A Diagnosis of the Role of Anticyclonic Rossby Wave Breaking in Increasing Zonal Available Potential Energy

Zonal available potential energy (A_Z) is, to first order, a measure of the magnitude of meridional temperature gradients and static stability of a domain, and can act as a measure of the strength of the hemispheric general circulation. Here, we examine the role of dynamic tropopause Rossby wave breaking in supporting an environment facilitating buildups of A_Z on synoptic time scales (3-10 days). Rossby wave breaking occurs when the phase speed of a Rossby wave slows to the advective speed of the atmosphere, resulting in the cyclonic or anticyclonic breaking (CWB and AWB, respectively) of the trough and ridge associated with the wave. These events have robust dynamic and thermodynamic feedbacks through the depth of the troposphere that can modulate A_Z.

A climatology of buildup periods in A_Z as well as Rossby wave break events are objectively identified from the National Centers for Environmental Prediction Reanalysis-2 dataset from 1979 to 2011 for 20-85˚N. Anomalies in AWB and CWB are assessed seasonally for buildup periods of A_Z. Widespread positive anomalies in AWB and negative anomalies in CWB are due to a poleward-shifted jet stream, while west-east dipoles in wave breaking anomalies were attributed to elongated and contracted jet streams.

Finally, an analysis of long-duration wave break events for winter A_Z buildup events to an anomalously high state are examined using a quasi-Lagrangian grid shifting technique. Thirty-five long duration AWB events are identified and composited. These events are then analyzed through the life cycle of the event, as well as the period one day following the completion of wave breaking. We show that the AWB acts as a focusing mechanism which allows for an effective poleward transport of moisture in ascent. Following the completion of the wave break event, high latitude air mass cooling continues through radiative processes. These mechanisms play a critical role in establishing an environment poleward of the wave break capable of diabatic cooling and a region of diabatic warming near the center of the wave break event, acting to effectively generate A_Z and elongate the North Pacific jet.