3: The Physical Setting
- Page ID
- 30034
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Earth is an oblate ellipsoid, an ellipse rotated about its minor axis, with an equatorial radius of \(R_{e} = 6,378.1349\) km (West, 1982) slightly greater than the polar radius of \(R_{p} = 6,356.7497\) km. The small equatorial bulge is due to Earth’s rotation.
Distances on Earth are measured in many different units, the most common are degrees of latitude or longitude, meters, miles, and nautical miles. Latitude is the angle between the local vertical and the equatorial plane. A meridian is the intersection at Earth’s surface of a plane perpendicular to the equatorial plane and passing through Earth’s axis of rotation. Longitude is the angle between the standard meridian and any other meridian, where the standard meridian is the one that passes through a point at the Royal Observatory at Greenwich, England. Thus longitude is measured east or west of Greenwich.
A degree of latitude is not the same length as a degree of longitude except at the equator. Latitude is measured along great circles with radius \(R\), where \(R\) is the mean radius of earth. Longitude is measured along circles with radius \(R \cos \varphi\), where \(\varphi\) is latitude. Thus \(1^{\circ}\) latitude = \(111\) km, and \(1^{\circ}\) longitude = \(111 \cos \varphi\) km.
Because distance in degrees of longitude is not constant, oceanographers measure distance on maps using degrees of latitude.
Nautical miles and meters are connected historically to the size of Earth. Gabriel Mouton proposed in 1670 a decimal system of measurement based on the length of an arc that is one minute of a great circle of Earth. This eventually became the nautical mile. Mouton’s decimal system eventually became the metric system based on a different unit of length, the meter, which was originally intended to be one ten-millionth the distance from the Equator to the pole along the Paris meridian. Although the tie between nautical miles, meters, and Earth’s radius was soon abandoned because it was not practical, the approximations are very good. For example, Earth’s polar circumference is approximately 40,008 km. Therefore one ten-millionth of a quadrant is 1.0002 m. Similarly, a nautical mile should be 1.8522 km, which is very close to the official definition of the international nautical mile: \(1\) nm \(\equiv 1.8520\) km.
- 3.1: Ocean and Seas
- Geographical definition of the three oceans. Brief description of the classification of seas.
- 3.2: Dimensions of the Ocean
- The dimensions of the ocean, with a focus on their surface areas relative to their depths. How the disparities between these dimensions affect models for oceanic currents and turbulence.
- 3.3: Sea-Floor Features
- Definitions of various seafloor features. Brief discussion of how they may impact ocean circulation.
- 3.4: Measuring the Depth of the Ocean
- The two main methods of measuring the depth of the ocean: acoustic echo sounders on ships, and satellite altimetry. Discussion of the relationship between sea surface shape and ocean depth.
- 3.5: Sea Floor Charts and Data Sets
- Publication of seafloor charts and digital data sets.
- 3.6: Sound in the Ocean
- The speed of sound in the ocean, and its dependency on temperature, salinity, and depth. Absorption of sound in the ocean, and its variation relating to sound frequency. Some applications of sound in the ocean.
- 3.7: Important Concepts
- Summary of major concepts in this chapter.