Prominent Northern Hemisphere Winter Blocking Episodes and Associated Anomaly Fields of Sea Surface Temperatures

Abstract

From a 34-year data period, twelve major winter blocking episodes in the northern hemisphere are selected for examination: four episodes for each category of Pacific, Atlantic and double blocking. It is shown that the single blockings in the Pacific or Atlantic are formed through constructive interference of the traveling zonal wave of n=1 and stationary wave of n=2. The n=1 is supported by the energy input through the nonlinear wave-wave interaction, and the n=2 by in situ warming over the Pacific and Atlantic. The concurrent double blocking in the Pacific and Atlantic are formed by the stationary n=2 when the traveling n=1 is weak. The negative anomaly fields of sea surface temperatures in the Pacific and Atlantic are associated with the single blocking in the Pacific and Atlantic. On the contrary, the positive anomalies in both the Pacific and Atlantic are associated with concurrent Pacific and Atlantic blockings, indicating the baroclinic nature of the double blocking.

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