An Objective Composite of the African Easterly Wave Lifecycle

Matthew Janiga

What is an AEW?

From the YOTC 0.225° analysis

African easterly waves (AEWs) are defined as disturbances of the mid-level PV strip. These disturbances interact with the low-level baroclinic zone perturbing the surface θ field.

Since the July-September 1989-2005 ERA-Interim mean PV strip is best defined at 700 hPa this level is used for tracking.

Tracking Procedure

Raw ERA-Interim 700 hPa PV

After 2 day low-passAfter application of Gaussian smoothing with a radius of 6°

and one standard deviation at 3°.

1. Look for maxima within a radius of 6° which exceed 0.15 PVU and the average of that radius by 0.02 PVU.2. Continuation is determined by matching closest maxima within 6°. 3. Tracks are 1-2-1 smoothed and trimmed for continuous westward propagation.4. We select those trimmed tracks lasting > 3 days and with 15° westward movement.

Hovmöller Validation