Niamey Dust Product from AOS and MFRSR Measurements
| Annette Koontz | Pacific Northwest National Laboratory |
| Connor Flynn | Pacific Northwest National Laboratory |
| Anne Jefferson | NOAA GMD |
Category: Aerosols
Although the radiation budget at the top of the atmosphere is now well determined by satellite, significant disagreement persists between measured and modeled fluxes at the surface. As a result, estimates of the globally averaged absorption of solar and infrared radiation within the atmosphere vary by tens of watts per square meter. In 2006, the ARM Mobile Facility (AMF) was deployed in Niamey, Niger, to help address the disparity in radiation budget at the surface. This one-year deployment included observations during the dry season with intense Saharan dust storms and throughout the monsoon season with deep convective clouds and heavy column water vapor burdens. Thus, the AMF sampled many of the sources hypothesized to contribute to radiative absorption. The Saharan dust storms are also of interest due to long-distance transport observed to extend across the Atlantic Ocean and even to the Pacific coast of the Americas.
Dust storms at Niamey have several identifying characteristics that help to distinguish them from combustion and locally generated sources. During dust events, measurements of surface properties are dominated by the large particle size fraction. In addition the dust particles, while somewhat absorbing still have significantly higher single-scattering albedo than aerosols and soot associated with local biomass burning. Similar observations hold for the column optical depth with large particle sizes leading to near-zero angstrom exponent in tandem with very high aerosol optical depths.
We present initial results combining a time series of column-integrated optical depth measurements with in situ measurements of surface aerosol properties at the AMF deployed in Niamey, Niger throughout 2006. Included with this time series is a determination of whether the conditions comprise a “dust event” dominated by non-local sources such as a Saharan dust storm or whether the conditions are typical of local influences such as biomass burning.
The column optical depth measurements were determined from Multi-Filter Rotating Shadowband Radiometer (MFRSR) data at 5 wavelengths (nominally 415 nm, 500 nm, 615 nm, 673 nm, 870 nm) in 15 second intervals during daylight hours, and from nearby Aeronet sun photometer measurements collected on a coarser temporal scale at Niamey and Banizoumbou. In-situ measurements of surface optical properties were collected by the Aerosol Observation System (AOS). AOS princip
This poster will be displayed at ARM Science Team Meeting.
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