Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Geological and Atmospheric Sciences


The spectral energetics of individual blocking case studies selected from the winters of 1976-77, 1977-78, and 1978-79 are calculated. The time evolution and geographical distribution of the energetics of the ensembles of planetary-scale waves (zonal harmonic wavenumbers 1-4) and intermediate-scale waves (zonal harmonic wavenumbers 5-10) are examined to qualitatively identify the physical mechanisms important in the blocking process;Distinctions are drawn between blocks occurring over the North Atlantic and North Pacific Oceans, as well as between high latitude and middle latitude blocks. Two distinct forcing mechanisms were found. Atlantic blocking in our sample of cases was forced primarily by the nonlinear interaction of intense, baroclinic cyclone-scale waves with the ultralong waves. Pacific blocking resulted from the baroclinic amplification of planetary-scale waves;In addition, at least two necessary conditions are required for the development of blocking. First, one of the forcing mechanisms must be in operation, and second, the phase of the antecedent planetary-scale waves must be such that the forcing mechanism can amplify them into a blocking pattern. Energetically similar developments that lead to blocking in some instances fail to do so in others, apparently because the position of the existing planetary-scale waves is not conducive to block development;In each of the cases studied, the block developed downstream of intense cyclogenesis at either intermediate or planetary-scale wave-lengths. The possible relationship between this cyclogenesis, subsequent block development, and the pattern of sea surface temperature anomalies in the western portions of the oceans is discussed.



Digital Repository @ Iowa State University,

Copyright Owner

Anthony Regis Hansen



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198 pages