Physical OceanographyPhysics 3300

2

U. Texas

Eras Eras in in

OceanographyOceanography

u Expeditionary - Maury, Darwin (Beagle), Challenger ( >> 1885)

u Geostrophic - Mohn, Bjerknes, Sverdrup, Rossby (1885-1945)World War II - Technology and applications

u Post-Geostrophic - Munk, Stommel (1945-1970)

u Computational/Electronic - Us (1970 >>)

GoldenGoldenAgeAge

SiliconSilicon

Golden Age StudiesGolden Age Studies

u Limited technological capacity, difficult to sample, many ocean parameters simply not measured

u Analytical problem solving still the key approach u Narrow inter-disciplinary collaborations, little to offer othersu International collaborations take many years to develop, even global

programs tend to be national in characteru Gradually filling in gaps in the descriptive database (where the current

systems are, seasonal water properties)u Nearly unlimited (from the modern perspective) ship opportunities

(relatively small demand)

u Still developing fundamental dynamical concepts, programs searching for data, finding ideas, limited possible applications, little predictive power.

PostPost--war studies: Developing technology war studies: Developing technology and understandingand understanding

u Water sampling still required titrations to determine salinity -hence limiting vertical resolution to meters or tens of meters (changed around 1970)

u Current measurement was very difficult, mechanical instruments (film, mechanical counters), limited moored applications

u Instrumentation and sensor development was very difficult, no modularity, systems developed for very specific applications

u Much development was supported by the US military; particularly instrumentation, but also modelling and theory

Rapid expansion led to new thinking but perhaps unrealistic expectations about how the discipline should function and be supported.

Development of Development of Canadian Canadian InstitutionsInstitutions

u Scattered descriptive studies prior to the war: e.g. Dawsonu Post-war developments: Institute of Oceanography (UBC), Fisheries

Research Board, BIO (1960’s)u University program development: McGill, GIROQ, Dalhousie (1970) ,

IOSu New expansions: Memorial (1980), University of Victoria (1990)u New major international projects in the 1990’s and shift into the Arctic

From gold to siliconFrom gold to silicon

u Beginning developments in the 1960’s but things really took off in the 70’s and 80’s

u Development of microprocessor technology, modular sensors, application of numerical techniques

u Remote sensing techniques : satellite imaging (passive and active), coastal radar (CODAR), acoustic

u Instrumentation developed for long-term deployment at fixed sites (moorings) and drifting (neutrally buoyant floats SOFAR, satellite drifters, profiling drifters ALACE)

u Some technological development is internal to the discipline (e.g. CTD’s, acoustics) but much is spun off from elsewhere (e.g. microprocessors, tomography)

Ideas and theory develop quickly spurred on by new data and new technology

New techniques invariably New techniques invariably lead to new insightslead to new insightsu New observational techniques have led to new

interpretation, new theory but only rarely has the reverse happened

u Satellite imagery alone have changed how we view the ocean

Difficult to predict future possibilities because of technological dependencies.

Woce Drifters

Developing predictive skillDeveloping predictive skillu Early developments were limited,

predictive power was pooru Numerical interpretations of theory

(models) have begun to worku Skill leads to applications, both

directly and with other disciplines (marine biology, fisheries, geochemistry, paleo-oceanography)

u Real time data collection now a realistic possibility

u We are moving towards real time monitoring as for the atmosphere, but can we ever sample at the equivalent scales (5 km)?

Comparisons with meteorology are difficult, the ocean is opaque and the scales are very different.

So is there nothing left to discover?So is there nothing left to discover?

u There remain many gaps in our Model of how the ocean works:mixing and dissipation

interaction with topography (e.g. shelf break processes)intermediate scale processes (below 10 km), patchinessinteractions with the atmosphereocean-basin water movements

u Many of these problems have been recognized for a long time

u We do not do well in translating from the small scale (mixing) to the large spatial scale or long time scales

The Slocum Missionu In a visionary article – a work of fiction, Henry Stommel (1989)

suggested that small autonomous buoyancy-driven vehicles could roam the global ocean returning observations of its changing state:

“They migrate vertically through the ocean by changing ballast, and they can be steered horizontally by gliding on wings at about a 35 degree angle. They generally broach the surface six times a day to contact Mission Control via satellite. During brief moments at the surface, they transmit their accumulated data and receive instructions telling them how to steer through the ocean while submerged. Half are devoted to a program of routine hydrographic observation, much like the meteorologists upper air network. The rest make soundings of temperature, salinity, oxygen, nutrients, and those geochemically important tracers that the geochemists have been clever enough to find automatic measuring devices and sensors for.”

-Dr. Henry Stommel, published in Oceanography, April 1989.

Typical glider features:

●Buoyancy driven (e.g. variable volume/weight)

●Fixed wing and tail

Attitude controlled by sliding and rolling internal mass, control surfaces

WRC Slocum

Today’s Autonomous Underwater Glider - Slocum

Slocum Glider Specificsu Weight – 52 kg

u Length – 1.5 m

u Endurance ~ 30 days

u Vertical Speed ~ 20 cm/s

u Top Forward Speed ~ 40 cm/s

u Operating Depth – 4-200 m

u Range ~ 1500 km

The Buoyancy EngineWhat is a buoyancy engine?

A device that generates a change in Volume (ΔV) without a change in the enclosed mass (M).

As a result the buoyancy engine allows the vehicle to accurately control its weight in water. Neutrally

Buoyant

Positively Buoyant

Negatively Buoyant

Candidates for buoyancy engines are:

•Pump-bladder systems

•Single Piston drives

•Thermal contraction/expansion

The vehicle weighs about 50 kg in air and is a little over 2 m in length and can be handled easily by two people

Launching A Glider

Controlling the GliderBefore a mission begins,

several variables are set:

u Waypoints (latitude, longitude)

u Distance when waypoint reached

u Dive Depthu Altitudeu Climb Depthu Communication Interval

Altitude

Dive depth

Climb depth

Communication Interval

Waypoint 2

Dist. whenwpt. reached

Waypoint 1

u A high frequency radio (RF) communication link (FreewaveTechnologies) allows for high speed, line of sight data transmission and a repeater can be used to increase the distances of communication.

u Satellite telephone link (Iridium Satellite LLC) also provides global communication coverage.

• ARGOS transmitter is also located in the tail and broadcasts GPS coordinates to locate the glider in case of an emergency.

Communication

At The Surface – Transmitting Data

Instrument integrityu Battery voltageu Leak detection

Track performanceuSurface locationuDepth trackuEstimated current

Oceanographic datauTemperatureuConductivity

Conception Bay test runs with 049

Currents

The glider can give us the surface currents (not shown) and the depth averaged currents over its track

The depth averaged currents (peak speed about 30 cm/s) are calculated by taking the difference between the expected position (based upon its flight trajectory) and the observed location

This assumes a model for the glider performance (something that we are exploring)

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Bonavista Temperature: Spring 2005

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Bonavista Section Temperature: July 2005

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Bonavista Temperature: Fall 2005

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The line, about 350 km long, takes about 20 hours to steam in a ship and would require, for 15 stations, about 15 hours of station time – for a total of roughly 35 hours – a day and a half

For comparison a glider would take about two weeks to cover the same line

Bonavista line, from ship survey in 2005

Waypoint distance (10 m)

Next waypoint too far (100km limit)

Strong currents

One example of complexity is the growing understanding of the coupling between terrestrial storms and ocean productivity

Dust storms from Asia and the Sahara influence coral reef survival, local productivity and ocean primary production as far away as the Northwest Atlantic

How important are such events, and such detail, in the response of the oceans and atmosphere to climate jumps, e.g. CO2 and CH4 increases?

Complexity …