APL Colloquium

May 9, 2003

Colloquium Topic: The Electro-Meteorology of Dust Devils

Dust devils and dust storms exist both on Earth and Mars. Dust devils, in particular, are known to have distinct meteorological (fluid) signatures, including cyclonic winds and thermally-hot centers. However, in arid environments, wind and dust also produce electricity through a process call “triboelectricity”, where mixing dust and sand grains of different composition and size both generate and exchange electric charge upon collision. In this presentation, we will discuss the micro-physics of triboelectricity, and describe applications of this charging process to large coherent convective structures such as dust devils and dust storms. Modeling and laboratory efforts will be described along with the instrumentation required to quantify the most fundamental electrical and fluid variables. Especially highlighted will be desert field studies of the devils that demonstrate their physical impressiveness and electrical complexity. Extrapolating these results, it will become apparent that Mars might also possess a very complex dust-driven atmospheric electrical environment, an environment that has yet to be fully quantified. Martian atmospheric electricity may be very relevant to the larger goals of the Mars Exploration Program, including electricity as a potential hazard. Through example, it is anticipated that there will be a new appreciation of wind, dust, and electricity as systemic processes, a part of any convective dust feature on either planet.

Colloquium Speaker: William Farrell

Dr. William Farrell is a space scientist at NASA's Goddard Space Flight Center with a research emphasis in atmospheric electricity and radio emission processes from the planets. He received his degree from the University of Iowa in 1987 and became a GSFC staff scientist in 1990, specializing in planetary radio emissions including the radio signatures of lightning detected by Voyager-2 during the Uranus and Neptune flybys. His terrestrial thunderstorm research includes the development of radiation models for upward lightning or “sprites” and the coupling of low frequency radiation sources in the lower atmosphere (thunderstorms, power lines, etc) to the ionosphere. In the process of gaining further understanding of thunderstorms, he became actively involved in basic research regarding grain-grain electrical interactions and their applications to Mars. In the summer of 2002, his team built a Poynting vector package that flew on an uninhabited aerial vehicle (UAV) directly over thunderstorm tops in search of intense upward-directed radio power from lightning. As a Cassini Co-investigator on the radio experiment, he is getting prepared for the 2004 encounter with Saturn to help look for the radio signatures of lightning from that gas giant. He is a scientific co-investigator on numerous NASA missions, including the Global Geospace Science, International Space Station’s Electrostatics of Granular Material experiment, and Code Y's Remotely Piloted Vehicle Program and has published over 80 articles in the fields of space science, atmospheric science, and radio instrumentation.