STERAO storms into action
A field program designed to examine the effects of thunderstorms on the chemical composition of the troposphere and lower stratosphere found all the action it wanted last summer in northeastern Colorado. The Stratosphere-Troposphere Experiment: Radiation, Aerosols, and Ozone--a.k.a. STERAO--Deep Convection field program was the first installment of a multiyear, multisite experiment designed to examine physical and chemical processes that occur near the tropopause.
"We were exceptionally fortunate in terms of weather," said co-principal investigator James Dye (NCAR). "In a one-week period in mid-July we had four excellent storm cases, and that's more than you can even dream of in the weather business."
The interdisciplinary experiment was led by principal investigators Dye, Steve Rutledge of Colorado State University (CSU), and Adrian Tuck of the NOAA Aeronomy Laboratory and joined by other investigators from five universities and six research institutions. Equipment included two aircraft, a Doppler radar, NCAR's mobile cross-chain Loran atmospheric sounding system (CLASS) unit, and some specialized instruments for lightning detection and chemical analysis. According to Dye, "This is the first major project that includes comprehensive, coordinated chemical, electrical, and dynamical measurements in and around thunderstorms."
STERAO focused on what happens when thunderstorms suck air from the boundary layer and transport it to the upper troposphere and lower stratosphere, up to about 15 kilometers. Dye described the main effects of this convection:
The ground-based CSU/University of Chicago/Illinois State Water Survey Radar (CHILL) multiparameter Doppler radar provided remote measurements of microphysical conditions and air motions within the storms. The CSU/CHILL radar site near Greeley also was the operations center for coordinating the experiment and communicating with aircraft. A unique part of the experiment was the French ONERA (Office National d'Etudes et de Récherches Aerospatiales) lightning interferometer, which mapped three-dimensional lightning channels and obtained counts of intracloud and cloud-to-ground flashes. These measurements were supplemented by cloud-to-ground lightning measurements from the National Lightning Detection Network and three electric-field-change meters, one mobile and two fixed, that could detect both intracloud and cloud-to-ground lightning. The NCAR mobile CLASS unit was used to make both morning soundings for forecasts and afternoon soundings to characterize the environment in which the storms grew. Weather forecasting for the project was done by the NOAA Forecast Systems Laboratory with supplementary forecasts from CSU.
The combination of lightning and chemical data will allow researchers to quantify how much NOx was produced by lightning in these storms and how the resulting output varied with altitude. In 1989 Brian Ridley of NCAR and Dye, in an exploratory study in New Mexico, found that most of the NOx produced by lightning was in the upper part of the anvil. Although STERAO's data are just beginning to be analyzed, "that seems to hold true here as well," says Dye.
For further information, contact Dye (303-497-8944 or firstname.lastname@example.org) or Ridley (303-497-1420 or email@example.com).