Physical and Dynamical Oceanography

1. Physical and Dynamical Oceanography CLIM712 Mon@Wed: 10:30am – 11:45am Bohua Huang Climate Dynamics Program School of Computational Sciences George Mason University Center for Ocean-Land-Atmosphere Studies Phone: 301-902-1246 Email: huangb@cola.iges.org

2. References Texts: • Pond, S., and G.L. Pickard, 1983: Introductory Dynamical Oceanography. 2nd edition, 329pp, Butterworth-Heinemann. • Pickard, G.L., and W.J. Emery, 1993: Descriptive Physical Oceanography, 5th enlarged edition, 320pp, Pergamon Press. Other titles of interest: • Mellor, G.L., 1996: Introduction to Physical Oceanography, 260pp, AIP Press. • Knauss, J.A., 1997: Introduction to Physical Oceanography, 309pp, 2nd edition, Prentice-Hall. More readings: • Tomczak, M., and J.S. Godfrey, 1994: Regional Oceanography: An Introduction, 422pp, Pergamon Press. • Apel, J.R., 1987: Principles of Ocean Physics, 634pp, Academic Press. • Warren, B.A., and C. Wunsch, (ed.,) 1981: Evolution of Physical Oceanography, 623pp, The MIT Press. • Pedlosky, J., 1996: Ocean Circulation Theory,453pp, Springer.

3. Useful Websites Physical Oceanography Courses • M. Tomczak: Introduction to Physical Oceanography(http://gaea.es.flinders.edu.au/~mattom/IntroOc/newstart.html) • F. Webster: Introduction to Physical Oceanography (http://www.cms.udel.edu/mast602) • L. Talley, P. Robbins, and M. Hendershott:Introduction to Physical Oceanography (http://gyre.ucsd.edu/sio210)

4. Requirement • Attending class (advance notice of absence) • Homework: 4-5 • Mid-term exam (close book) • Final exam (open book) • (Project or term paper) Possible changes of class time: Oct. 5-7 Nov. 8-10 Nov. 29-Dec.3

5. Major Topics • Properties of seawater • T-S forcing and conservation laws • Global T-S distribution • Fluid dynamics on rotating sphere • Description of large-scale gyres • Barotropic dynamics of large-scale gyres • Mixing, turbulence, surface layer • Large-scale overturning and thermohaline circulation • Surface gravity waves (nonrotating and rotating) • Tides • Internal gravity waves • Rossby waves, instability and mesoscale eddies • Coastal processes: currents, fronts, estuaries • El Nino

6. Course Outline [Numbers in brackets give chapters to read in Descriptive Physical Oceanography, 5th Ed.(Des), and Introductory Dynamical Oceanography, 2nd Ed.(Dyn). Lectures do not cover the entirety of all chapters assigned; students will only be responsible for material covered in lectures. For some topics, additional reading materials will be supplied with class notes] • Properties of seawater [Des 2, 3, 6] • composition • equation of state • measurement: T, S, pressure • Global T-S distribution [Des 4 ] • surface profiles • vertical profiles • static stability • annual cycle and interannual variability • T-S Forcing and conservation laws [Des 5] • heat flux components • heat flux distribution • evaporation, precipitation, runoff • box models • Fluid dynamics on rotating sphere [Dyn 6, 8, 9.1-9.4] • Coriolis force • equations of motion • geostrophy • Ekman layers • Description of large-scale gyres [Des 7] • wind patterns and gyres • western and eastern boundary currents • polar currents • equatorial currents • Barotropic dynamics of large-scale gyres [Dyn 9.5-9.14] • vorticity dynamics • gyres and western boundary currents • Sverdrup, Stommel, and Munk

7. Mixing, turbulence, surface layer [supplied reading] - descriptive Kelvin-Helmholtz instability - surface mixed layer dynamics - sources of subsurface mixing • Large-scale overturning [supplied reading] - thermohaline structure and meridional overturning - advective-diffusive balance and overturning - Stommel-Arons patterns - subduction and shallow cells • Surface gravity waves (nonrotating and rotating) [Dyn 12.1-12.8, 12.10.1-12.10.3] - short and long nonrotating SGWs - Poincare and Kelvin waves - nonlinear effects • Tides [Dyn 13.1-13.7] - tidal forcing - equilibrium theory - forced response • Internal gravity waves [Dyn 12.9] - two-layer fluid - rotational effects - continuous fluid • Rossby waves, instability and mesoscale eddies [supplied reading] - Rossby wave dynamics - observations of eddies • Coastal processes: currents, fronts, estuaries [Des 8] • El Nino [supplied reading] - air-sea feedbacks - equatorial waveguide - ENSO description

8. Introduction Why is ocean important for climate? What is Physical Oceanography? How do we do it?

9. Ocean is a major component of the earth climate system

10. Ocean plays important roles in maintaining the earth climate •Ocean has large heat storage -- 3 meters of sea water has about the same heat capacity as the whole atmospheric column above it -- Ocean heat storage modulates diurnal and seasonal cycles and climate variations -- Maritime climate is generally milder than continental climate

11. • Ocean transfers heat and freshwater over a wide range of time and space scales -- The earth system is not in radiative balance -- The tropics gaining and the polar regions losing heat -- Meridional oceanic heat transport is comparable to that of the atmosphere

12. Fluctuations within the ocean affect the climate significantly. Sea surface temperature (SST) changes from year-to-year significantly. The SST anomalies can persist for a long time. Nino3 and southern oscillation indices 

13. The SST anomalies have serious consequences to the weather and climate

14. Air-sea interaction is an important source for global climate variability (e.g., ENSO) Ocean provides the “memory” of the low frequency fluctuations

15. ocean plays a significant role in the global change. The figure depicts atmospheric CO2 concentrations from 1958 to the present as measured at Mauna Loa, Hawaii. These data, obtained by Keeling and Whorf (1998), represent the longest continuous record of directly measured CO2 concentrations. As the graph of these data indicates, there has been a substantial and sustained rise in the air's CO2 content over the past four decades, from about 315 ppm to over 360 ppm.  The greenhouse effect tends to increase atmospheric temperature. Ocean is a major part of global carbon cycle and our knowledge of oceanography may be important for estimating the trend of global warming. 

16. It is likely that much of the rise in sea level has been related to the concurrent rise in global temperature over the last 100 years. On this time scale, the warming and the consequent thermal expansion of the oceans may account for about 2-7 cm of the observed sea level rise, while the observed retreat of glaciers and ice caps may account for about 2-5 cm.

17. Global ocean circulation may be changed fundamentally by global warming And the oceanic circulation change will feedback seriously to the earth climate.

18. Other issues • Knowledge of ocean circulation is important for marine biology -- T and S distribution affects organisms -- Current affects the concentration and dispersion -- Mixing and upwelling are important to provide nutrients • Knowledge of ocean circulation is helpful for environmental protection -- pollution -- oil spills -- sewage out falls -- industrial waste

19. What is Physical Oceanography? 1). A description of the temperature, salinity, and density patterns in the ocean, including their variability. 2). The three dimensional water movement (the circulation: currents and vertical movements; also, waves and tides). 3). The transfer of mass, energy, and momentum between the ocean and the atmosphere. 4). The special properties of sea water (e.g., the propagation of sound and light energy). 5). The mechanisms of these properties and processes. Simply: • What temperature is the water? • What salinity is the water? • Where is the water going? • Why is that?

20. The approach of physical oceanography research • observations to get the picture • applying laws of physics to explain the features we find (hypothesis/theory) • theory lead us to find new information (observation) • new observations test (verify, modify, or disprove) the theory (improved theory)

21. Gulf Stream: An ExampleQuestions:Why does the Gulf Stream concentrate near the western boundary?What determines its width and speed?Why are there meanders and rings?…….