In 2006, NASA led a field campaign to investigate the factors that control the fate of African easterly waves (AEWs) moving westward into the tropical Atlantic Ocean. Aircraft and surface-based equipment were based on Cape Verde's islands, helping to fill some of the data void between Africa and the Caribbean. Taking advantage of the international African Monsoon Multidisciplinary Analysis (AMMA) program over the continent, the NASA-AMMA (NAMMA) program used enhanced upstream data, whereas NOAA aircraft farther west in the Atlantic studied several of the storms downstream. Seven AEWs were studied during AMMA, with at least two becoming tropical cyclones. Some of the waves that did not develop while being sampled near Cape Verde likely intensified in the central Atlantic instead. NAMMA observations were able to distinguish between the large-scale wave structure and the smaller-scale vorticity maxima that often form within the waves. A special complication of the east Atlantic environment is the Saharan air layer (SAL), which frequently accompanies the AEWs and may introduce dry air and heavy aerosol loading into the convective storm systems in the AEWs. One of the main achievements of NAMMA was the acquisition of a database of remote sensing and in situ observations of the properties of the SAL, enabling dynamic models and satellite retrieval algorithms to be evaluated against high-quality real data. Ongoing research with this database will help determine how the SAL influences cloud microphysics and perhaps also tropical cyclogenesis, as well as the more general question of recognizing the properties of small-scale vorticity maxima within tropical waves that are more likely to become tropical cyclones.
University of Utah, Salt Lake City, Utah
Oregon State University, Corvallis, Oregon
NASA Goddard Space Flight Center, Greenbelt, Maryland
Science Systems and Applications, Inc., Lanham, Maryland
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California
The Florida State University, Tallahassee, Florida
Earth System Science Interdisciplinary Center, University of Maryland, College Park, College Park, Maryland
Howard University, Washington, D.C.
NASA Langley Research Center, Hampton, Virginia
NASA Marshall Space Flight Center, Huntsville, Alabama
National Center for Atmospheric Research, Boulder, Colorado
University of Maryland, Baltimore County, Baltimore, Maryland
NOAA/AOML/Hurricane Research Division, Miami, Florida
NOAA/National Severe Storms Laboratory, Norman, Oklahoma
Colorado State University, Fort Collins, Colorado