Synoptic climatology of Northern Hemisphere available potential energy collapses

Three recurring regional patterns of extratropical baroclinic development a ssociated with synoptic-scale collapses of Northern Hemisphere available po tential energy (APE) are identified using a 1979-95 time series derived fro m the National Centers for Environmental Prediction (NCEP) reanalysis. A ti me series of the intraseasonal signal (from 1.6 to 180 days) of APE is used to discern an average cycle of approximately 3 days in the APE generation rate dA/dt (referred to as APE. depletion rate if negative). An APE depleti on event is defined as a fall and subsequent rise in the time series of dA/ dt associated with this cycle. We define synoptic-scale APE collapses as AP E depletion events with maximum depletion rates (dA/dt(min)) and maximum AP E falls (Delta A(min)) of less than -0.145 x 10(6) J m(-2) day(-1) and -0.2 80 x 10(6) J m(-2), respectively. All are cold season (15 October 15 April) events. APE collapses were classified based on the evolution of regional s ynoptic patterns during the 2 days centered at the time of dA/dt(min). All are accompanied by deep tropospheric warming. The west Pacific warm surge ( Type A) is driven by cyclogenesis over Japan and anticyclogenesis over the west-central North Pacific. The Bering warm surge (Type B) is associated wi th an intense southerly Row across the Bering Strait brought on by cyclogen esis near the Kamchatka Peninsula and an intense anticyclone over Alaska. T he Atlantic Canada warm surge (Type C) is characterized by an onshore flow of warm air ahead of a continental storm track over eastern North America.