Synoptic climatology of Northern Hemisphere available potential energy collapses

Abstract

Three recurring regional patterns of extratropical baroclinic development associated with synoptic-scale collapses of Northern Hemisphere available potential energy (APE) are identified using a 1979–95 time series derived from the National Centers for Environmental Prediction (NCEP) reanalysis. A time 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 depletion 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 APE depletion events with maximum depletion rates (dA/dt_min) and maximum APE falls (ΔA_min) of less than — 0.145×10⁶ J m^-2 day^-1 and —0.280×10⁶ J m^-2, respectively. All are cold season (15 October–15 April) events. APE collapses were classified based on the evolution of regional synoptic 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 with an intense southerly flow across the Bering Strait brought on by cyclogenesis near the Kamchatka Peninsula and an intense anticyclone over Alaska. The 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.