Field Projects
Field projects are critical to our understanding of lightning and use many of the observing systems described here.
TELEX
The Thunderstorm Electrification and Lightning Experiment had two broad objectives. One was to try to understand better why storms produce a lot of positive cloud-to-ground flashes. Scientists think this is related to severe weather and storm intensity, and want to understand the conditions that are producing these flashes. The other objective was to start looking at the electrification of Mesoscale Convective Systems. With all of the observing systems that are available, they wanted to look at how winds move and how particles form, and be able to relate that to the wind field and lightning - getting "the big picture."
The field observational phase of the Thunderstorm Electrification and Lightning Experiment (TELEX) was held in 2003 and 2004, and data were collected using a number of sensors. Scientists relied heavily on the polarimetric KOUN radar, which allowed them to determine the kinds of particles that are inside the storm. Very high-resolution dual-Doppler data was also collected in TELEX from two mobile radars (SMART-R's). The SMART-R's would drive close to a storm and scan very rapidly through the storm to give researchers the quickly evolving characteristics of the storm. The OK-LMA, unique to central Oklahoma, was one of the core instruments for TELEX. The OK-LMA allowed them to look at the structure of lightning inside of clouds as well as see the things outside of the clouds. Scientists could then look at where lightning was occurring relative to updrafts, relative to where the rain was falling, and relative to severe weather. The other critical instrument was NSSL's balloon system. The weather balloons carried instruments to measure the thermodynamics of the storms, temperature, winds, and humidity. The balloons also contained electric field meters (EFM's - see above), instruments that could measure the electrical properties of the storm so researchers could learn about things that cause lightning to occur. An environmental sounding system was also used to allowed researchers to look at the conditions that produced the storms. This information is important in the development of models to help scientists understand how all these things work together.
The TELEX field program was highly successful. In the two seasons, about 55 flights were made during 20 missions. The TELEX researchers succeeded in flying in non-severe and severe storms, and even one supercell where eight soundings were made - a first. Also flights were made in the convective and stratiform regions of larger storms, i.e., mesoscale convective systems, a specific target of TELEX.
What we are learning
From data collected from a tornadic supercell thunderstorm, NSSL scientists were able to relate the retrieved 3-D airflow to the total lightning flash rate observed by the LMA and analyze both the pre-tornadic and tornadic stages of the storm, giving us more information on the electrical structure of storms.
Lightning flashes from a MCS were continuously measured and recorded over the same region where simultaneous Doppler radar volume scans were collected every 2.5 to 3 minutes. The high spatial resolution of this integrated data set provides valuable information for relating storm dynamics to cloud electrification for this class of MCS. In this case, a rapid decrease and re-intensification of the convective system and the associated lightning flash rate was documented.
STEPS
The Severe Thunderstorm Electrification and Precipitation Study (STEPS) was a field project held in 2000 to make a wide range of meteorological and electrical observations of supercell thunderstorms to better understand supercell physics. The specific storm electricity goals were to study how severe storms become electrified and to better understand how variations in the type and flash rate of lightning relate to the type of severe storm and its evolution. Of particular interest were severe storms that produce unusual lightning activity, including ground flashes that lower positive charge to the ground, and cloud flashes whose polarity is reversed from what is normally seen.
A T-28 armored aircraft penetrated the target storm to collect data on cloud particles and the electric field. Researchers launched balloons from several mobile sounding syste4ms, while mobile ground units and mobile mesonet vehicles took measurements. Data was also gathered using a network of three Doppler radars, two dual-polarized radars, and a deployable lightning mapping system.
What we have learned
NSSL scientists observed that some storms had an "inverted" electrical structure, with positively-charged areas near the ground and negatively-charged areas near the top. Scientists hypothesize that they are possibly due to a larger than usual rime accretion rate for graupel in a strong updraft. Other ideas are: an unusually small concentration of frozen precipitation in the strong updraft, unusually large liquid water concentrations in the mixed phase region, or fewer precipitation trajectories re-circulating through the updraft. Although the cause(s) is unknown, the evidence is compelling that inverted-polarity storms exist.
MEaPRS
The MCS Electrification and Polarimetric Radar Study (MEaPRS) was a field project in 1997 to investigate polarization radar signatures and electrification processes in MCS's. A lightning mapping system was used to detect all in-cloud and cloud-to-ground flashes produced by a target MCS.
