Aquarius SSS-max and SSS-min views of the SeaArnold L. Gordon, Lamont-Doherty Earth Observatoryof Columbia University

For decades oceanographers have had global near synoptic time series views of the sea surface from space: visible images, ocean temperature, height, color, sea ice, wind and marine rainfall patterns, all of which have dramatically expanded our knowledge of the ocean condition, enabling quantitative investigating of ocean processes and their coupling to the

atmosphere/climate and marine ecosystems.

Earth still looks insignificant in this image from NASA’s Cassini probe, more than 1.4

billion kilometers away,.

EarthSome views of Earth are from very away far.

GHRSST combined Sea Surface Temperature (SST) daily dataGHRSST combined Sea Surface Temperature (SST) daily data

WPWPEPWP

Synoptic SST global views reveal the complex array of meanders and eddies

Passive microwave: sea ice

Time series of the changing sea ice cover;

Discovery: The Great Weddell Polynya of the mid-1970s:

August 2014August 2014

http://nsidc.org/data/seaice_index/http://nsidc.org/data/seaice_index/

from ship data we knew of Gulf Stream meanders/rings, but

never before have we seen the full dimension on a global scale

of these features.

Arctic Southern ocean

Satellite altimeter image the relief of the sea surface (to a few cm resolution!), a reflection of the

ocean density field, with all of its gyres and bumps and wiggles that

change in time;

and from orbiting scatterometers, we see the winds acting on the

ocean surface, driving circulation.

§ MODIS Aqua Ocean Color, Chlorophyll-a concentration – weekly data§ MODIS Aqua Ocean Color, Chlorophyll-a concentration – weekly data

See: NASA Earth Observatory:http://earthobservatory.nasa.gov/GlobalMaps/

More of Earth from space:

§ Tropical Rainfall Measuring Mission (TRMM) http://trmm.gsfc.nasa.gov/

Wind over the ocean!

met

er

What an impressive array of ocean information derived from orbiting satellite! but what about salinity, an equation of state parameter, an indicator

of the marine hydrological cycle?

All we had were blurry atlas views of salinity, built from many decades of data gathering, depicting a climatology that never exists at all points at the same time; and a few lines of surface salinity from underway research ships and

VOS.

SSS

VOS

August 2014

February 2014

Aquarius: global observations of ocean surface salinity, flying 657 kilometers above Earth in a sun-

synchronous polar orbit, repeats every 7 days

sea surface salinometer

657

km

Line winched in when passing over land and ships at sea; aircraft and birds are alerted.

Gary tells me: its more complicated

With the advent of NASA/CONAE Aquarius/SAC-D satellite mission(June 2011 launch) and ESA's Soil Moisture and Ocean Salinity (November 2009 launch), we now have, at long last, near synpotic global views of the sea surface salinity (SSS) from orbiting satellites!!!

Water vapor

~0.2 SvWater vapor

~0.2 Sv

Agulhas leakage Salty waterAgulhas leakage Salty water

blockedWat

er v

apor

Wat

er v

apor

Low SSS

SPURS 1

SPURS 2

Central America Gap winds calculated Gordon and Giuilivi May 2014 from data: http://www.ecmwf.int/ Dee, D. P., et al.. (2011) The ERA-Interim reanalysis: configuration and performance of the data assimilation system. Q.J.R. Meteorol. Soc., 137: 553–597. doi: 10.1002/qj.828

Amazon Congo

limited water vapor flux

~0.2 sv water vapor flux

South Atlantic water vapor flux: Gordon, A.L. & A. R. Piola (1983); Agulhas leaakge: Gordon 1985, 1986

Aquarius tracking SSS trends in a near synoptic fashion enables investigation of the coupling between SSS regimes (e.g. the salt bridge defining

Agulhas leakage; Atlantic vs Pacific SSS; subtropic vs subpolar SSS): how their fluctuations relate to the larger scale SSS and circulation.

August 2014

Southeast Asian fresh

pool

Aquarius data reveal river plume spreading surprising far into the ocean; the SSS-max driven by subtropical evaporation, the SSS-min induced by ITCZ downpours; Southeast Asian freshpool, in sharp contrast to the salty Arabian Sea.

ITCZ

Why is the Atlantic so salty? One of my favorite topics

Annual average SSS from the Monthly Isopycnal Mixed Layer Ocean Climatology (MIMOC) data. The white contours: mean dynamic topography (MDOT). The arrows represent the Ekman transport in Sverdrups computed using ERA-40 wind stress data.

Aquarius (v3.0 Level3) 2012-2013 mean SSS and Evaporation minus Precipitation contours, m/yr, E > P with solid lines. E data from the WHOI OAFlux Project (http://oaflux.whoi.edu/) and P from the GPCP v2.2 combined observations and satellite data (NASA's GPCP project at http://precip.gsfc.nasa.gov/.)

§ The South Atlantic & South Pacific SSS-max are closer to the equator, 15° and 20°S; the southern Indian Ocean SSS-max near 30°S is the most poleward; they all fall to the poleward side of the maximum ‘trade’ wind Ekman transport, within the Ekman convergence zone, and largest E-P.

§ North & South Pacific SSS-max is close to the SSH ridge. The South Atlantic SSS-max 'pressed' against the western boundary. In the western South Pacific there is a secondary (weaker) SSS-max in the Tasman Sea.

§ The North Atlantic and south Indian Ocean have saltiest eastern boundary currents, the Canary and Leeuwin Currents respectively; in both cases, the low salinity subpolar water input is stymied by larger scale circulation patterns (AMOC, Mediterranean surface water inflow; ITF ).

The differences of the 5 subtropics regions are covered in more detail in an article for the SPURS Oceanography issue: "Differences between the Subtropical Surface Salinity Patterns" by A. L. Gordon, C. F. Giulivi, J. Busecke and F. M. Bingham [in revision]

Yes, they are all salty, but they stand out more by their differences.

The subtropical salty pools

Time series of SSS anomaly relative to the basin reference.

The Aquarius SSS-anomalies seasonal cycle greater amplitude than that of Argo, which may reflect more complete synpotic spatial coverage of Aquarius, and/or the Aquarius data represent the sea surface while that Argo surface values are measurements from depths >meter, and the uncertainty in the Aquarius data.

Differences of Aquarius SSS to that of MIMOC may also reflect the improved spatial coverage.

With Aquarius we are seeing new features!The south pacific seasonality is strange.

The South Atlantic has largest SSS anomaly relative to its reference SSS; Indian the smallest.

Aug-Nov NH

Feb-Apr SH

Aug-Nov NH

Feb-Apr SH

Jan-Mar NH

July-Sept,SH

Jan-Mar NH

July-Sept,SH

Dashed: Argo

Solid: Aquarius

Seasonal amplitde = SSS ~0.07

Aquarius SSS 2012-2013 displays a fresher South Pacific SSS-max than MIMOC climatology, while the North Pacific SSS-max is saltier [hydro data suggest interannual/decadal changes in the SSS-max,

often with correlations with other SSS-max regions, Aquarius is ‘seeing’ this in clearer detail]

shifted 6 months

20132012

20132012

Fall maximum, Spring minimum, tracking E-P and ocean processes;

wimpy

split personalitypressed again the

west

the real thing

SE Asian freshpoolArabian Sea

really wide; the strange eastern boundary:

Leeuwin current (ITF?)

**

The northern Indian Ocean got it sideways wide [weak Canary Current,

AMOC, Med effect?]

A summary of the differences of the salty subtropical regions

*The differences of the 5 subtropics regions are covered in more detail in an article for the SPURS Oceanography issue: "Differences between the Subtropical Surface Salinity Patterns" by A. L. Gordon, C. F. Giulivi, J. Busecke and F. M. Bingham [in revision]

Kind-a-like the Indian Ocean

§ The atmospheric and oceanic processes governing SSS are influenced by regional ocean basin configuration, e.g. subtropical SSS-max patterns and locations display marked differences between the 5 subtropical regimes (North and South Atlantic and Pacific; southern Indian Ocean), each is unique in its own way*.

Aquarius will divulge how these regimes couple to each other and other aspects of the global system

February 2012Aquarius L3 V3 Sea Surface Salinity – weekly dataAquarius L3 V3 Sea Surface Salinity – weekly data

August 2012

South Chnia Sea;SCS

Bay of BengalBoB

ITF

Sout

h C

hina

Sea

;

Bay of Bengal

ITF

SEA-FP

Two topics of the Southeast Asian Freshpool (SEA-FP):

§ South China Sea effect on the Indonesian Throughflow (ITF);

§ Export of the Bay of Bengal freshwater

Arabian Sea

Sout

h C

hina

Sea

;

Bay of BengalArabian Sea

February 2012

Gordon, A.L., Huber, B.A., Metzger, E.J., Susanto, R.D., Hurlburt, H.E., Adi, T.R. (2012) South China Sea Throughflow Impact on the Indonesian Throughflow” Geophysical Research Letters: doi:10.1029/2012GL052021 vol (39) L11602

Gordon, A.L., Huber, B.A., Metzger, E.J., Susanto, R.D., Hurlburt, H.E., Adi, T.R. (2012) South China Sea Throughflow Impact on the Indonesian Throughflow” Geophysical Research Letters: doi:10.1029/2012GL052021 vol (39) L11602

ENSO induced change of the South China Sea (SCS) throughflow drawn from the Luzon Strait is the likely cause: increased westward Luzon Strait throughflow during El Niño forces buoyant SCS surface water into the Sulawesi Sea, inhibiting tropical Pacific surface water injection into the ITF; During La Niña, when the Luzon Strait transport is reduced, the SCS freshwater inventory is recharged.

X

X: Makassar Strait mooring

X

La Niña

El Niño

gets saltier

fresher

saltier

Aquarius and SMOS provide a SSS time series to relate the SCS throughflow to the ITF profile

Using SODA (not shown here): The freshwater increase 1998-2000 (La Niña) and decrease in 2002-2004 (El Niño) is equivalent to ~0.3 m/year, well in excess of expected ENSO variability of freshwater (FW, P-E+R) input, and therefore likely that SCS throughflow plays a role in SCS SSS.

Salinity on the 28-30°C slab, June-September

Salinity on the 26-28°C slab, Dec-March

ITF

February 2012 August 2012

ITF

BoB’s freshwater is exported into the surrounding ocean

The Bay of Bengal displays energetic eddy field, discerning the regional circulation is difficult:

• In the winter monsoon fresher SSS spreads along the western margin of the Bay of Bengal, to pass around the southern rim of Sri Lanka into the salty Arabian Sea; in the summer monsoon this pattern is reversed;

• It is likely that during the summer monsoon the freshwater is channeled southward along the eastern margin, reaching to more tropical latitudes, towards the ITF export passage.

Related to ONR ASIRI program

§ As salinity is a seawater equation-of-state parameter, an active component of ocean dynamics, and an indicator of the marine hydrological cycle, the SSS global near synoptic time series is revolutionizing our understanding of the ocean and earth's climate system.

§ The number of research papers utilizing satellite SSS data is expanding at an ever increasing rate; discoveries are being made and many more will be forthcoming as the SSS time series grows, capturing the interannual [and eventually decadal] scales of variability, by Aquarius and SMOS and their followups.

Week 40 1 Oct — 7 Oct 2014

Cold water Aquarius SSS is improving