92nd American Meteorological Society Annual Meeting (January 22-26, 2012)

Thursday, 26 January 2012
A Multiscale Analysis of African Easterly Waves
Hall E (New Orleans Convention Center )
Chris Thorncroft, University at Albany, SUNY, Albany, NY

The life-cycle of African easterly waves will be reviewed. Based originally on the work of Berry and Thorncroft (2005) a conceptual AEW life-cycle is envisaged with 3 phases: (i) Initiation, (ii) Baroclinic developments and (iii) West coast developments. (i) Initiation: Results indicate that the genesis of the AEWs is often preceded by several mesoscale convective systems (MCSs) triggered over elevated terrain. We hypothesize that the dynamical response to the heating associated with this outbreak of convection close to the axis of the African easterly jet (AEJ) results in downstream development of baroclinically growing AEWs. Recent published work has also suggested a role for midlatitude troughs in this stage. (ii) Baroclinic Development: Synoptic scale perturbations to the low-level gradient interact with synoptic scale perturbations to the AEJ level potential vorticity (PV) strip, that includes sub-synoptic PV anomalies associated with mesoscale convective systems (MCSs). The synoptic perturbations can move together coherently for several days in a configuration that is consistent with baroclinic growth and offers an ideal opportunity to study scale interactions n the tropics. (iii) West Coast Developments: As the AEW trough approaches the West African coast, significant convection develops over the Guinea highlands and coastal region. The PV generated in the Guinea highlands region merges with the sub-synoptic scale PV anomalies embedded in the propagating AEW. This presentation will review these aspects from a historical perspective and will provide perspectives for future research.

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