Synoptic energetics of planetary-scale collapses of available potential energy.

摘要

We identify physical processes and localized atmospheric structures that modulate the global-scale atmospheric available potential energy (APE). A 1979--95 time series of Northern Hemisphere APE is derived from the National Centers for Environmental Prediction (NCEP) reanalysis. We discern an average three-day cycle in the APE depletion rate dA/dt with a time series of intraseasonal (1.6--180-day) fluctuations. Synoptic-scale APE depletion events are falls and subsequent rises in dA/dt, and are classified as APE collapses when exceeding climatologically-derived thresholds of APE fall and dA/dt. Three associated regional baroclinic waves are observed. West Pacific warm surges (Type A) accompany cyclogenesis over Japan, anticyclogenesis over the west-central North Pacific, and shallow East Asian cold surges. Bering warm surges (Type B) comprise intense southerly flow across the Bering Strait, cyclogenesis near the Kamchatka Peninsula, and intense anticyclogenesis over Alaska. Atlantic Canada warm surges (Type C) include onshore warm flow and eastern North American storm tracks.; January/February 1989 brought the largest vacillation- and synoptic-scale APE collapses of the study period. A pronounced Madden-Julian Oscillation (MJO) modulated equatorial convection over the Indian Ocean during the APE build-up. The initial APE collapse coincided with Type A development and intensifying MJO convection shifting to the West Pacific warm pool, which was prominent because of the 1988--89 La Nina. Extensive large-scale ascent amplified the thermally direct Hadley cell circulation, with descent strong over East Asia. The second collapse was associated with Type B development characterized by a record-breaking Alaska anticyclone.; Factors explaining lacking precision in energy budget calculations include missing o values above 100 hPa, limited representation of subgrid processes, and limited temporal resolution of diurnal convection over tropical landmasses.; Correlation analysis shows baroclinic conversion (diabatic generation) accounting for 80% (20%) of vacillation-scale dA/dt fluctuations. Baroclinic conversion contributes considerably (69%) to the synoptic variability only during synoptic-scale APE collapses (23 January to 4 February), illustrating the prominence of resolvable baroclinic processes during these periods.