Interdecadal Variation in U.S. Pacific Coast Precipitation over the Past Four Decades

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  • 1 Atmospheric Science Program, Department of Geological and Atmospheric Sciences, Iowa State University, Ames, Iowa
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The interdecadal variation of precipitation along the U.S. Pacific coast over the past 45 winters (1950–94) was examined with station observations. An interdecadal decreasing (minor increasing) trend appeared north (south) of 36°N. This interdecadal trend in precipitation is related to the development of an anomalous dipole structure (a major anomalous high centered over the Pacific coast at British Columbia and a minor anomalous low centered over northern Baja California) throughout the past several decades. The correlation coefficient patterns between the Pacific coast precipitation and upper-air geopotential heights, and the difference charts of upper-air geopotential heights between the first (1950–59) and last (1985–94) 10 winters revealed that the interdecadal variation of the western U.S. circulation is a part of that in the Northern Hemisphere wintertime circulation. In turn, the interdecadal variation of the Pacific coast precipitation is a consequence of the interdecadal variation of the Northern Hemisphere wintertime circulation.

Corresponding author address: Tsing-Chang Chen, 3010 Agronomy Hall, Atmospheric Science Program, Department of Geological and Atmospheric Sciences, Iowa State University, Ames, IA 50011. E-mail: ZNTCC@CLIMATEl.AGRON.IASTATE.EDU

The interdecadal variation of precipitation along the U.S. Pacific coast over the past 45 winters (1950–94) was examined with station observations. An interdecadal decreasing (minor increasing) trend appeared north (south) of 36°N. This interdecadal trend in precipitation is related to the development of an anomalous dipole structure (a major anomalous high centered over the Pacific coast at British Columbia and a minor anomalous low centered over northern Baja California) throughout the past several decades. The correlation coefficient patterns between the Pacific coast precipitation and upper-air geopotential heights, and the difference charts of upper-air geopotential heights between the first (1950–59) and last (1985–94) 10 winters revealed that the interdecadal variation of the western U.S. circulation is a part of that in the Northern Hemisphere wintertime circulation. In turn, the interdecadal variation of the Pacific coast precipitation is a consequence of the interdecadal variation of the Northern Hemisphere wintertime circulation.

Corresponding author address: Tsing-Chang Chen, 3010 Agronomy Hall, Atmospheric Science Program, Department of Geological and Atmospheric Sciences, Iowa State University, Ames, IA 50011. E-mail: ZNTCC@CLIMATEl.AGRON.IASTATE.EDU
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