found that at
seasonal time scale, this high variability is explained from barotropic
instability associated with the horizontal shear of the SECC-SEC system.
North (the Bismark Sea) and south of the Solomon Sea (11°S) the
variability falls from 15 cm to 10 cm.
In conclusion, the highest variability are concentrated in the Solomon
Sea, and just to the east of the Solomon Islands. The explanation of
Qiu and Chen (2004) for the seasonal variability east of the Solomon
Islands doesn't seem a good one for the Solomon Sea where neither the
SECC nor the SEC can easily flow into the Solomon Sea
Some questions:
- From which temporal frequencies is this variability representative?
- How is different the variability inside and outside the Solomon Sea?
- Can the variability of the WBC be observed from altimetry?
Filtering of the data
- The SLA are filtered with a 1-month
triangle filter:
Fig.E6a: rms
of along
track filtered sea level.gif
Fig.E6b: rms of the
sla annual cycle.gif
Fig.E6c: rms of sea
level once the seasonal cycle is removed.gif
Fig.E6d: rms of the
interannual sla signal.gif
A 3 cm rms noise is filtered from the raw data. The
description of the variability of the filtered sla is the same than
above (check the track 188).
The spatial distributions of the variability of the annual and
interannual sla signals are similar, but east of the Solomon Islands,
the highest annual variability is centered at 6°S whereas it is at
8°S for interannual variability. The interannual sla signal
exhibits higher variability than the annual cycle, 13 cm rms against 8
cm rms respectively. The comparison between the interannual variability
and the sla variability free from the annual cycle shows that other
time frequencies could exist (bi annual?? noise? see spectrum)
- Check of the track 188. All the data
are plotted on: track 188.gif
(Fig. E7)
; some data seems wrong. Sla greater than .45m are filtered.
The other tracks are also checked
Spectra
- Spectrum at some locations characteristic of
different dynamics:
- North of the Vitiaz
strait:
Track 23, 4°S
(Fig. E8a); AvisoT023,4S
- South of the Vitiaz
strait:
Track
112, 7°S
(Fig. E8b); AvisoT112,7S
- Solomon Sea, east
part:
Track 10, 8°S
(Fig. E8c); AvisoT010,8S
- Milne Bay:
Track
188, 10°S
(Fig. E8d); AvisoT188,10S
- 10°S, middle west of
Solomon Sea Track 073, 10°S
(Fig. E8e); AvisoT073,10S
- 10°S, middle east of
Solomon Sea: Track
149, 10°S
(Fig. E8f); AvisoT149,10S
-
Makira:
Track 225, 10.5°S
(Fig. E8g); AvisoT225,10.5S
- East of Solomon Islands:
Track
239, 8°S
(Fig. E8h); AvisoT238,8S
- South of Solomon
Sea:
Track 086, 14°S
(Fig. E8i); AvisoT086,14S
- West of the Coral
Sea:
Track099, 11°S
(Fig. E8j); AvisoT099,11S
- Around the Solomon Sea
South of the Solomon Sea, at 14°S, interannual and annual
frequencies are dominant with a 5 cm magnitude. More to the west, at
11°S, there is no dominant variability. High interannual signal is
present east of the Solomon Island at 8°S with magnitude up to 11
cm. In addition, three peaks between 1 and 1.5 years (4-6 cm) exist (??). North of the Vitiaz strait, the
dominant frequency is dominant with a 9 cm magnitude. There is also a
clear annual signal (4 cm), and there are also some energy at 4-6
months.
- Inside the Solomon Sea
We check the signal at 10°S from the east to the west between
152°E-162°E. The interannual signal is dominant (up to 10 cm)
everywhere, except in the far west part of the section (down to 3 cm).
The annual signal is always present but with different amplitude (>4
cm). The amplitude is maximum (up to 9 cm) on the central east part of
the section. In the west part of the section, frequencies greater than
the annual cycle are distinguishable, particularly a 60 days period. In
the basin, there are more energy, at all frequencies, in the eastern
part than in the western part. In the East, we retrieve both the 10 cm
amplitude of the interannual signal, and the 9 cm amplitude of the
annual signal. The 60 day peak is also high with a 3 cm amplitude. In
the West, the annual cycle is dominant (6 cm), the interannual signal
is only of 4 cm. The 60 day period is also present.
- In conclusion, a 60 day period exists in the
Solomon Sea and not outside. The annual cycle is relatively high in the
Solomon Sea compared to the surrounding areas. In the Solomon Sea, the
interannual variability is particularly located on the central-east
part of the basin. Outside, the interannual signal is high everywhere
north of 10°S
Difference Between the east-West sides
of the Solomon Sea
For each tracks, the points inside the Solomon Sea are selected.
Another selection consists to distinguish the west and east parts of
the Solomon Sea based on the location of the tracks inside the basin,
and a criterion in variability (rms < or > 11 cm, respectively
West and East). The west part is the area where is the NGCC. This
separation between the East and the West is critical. Noted that the
area of the West part is smaller than the East one.
Both time serie are highly correlated (0.87): Fig.E9: West/east correlation
And present energy at the same frequencies, mostly at annual and
interannual period: Fig.E10:
West/east spectra
Logically, there are more energy in the West part than in the East. The
interannual signal is dominant in the East part (11 cm), whereas
the annual and interannual signals have same magnitude in the west part
(4 cm). A peak at 60 days is visible in the West, and a semi annual
signal is visible in the East. We retrieve the conclusion from the
spectra at individual locations.
We look at the correlation between the West and the East function of
latitude: Fig.E11: West/East
correlation
The correlation is high, around .9 for the annual and interannual
signals from 6°S to 9°S, and decrease to .7 at 10.8°S.
South of 10.8°S, we are out of the Solomon Sea, and there is a
break in the correlation. For the interannual signal, the correlation
increases to .99 whereas it decreases for the annual signal
In conclusion, the solomon sea seems to invole in phase between the
West and the East, particularly north of 9°S (north of Milne bay)
for period higher or equal to the annual signal. South of 9°S, the
West part is representative of Milne bay and there are just few points
available in this area, therefore may be correlations are less robust.
The break between 11°S and 10.5°S seems to delineate the south
boundary of the Solomon Sea.
Solomon Sea: East
side
Is the SLA correlated between the north and the south of the domain.
We look at the correlation at 7°S function of latitude: Fig.E12: Correlation function of
latitude.
The correlation is very close to 1 for the annual and interannual
signals. It begins to decrease south of 10°S, and north of 6°S
which are the limits of the domain. for the high frequency signal, the
correlation falls down to .8 in a distance of 100° km
(Decorrelation scale, rayon de rossby??)
Hovmuller: Fig. E13 a)full
signal
b)Annual c)Interannual
Sea level anomalies may each 30-35 cm. The amplitude of the annual
signal is of 10-15 cm. It is interesting to see that the maximum (in
march) and the minimum (in september) have a 2° extension in
latitude, and they are not centered at the same place, 8°S and
9°S respectively. It deseappears at 10.5°S (the south boundary
would be Guadalcalnal and not Makira. May be a significant flow exist
between the two islands), and it reappears more south with a 4 months
lag. The amplitude of the interannual signal is of 15-20 cm, the
positive anomalies being higher than the negative anomalies. There are
3 negative events: the 1993, and the 1997-1998 are the most
significant. The third one is present during the second half of 1994.
There are 3 positive events, Each one having a marked signature during
the first half of a year. The 2000- 2001 are the stongest events. There
is another one in 1996.
The anomalies in the full signal are clearly a combination of annual
and interannual signals.
.
Solomon Sea: West
side
Is the SLA correlated between the north and
the south of the domain. We look at the correlation at 7°S
function of latitude: Fig.E14:
Correlation function of latitude.
The correlation decreases slowly down to .9 at 10°S.
South of 10°S, the annual and interannual signals behave
differently. For the annual signal the correlation falls down quickly
wheras for interannual signal the correlation decreases significantly
south of 11°S and reachs .5 at 12°S. For the high frequency,
the correlation decreases firstly drasticaly in less than 1°,
before to decrease continuously with the latitude. Is the observed
decrease of correlation with latitude for the different signals due to
some propagation??
Hovmuller: Fig. E15 a)full signal b)Annual
c)Interannual
There is a break at 10°5°S in the SLA signal which
means that the SLA signature of the Solomon Sea is different from the
surroundings. The annual signal has a 5 cm amplitude extending between
9.5°S and 7.5°S. The anomalies are maximum in march and minimun
in September. There is a clear 4 months lag with the signal at 11°S
(maximum in December). The interannual signal is relatively small with
a maximum amplitude between 5-10 cm.
Relation between the Solomon Sea (east
side) and the variability at the east of the Solomon Islands
Sal-eastof_ft.gif
Sal-eastof_spe.gif
East of Solomon Islands:
Hovmuller: full
signal Annual
Interannual HF
Correlation
fonction of latitude
Relation between the Solomon Sea and
the variability at the south of the Solomon Islands
Because the south west corner of the Solomon Sea is located more to the
south than the south east corner, we look at the east side of the
Solomon Sea with the south of the Solomon Sea between 10.5°S et
11.5°S, and we look at the west side of the Solomon Sea with the
south of the Solomon Sea between 11.5°S and 13°S.
The two latitudinal bands don't have similar variability: temporal series of SLA south of the
Solomon Sea; corresponding
spectra
Relation between the east side of the Solomon sea and the
[10.5°S-11.5°S] band: temporal
series; spectra
Relation between the west side of the Solomon
sea and the [11.5°S-13°S] band: temporal
series; spectra
Relation between the west side of the Solomon
sea and the south of PNG: temporal
series; spectra
North of New Britain
Relation with the west side of the Solomon Sea: temporal
series; spectra
Relation with the ocean at the east of the Solomon Islands:
temporal
series; spectra
First summary:
What is the role of the Solomon Sea to exchange anomalies
between the subtropics and the western equatorial Pacific? What do we
learn from altimetry??
The Solomon Sea is a pathway for the western boundary current and this
boundary current connects both regions. Therefore the WBC may play a
significant role in ENSO variability. It is a question to know the
exact role of the WBC.
The solomon Sea is divided is two areas: a West side characteristic of
the WBC (SalW) and a East Side (SalE).
The Solomon Sea is located inside an area of high sea level anomalies.
It means that this high variability at the east of the Solomon Islands
(EastOf) is at the latitude of the Solomon Sea, and could be due to
barotropic instability (Qiu and Chen, 2004) at seasonnal time scale and
also to propagating Rossby waves.
A crucial question is to know the story of these anomalies once they
meet the Solomon Islands.
May be, there are some similitude with Hawaii.
Spectra of sla provide some insights:
- First,
SalE and EastOf have similar
spectra: SalE-eastof_spe.gif
Ce qui veut dire que les îles Salomons ne sont pas un obstacle
à la propagation du signal. Le signal qui arrive à la
côte est des iles Salomons va se propager le long des îles
et va pouvoir penetrer par les extremites nord (Solomon strait) et
sud (Guadalcanal-Makira). En effet, la région au sud de
Guadalcanal (SudOf,
10.5°S-11°S)
montre une variabilité interannuelle proche de
celle observée sur EastOf: SalE-Sudof_spe.gif
- Time series
SalE/EastOf: Climatology
; low
frequency; residual
Pour les 3 signaux (Clim, interannual, haute
fréquence), SalE et Eastof ont la même variabilité.
Si l'on regarde le signal haute fréquence, il est en retard
(1mois) dans SalE par rapport à EastOf
- Time series
SalE/SudOf : Climatology;
low frequency; residual
Si la variabilité climatologique est nettement differente entre
SalE et SudOf, la variabilité haute et basse fréquence
est relativement concordante.
- Second,
the variability north of New Britain (NorthOf) is more related to
EastOf than to SalW:
NorthOf-EastOf_spectra.gif;
NorthOf-SalW_spectra.gif
Ce qui voudrait dire que la variabilité au nord
ouest de la mer des Salomons est directement associée à
celle qui de trouve à l'est des iles Salomons et cette relation
ne se fait pas forcemment par la mer des Salomons. Le signal arrivant
de l'est va donc contourner la Nouvelle Irlande et se propager vers
l'Ouest.
- Time series
NorthOf/EastOf: Climatology;
low frequency; residual
Pour les 3 signaux (Clim, interannual, haute
fréquence), SalE et Eastof ont la même variabilité.
- Time
series NorthOf/SalW: Climatology;
low frequency; residual
NorthOf a clairement un signal semi annuel visible aussi dans EastOf
mais qui n'existe pas dans SalW. La variabilité interannuelle
est moins prononcée dans SalW que NorthOf mais les deux signaux
sont en phase.
- Third,
SalW exibits a lower variability than SalE that seems to be a
combination of Signals from SalE, SudOf (11°S-13°S), and from
the WBC south of PNG (SouthPNG)
SalW/SalE
spectra.gif
Time series SalW/SalE: Climatology; low frequency; residual
La différence des spectres
suggèrent que la partie ouest et est de la mer des Salomons ont
des régimes dynamiques différents. La
variabilité basse fréquence est en phase entre les deux
séries.
SalW/SouthPNG_spectra.gif
Time series SalW/SalE: Climatology;
low
frequency; residual
SouthPNG montre une faible variabilité interannuelle
ce qui suggère que la variabilité interannuelle
observée en mer des Salomon (SalW) ne provient pas de
façon majoritaire de cette région. La ressemblance des
spectres pour les fréquences à 60 jours et annuelle
indique bien que le WBC au sud de la PNG contourne l'extremité
sud est de la png et longe la cote est de la png. La variabilité
"climatologique" est similaire entre les deux séries avec un
retard de 2 mois pour SalW
SalW/SouthOf_spectra.gif
Time series SalW/SalE: Climatology;
low
frequency; residual
Les spectres sont similaires surtout pour les
fréquences annuelles et interannuelles. Les series
climatologiques SouthPNG, SouthOf, SalW sont trés ressemblantes
avec des déphasages. Il n'est pas facile de voir si SouthOf est
capable d'influencer SalW. On peut penser que si c'est le cas l'effet
de SouthOf se fait au détriment de SouthPNG
Il est clair que SalW est associé à SouthPNG et à
SalE, le role de Southof est moins évident. Cela voudrait dire
que SouthOf se propage vers l'ouest avant de rejoindre SouthPNG.
TOP
F. EKE
Use of gridded SLA from AVISO
Qiu and Chen (2004) have focussed on the Seasonal cycle of the EKE in
the SECC box (150°E-170°W; 15°S-5°S).
First, we do similar plots than in their paper.
We retrieve the results from the figures 4a and 5a of Chen and Qiu
(2004)
- F.1: EKE averaged over the SECC
box.gif
- F.2: EKE
as a function of calendar month in the SECC box.gif
But when looking at the spatial distribution of the mean EKE, we see
strong heterogeneous areas. High EKE is cencentrated in the Solomon Sea:
- Fig.3: Spatial
distribution of mean eke.gif
The SECC box is divided in two parts: 150°E-160°E and
160°E-170°W
- Fig. 4: EKE
averaged over the differents boxes.gif
Mean EKE in the box included the Solomon Sea: 341 cm2/s2 against 174
cm2/s2 for the other part. Results from Qiu and Chen (2004) are
relative to the area at the east of the Solomon Sea.
EKE in the Solomon Sea:
- Fig. 5: EKE
averaged in the Solomon Sea.gif; 150°E-155°E:
9°S-5°S; Mean EKE: 679 cm2/s2
- Fig.6: EKE
as a function of calendar month in the Solomon box compared to the east
part.gif
Contribution of the U component (y
derivative):
Fig.7: EKE averaged in the Solomon
Sea.gif
Fig.8: EKE
as a function of calendar month in the Solomon box
Spatial Distribution of mean EKE: U2; V2
- EKE has a dominant interannual signal
- Fig.9: Low frequency
- Fig. 10: High frequency
TOP
G. EOF
Analysis
Use of the gridded SLA from AVISO: 1992-2004
EOF analysis are performed both on a climatological series and on a
series where the climatological signal has been removed.
First, we consider the domaine 142°E-170°E; 13°S-12°S
- Climatological series: Mode 1; Mode 2; Mode 3; Mode 4; Mode 5
The mode 1 explains 74% of the variance; and the first 3 modes 92%
- "Inter-intraannual" series: Mode 1;
Mode 2; Mode 3; Mode 4; Mode 5;
Mode 6
The mode 1 explains 71% of the variance
EOF performed on the Solomon Sea only:
- raw data: Mode 1 The
mode 1 explains 81% of the variance (Variance=9.8E-3 m2)
-
Climatological series: Mode 1;
Mode 2; Mode 3
The mode 1 explains 88% of the variance
- "Inter-intraannual" series: Mode
1;
Mode 2; Mode 3
The mode 1 explains 81% of the variance
TOP
H.
Harmonic Analysis (Annual cycle)
- Amplitude
and Phase
- Velocity
anomalies in March and September
- Amplitude
and phase curl tau
TOP
I.
Climatologic year
- Hovmuller at different latitute: msla_hov.html
TOP
J. Transport
L'approche de Ridgway (1993) est utilisée ici pour
estimer la variabilité des transports entrant et sortant de la
mer des Salomon à partir de l'altimétrie. La SLA est
censée représenter la variabilité des 150
premières mètres sus la surface. On utilise les sorties
du modèle ORCA05 pour confirmer cette approche.
1. Rms de SLA sur le
domaine: Modèle; Altimétrie
Le transport est estimé soit par différence de sla
aux extrémités de la section en utilsant
l'altimétrie ou la SSH du modèle, soit directement avec
le
courant méridien du modèle.
2. Flux entrant en mer des
Salomons (entre la pointe sud est de la PNG et Makira)
a. Courant méridien du modèle le long de la section: Mean; RMS
b. Spectres des transports
c. transports fonction du temps: Non
filtrés, basse
fréquence; climatologiques
3. Flux sortant par Vitiaz (trace 99)
a. Courant méridien du modèle le long de la section: Mean; RMS
b. Spectres des transports
c. transports fonction du temps: Non
filtrés, basse
fréquence; climatologiques
4. Flux sortant par Solomon strait
a. Courant méridien du modèle le long de la section: Mean; RMS
b. Spectres des transports
c. transports fonction du temps: Non
filtrés (0-150) (0-bottom),
basse
fréquence; climatologiques
5. Flux sortant à travers la section allant de Makira
l'ouest du détroit des Salomon
a. Spectres des transports
b. transports fonction du temps: Non
filtrés (0-150) (HF
filtrée), basse
fréquence; climatologiques
6. Flux
sortant à travers la section allant du sud est de la PNG
à l'est de Vitiaz
a. Spectres des transports
b. transports fonction du temps: Non
filtrés (0-150), basse
fréquence; climatologiques
7. Comparaison du flux entrant avec la somme des flux sortants
Altimetrie;
Modèle
TOP
K. Low Frequency
Les données sont filtrées à 7 mois (spz41,
dt=10 jours)
Les sea level sont soit des données
along track, soit des données AVISO grillées
Le signal EKE est issu de AVISO grillé
1. Along track sea level anomalies averaged over the
Solomon box
a. Sla/SOI.gif
b: Sla/EKE
2. SLA Aviso averaged over the Solomon box:
a. SLA calculé partir d'un masque sur la mer des Solomon: Slab/SOI.gif
3. L'activité
turbulente (EKE) sur la mer des
Salomon est liée à la variabilité interannuelle de
type ENSO (représentée par la SOI):
a. EKE/SOI.gif
b. EKE calculé sur la mer des Salomon: EKEb/SOI.gif
4.Relation entre l'activité turbulente (EKE)
et la variabilité des transports mesurée dans les
détroits.
Inflow: ce qui rentre par le sud et l'est
Outflow: ce qui sort par Vitiaz
et Solomon straits
A. transports calculés
à partir des données along track.
1. Correspondance entre Inflow
et Outflow: In/out flow.gif
2.
Correspondance entre EKE et Outflow (variables normalisées): EKE/outflow.gif
3. transports
at Vitiaz and Solomon strait: Vitiaz/Solomon.gif
B. transports calculés à
partir de Aviso (résultats
similaires avec le produit along track):
1. Correspondance entre Inflow
et Outflow: In/out flow
Aviso.gif
2.
Correspondance entre EKE et Outflow (variables normalisées): EKE/outflow.gif
5. Relation avec le Warm Water Volume de Meinen
(ouest)
1. en terme
de niveau de la mer sur les Salomon: SLA/wwva.gif
2. en terme
de transport à travers Vitiaz et Solomon strait: Outflow/d(wwv)/dt.gif
6. EOFs
1.
SLA Pacifique (14s-14n)/SOI: Mode1/WWV West.gif; Mode2/WWV Pac.gif
2. SLA Pacifique Sud
(14s-5s)/SOI: Mode1/WWV
West.gif; Mode2/WWV
Pac.gif
3. SLA Salomon/SOI/WWVaWest: Mode
1.gif;
Mode 2.gif
7. Wind Curl from ERS
1. Pacifique
(14s-14n)/SOI: Mode1/WWV
Pac.gif; Mode2/WWV
West.gif
2. Pacifique
Sud Ouest/SLA_Sal/SOI: Evolution
temporelle.gif
3. Pacifique
sud Ouest/Sv: Temporal
Evolution.gif
8. TAO
1. 5S156E,
Heat Content/SLA_Sal/SOI: Temporal
evolution.gif
2. 5S156E/Sv: Temporal
Evolution.gif
9. SST
1. Anomalies over the
Solomon Sea/SLA_Sal/SOI: Temporal
Evolution.gif
10. Relation between SLA and transports in the
Solomon Sea: Temporal
Evolution,.gif
TOP
L. Ideas for a discussion
on
Low frequency variability in the Solomon Sea
On the specific role of the Solomon sea to fill/empty the equatorial
band in the western Pacific
The
importance of the South West Pacific Ocean, and of the Solomon Sea, to
connect the subtropical region to the Western equatotrial region is
largely discussed in the SPICE programm.
This study is based on altimetric data and focusses on the
interannual
variability in the Solomon Sea. The Sla are analyzed with regard to the
WWV anomalies provided by C. Meinen. Results are supported by model
analysis. This study emphasizes that most of the water necessary to
balance the discharge/recharge of the equatorial Pacific transit
through the Solomon Sea. They point out the importance of the South
hemisphere and of the western boundary current in ENSO dynamics.
The results presented below is a synthesis of the work
Data are filtered with a triangle filter and a 7-months cutoff
1. Maxima of high variability are located in the western Pacific
ocean of each hemisphere around 8°. The western end of the ocean is
characterized by the recirculation of zonal currents crossing the
Pacific basin into western boundary currents. In the South hemisphere, the
high SLA variability between 5S-10S and 140E-170
encompasses the Solomon Sea. We will try to characterize the specific
role of the Solomon Sea at ENSO time scale.
FigA: RMS LF 92-07.gif
2. An EOF analysis over the tropical Pacific (14S-14N) shows two
dominant modes explaining respectively 54%
et 23% of the variance. These two modes are discussed a lot in the
literature. The mode 1 represents a tilting mode and the mode 2 a
discharge and recharge of WWV. Mode 1 is in phase with the SOI whereas
mode 2 is negatively correlated with the SOI. (Fig.B)
Fig.B: a) Mode1/WWV
West.gif; b) Mode2/WWV
Pac.gif
3. Altimetry is a good way to track changes in WWV (already shown by
Meinen, 2005). It is worth noting that the WWVa for the western region
lags the mode 1 in SLA (and the SOI) by 5-7 months, and the WWVa for
the equatorial band is in phase with the mode 2 in SLA. (Fig. B).
The Mode 1 is correlated with the western WWV by about
0.58, and leads the western WWV by about 5 months with a 0.83
correlation.
4. A zoom in the Solomon shows that the first EOF mode explains up to
95% of the interannual variance. In a statistical point
of view, the Solomon Sea exhibits a relatively simple variability. This
mode is highly correlated to the SOI and leads the western WWVa by few
months (Fig.C). The temporal function of this mode is very closed to
that one of the mode 1 over the tropical Pacific (Fig. Cb), and their
spatial structure over the Solomon Sea are similar with maxima of
varialility along the western coast of the Solomon Islands. The
correlation between the two EOF temporal function is
high 0.82. The Solomon Mode is correlated with the western WWV by about
0.87, and 0.89 considering a two months lag.
Fig.Ca: Mode_Sal 1.gif
Fig.Cb: Mode1: Sal/Pac.gif
5. For the spatial EOF 1 mode, looking
at zonal sections in the latitudinal range spanning the Solomon sea
from 5S to 10S, we clearly see that inside the Solomon Sea, the slope
of SLA variability is inverse of the slope outside the Solomon Sea
(Fig.D). The crosses in Fig.Db delineate the location of the Solomon
Islands. It means that the corresponding meridional flow is in phase
opposition inside and outside the Solomon Sea. When the interior ocean
discharges (recharges), it recharges (discharges) through the Solomon
Sea. Looking at a similar figure for the northern hemisphere, we don't
see a so strong signature. This result argues for the predominance of
the Solomon Sea to fill or deplete the Western Equatorial Pacific.
Fig.D: a) EOF1 South.gif; b) EOF1 South West.gif (the
Solomon Islands are located by crosses); c) EOF1 North.gif
6. To illustrate the discussion above, the velocity field corresponding
to the spatial EOF1 mode is plotted (Fig.E). When there is a meridional
divergence in the equatorial band, a westward surface geostrophic flow south
of 10°S enters the Solomon Sea, and goes north. It
bifurcates at the New Britain coast before to escape throuh Vitiaz and
Solomon straits. Just a smal part of this westward flow continues
to the Australian coast decreasing the NQC. It seems that a part of the
interannual variability of the Australian WBCs is in fact controlled by
the SEC inflow. Similar conclusion have been done By Kessler and
Gourdeau (2007) when looking at the annual cycle
Fig.E: EOF1_vector.gif
7. It is an uneasy task to physically interpret the statistical EOF
modes. Because there is only one dominant mode in the Solomon Sea,
there is no particular interest any more to use EOFs to analyse
interannual varaibility inside the Solomon Sea. We retrieve the same
relations between the western WWVa, the SOI and the EOF mode than using
directly the high-pass filtered SLA time series. Compare Fig.F with
Fig.C
Fig.F: Solomon Sea: relation between
SLA, SOI and western WWVA.gif
8. We use a numerical simulation: the
one used in
Kessler and Gourdeau (2007) to check the interannual
variability of the model with regard to the
results above. We performed similar EOF analysis (Fig.Ga), and in the
Solomon Sea we look at the ssh variability (Fig.Gb) and the relations
between the SSH signal averaged in the Salomon Sea, the SOI and the
western WWV (Fig.Gc). Model analysis are very close to the altimetric
analysis giving confidence both in the model and in the data analysis.
ORCA05:
Fig.Ga: EOF1.gif; EOF2.gif
Fig.Gb: RMS.gif
Fig.Gc: Relation between SSHa averaged
over the Solomon Sea, the SOI and the western WWVa.gif
9. Once the relations between the SLA in the Solomon Sea and the
SOI
and the Western WWVA are established, we try to provide an estimation
of the transports crossing the Solomon Sea. We use the same idea
already developped in Ridgway et al (1993) with tide gauges. The
geostrophic mass transport is estimated from the expression gdHD/f
where dH is the sea level difference between each side of the straits,
and D=150 is representaive of the depth of the upper thermocline. It is
a crude estimation of the transport because D is fixed and transports
at deeper levels may exist, particularly in the WBC. These estimations
are assessed with the use of the numerical simulation.
10. Transports are estimated at the south entrance of the Solomon
Sea between the south east extremity of the PNG coast and the southern
islands of the Solomon Islands (y=10.5°S) for the inflow and at the
Vitiaz
and Solomon straits for the outflow (y=-6.41°S, and x=151°E is
the longitude which divide th eoutflow into the straits). We need only
two SLA measurements
(one at each extremity of the sections) to estimate the transports.
We check that the inflow balances the outflow
(Fig.H). The inflow is defined by the addition of the flow at the
souterhn entrance of the Solomon Sea and of the flow crossing the
Solomon Islands. except some differences existing at the peaks of
transports anomalies, both curves are greatly similar. Transports
anomalies may reach 10 Sv during the 1997-1998 ENSO event
Fig.H: Inflow/outflow transports from Aviso.gif
11. The model is used to verify the estimation from altimetrie
(old plots). We remember that the bathymetry of the model is not very
good in this area, very poor representation of the Solomon Islands.
transports from the model are estimated in differents ways: by using
the same method used for altimetry (using modeled SSH), ans directly by
using the velocity fields (0/150m and 0/bottom transports are
estimated) (Fig.I)
- Inflow at
the south entrance: Fig.Ia Comparison Model/altimetry ;
Spectra
-
Outflow at Vitiaz straits: Fig.Ib Comparison Model/altimetry
; Spectra
- Outflow at
Solomon straits: Fig.Ic
comparison
Model/altimetry ; Spectra
Altimetry and model provide similar estimation with similar
amplitude and a good phasing. Therefore the crude astimation of
transports from altimetry is not so bad. Discrepancies exist for the
Solomon strait. It is not surprizing because of an unrealistic
bathymetry in the model.
12. The model has the advantage to provide the vertical structure of
the currents (Fig.J)
-
Inflow at the south entrance: Fig.Ja Mean; RMS
-
Outflow at Vitiaz straits: Fig.Jb Mean; RMS
-
Outflow at Solomon straits: Fig.Jc Mean; RMS
13. Relation between the flux in the Solomon Sea (through Vitiaz and
Solomon straits) and the flux from the recharge/discharge of the
Western WWVa (dWWVa/dt) (Fig.K). Both time series are
out of phase and their magnitude are similar.
Fig.K
Outflow/d(wwv)/dt.gif
It is the most important plot!
14. We can separate the contribution of Vitiaz and Soloon straits (Fig.
L.)
Fig.L: Vitiaz/Solomon straits.gif
Reste à developper tout ceci avec la biblio qui va bien, le
message étant 1. que la mer des Salomon est un endroit majeur
pour "équilibrer" les recharges/décharges qui ont lieu en
plein océan. 2. que l'altimetrie avec juste quelques points de
part et d'autres des détroits donne des informations assez
fiables sur la variabilité basse fréquence" de la
circulaiton à travers la mer des Salomon.
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