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Title: Potential Vorticity Generation by West African Squall Lines
The West African summer monsoon features multiple, complex interactions between African easterly waves (AEWs), moist convection, variable land surface properties, dust aerosols, and the diurnal cycle. One aspect of these interactions, the coupling between convection and AEWs, is explored using observations obtained during the 2006 African Monsoon Multidisciplinary Analyses (AMMA) field campaign. During AMMA, a research weather radar operated at Niamey, Niger, where it surveilled 28 squall-line systems characterized by leading convective lines and trailing stratiform regions. Nieto Ferreira et al. found that the squall lines were linked with the passage of AEWs and classified them into two tracks, northerly and southerly, based on the position of the African easterly jet (AEJ). Using AMMA sounding data, we create a composite of northerly squall lines that tracked on the cyclonic shear side of the AEJ. Latent heating within the trailing stratiform regions produced a midtropospheric positive potential vorticity (PV) anomaly centered at the melting level, as commonly observed in such systems. However, a unique aspect of these PV anomalies is that they combined with a 400–500-hPa positive PV anomaly extending southward from the Sahara. The latter feature is a consequence of the deep convective boundary layer over the hot Saharan Desert. Results provide evidence of a coupling and merging of two PV sources—one associated with the Saharan heat low and another with latent heating—that ends up creating a prominent midtropospheric positive PV maximum to the rear of West African squall lines.  more » « less
Award ID(s):
1853633
PAR ID:
10158149
Author(s) / Creator(s):
;
Date Published:
Journal Name:
Monthly Weather Review
Volume:
148
Issue:
4
ISSN:
0027-0644
Page Range / eLocation ID:
1691 to 1715
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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