Operations Updates
ARM Climate Research Facility Operations Update - January 15, 2006
This bimonthly report provides a brief summary of significant accomplishments and activities in the operations area of the ARM Climate Research Facility (ACRF).
ARM Mobile Facility Begins Year-Long Deployment in Africa
Beginning on January 9, the ARM Mobile Facility began officially collecting atmospheric data from a location at the airport in Niamey, Niger, Africa. As part of the RADAGAST field campaign, the AMF will measure the effects of absorbing aerosols from desert dust in the dry season, and the effects of deep convective clouds and associated moisture loadings on the transmission of atmospheric radiation during the summer monsoon. These measurements will be combined with associated satellite data to provide the first well-sampled direct estimates of the energy balance across the atmosphere. This dataset will provide valuable information to an ongoing effort called the African Multidisciplinary Monsoon Analysis, or AMMA, in which scientists are studying the interaction between West African monsoon dynamics and scale, continental water cycle, aerosols, atmospheric chemistry, food, water and health. For more information, see the DOE Press Release.
Routine maintenance at the ancillary site includes resupplying the cooler (inside the large white box) that keeps the instrument system's batteries at an even temperature in the hot Sahel environment.
From November 28 to December 2, 2005, ARM scientists involved in the RADAGAST field campaign traveled to Dakar, Senegal, to participate in the AMMA 2005 DAKAR International Conference. They presented various aspects of the AMF deployment to more than 255 attendees from 23 countries. They also discussed the relationship between the AMF and other AMMA observation stations in and near Niamey with regional officials and national meteorological authorities. After the conference, they traveled to Niamey to check on the status and readiness of the AMF at the airport site. They inspected preliminary data streams and recommended some minor site modifications. They then visited the ancillary site about 60 km away, in Banizoumbou, and assisted with instrument systems there.
A recent development in the scientific enhancement to the campaign was the welcome announcement that a scanning C-Band radar, sponsored by the National Aeronautics and Space Administration, will soon be deployed to Niamey. This radar will record the intensity and track the movement of precipitating weather systems within a few hundred kilometers from the AMF during the summer monsoon (rainy) season. Additional data provided by the radar will help in the interpretation of data collected by the various AMF remote sensing systems.
Location, Location, Location... Field Campaign Focuses on Latitude Effects
A scintillometer was used to detect atmospheric optical disturbances-called scintillations-caused by temperature, pressure and humidity. The instrument emits light from two transmitters, shown at left. The light traverses the local atmosphere, perturbed by density fluctuations. Some of the light enters the receiver, shown at right. (Image from Scintec at www.scintec.com.)
This month, scientists from the University of Alaska-Fairbanks and the U.S. Army Research Laboratory (ARL) completed a joint field campaign at the ACRF site in Barrow, Alaska. The objective of the year-long "High Latitude Optical Turbulence Characterization" field campaign was to characterize near-surface atmospheric optical turbulence over a flat, relatively low humidity, high-latitude location. Results from the data collection effort will be compared to those from an equivalent flat, relatively low humidity, mid-latitude desert site. Ultimately, these comparisons will be used to improve the ARL Surface Layer Stability Transition Forecast Model, which was shown to display a strong seasonal contribution in the diurnal atmospheric stability transition patterns.
In a reciprocal setup, each side of the instrument has both a transmitter and a receiver; shown is an enclosure containing both.
On the left is a view of the transmitter from the back with the enclosure open (top), and a view from the front with the enclosure closed (bottom). A circle of red LEDs indicates the instrument is functioning correctly. At right is the receiver.
In September 2004, a reciprocal-path scintillometer system was set up between the ACRF Skydeck and an abandoned microwave relay tower approximately 800 m away. However, it was found that radar interference inflicted a high noise level on the data stream every few seconds, compromising the intended time averages. The data processing software was subsequently modified to provide shorter time averages to exclude the noise-impaired data (0.33 second sample rate). Software to quality control the data acquired from this revised method is now under development. Communication difficulties with hardware required a single-path scintillometer design to be utilized for a portion of the 1-year IOP.
Data from the field campaign will be used to improve the forecast model's applications. The goals are to (1) determine what, if any, latitudinal dependencies exist, and (2) better define the two extremes-hot/dry versus cold/dry-for characterizing and forecasting the surface stability transition. Applications of this model range from defining the convective modeling starting and ending points, to improving long-range electro-optical propagation opportunities.
