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VOLUME 88 NUMBER 40 2 OCTOBER 2007
Each year, devastating hurricanes originat-
ing from the tropical Atlantic Ocean cause
severe loss of life and property damage.
Efforts to predict and forecast the behavior of
such phenomena range from satellite-derived
sea surface temperatures to coupled ocean-
atmosphere models. Nonetheless, predicting
cyclone occurrence and behavior remains
elusive.
New research suggests that the presence of
lightning activity in storms crossing the West
African coast could be used as a precursor to
cyclone formation. This article analyzes the
lightning activity monitored during the 2004
hurricane season by the University of Con-
necticut’s Zeus Long-Range Lightning Moni-
toring Network (http://sifnos.engr.uconn
.edu/realtime.htm). The Zeus system was
used to follow the westward progression of
African Easterly Waves (AEWs) and their
embedded convective regimes, as these
propagate over continental Africa and fi nally
cross into the Atlantic Ocean. Those distur-
bances that exhibit sustained lightning in the
Atlantic were shown to be far more likely to
produce tropical cyclones (TCs) than those
for which lightning ceases at the coast.
Lightning in African Easterly Waves
During boreal summer, AEWs are formed
as the result of strong lower atmospheric
contrasts in temperature, moisture, and
wind fl ow properties across West Africa.
The AEWs propagate westward with varying
periods (3–6 days) and with typical wave-
lengths ranging from 2000 to 3000 kilome-
ters. Typically, 30–60 AEWs are produced
during each boreal summer [Avila and
Pasch, 1992]. Roughly 10% of these distur-
bances become “seeds” for the development
of TCs and potential hurricane formation off
the West African coast, especially between
the latitudes of 10º and 15ºN [Carlson, 1969].
A key component to the generation of these
cyclones is vertical air motion that concen-
trates the necessary angular momentum of
the local atmosphere. This vertical motion,
associated with deep convective cloud s