Atmospheric Energetics in the Wavelet Domain. Part II: Time-Averaged Observed Atmospheric Blocking

Abstract

Wavelet energetics (WE) is a useful generalization of traditional wavenumber energetics, for analyzing atmospheric dynamics. WE is doubly indexed by wavenumber band j and location k. The interpretation is that 2 to the jth power is proportional to zonal wavenumber bandwidth and bandcenter, and k is proportional to longitude. Here, all 44 Atlantic and 16 Pacific atmospheric blocking events that are observed in 53 winters of the NCEP–NCAR reanalysis, and last no less than 6 days, are analyzed. Temporal average and variance maps suggest that persistent blocking structures are associated with smaller-scale eddy activity concentrated on either side of the block. Wavelet energetics, partitioned by blocking state and sector, are averaged over 30°–80°N and 10–100 kPa. For j above two, WE indicates that kinetic energy (KE) and enstrophy increase upstream and decrease downstream of both Atlantic and Pacific blocking. At smaller j the increases are at the block; this includes zero j for Pacific, but not Atlantic. As measured by new wavelet flux functions, at j above one, on average there are localized upscale KE and enstrophy cascades upstream, and localized downscale cascades downstream of the blocks. This is not significantly determined for KE in the Atlantic. Correlating WE, blocking relative to nonblocking, suggests a similarity of Pacific to Atlantic energetic patterns if the former are shifted over the latter; this holds for all enstrophy WE, and for KE stocks, but not for other KE wavelet energetics. The theoretical conservation of wavelet flux is numerically supported. Statistical significance is strongly suggested, if not rigorously established.