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First Tropical Lecture

First Tropical Lecture

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First Tropical Lecture

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  1. First Tropical Lecture Jon M. SchrageSummer 2009

  2. Why Is Tropical Meteorology a Separate Course? • Too big to ignore • Lots of differences between the tropics and the extratropics • Interesting and unusual phenomena

  3. Differences between Tropical and Extratropical Meteorology • Physical Differences • Observation Differences • Paradigm Differences

  4. Physical Differences Warmer at the surface Colder aloft Less stable More thunderstorms Higher moisture content Warm cloud processes Weak Coriolis Force Weak temperature and pressure gradients (no fronts) Small annual cycle of temperature Relatively large diurnal cycle of temperature Differences between Tropical and Extratropical Meteorology

  5. Observation Differences Differences between Tropical and Extratropical Meteorology

  6. http://www.lib.utexas.edu/maps/national_parks/pacific_theater_1941_45.jpghttp://www.lib.utexas.edu/maps/national_parks/pacific_theater_1941_45.jpg

  7. http://www.freewebs.com/jim4jet/titlepgeMap.jpg

  8. Differences between Tropical and Extratropical Meteorology • Observation Differences • Mostly ocean • Mostly developing countries • Western interests are focused on wartime needs • Emphasis on remote sensing

  9. Differences between Tropical and Extratropical Meteorology • Paradigm Differences Paradigm: a philosophical and theoretical framework of a scientific school or discipline within which theories, laws, and generalizations and the experiments performed in support of them are formulated; broadly: a philosophical or theoretical framework of any kind (m-w.com)

  10. Differences between Tropical and Extratropical Meteorology • Paradigm Differences • Paradigms in Meteorology: • Polar Front Theory • Air Parcel Theory • Quasigeostrophic Theory

  11. Differences between Tropical and Extratropical Meteorology • Paradigm Differences • Paradigms in Meteorology: • Polar Front Theory • Air Parcel Theory • Quasigeostrophic Theory Not all of these work as well in the tropics as they do in the extratropics!

  12. Differences between Tropical and Extratropical Meteorology • Paradigm Differences • Paradigms in Meteorology: • Polar Front Theory • Air Parcel Theory • Quasigeostrophic Theory Not all of these work as well in the tropics as they do in the extratropics! • Tropical meteorologists have their own paradigms, too: • e.g., Oscillations

  13. Definitions of the Tropics • Latitudinal Definitions (used in McGregor and Nieuwolt) • e.g. 23.5°N to 23.5°S • e.g. 5°N to 5°S are the “deep tropics”

  14. Definitions of the Tropics • Climate Definitions (a la Koeppen)

  15. Definitions of the Tropics • Kinematic Definitions • e.g., where there are trade winds at the surface

  16. Definitions of the Tropics • From Buckle:

  17. Definitions of the Tropics • In this class, the tropics are where tropical weather happens.

  18. Observing the Tropics Jon M. Schrage

  19. Observing SST • Observing the Atmosphere • Divergent and Rotational Flow • Observing Precipitation

  20. Observing SST • The ocean absorbs tremendous amounts of sunlight. • All of this energy must eventually be transferred back into the atmosphere.

  21. Observing SST • Overall, the ocean has a very LOW albedo.

  22. Observing SST • SST is the single most important variable over the tropical oceans. • SST is the major factor controlling the flux of sensible heat and latent heat into the atmosphere. • Keep in mind that winds are important, too!

  23. 3 Ways to Observe SST • Buoys • Moored or drifting • A maintenance nightmare

  24. Drifting Buoys

  25. TAO Array (fixed)

  26. Example from the TAO Array

  27. 3 Ways to Observe SST 2. Ships • Merchant ships • Disadvantages: • Taken by nonprofessionals • Calibration issues • SST depends on the weight of the cargo • Limited to shipping lanes

  28. 3 Ways to Observe SST • Remote Sensing from Space • SST is one of the easiest things to estimate from space • Sea water radiates at known emissivities

  29. 3 Ways to Observe SST • Remote Sensing from Space • Problems: • Calibration issues • Bulk temperature v. skin temperature

  30. Key Features Some salient features of the global sea surface temperature distribution include:

  31. 1. Meridional SST gradients are weak in the tropics and great at midlatitudes.

  32. 2. Zonal temperature gradient across the tropical Pacific is large.

  33. January July 3. Almost no annual cycle of SST in the tropics (except in the Western Atlantic).

  34. 4. Warmest waters are in small, enclosed subtropical basins…

  35. Key Features 5. The Western Pacific Warm Pool– the warmest open-ocean water in the world.

  36. Key Features 6. The Eastern Pacific Cold Tongue is due to:

  37. 1. The cold “Humbolt Current” of the South Pacific Gyre.

  38. 2. Upwelling off the coast of Peru and Chile.