Physical Oceanography

Nebular Hypothesis

1. Gravity concentrates material at center of sun
2. Nebula evolves into a rotating disk
3. protoplanets form from smaller matter concentrations
4. Orbits are cleared of gas and small bodies completing their formation

Protoearth

Larger than today’s earth, homogeneous composition, bombarded with meteorites. Moon formed from collision

Density Stratification

In the earths formation, highly dense materials settled at the core and les dense formed concentric spheres around it

Outgassing

Volcanic activity releasing large amounts of water vapor into atmosphere

Early Atmospheric composition

water vapor, carbon dioxide, hydrogen, other gases

Origin of earth’s oceans

1. Outgassed water vapor fell as rain
2. first permanent ocean formed 4 billion years ago


1. salinity developed from dissolved rock elements

Earth’s Chemical Layers

1. Crust
2. Mantle
3. Core

Earth’s Physical Layers

1. Lithosphere
2. Asthenosphere
3. Mesosphere
4. Outer Core
5. Inner Core

Lithosphere

Cool, rigid shell, includes upper crust and some mantel, approx 100km thick

Asthenosphere

Relatively hot plastic, high viscosity flow, 100-700km deep, mantel convection, rock flow

Mesosphere

Rigid due to increased pressure, 700-2885km

Outer Core

Liquid and capable of flowing 2885-5155km

Inner COre

Solid from pressure, does not flow, 5155-6371

Continental Drift

Pangaea: One large continent from 200 million years ago

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Panthalassa: One large ocean, including tethys sea

Radiometric Dating of Ocean Rocks

* Can date ocean rocks
* oldest on ocean floor is only 180 million years, hence our ocean is always recycling
* oldest continental is 4billion like the ocean itself cause it doesn’t recycle the same way

Ocean Ridges

* Continuous submarine mountain chain extending through the world’s oceans.
* Rise from 5km to 2.6km and are roughly symmetrical in cross section. Thousands of km’s wide
* associated with youngest crust

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Ocean Trenches

* Long, narrow, steep sided depression in the bottom of the ocean associated with max depths from 7300m-11000m
* Form at subduction zones when one plates subducts under another
* some of the oldest oceanic crust is found in trenches

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Abyssal Plains

Flat, seafloor area at abyssal depth (4000-6000m), adjacent to continent, majority are found in atlantic ocean. Silt, sediment and sand

Continental Shelf

Broad shallow submarine terrace of crust at edge of continent. Similar geology to continent. 8% of oceans floor, 100-200 meters depth. average slope of 0.1 degree

Continental Rise

Found at base of continental slope, between 3000-400m

Continental Slope

Extends from the shelf at an average depth of 135 m. Slopes steeply down from 1-25 degrees with an average of 4. ends at about 2000m depth.

Submarine Canyons

* V-shaped canyons cut into continental slopes
* up to 1200m deep
* can lead to large waves
* often associated with rivers

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Equatorial Buldge

Due to the earth’s rotation the earth is ellipsoidal

The Geoid

* If the ocean surface was at rest it would be aligned with an equipotential surface
* Bottom bathymetry such as seamounts influence the gravitational field and deflect the surface of the ocean
* only about 10m elevation over 200km
* this deviation in surface is ‘ocean or dynamic topopgrahpy”

Earth’s Oceans

1. Pacific 50%
2. Atlantic 26%
3. Indian 20.5%
4. Artic 3.4%
5. Antarctic

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Oceans cover 70.8 % of earths surface and make up 97.2% of our water

Mediterranean Seas

Surrounded by land and have limited connections with global ocean

Marginal Seas

Defined by only an indentation in the coast

Planetary Energy Balance

Earth must radiate energy away at same rate it is received

Solar Lumoinosity

Sun puts out a nearly constant flux of energy called the solar lumonisty, Lo=3.827x10^26. Average flux density, Sd=Lo/4pid^2

Solar Constant

The intensity of the solar irradiation directly outside the earth’s atmosphere on horizontal surface is constant at So=1.360W/m^2

Planetary Albedo

* Not all of the solar energy pointed at earth is absorbed
* some is reflected back into space
* This reflection back is the albedo, a
* average is about 30%

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Sun’s Radiation

Distribution of EM energy(stream of massless particles), close to theoretical blackbody theorem. Emits mostly in the visible part of the spectrum

Blackbody Radiation

High temperatures mean small wavelengths i.e higher frequencies

Earth’s Radiation

The earth radiates in the far infrared.

Much of the radiation from the earth is absorbed by the atmosphere and then re-emitted. We get a greenhouse effect

Leaky Greenhouse Effect

We would think the solar flux=earths absorbed solar radiation, but that is to cold, so than we account for the greenhouse effect of infrared radiation being trapped inside and remitted. but this is to hot. We need to use the leaky greenhouse model where we trap some but not all giving us our earth temp

Atmospheric Circulation

Driven by solar heating

Distribution of solar energy

* Near the equator (at low latitudes) photons are distributed over a smaller area whereas they diffuse more at higher latitudes hence colder
* Atmospheric absorption/thickness
* Albedo
* Angle of sun

Excess Radiation

The earth receives excess radiation in the tropics and emits more than it receives in the poles. The atmosphere/ocean must move 10^16 W of heat towards the poles to balance the excess/deficits.

Convection Cell

Rising and sinking air: warm air rises it is less dense, cool air sinks and is more dense

Three Cell Model of Circulation

* Hadley Cell 0-30 degrees latitude (strongest)
* Ferrel Cell 30-60 degrees latitude
* Polar Cell 60-90 degrees latitude
* same in both hemispheres (6 total cells)
* Rising and descending air from cells generates high and low pressure zones

Troposphere

* Lowest layer of the atmosphere
* Atmosphere is mostly transparent
* where weather occurs
* Temperature decreases with altitude

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Stratosphere

* Next layer of atmosphere
* Temperature increases with height
* Ozone heating

Upper Atmosphere

* Very Thin low density
* Ideal gas law breaks down

Subtropical and Subpolar Jets

* Two jet streams flow along the top of the troposphere between 9-17km above
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Polar Jet Stream

* Westerly jet at the upper boundary of the troposphere
* Warm moist air from the tropics moves north in the lower ferrel cell
* cool dry air moves south in the lower branch of the polar cell
* The Polar front is where these two air masses meet
* Associated with meridional temperature gradient

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Global Wind Belts

* Trade Winds
* Northeasterly trade winds
* Southeasterly trade winds
* Prevailing westerly winds (30-60’ degrees) Stronger in the southern hemisphere because lack of land and corolis
* Polar Easterly wind belts (60-90’ degrees)
* Doldrums (equator)
* Horse Latitude (30 degrees)

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Wind Stress

* Wind stress drives the ocean, transfer of momentum from wind to ocean

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Latent Heat

Latent heat is the heat released or absorbed per unit mass when water changes phase. Is it an efficient way of transferring energy globally and is an important energy source for earth’s weather climate including weather and hurricanes.

* Loss (energy out of the ocean and into atmosphere)

Sensible Heat Flux

is the conductive heat flux from the earths surface to the atmosphere

* Loss (energy out of the ocean and into atmosphere)

Hydrogen Bonding

Hydrogen bonds are weaker than covalent bonds, create weird characteristics in water

* high surface tension
* Unusual density/ thermal properties
* high latent heat
* high heat capacity
* high melting point

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Melting/ boiling points of water

are unusually high compared to compounds of similar mass

Salinity

total amount of dissolved solids in water including dissolved gasses

Determining Salinity

* Evaporation
* Weigh water and weigh evapourated salts
* Principle of Constant Proportions:
* Chemical analysis via titration
* Salinometer
* Measures waters electrical conductivity

Equation of State

The density of a parcel of seawater is determined by its temperature salinity and pressure. Usually calculated by observations. Using the equation of state of seawater

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Density and Salinity: Brine Rejection

* When salty water freezes, the salts no longer fit into the crystal structure of the ice


* Salts are drained into the surrounding seawater creating saltier denser brine
* The heavier brine can then sink influencing ocean circulation

In-Situ Temperature

Actual local values of T and rho/sigma, for a fluid parcel at its current position and depth.

Energy Budget

Net heat flux= solar in - longwave - latent - sensible

Salinity Distribution

* Lesser in poles due to run off of fresh water from land
* Decreasing rapidly with depth than is relatively constant

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Archimdedes Prinicipal

Bouyant force on ocean fluid parcel

* Causes parcel to sink if density> water
* Cause parcel to float if density< water

Leads to Normal Stable ocean stratification

Unstable Stratification

Heating atmosphere from below, puts warm bouyant particles beneath

Cooling from above puts cold heavy ones on top

Ocean Water Masses

Atmospheric conditions effect parcel characteristics but once they sink they are pretty constant

Ocean Convection

Contact with cold atmosphere causes surface water to sink

* global themohaline circulation
* transports heat globally

Dense Water formation

Formed in med/marginal seas

* Small volume is trapped and exposed to intense evaporation or cooling so large density increase for a small volume. It will overflow the sea and topple into the ocean. The sinking and circulation or high density fluids helps drive ocean circulation

Lagrangian (material Approach)

Break fluid up into water parcels and follow individually

Eulerian of Field Approach

Track a point and see how it changes over time with the parcels moving through it

Atmospheric Transparency

1. Transparent to visible spectra
2. opaque to UV Spectra
3. variable opaque to infrared spectra
4. opaque to green house gases
5. transparent to atmospheric contsituents

Material Deriviative

Rate of change of a quantity following a material fluid parcel

Variables describing ocean state

P: Pressure

T: Temperature

rho: density

S: Salinity

Continuity Equation

Drho/Dt=toh(gradient\*u)

Divergence in Continuity

Parcel is expanding but mass is remaining constant thus the density is decreasing

Convergence

Parcel size is shrinking and mass is remaining constant, thus the density is increasing

Pressure Force

Fluids exert pressure forces on surfaces. Fluid particles bounce off and momentum flux is imported into the wall

Viscous Force

Molecular motions also redistribute momentum in the pressure velocity gradients. It is the force of a fluid resistance the change in velocity

Gravitational Force

Attraction force acting on every mass

Inertial Reference Frame

Stationary of moving at a constant velocity

Non Inertial

accelerating frames

Laplacian Operator

Sum of second derivatives

Pressure Gradient

The rate of pressure change over a distance

Dynamic Viscosity

Quantity measuring the force required to overcome internal fluid friction in m^2/s

N^2 Levels

N2>0 = Stable stratification, harmonic oscillation

N2=0, = Neutral stratification, buoyancy=weight

N2

Water Mass depths

Central Water Mass 0-500m

Intermediate 500-1500m

Deep Water 1500-3000m

Bottom Water 3000+

Ocean Conveyor

In the poles, the surface water cools and sinks cause highly dense water, feeding deep water currents. Warm currents replenish this and the cycle goes on an on

2 Apparent Forces

Centrifugal Force and Coriolis Force

Centrifugal Force

* Directed Radially Outwards


* Responsible for ellipsoidal shape of earth
* Can be absorbed by gravity force
* not important to oceanography

Coriolis Force

* Apparent Force on moving parcels
* very important for geophysical fluids
* effects navier stokes eq
* orthogonal to direction of motion

Cartesian Approximation of the f-plane

Rotation of the earth is central to many phenomenon in geophysical fluid dynamics. We can often ignore the sperecity of the earth and get a tangential plane

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Traditionally we just keep the omega terms with z in them

f=2Ωsinθ

* f>0 in northern hemisphere
* f

Northern/Southern Hemisphere Parcel Deflection

Parcels are deflected to the right in NH and Left in SH

Fridtjof Nansen

* helped establish norway as an indpendent country
* developed Nansen bottle
* two nobel peace prizes
* cofounder of UNICEF

Niskin Bottle

A device used to collect water samples at specific depths in the ocean. It consists of a cylindrical container with two caps that can be triggered to close simultaneously, capturing a water sample at a desired depth.

Ekman Spiral

Explains balance between friction and Coriolis effect. Describes direction and flow of surface waters at different depths. In the northern hemisphere, wind driven surface water is directed at 45 degrees to the right of the wind while the transport is 90 degrees to the right. Ekman Spiral is unstable we’re better off using transport

Ekman Transport

Average movement of surface waters, 90 degrees to right in NH and 90 degreees to left in SH

Upwelling

Vertical movement of cold nutrient rich water to the surface. There is high biological productivity an abundance of algae down at the bottom.

Downwelling

Vertical movement of surface water downward in the water column

Equatorial Upwelling

Near the equator, the trade winds move from east to west, this means in the NH transport is to the north and in the SH it is to the south. Upwelling occurs along the equator to replenish surface water moving out.

Costal Upwelling

Ekman transport moves surface seawater away from shore, cool nutrient rich deep water comes up to replace the displaced surface water

Coastal Downwelling

Ekman transport moves surface seawater toward the shore, water piles up and moves downward in columns, lack of marine life

Loop Current

Warm ocean surface current in gulf of mexico, generates warm loop current eddies and hurricanes intensify when passing over warm cores

Ekman Pumping / Convergence

When water is forced together having no where to go it will sink out of the surface layer. This is called Ekman Pumping but is also, sinking, downwelling, convergence

if curl of Τ/ρ\*f is < 0 it is pumping

`Ekman Suction/Divergence `

When water is forced away from the middle, water must be replaced with upwelling this is called Ekman Suction, rising divergence or upwelling

if curl of Τ/ρ\*f is > 0 it is suction

Dominant Balance

The idea that only two terms are important at the same time, they balance each other out and are enough for an accurate explanation of the solution