Location, Location, Location… Field Campaign Focuses on Latitude Effects

Published: 15 January 2006

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 [http://www.scintec.com][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 ARM 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 September 2004, a reciprocal-path scintillometer system was set up between the ARM 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.

In a reciprocal setup, each side of the instrument has both a transmitter and a receiver; shown is an enclosure containing both. ARM file photo.

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. ARM file photo.

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.

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The ARM Climate Research Facility is a DOE Office of Science user facility. The ARM Facility is operated by nine DOE national laboratories, including .