ENSO_2010

ENSO_2010 - Tropical Circulation in a Global Context Mean...

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Unformatted text preview: Tropical Circulation in a Global Context Mean surface pressure and winds during DJF Westerlies Westerlies Westerlies W e s te r lie s S E t r a d e s S E t r a d e s N E t r a d e s N E t r a d e s S E t r a d e s S E t r a d e s N E t r a d e s N E t r a d e s N E t r a d e s N E t r a d e s E a s t e r l i e s E a s t e r l i e s E a s t e r l i e s E a s t e r l i e s N E t r a d e s N E t r a d e s El Nio Southern Oscillation ENSO 2 ENSO - Mode of Variability of Atmosphere-Ocean System Climate System has many modes of variability Some modes are induced by external forcing from Sun (diurnal, seasonal, Milankovitch cycle relate to changes in orbital parameters of the Earth) Some modes are internal to the system and result from complex and non-linear interactions between the systems fluids (atmosphere and ocean) over a variety of time scales 3 Internal Climate System Oscillations Climate system has its own internal oscillations independent of external forcing Modes of internal variability (Oscillations) vary over a variety of time scales Some of the strongest oscillations are: 20 100 days tropical waves (hold your curiosity for a few more classes) El Nino Southern Oscillation - ENSO North Atlantic Oscillation NAO Pacific Decadal Oscillation PDO Arctic Oscillation AO Antarctic Oscillation AAO 4 High signal in high High signal in high latitudes but can affect latitudes but can affect low latitudes too low latitudes too What is El Nio: Tropical Pacific Sea Surface Temperature Anomalies 5 History of El Nio Locally recognized in precolonial times Sir Gilbert Walker (1924) While working for the Indian Meteorological Service, he noticed pressure anomalies Attempted to relate anomalies to the failure of the Indian Monsoon, but failed H.P. Berlage (1950s): Develops Southern Oscillation Index (SOI) 1972-1973: Major El Nio causes collapse of Peruvian fishing 1983: Major El Nio causes flooding in Southern California 1998: Strongest El Nio of 20 th century Pressure Anomalies From Caviedes, C., 2001, El Nio in History Pg. 8 6 Sea Level Pressure at Darwin Negative correlation: Sea Level at S Pacific High 7 Tahiti Darwin The Southern Oscillation Index - SOI Calculated as the pressure differences between Tahiti and Darwin (Tahiti-Darwin) Negative SOI is an indicator of El Nio Sea Surface Temperature at equator and 110 o W 8 T D 9 10 11 The Walker Circulation 12 Typical Atmospheric Circulation Walker Cell 13 14 Thermocline: Depth at which the rate of decrease of temperature with increase of depth is the largest. It separates the zone between the mixed layer above, much influenced by atmospheric fluxes, and the deep ocean. In the tropics, the thermocline is shallow on average, as in the eastern Pacific (50m), or deeper as in the western part (160-200m). Overview of Atmosphere-Ocean System during El Nio Increased SST in the Eastern Pacific Weakened Easterlies...
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ENSO_2010 - Tropical Circulation in a Global Context Mean...

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