The Indonesian Seas & its throughflow
Why & How to observe
Arnold L. Gordon
Division of Ocean & Climate Physics
Lamont-Doherty Earth Observatory,
Columbia University
• Attributes of the Indonesian seas to be considered in a long-term observational strategy;
• Observational strategies, that they can and can’t do;
But first: It is not just the Indonesian throughflow [ITF] that is important to the regional and largerscale climate- the processes within the Indonesian seas alter the profile [mass, temperature, salinity]
of interocean stream, coupled to the local sea-air fluxes and mixing environment.
The Oceanography Society magazine, Dec 05: The Indonesian Seas
Gordon- OOPC-11, May 16-20, 2006
The Indonesian Throughflow [ITF] sees
This:
Heat/freshwater
[buoyancy]
Pacific
Indian
Not this:
Pacific
Indian
upwelling
[tidal] mixing
Pacific Water is modified within the Indonesian seas;
“Stuff Happens” in the Indonesian seas, it is not a passive pass-thru.
The Indonesian seas: It’s a big
place, a complex array of seas
and wide range of depths
depths; it’s where ENSO
meets the Asian Monsoon
The ITF is a product of ocean scale wind stress
(Godfrey, 1996) and the moist Pacific climate.
But the Indonesian seas add buoyancy and
regional tidal induced mixing alters the
stratification
N.Pacific
Secondary ITF portals
1350-m
Large Freshwater
flux.
Primary ITF portals
2800-m
Heat/FW [buoyancy] injection fm the atm.
580-m
S.Pacific
1940-m
Complex morphology [ITF pathways]
~1000-m
680-m
Tidal mixing; monsoonal reversals
~1200-m
280-m
1300-1500-m
Indonesian
Blend
~zero
• Large-scale observation based studies (including inverse solutions) reveal significant Pacific export
of mass, heat and freshwater into the Indian Ocean (Piola and Gordon, 1984, 1986; Toole and
Raymer, 1985; Wijffels et al., 1992; Toole and Warren, 1993; MacDonald, 1993; MacDonald and
Wunsch, 1996; Ganachaud et al., 2000; Ganachaud and Wunsch, 2000). Uncertainty in the size of the
ITF is the dominant source of error in analyses of the basin-wide budgets of heat and freshwater for
the Pacific (Wijffels et al., 2001) and Indian Oceans (Robbins and Toole, 1997).
• Oceanic heat and freshwater fluxes into the Indian Ocean - at the expense of the Pacific - affect
atmosphere-ocean coupling with potential impacts on the ENSO and monsoon phenomena (Webster
et al. 1998).
• Models reveal dependence of Pacific and Indian Ocean SST and upper layer heat storage on the
throughflow (Hirst and Godfrey, 1993; Verschell et al., 1995; Murtugudde et al., 1998). The Indian
and Pacific Oceans would be very different if the ITF were zero (MacDonald, 1993; Schneider, 1998;
Maes , 1998; Wajsowicz and Schneider, 2001; Wajsowicz, 2001; Lee et al., 2002). The ΔSST
[ITF/NoITF] patterns are model dependent.
It is often said that the ITF warms the Indian Ocean and cools the Pacific: tropical deep precipitation is thus
moved west by this effect in coupled ocean/atm. models – this affects the atmospheric circulation globally.
Schneider, 1998.
The ~10 Sv ITF must affect the Pacific
and Indian Ocean thermohaline
stratification and surface layer. The ITF
peals off Mindanao Current otherwise
destine for the Pacific’s NECC, hence
disturbs the Pacific subtropical/tropical
connectivity.
But the Pacific is immense, hardly
noticing a paltry ~10 SV. It’s the littleolde monsoonal Indian Ocean gets hit
harder, as its SEC is boosted by maybe
30% with a jet of cool/fresher Pacific
thermocline to intermediate depth water.
We often see reported ITF heat flux into the Indian Ocean, 0.5 to 1.0 PW. These are based on relating the ITF
temperature and transport to a reference temperature: the temperature of the compensatory transport out of the
Indian Ocean [~10 SV cools from ~15°C to 3.75°C, or more often relative to 0°C].But what would the Indian
Ocean look like if it were not for the ITF? A simple questions:
• Does the ITF warm or cool the Indian Ocean? it cools the thermocline, if no ITF, the Indian O would be
warmer. The ITF flushes out the tropical waters of the Indian Ocean to the Agulhas Current, it leaves it entirely
to the Indian Ocean meridioanl overturning circulkation to cope with the atmosphere forcing.
10-12 yrs
Spreading of the Indonesian Throughflow in the Indian Ocean Q. Song, A. L. Gordon and M. Visbeck JPO 2004
Upon reaching the western boundary within the South Equatorial Current (SEC), the trajectories of the ITF tracers within the thermocline
exhibit bifurcation: at the western boundary about 38%±5% thermocline ITF water flows southward to join the Agulhas Current, consequently
exiting the Indian Ocean, and the rest, about 62%±5%, flows northward to the north of SEC. In boreal summer, ITF water penetrates into the
Northern Hemisphere within the Somali Current. The primary spreading pathway of the thermocline ITF water north of SEC is upwelling to the
surface layer with subsequent advection southward within the surface Ekman layer toward the southern Indian Ocean subtropics. All the ITF
water eventually exits the Indian Ocean along the western boundary within the Mozambique Channel and the east coast of Madagascar and,
farther south, the Agulhas Current region.
The advective spreading time scales, represented by the elapsed time corresponding to the maximum of transit time PDF, show that in the upper
thermocline the ITF crosses the Indian Ocean, from the Makassar Strait to the east coast of the African continent, on a time scale of about 10 yr
and reaches the Arabian Sea on a time scale of over 20 yr.
• ITF cools and freshens the Indian Ocean thermocline [on isopycnals] relative to the ambient thermocline.
• ~10 Sv of ITF water flushes the Indian Ocean thermocline waters to the south by boosting transport of the
Agulhas Current [by ~15%], increasing southward ocean heat flux across 20-30°S over the no-ITF condition,
thus altering the meridional overturning of the Indian Ocean [Pacific too]
Temperature on sigma-0 = 25.0, upper thermocline
Wa
rm
ITF
cool
po
ol
Salinity on sigma-0 = 25.0, upper thermocline
freshwater
input
Low salinity
Agulhas with ITF add-on
N. Pacific water peeled-off
to the Indian O, rather
than feed the Pacific warm
pool
Indonesian
Mix-Master
S. Pacific, deeper
feed to ITF
Indonesian Throughflow must exit the Indian Ocean within the Agulhas Current, the ITF
follows a torturous route to the Agulhas Current [Song, Q., A. Gordon, and M. Visbeck (2004),
J Phys Oceanog]
A.L. Gordon, 13 July 05
The ITF cools the tropical Indian
Ocean, and flushes Indian Ocean
heat into the Agulhas Current.
Tropical heat
No northern
Agulhas
Return
Eq.
Agulhas + ~10 Sv
“cool”
…ITF
Northern Indian O polar cooler
upwelling
Monsoonal regime
anomalous
deep thermocline
Deep/Bottom overturning
A.L. Gordon, 13 July 05
X
A “thought” coupled model: What if no ITF? Diminished flushing
of tropical water to south may allow for: 1. Reduced heat flux across 30°S [4°C ≈
10Sv]; 2. deeper monsoon regime thermocline; 3. hotter SST in tropical Indian
[>evaporation:stronger monsoon?]
Hotter SST
Agulhas
Return
Eq.
Reduced southward Qf
No
ITF
Deepened
isotherms
reduced upwelling
of cool ITF water
Deep/Bottom overturning
A.L. Gordon, 13 July 05, Bali
SST Summer
[Jun-Aug]
SST Winter
[dec-feb]
upwelling
Chl-a Summer
downwelling
Chl-a Winter
[dec-feb]
[Jun-Aug]
High chl-a
low chl-a
Top: Satellite derived fields of sea surface temperature from Aqua-MODIS [northern summer: left; northern winter:
right] Bottom: Sea Surface Salinity [archive hydro stations]
Barotropic M2
tidal speeds
Fm Ray et al TOS
Dec’05 issue
Non-linear scale
NP s-max
NP s-min
Maybe?
from Banda Sea
Western
August 1993 Salinity
Path
Eastern Path
South Pacific lower thermocline
water enters Seram from Halmahera
Upper Thermocline: Attenuation of the smax [Makassar to Timor] with reasonable
residence time implies a thermocline Kz of 1
cgs.
Kz = 1 cgs coupled with intense thermocline
yields vertical heat flux of 40 W/m2. This
balances the sea-air heat flux, so that the
atmosphere buoyancy input to the Indonesian
seas penetrates into subsurface, with impact
on Indian Ocean stratification.
Additionally: fortnightly [tidal] variability Δ
Lower
thermocline:
1°C
in SST
provide high freq signal on sea-air
heat flux
North Pacific subtropical salinity
maximum
Upper thermocline
Lower thermocline
South Pacific subtropical salinity
maximum
North Pacific
Intermediate Water
Ffield and Gordon, 1992,96
vertical mixing?
Upper thermocline
lower thermocline
NPIW
SPtherm
Isopycnal mixing?
Salinity @ Lower thermocline
Shallower thermocline during El Niño exposes thermocline to wind induced mixing;
also reduced ITF during El Niño…La Niña flushed out the El Niño signal.
Eastern passages:
Deep Banda Sea overflow [Lifamatola Sill, black line]
Also: ENSO variability [N.Pac thermocline water via
eastern seas during 1996 La Niña, dashed line,] [for
brevity I removed this section]
Banda Sea
southward
~0
~350-m
1 kt
Downslope, overflow into
Banda Sea, ~1 to 2 Sv
~1750-m sill = 1950-m
From: Hendrik M. van Aken
[INSTANT PI], The Netherlands
~0.25 m/s overflow into the
Banda Sea.
Fortnightly tidal beat;
0.25 m/s for a slab of 300 m
yields 1.2 Sv across the ~15
km Lifamatola channel
Water masses suggest this ITF pattern within the thermocline
?
La Niña
extra
Lifamatola deep overflow
none
ITF: ~10 Sv [somewhere in range 8-14 Sv, with
interannual modulation by ENSO] is a pretty good
‘ball-park figure*
Above Makassar 680-m sill depth: The transport of
Timor Passage and Ombai Strait [Molcard], sea surface
and 680 m is between 5.6 to 9.0 Sv, with the Lombok
Strait transport ~ 1.7 Sv [Murray], total 0-680 m transport
is 7.3 to 10.7 Sv. which is not significantly different than
the Makassar Strait transport of ~8 to 9 Sv [~ 1 or 2 Sv
from eastern route?]
Below Makassar 680-m sill depth: The total ITF export
below 680-m into the Indian Ocean is 1.8 to 2.3 Sv. The
Lifamatola Passage overflow [VanAken] of 1.5 Sv can
explain roughly all but 0.3 to 0.8 Sv of the >680 m export
to the Indian Ocean. Noting the short time span of the
Lifamatola moorings, an additional 0.5 Sv of Lifamatola Passage
overflow as required to close the deep throughflow budget, is
reasonable.
Caution: All of the measurements were made at different times
and the assumptions of a steady state system does not necessarily
apply in this case, but the near balance is instructive.
0-680 m
INFLOW
thermocline
Makassar [8-9 sv]
Eastern route [1 sv?]
Relative steady inflow
Lif ~1.5
Episodic overflow
Sill @680-m
ITF segmented into 3 streams;
Strong intraseasonal activity
Regional ITF transports
EXPORT [timor; ombai; lombok]
7.3 to 10.7 sv [average 9 sv]
__________________680-m _________Makassar Sill_______________
> 680 m
Lifamatola [1.5 sv]
Deep water
1.8 to 2.3 sv [average 2.1 sv]
January to March 1985, the estimated overflow transport
through the Lifamatola Passage
deeper than 1500 m is 1.5 Sv (Van Aken et al. 1988)
March 1992 to April 1993 the average transport within the Timor Passage (south
of Timor) measured during the JADE French-Indonesian program, from the 0 to
1250 m was 3.4 to 5.3 Sv (Molcard et al. 1996).
Arlindo Makassar moorings dec 96-july 98
7-11 Sv (Gordon et al 1999)
4.5±1.5 Sv from 120 -1050 m,
Aug 1989 - Sept 1990(JADE;
Green
= JADE [Timor]
Blue
= CTD
Molcard et al. 1994)
+SOI = Higher ITF transport
Red
Red= =moorings
Arlindo [Makassar]
La Niña
La Niña
La Niña
INSTANT INSTANT
DEC03-DEC06
DEC03-DEC06
Mak moorings
1985
El Niño
El Niño
Lombok Strait transport of 1.7 Sv
measured from Jan 1985 to Jan 1986
(Murray and Arief, 1988)
-SOI = Lower ITF transport
El Niño
November 1995 to November 1996 in Ombai Strait,
North of Timor, yielded a transport of 4 to 6 Sv (JADE; Molcard et
al 2001).
ITF pathways within the thermocline; water masses indicate that Makassar
Strait is the primary ITF pathway
Lifamatola overflow
MAK-1
MAK-2
Sill @680-m
The great 97/98 El Niño
Labani Channel Mak 1 and 2
NW Monsoon
SE Monsoon
Makassar transport for
1997 is ~ 8.0 Sv;
uncertainty ~ 2 Sv.
A cool ITF: Makassar ITF Thermocline intensified
Transport weighted temperature ~15°C
Indian O Kelvin Wave
See: Gordon et al, 1999; Susanto &
Gordon, 2005
NW Monsoon
Lots of Intraseasonal
<90 day, variability
The great 97/98 El Niño
Lesser transport (4.6Sv)
is observed during the
peak of 1997/98 El Niño
from September 1997 to
February 1998 compare
to the rest of the
mooring record.
Surface layer data gap [July 97=June 98] required creative solutions. The 7 months of surface record [Dec 96 - June
97] shows a remarkable correlation with zonal wind in the Java Sea [Gordon et al. 2003] The ADCP time series
extrapolation based on regression analysis to the 200-m current meter data and the Java Wind was used to fill the
surface layer data gap.
WHY IS THE ITF SO COOL?
[~15°C transport weighted]
May-June
~june 27
v profile
• The cool transport-weighted temperature is the
consequence of restricted contribution from the
warm surface layer. Why?
~march 1
v profile
Jan-Feb
transport Sv
in 50 m slabs
• During the northern winter monsoon buoyant,
low salinity surface water [upper 50 m] from the
Java Sea is ‘blown’ into the southern Makassar
Strait. This induces a northward pressure
gradient within the surface layer of Makassar
Strait, counteracting the seasonal southward
winds.
• During the summer monsoon, reversal of Java
Sea winds force more saline surface water from
the Banda Sea into the southern Makassar
Strait, eliminating the northward pressure
gradient, though northward summer winds over
Makassar act to constrain the surface
throughflow.
Gordon, A.L., R.D. Susanto, and K. Vranes (2003) Cool Indonesian
Throughflow as a consequence of restricted surface layer flow. Nature,
425, 824-828.
Significance of the vertical profile of the Indonesian Throughflow
transport to the Indian Ocean. Q. Song and A. L. Gordon GRL 2005
Using an ocean general circulation model, we find that the vertical profile of the Indonesian Throughflow (ITF)
transport is important in regulating the stratification and surface heat fluxes of the Indian Ocean. With the same total ITF
transport, a thermocline-intensified ITF, relative to a surface-intensified ITF, not only cools the surface layer of
the Indian Ocean while warming the Indian Ocean below the thermocline, but also induces negative temperature anomalies at the
sea surface throughout the Indian basin. As a consequence of this surface effect the net heat gain of the Indian Ocean is
increased. The results suggest that it is necessary to properly represent the vertical profile of ITF transport within ocean and
climate numerical models.
X
ITF reduces the net heat gain by ocean. This is partly off set
if the ITF were thermocline intensified. The net heat gain of
the Indian Ocean from the atmosphere in ITF10TH is 0.02
PW more than that in ITF10.
SST
SSS
Wind arrows
shown
Low SSS
Java Sea ~<50 m
deep
Higher SSS
Surface σ
Buoyancy gradient
buoyant
Not so
buoyant
So…The ITF heat and freshwater flux depends on
the regional freshwater input and its distribution.
All sorts of couple ocean/climate feedbacks
implied.
Changes in the freshwater budget of the western Indonesian seas
and Southeast Asian monsoon winds would be expected to alter the
intensity of the ‘freshwater plug’. Greater amounts of freshwater
expelled from the Java Sea into the southern Indonesian seas would
induce a colder ITF (lesser amounts would lead to a warmer ITF). As
the regional precipitation changes with the phase of ENSO, Asian
monsoon and at longer temporal scales, the ITF temperature
may adjust accordingly. A strong ‘freshwater plug’ would
reduce transfer of the western Pacific’s warm pool into the
Indian Ocean, with potential feedback to ENSO. The Indian
Ocean surface layer would receive less Pacific heat, affecting its
surface temperature and altering the pattern of heat and water
vapour exchange with the atmosphere, Asian monsoon and the Indian Ocean dipole.
Significance of the vertical profile of the Indonesian Throughflow
transport to the Indian Ocean
Q. Song and A. L. Gordon GRL, 2005
Using an ocean general circulation model, we find that
the vertical profile of the Indonesian Throughflow (ITF)
transport is important in regulating the stratification and
surface heat fluxes of the Indian Ocean. With the same total
ITF transport, a thermocline-intensified ITF, relative to a
surface-intensified ITF, not only cools the surface layer of
the Indian Ocean while warming the Indian Ocean below
the thermocline, but also induces negative temperature
anomalies at the sea surface throughout the Indian basin.
As a consequence of this surface effect the net heat gain
of the Indian Ocean is increased. The results suggest that
it is necessary to properly represent the vertical profile
of ITF transport within ocean and climate numerical
models
Kelvin
Wave
Total 1 to 15 Sv, mean ~8 Sv
15 Sv
Mean: 8.1 Sv
1st Baroclinic
El Nino low
1 Sv
Nino3
2nd Baroclinic,
Susanto & Gordon, JGR, jan 2005
The Banda Sea:
Inhale-Exhale effect
The Makassar path provides most of the total ITF, maybe >80%. But the
Makassar water, which is Pacific water, is altered by sea-air flux of heat and
freshwater, by mixing [mostly tidal], ekman upwelling. What finally emerges
into the Indian is not just Pacific water, it is now Indonesian water.
Much of the conversion takes place
in the Banda Sea where
“inhale/exhale” due to seasonally
reversing Ekman convergence
induce thermocline heaving of ~40
m [Gordon & Susanto’01]
Inflow
Outflow
Inflow/outflow not in
phase due to Banda
seasonal storage
deep thermocline
warm SST
Upwelling
Warmer
Thermocline depth
seasonal oscillating = 40-m in La Niña
Cold SST
Downwelling
Colder in
El Ninõ
Shallow thermocline
Banda Sea inhales and exhales: Upwelling/downwelling cycle within the Banda Sea induces a 40 m seasonal
oscillation of the thermocline depth [0.33 m in sea level] instilling a seasonal divergence / convergence pattern of
surface water volume and affecting the phase relationship between the Makassar ITF and the Sunda passage
export.
Maximum divergence ~2 Sv is attained during the transitional monsoon months, of
October/November and April/May.
During the El Niño growth period of 1997 the surface layer is divergent, but in 1998 when the El
Niño was on the wane, the average rate of change is convergent. Surface layer divergence attains
values as high as 4 Sv.
Makassar transport
100 day lag
Vranes and Gordon submitted to GRL
South of Java transport
The geostrophic transport between
0-400 meter time series constructed
from XBT data from December
1996 to July 1998 with a 100 day
lag correlates at r = 0.82 with the
Makassar Strait 0-400 meter
transport as measured by current
meter moorings for that time
interval, providing confidence in
the utility of repeat XBT data to
detect ITF variability over at least
two decades. Mean speed from
Makassar to XBT line is 0.5 m/s.
Vranes and Gordon submitted to GRL
Kelvin W
International Nusantara Stratification and Transport (INSTANT), is a multi-national program
to measure the velocity, temperature and salinity of the Indonesian throughflow with
simultaneous mooring deployments in the inflow and outflow passages, the over a 3-year period.
INSTANT PIs:
USA: Gordon, Susanto,
Sprintall, Ffield
The Netherlands: Van Aken
Australia: Wijffels
France: Molcard
Indonesia: Indra Jaya,
Irsan Brodjonegoro
Schematic of Indonesian Throughflow pathways (red numbers represent previously
determined transport in Sv (106 m3/sec); the smaller black numbers refer to the literature
source). Inserts A-D show positions of INSTANT moorings. Insert A: 2 United States
Makassar Strait Inflow moorings (red diamond) within Labani Channel. Insert C: The
Netherlands mooring within the main channel of Lifamatola Passage (yellow triangle).
Insert B, D: Sunda moorings in Ombai Strait, Lombok Strait, and Timor Passage: United
States (red diamonds); France, (purple square); Australia (green circles). The positions
of the shallow pressure gauge array (United States, green X).
Here, we focus on the INSTANT measurements in Makassar Strait, but
a composite along-axis speed time series as last slide.
Makassar Stream,
primary inflow
pathway
deployment --- rotation ------ final recovery
Dec03/Jan04 - June/July05 - Dec06/Jan07
El Niño: ITF reduced
INSTANT
Arlindo
La Niña: ITF increased
El Niño: ITF reduced
INSTANT
Arlindo
La Niña: ITF increased
fortnightly
a
Tidal oscillation~40 cm/s
Thermocline max to ~1.30 m/s
x
Kelvin?
SE monsoon
Apr’05
Jan’05
NW monsoon
INSTANT Makassar ADCP Record
July’05
SE monsoon
Oct ’04
April’04
NW monsoon
Intraseasonal
July’04
Kelvin?
Speeds in cm/sec; negative
values are towards the south.
Makassar Strait throughflow
over the initial 1.5 year
INSTANT record is ~8 to 9 Sv
Mak-East
Min south speeds
140-m; vm = -61 cm/sec
Mak-West
Max south speeds
Max south speeds
MAK-East ~ 75-82% of
MAK-West speeds
300-m; vm = -44 cm/sec
• Minimum thermocline
speeds toward south at end of
the monsoon transition
months: May/June 04 and 05
and Nov/Dec 04;
• Maximum thermocline
speeds toward south in late SE
and NW monsoons.
~680-m
750-m; vm = -3 cm/sec
• 750 m record is 180° out of
phase with the 1500 m time
series, ~30-50 day period.
1500-m; vm = 0 cm/sec
04-05 SOI: Neural to slightly
ElNiño
Southern Makassar Sill
INSTANT Makassar
time series, the 1st 1.5
years.
Min south speeds
ADDITIONAL
SLIDE:
INSTANT Makassar
time series at 140 m,
upper panel. Tides
removed
The time series for the
same place and time
from the NRL EAS16
model. Tides not yet
removed
Min south speeds
Mak-East
Min south speeds
Mak-West
Max south speeds
Min south speeds
Max south speeds
Min south speeds
Mak-East
Max south speeds
Max south speeds
Mak-West
Speeds in cm/sec;
negative values are
towards the south.
Is the model good enough? What
is good enough?
Southern Makassar Sill
~680-m
From J. Sprintall:
Lombok West Velocity Comparison
INSTANT (left) vs. GLBa0.08-05.3 (right)
Note: INSTANT observations span Jan 2004 – Jun 2005,
while HYCOM output spans Jan 2004 – Dec 2004
From J. Sprintall:
Lombok East Velocity Comparison
INSTANT (left) vs. GLBa0.08-05.3 (right)
Note: INSTANT observations span Jan 2004 – Jun 2005,
while HYCOM output spans Jan 2004 – Dec 2004
INSTANT, Sunda passages
Strong intraseasonal (<90 days)
signal due to Indian Ocean
tropical winds Wijfels and
Meyers 2004
Frequently Repeated XBT lines:
1984-present;
low spatial resolution (~1degree)
monthly
fortnightly
• seasonal range: -10 to 25Sv
• interannual range: 5 – 15Sv.
Transport Correlations with Equatorial zonal wind stresses
SOI: 0.61,4 months lag
Pacific Zonal Stress: 0.74, 4 months lag
Indian Zonal Stress: -0.57, 4 months lag
Can we explain transport variability
using a linear sum of equatorial wind
stress-variability?
Best fit:
T = 2.9*<Eq. Pacific zonal winds (4 months lag)> + 0.3*<Eq. Indian zonal winds(zero month lag)>
Accounts for 56% of interannual transport variance.
Blue: Makassar [Gordon; Susanto; Ffield]
Green: Lifamatola [Van Aken]
Orange: Lombok [Sprintall]
Purple: Ombai [Sprintall; Wijffels]
Red: Timor [Wijffels; Molcard]
Some comments: there is so much here!
Negative speeds are
towards Indian Ocean;
values in cm/sec
100-150 m
• Makassar Strait thermocline throughflow
is relatively steady, in comparison to
Lombok and Ombai, with a transport of ~9
Sv
• Timor is the most steady export route of
the Sunda passages, with thermocline
speeds ~30-50% of Makassar speeds;
• Lombok and Ombai exhibit speed
reversals, dominant intraseasonal signal;
350-450 m
• Lifamatola sill overflow is far more
vigorous than deep flow in other passages.
• The sub-sill Makassar flow [750 / 1500 m]
are 180° out of phase.
• What are: mass, heat
transports and profiles;
their intraseasonal,
seasonal variability;
Timor, 700 m
>700 m
Makassar 750
• Inflow/outflow
imbalances, interiro sea
and 1500 m time series
seasonal storage.
Lifamatola ~300 m above sill of
1950 m. negative speeds along
the channel axis, 124°
Dynamics of the
Lombok Striat, a
developing research
program for 2008
Sustained Observing of the ITF, must be cost effective and compatible with the Indonesian government
concerns. The ITF data stream must be assimilated into a proper model to anchor the model in reality.
Approaches may include these method:
Sea Level
Tide gauges
shallow pressure gauges
satellite altimeter
Stratification
Repeat XBT/XCTD
Gliders
PIES [pressure sensor-equipped inverted echo sounders]
Argo floats
Circulation
Argo floats
gliders
ADCP moorings
drifters
A
B
Sulawesi Rossby Waves
Seasonal variability of N-S sea surface tilt
A
Weak N to S surface slope
B
Strong N to S
surface slope
but the Makassar ITF is thermocline intensified, does sea
surface slope tell the whole story?
BAKOSURTANAL and NOAA have been discussing collaboration in the collection of, and timely access to, observations
of sea level from tide gauges at the following GLOSS locations [X]:
1.
2.
3.
4.
5.
6.
7.
8.
9.
Padang, West Sumatra,
Cilacap, South Java,
Kupang, Timor,
Bitung, Celebes (together with Davao in the Philippines, this is important for monitoring the Throughflow),
Kokenau or Agats, Irian Jaya,
Benoa, Bali,
Sorong, West Irian,
Surabaya, East Java, and
Ambon, Ambolina.
X
X
X
X
X
X
X
X
Janet Sprintall maintains the
Shallow Pressure Gauge Array
[set in ~15 m depth] since 1996,
which is continuing as part of the
INSTANT program. Shallow
pressure gauges are used to
estimate the upper 100 m, which
is better than just the sea level
slope, but the ITF profile is not
constant and extends to 1300 m.
Detided Pressure from Bali (Jan 04 – July 05)
Kelvin
wave
TABLE II Location of Shallow Pressure Gauges
Sensor No.
Latitude
Longitude
Description
1
12 11.2 S
123 4.0 E
Australian territorial waters (separate
deployment)
2
8 22.0 S
125 3.0 E
N. Ombai Strait
3
8 38.5 S
125 6.5 E
S. Ombai Strait (E.Timor waters, separate
deployment)
4
10 49.0 S
122 41.0 E
SW Roti
5
8 24.0 S
115 43.0 E
W. Lombok Strait
6
8 21.0 S
116 1.5 E
E. Lombok Strait
7
10 15.2 S
120 31.1 E
S. Sumba (recovery in 2003 only)
Surface drifters usually don’t
make it through the
Indonesian seas, and anyway
their direct data reporting to
satellite runs afoul with
Indonesian authorities.
Profilers can also provide a time series of the stratification, though the satellite reporting
from Argo is a problem within Indonesian waters.
Seaglider and Sensors [C. Lee UW/APL]
Inferred
• Depth-Averaged Current
• Surface Current
• Vertical Current Profile (|w|>0.5 cm/s)
•
•
•
•
Hull length: 1.8 m, Wing span: 1.0 m
Mass: 52 kg
Easy to deploy and recover
Surface to 1000 m.
• Horizontal speed 0.1 - 0.45 m/s (~22 km or 12 nm per
day @0.25 m/s)
• Vertical speed 0.06 m/s (minimum)
• Buoyancy range ~840 g
5 kg/m3 density range ►250 g
Sensors
• SBE Conductivity/Temperature
• Endurance depends on ambient stratification, dive depth
and desired speed
• SBE 43 Dissolved Oxygen
• Longest range to date: 3900 km
• WETLABS BB2SF- Chlorophyll a
Fluorescence, Optical Backscatter (red & blue)
• Longest endurance to date: 31 weeks
Gliders are effective, but their satellite reporting is a problem…but we will use gliders ]and
EM-APEX profilers in the 2008 program, with the data reported to the net and to a local site
at the same time.
Getting below the surface layer,
through the thermocline:
XBT and XCTD are very effective in
monitoring the ITF
monthly
fortnightly
Temperature variability off Shark Bay, WA.
data
Out of fish net way
Bottom moored ADCP in
shallow passages
Sea floor
Mooring with deep
ADCP will provide
time series in key
passages, e.g.
Makassar Strait
To get discussion going:
here is a strawman
2800-m
SeaGlider
580-m
ADCP/PIES
1940-m
~1000-m
680-m
OUT
Interior
280-m
W
FLO
XBT/XCTD
PIES
SeaGlider
OW
Satellites,
tide gauge
aray
FL
IN
XBT/XCTD
1350-m
PIES
1300-1500-m
Shallow Pressure Gauges
~1200-m