OEAS 604 Introduction to Physical Oceanography

Eileen HofmannJohn KlinckChet Grosch

Reading for Introductory Class

• Chapter 1: Introduction to Physical Oceanography – Talley et al. (2011)

• Chapter 2: Ocean dimensions, shapes and bottom materials – Talley et al. (2011)

Two Divisions of Physical Oceanography

• DESCRIPTIVE – description of the state of the ocean based on observations which are reduced to a summary or statement of the characteristic features of the ocean

• DYNAMICAL (theoretical) – apply laws of physics and use force balances and process to determine why and how the state of the ocean develops

Two Divisions of Physical Oceanography

• DESCRIPTIVE – Use observations and numerical model output to provide quantitative descriptions of oceanic flow

• Descriptive oceanography relies on understanding the processes that govern heat and salt content and distribution (density) in the ocean (thermodynamics)

• DYNAMICAL – Use theoretical studies and process-based numerical model experiments to understand what governs fluid flow in the ocean

Approach

• Observations are used to determine what features need explanations

• Laws of physics are used to derive equations that give balance of forces

• Solve equations to learn how motions behave in space and time

• Iterate between observations and theory to develop understanding and predictive capability

Historical Background

• Most knowledge of physical oceanography derived from observations and theories from past 100 years

• Knowledge of circulation goes back much longer

• Descriptive physical oceanography goes back to 1700s – voyages of Captain Cook

• Location of Gulf Stream known since late 1700s – Benjamin Franklin

Franklin-Folger map of the Gulf Stream(Richardson, 1980, Science, Reprinted in Talley et al., 2011)

Background – Descriptive Physical Oceanography

• First systematic treatment of physical oceanography was by Matthew Fontaine Maury in about 1850

• Developed charts of ocean circulation by combining available hydrographic data and observations

• Late 1800s and early 1900s several major oceanographic expeditions – HMS Challenger (1872-1876), Meteor (1925-1927), HMS Discovery (1930s)

Background – Dynamical Physical Oceanography

• The basis for much of theory in physical oceanography comes from Newton (1687) and Laplace (1775)

• Major advances in theoretical development were made by Gustav Ekman (1905), Carl Gustaf Rossby and Wilheim Bjerknes (1930s)

• Modern dynamical oceanography has origins in work by Harald Sverdrup and Henry Stommel in 1940s and 1950s

• Development of large field programs in 1960s and 1970s provided observational basis needed to evaluate theoretical understanding

Course Focus

• Average large-scale ocean circulation • Also consider coastal circulation, estuarine

circulation, waves, tides, diffusive and turbulent processes

• Include climate effects and interactions with atmospheric system

• Consider ocean circulation processes a range of space and time scales

Time and space scales associated with physical oceanographic processes (Talley et al., 2011)

Satellite-derived sea surface temperature

Advanced Very High Resolution Radiometer (AVHRR) instrument

(Talley et al., 2011)

Circulation Background

• Bathymetry of ocean basins is important to understanding of ocean circulation

• Earth is about 70% water, 30% land• Most land is in the northern hemisphere – ratio of

water to land is greatest in southern hemisphere • Major ocean basins are divided by land

boundaries and separated by ridges within basins– Atlantic, Pacific, Indian, Arctic

• Circumpolar ocean – Southern Ocean

World elevation map based on ship soundings and satellite altimeter derived gravity (Data from Smith & Sandwell (1997), Becker et al. (2009), SIO (2008); reprinted in Talley et al., 2011).

Sea Floor Bathymetry

(From Smith and Sandwell bathymetry data; satellite altimetry)

Sea floor age (millions of years)Black lines indicate tectonic plate boundaries

(Müller et al.2008; reprinted in Talley et al. (2011)

From Chapter 1Sverdrup,

Johnson, Fleming

Also seeTable 1.4 inKnauss

Oceans Background

• If include Southern Ocean with ocean north of it the total ocean area is:– Pacific Ocean – 46%– Atlantic Ocean – 23%– Indian ocean – 20% – Rest is about 11%

• Smaller seas that are partially separated from ocean by land barriers – Gulf of Mexico, Mediterranean

Areas of Earth’s surface above and below sea level as a percentage of the total area of Earth (in 100 m intervals).

(Data from Becker et al. 2009; reprinted in Talley et al. 2011)

See Table 1.4 in Knauss

(8,848 m)

(10,994 m)

Bathymetry

• Average ocean depth is about 4000 m• Small relative to horizontal dimensions of ocean

basins which are 5000 to 15,000 km • Vertical dimension is distorted relative to

horizontal dimension • Other important features are – continental shelf – borders coast and extends seaward – shelf break/slope – important dynamically– Islands and seamounts

Schematic section of ocean floor

Bathymetrymeasured along South Pacific ship track

(Talley et al. 2011)

Ocean Basins

• Topography controls deep circulation • Ridges determine deep water pathways and

exchanges between ocean basins • Sills control flow into ocean basins from

marginal seas – Mediterranean, Norwegian Sea, Gulf of Mexico

Pacific Ocean

Bathymetry

Data from NGDC (2008); reprinted

in Talley et al. (2011)

Data from NGDC (2008); reprinted in Talley et al.

(2011)

Atlantic Ocean

Bathymetry

Data from NGDC (2008); reprinted in

Talley et al. (2011)

Indian Ocean

Bathymetry

Data from NGDC (2008); reprinted

in Talley et al. (2011)

Arctic Ocean

Bathymetry

Data from NGDC (2008); reprinted in

Talley et al. (2011)

Southern Ocean

Bathymetry

Next Class

• Matlab Introduction – Information posted on class website

• Ocean and Atmospheric Circulation – No assigned reading