GARP Atlantic Tropical Experiment

GARP Atlantic Tropical Experiment. It was a major international field campaign conducted in 1974 as a cornerstone component of the Global Atmospheric Research Programme. The experiment focused on the tropical Atlantic region to gather unprecedented observational data on tropical weather systems, particularly African easterly waves and their transformation into tropical cyclones. Its primary goal was to improve the understanding and numerical modeling of tropical convection and its role in global atmospheric circulation, directly supporting the objectives of the First GARP Global Experiment.

Background and Objectives

The experiment was conceived under the auspices of the Global Atmospheric Research Programme, a collaborative effort between the World Meteorological Organization and the International Council of Scientific Unions. It was designed to address critical gaps in understanding tropical meteorology, which was poorly represented in the numerical weather prediction models of the era, such as those being developed at the European Centre for Medium-Range Weather Forecasts. Key scientific objectives included quantifying the heat and moisture budgets of the Intertropical Convergence Zone, studying the genesis and development of tropical cyclones from African easterly waves, and investigating the role of the Saharan Air Layer. The data was intended to validate and improve the general circulation models used for both weather forecasting and climate research.

Experimental Design and Operations

The field phase was executed during the summer of 1974, centered on a dense observational network in the eastern Atlantic Ocean between Africa and the Caribbean Sea. A vast array of platforms was deployed, including research aircraft from agencies like the National Center for Atmospheric Research and NOAA Hurricane Hunters, specially equipped ships such as the RV Oceanographer, a network of rawinsonde stations along the coast of West Africa, and constant-level balloons. Satellite data from the NOAA-2 and SMS-1 satellites provided synoptic context. Operations were coordinated from main bases in Dakar, Bridgetown, and the Azores, with intensive observation periods targeting specific weather phenomena like developing tropical depressions.

Key Scientific Findings

The experiment yielded transformative insights into tropical weather systems. It provided the first comprehensive dataset detailing the structure and evolution of African easterly waves, confirming their critical role as precursors to Atlantic hurricanes. Researchers quantified the importance of latent heat release from deep convection in driving the large-scale Hadley cell circulation. Studies of the Saharan Air Layer revealed its complex influence, often suppressing convection near Africa but potentially contributing to cyclone intensification later. The data also led to improved parameterizations of cumulus convection in numerical models, addressing a long-standing weakness in simulating the tropical troposphere.

Legacy and Impact

The legacy of the experiment is profound and enduring. It set the standard for large-scale, multi-national atmospheric field campaigns, directly influencing the design of subsequent projects like the TOGA COARE and DYNAMO projects. The vast dataset became a benchmark for testing and developing parameterization schemes in general circulation models, significantly improving the skill of numerical weather prediction in the tropics at centers like the European Centre for Medium-Range Weather Forecasts. Furthermore, it established a foundational understanding of tropical cyclogenesis that continues to inform forecast methodologies at the National Hurricane Center and research at institutions like the University of Miami.

Data and Publications

The data collected during the experiment was meticulously archived and remains a valuable resource for climate and weather research. Key datasets include enhanced rawinsonde soundings, aircraft reconnaissance, ship-based measurements, and satellite-derived products. Major findings were disseminated through a dedicated series of reports by the World Meteorological Organization and in seminal issues of journals like the Bulletin of the American Meteorological Society. The collective work contributed significantly to the scientific basis of the First GARP Global Experiment and was synthesized in influential monographs by leading scientists from the National Center for Atmospheric Research and the Massachusetts Institute of Technology.

Category:Atmospheric science Category:Meteorological expeditions and field projects Category:1974 in science