Dust from Africa's Sahara desert - the largest source of dust on the planet--reaches halfway around the globe. Carried by winds and clouds, the dust travels through West African, Mediterranean, and European skies, and across the Atlantic into North America. Unfortunately, Africa is one of the most under-sampled climate regimes in the world, leaving scientists to wonder about its contribution to global climate.

"As a point of origin for atmospheric disturbances that evolve into Atlantic storms, the Sahara is not only a driving force for the environmental conditions in Western Africa, but also for the development of weather systems that can reach the United States," said Dr. Raymond Orbach, Director of DOE's Office of Science.

"Our ability to predict the impact of the Saharan dust on weather and climate is dependent on gathering accurate and long-term data sets for computer models that simulate these effects."

Beginning in January, at a site in Niamey, Niger, the ARM Mobile Facility (AMF) will collect atmospheric data on absorbing aerosols from desert dust in the dry season, and deep convective clouds and large moisture generation during the summer monsoon.

Measurements obtained by the AMF will provide information about heating and cooling (known as "radiative feedback") of the Earth's atmosphere, the interaction of clouds with dust and aerosols, and West African monsoons. This will allow scientists to study possible reasons for the ongoing drought in West Africa and the genesis of tropical waves that may evolve into hurricanes.

Natural phenomena, such as the fine-powder dust found in the skies of Africa, present a particularly difficult challenge to scientists studying how dynamic cloud conditions affect the sun's incoming and Earth's outgoing energy and, in the longer term, our climate. As stated by President Bush, "The issue of climate change respects no border. With its potential to impact every corner of the world, climate change is an issue that must be addressed by the world."

Niger is located on the southern border of the Sahara, which covers most of North Africa. Niamey, its capital, is in southwest Niger, and is one of several sites throughout Western Africa involved in an international study known as the African Monsoon Multidisciplinary Analysis, or AMMA.

Scientists involved in AMMA are using airplanes, satellites, and instrumented ground stations to collect data for studying the interactions between monsoon dynamics and scale, continental water cycle, aerosols, atmospheric chemistry, food, water, and health. The extended series of measurements from the AMF, combined with those from satellite instrumentation sponsored by the European Union, will provide the first well-sampled, direct measurements of the solar and thermal radiation across the atmosphere.

Scientists sponsored by the ARM Program focus on the goal of reducing uncertainty and improving the representation of clouds and radiative feedback processes in climate models. They accomplish this by analyzing data collected from state-of-the-art remote-sensing instruments and radars situated in three primary climate regimes--high latitudes in Alaska, mid-latitudes at the Southern Great Plains in Oklahoma, and low latitudes in the Tropical Western Pacific. The portability of the AMF now allows scientists to study different climates--like the hot and dusty Sahara--for up to one year.

The AMF consists of two lightweight shelters and a baseline suite of instruments, data communications, and data systems. Its measurement capabilities include standard meteorological instrumentation, a broadband and spectral radiometer suite, and remote sensing instruments.

It can also accommodate instruments in addition to, or in place of, the baseline collection. Numerous DOE laboratories are involved in the scientific and operational capabilities of the AMF, including Brookhaven National Laboratory, Los Alamos National Laboratory, and Pacific Northwest National Laboratory.

Data obtained by the AMF during the international AMMA project will enable scientists to study the impact of Saharan dust on cloud properties and atmospheric absorption of radiation and to better quantify the impact of dust on cloud formation, precipitation, storm creation, and cloud dynamics. Ultimately, this information will help to improve model simulations of global climate, as well as increase scientific understanding of the influence of the West African Monsoon on the physical, chemical, and biological environment, both regionally and globally.

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