US Long-Term Ecological Research Network
Relations between El Nino/southern oscillation events and the climate and ice cover of lakes in Wisconsin
The term El Nino refers to the anomalous warming of the surface water of the equatorial Pacific Ocean, which occurs every two to seven years (Mysak 1986). Closely connected with the phenomenon is the Southern Oscillation, which refers to the seesawing of atmospheric pressure between the southeastern and western tropical Pacific Ocean (Rasmusson and Carpenter 1982). El Nino events have been shown to consistently occur when atmospheric pressure is unusually high over the western Pacific and unusually low over the southeastern Pacific. Collectively, these two phenomena have been referred to as ENSO events. Unusual climatic conditions near the tropics have been shown to be directly associated with ENSO events: warmer and wetter than normal in Peru and Ecuador and drier than normal in Australia and Indonesia (Quinn er al. 1978, Mysak 1986). Climatic anomalies in North America include unusually warm winters in southwestern Canada (Rasmusson and Wallace: 1983) and usually cool and wet conditions in the southeastern United Stares (Mysak 1986), especially in the: winter (Barnett 1981). Little or no correlation was found between ENSO events and unusual climatic conditions in the central region of the United Stares (Barnett 1981, Ramage 1986). Most of the climatic anomalies, especially in North America have been found in the: mature phase of the ENSO event (Year 1 used later), when sea-surface temperatures in the Pacific are most unusually warm and when the ocean is providing energy into the atmospheric (Barnett 1981 ).
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LTER Network Office: University of Washington
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