Dr. Elizabeth Smith sits in the backseat of a white Chevy pick-up truck surrounded by computer equipment on a windy day in Oklahoma.
Smith is a researcher at the University of Oklahoma Cooperative Institute for Mesoscale Meteorological Studies researcher supporting NOAA’s National Severe Storms Laboratory. On this day she’s testing equipment after a recent deployment on TORUS, or Targeted Observation by Radars and UAS of Supercells. The project aims at understanding the relationships between severe thunderstorms and tornado formation.
In the back of the pick-up truck is a lidar system, which stands for Light Detection And Ranging. Unlike radar systems, which use electromagnetic waves, lidar utilizes laser light. The lidar operates at an eye safe wavelength of 1.5 , just outside of the visible portion of the electromagnetic spectrum.
“The lidar sends out laser light to hit and scatter off particles that are small enough for that specific wavelength,” Smith said. “Those are things you and I cannot easily see, like really, really small dust and aerosol particles.”
The scattered light signal returns to the lidar and is analyzed, similar to the way a weather radar uses electromagnetic waves scattered off rain droplets. Via the Doppler effect, the lidar is able to retrieve information about wind in clear air.
“Understanding the wind field around severe storms and weather is very important for us to improve our understanding and forecasts,” Smith said.
The lidar is one of many instruments utilized in TORUS — a month [JEB1] long project in 2019 funded by the National Science Foundation and NOAA. TORUS will continue in 2020. The lidar is funded by the NOAA NSSL Director’s Discretionary Research Fund to support TORUS. The lidar in the Chevy truck, lovingly named Louise, is from the NOAA NSSL CLAMPS-2 trailer utilized during the Verification of the Origins of Rotation in Tornadoes EXperiment-Southeast project during the past few years. The lidar was removed from the trailer for increased mobility in the extreme environments expected during TORUS.
TORUS includes many instruments, including those on top of trucks known as mobile mesonets, as well as mobile radar trucks and unmanned aircraft vehicles. Mobile mesonets measure meteorological variables such as wind speed, temperature and humidity at the surface while radar can collect observations at higher levels. As a result there is often a gap in coverage just above the surface, which may be up to several hundred feet deep.
“We use the lidar and weather balloons with instruments attached to fill that gap,” Smith said. “The lidar system is able to provide us with rapidly updating wind information with a temporal resolution of minutes. There’s a lot about the environment near storms we don’t understand yet. Understanding the rapidly evolving complex flows in that region can be very important.”
Smith said two of the most vital factors OU CIMMS and NOAA NSSL teams are studying to improve forecasting tools are how supercell thunderstorms move and persist.
During the 2019 TORUS campaign, the lidar team deployed on 17 days during May and June across five states, traveling more than 9,000 miles. Overall, data were collected on 19 supercell storms, eight of which produced tornadoes. Deployments also focused on pre-convective environments and cases where forecast convection failed to occur. In the months since the TORUS field season, work has been underway quality-checking and preparing the data for analysis. In total, over 20 hours of lidar wind observations were collected during the 2019 TORUS campaign.
“We saw interesting turbulence structure in the wind field,” Smith said. “We don’t know what that means just yet, but this is unprecedented data because this specific lidar is faster than those used in past field projects.”
The lidar team looks forward to sharing preliminary findings at the 100th Annual AMS meeting in January.
For more information about this project, visit: http://cimms.ou.edu/index.php/2019/07/11/torus-project-expects-groundbreaking-results/
Story by Emily Summars at the OU cooperative Institute for Mesoscale Meteorological Studies and NOAA NSSL.