NASA's 2006 tropical cyclogenesis experiment in the east Atlantic

The origin and transformation of African easterly waves as they pass from the continent to the East Atlantic, and what controls whether they evolve into tropical cyclones, are important questions of long standing. The extensive database from the African Monsoon Multidisciplinary Analyses (AMMA) program in 2006 provided an opportunity for NASA to add a major observational component to follow disturbances out of Africa, across the coast, and well into the Atlantic. This NASA addition to AMMA became N-AMMA or simply NAMMA. During Aug.-Sept. 2006, the NASA DC-8 investigated 7 of these disturbances while based at Sal (Cape Verde), soundings were obtained at 4-hour intervals from Praia (Cape Verde), and Doppler radar data was obtained from Dakar and Praia.

The scientific objectives of NAMMA included distinguishing the characteristics of developing and nondeveloping waves, and learning the specific role of the Saharan Air Layer (SAL) in the cloud and precipitation microphysics over the Atlantic and how this may affect the fate of the storms. This presentation summarizes just a few of the early results from the NAMMA experiment, including some of the characteristics of the waves that developed, and those that failed to develop, and whether or not the interactions with the SAL may have been important. Some of the unique datasets on cloud microphysics in clean and dusty air are summarized. Last but not least, numerical simulation model output can be compared with detailed observations in some eastern Atlantic storms for the first time.