# A Voyage of Discovery Physical oceanography Instructor: Dr. Cheng-Chien LiuCheng-Chien Liu Department of Earth Sciences National Cheng Kung University.

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A Voyage of Discovery Physical oceanography Instructor: Dr. Cheng-Chien LiuCheng-Chien Liu Department of Earth Sciences National Cheng Kung University Last updated: 11 September 2003 Chapter 1

Significances of Physical Oceanography  Source of food Oceanic weather  fertilizes the sea  Man uses of ocean Near-shore structures, transportation, resources (e.g. oil, gas), recreation (e.g. swimming, boating, fishing, surfing, and diving)  Physical processes (e.g. waves, winds, currents, and temperature)

Significances of Physical Oceanography (cont.)  Weather and climate Rainfall, droughts, floods, regional climate, and the development of storms, hurricanes, and typhoons  Air-sea interactions, especially the fluxes of heat and water across the sea surface, the transport of heat by the oceans, and the influence of the ocean on climate and weather patterns

Goals  Aware of the major theories How they were arrived at Why they are widely accepted How to achieve order out of a random ocean The role of experiment in oceanography  Describe physical processes Influencing the oceans and coastal regions The interaction of the ocean with the atmosphere The distribution of oceanic winds, currents, heat fluxes, and water masses  Ideas > mathematical techniques

Four questions  The basis of of physics of the ocean What are the physical properties of sea water? What are the important thermodynamic and dynamic processes influencing the ocean? What equations describe the processes and how were they derived? What approximations were used in the derivation? Do the equations have useful solutions? How well do the solutions describe the process? That is, what is the experimental basis for the theories? Which processes are poorly understood? Which are well understood?

Four questions (cont.)  The sources of information about physical variables What instruments are used for measuring each variable? What are their accuracy and limitations? What historic data exist? What platforms are used? Satellites, ships, drifters, moorings?

Four questions (cont.)  Important process Heat storage and transport in the oceans The exchange of heat with the atmosphere and the role of the ocean in climate Wind and thermal forcing of the surface mixed layer The wind-driven circulation  Ekman circulation  Ekman pumping of the deeper circulation  upwelling The dynamics of ocean currents  Geostrophic currents  The role of vorticity

Four questions (cont.)  Important process (cont.) The formation of water types and masses The thermohaline circulation of the ocean Equatorial dynamics and El Ni˜no The observed circulation of the ocean plus the Gulf of Mexico. Numerical models of the circulation Waves in the ocean including surface waves, inertial oscillations, tides, and tsunamis. Waves in shallow water, coastal processes, and tide predictions

Four questions (cont.)  Currents What are the major currents and water masses in the ocean? What governs their distribution? How does the ocean interact with the atmosphere?

Organization  A brief overview of what is known about the oceans  A description of the ocean basins, for the shape of the seas influences the physical processes in the water  The external forces, wind and heat, acting on the ocean, and the ocean’s response  Dynamic response of the oceans The equations of motion, the influence of Earth’s rotation, and viscosity

Organization (cont.)  Wind-driven ocean currents The geostrophic approximation The usefulness of conservation of vorticity  Particular examples The deep circulation The equatorial ocean and El Ni˜no The circulation of particular areas of the oceans  Numerical models  Coastal processes Waves, tides, forecasting, tsunamis, and storm surges

Big Pictures  Theory Ocean processes are nonlinear and turbulent We don’t really understand the theory of non-linear, turbulent flow in complex basins Theories used to describe the ocean are much simplified approximations to reality  Observations Sparse in time and space Provide a rough description of the time-averaged flow Many processes in many regions are poorly observed

Big Pictures (cont.)  Numerical models Include much-more-realistic theoretical ideas Help interpolate oceanic observations in time and space Forecast climate change, currents, and waves Approximations to the continuous analytic equations that describe fluid flow Contain no information about flow between grid points Cannot yet be used to describe fully the turbulent flow seen in the ocean

Big Pictures (cont.)  We use theory, observations, and numerical models to describe ocean dynamics  Neither is sufficient by itself!

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