ARL Weekly News – May 25, 2018

Alice Crawford and Barbara Stunder are supporting the Washington Volcanic Ash Advisory Center (VAAC) in the VAAC’s response to the ongoing Kilauea eruption. They have been participating in daily conference calls with U.S. Geological Survey (USGS), VAAC, and Honolulu Weather Forecast Office staff. Alice is posting, on a password protected web page, ash dispersion graphics daily for an assumed continuous release based on the occasional brief ash eruptions that are occurring. Barbara added Kilauea to the hypothetical eruptions and trajectory web pages at The trajectories are run by the National Centers for Environmental Prediction (NCEP) but the graphics created by Barbara’s job and posted on the ARL server. (The transfer of the graphics processing to NCEP is in progress.)

Paul Kelley, Xinrong Ren, and Winston Luke installed in situ trace gas instrumentation (O3, CO, SO2, NO, NO2, NOY, and Hg0) in advance of the Ozone Water-Land Environmental Transition Study 2 (OWLETS-2), a NASA study examining the roles played by chemistry and meteorology in controlling levels of photochemical ozone and fine particulate pollution around the Northern Chesapeake Bay. The instrumentation was loaded into a trailer owned by the University of Maryland Baltimore County, and floated by barge to Hart-Miller Island, approximately 10 miles east of Baltimore’s Inner Harbor. The instruments were installed and calibrated, and are functioning well. Instrumentation to measure CO2, CH4, and H2O vapor will be installed next week. The project will formally start on June 6, and will continue for one month. ​​​Mark Cohen has developed forecast products for the Baltimore-Washington region for OWLETS-2, to inform flight planning of research aircraft, deployment of mobile sampling platforms (boats, automobiles), and preparation of special sampling programs at ground sites (e.g., ozonesonde launches, etc.).The product is nominally produced four times per day, and is based on the NOAA North American Mesoscale Forecast System 4km 48 hour forecast. Each PDF file contains an explanatory cover page and 47 hourly forecast pages. The graphics and other post-processing are being done with the NOAA HYSPLIT model. An example of the product is available here, and all current and past products are available here. The product is also being made available to study participants through a Google Group to which emails containing a link to each new product are automatically sent as soon as it is posted.

Now published: Plume Dispersion in Low-Wind-Speed Conditions During Project Sagebrush Phase 2, with Emphasis on Concentration Variability by D. Finn, R. G. Carter, R. M. Eckman, J. D. Rich, Z. Gao, and H. Liu. Abstract: Eight short-range, open-terrain SF6 tracer tests in low wind speeds were conducted during Phase 2 of Project Sagebrush using continuous releases. Four tests were made during very unstable conditions in July and August 2016, and four during very stable conditions in October 2016. All tests featured 10-min averaging and 1-Hz sampling of tracer concentrations together with an extensive suite of meteorological measurements. We find that the uncertainty in well-mixed daytime measurements of tracer concentrations, using the absolute value of the relative percentage difference in collocated duplicate samplers, approaches a downwind limit of about 7-8%. Concentration variability in collocated sampling, due to stochastic factors and independent of measurement uncertainty, increases the total observational uncertainty closer to the source from about 20% (daytime) to 40% (very stable conditions). Longer averaging periods moderately reduce the concentration variability. The data indicate that the large increase in concentration variability is linked with the suppression of turbulent mixing, small eddy length scales, and meandering in very stable conditions. These results should be considered when comparing observations with model predictions in evaluations.