Simulating Wet Deposition of Radiocesium from the Chernobyl Accident

In response to the Chernobyl nuclear power plant accident of 1986, a cesium-137 deposition dataset was assembled. Most of the airborne Chernobyl cesium was wet deposited, either via interception by falling raindrops or via absorption into cloud droplets destined to become raindrops. The Hybrid Single-Particle Lagrangian rated Transport (HYSPLIT) model, developed at Air Resources Laboratory, is used to simulate the transport and deposition of Chernobyl cesium-137. A cloud base parameterization modification is tested and appears to slightly improve the accuracy of one HYSPLIT simulation of daily Chernobyl cesium-137 deposition over the course of the accident at isolated European sites, and degrades the accuracy of another HYSPLIT simulation of deposition in Germany and Austria accumulated in the month of April 1986. Large uncertainties in the emission specifications, model precipitation fields, and deposition measurements prevent designating the results as conclusive, but most evidence points to improved performance within 50 kilometers of the emission source. Trial and error lessons learned from hundreds of preliminary model runs are documented, and the exact HYSPLIT settings of successful and meaningful simulations are appended