oeas 604 introduction to physical oceanography eileen hofmann john klinck chet grosch
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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
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