Journal
MONTHLY WEATHER REVIEW
Volume 143, Issue 12, Pages 4975-4995Publisher
AMER METEOROLOGICAL SOC
DOI: 10.1175/MWR-D-15-0106.1
Keywords
Circulation; Dynamics; Trajectories; Waves; atmospheric; Atm; Ocean Structure; Phenomena; Tropical cyclones; Mathematical and statistical techniques; Regression analysis; Models and modeling; Reanalysis data; Variability; Tropical variability
Categories
Funding
- NASA [NNX10AU44G]
- National Science Foundation (NSF)
- NASA [NNX10AU44G, 121995] Funding Source: Federal RePORTER
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African easterly waves (AEWs) are objectively tracked between West Africa and the tropical Atlantic based on the CFSRv2 data for 1979 to 2012. The characteristics of the troughs of the AEWs at the West African coast are explored and related to whether they favor tropical cyclogenesis over the eastern Atlantic. A logistic regression model was used to determine the optimum combination of predictors that relate AEW characteristics to tropical cyclogenesis. The most skillful model for genesis over the eastern Atlantic consisted of four variables of the AEWs dynamics over the coastal region and the absolute number of days from the peak in the AEW season. Using this diagnostic an equal number of favorable developing and nondeveloping waves were compared through a composite difference analysis. Favorable developing waves had significantly higher moisture content in the lower troposphere to the northwest of the trough as they exited the West African coast compared to favorable nondeveloping waves. Trajectory analysis for all the waves revealed that as the AEWs transition over the West African coast the troughs are typically open to the environment ahead and to the northwest of the trough. For developing waves this means that moist air is ingested into the lower levels of the system, while for nondeveloping waves dry air is ingested. At this point in the AEW life cycle this difference may be fundamental in determining whether a favorable wave can develop or not.
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