Kenneth Bryan Eack

TELEX The Thunderstorm Electrification and Lightning Experiment

Measurements during TELEX by a lightning mapping array, polarimetric and mobile Doppler radars, and balloon-borne electric-field meters and radiosondes show how lightning and other electrical properties depend on storm structure, updrafts, and precipitation formation.

Initial results from simultaneous observation of X-rays and electric fields in a thunderstorm

With an X ray detector designed for flight on a free balloon, we obtained a sounding of X ray intensity and electric-field strength in a mesoscale convective system (MCS) near Norman, Oklahoma, in the spring of 1995. The balloon passed through a region of high electric field strength, at which time an increase in X ray intensity of about 2 orders of magnitude occurred, lasting for approximately 1 min. The X ray intensity returned to background levels at the time of a lightning flash that reduced the electric field strength measured at the balloon. This observation suggests that the production mechanism for the X rays we observed is related to the storm electric field and not necessarily to lightning discharge processes.

X‐ray pulses observed above a mesoscale convective system

During a balloon flight into and above the stratiform region of a mesoscale convective system, we observed three x-ray pulses while the balloon was at an altitude of approximately 15 km MSL (atmospheric pressure of 130 mb). These pulses were one to two orders of magnitude above the background x-ray count rate with peak fluxes between 37 and 270 (cm²-s-sr)−1 and durations of about one second. No significant electric field was measured at the time of these pulses.

Gamma‐ray emissions observed in a thunderstorm anvil

Balloon-borne gamma-ray and electric-field-change instruments were launched into a daytime summer thunderstorm to evaluate a new experimental design to test hypotheses for the production of transient luminous events (TLE) (eg. sprites, and blue jets) in the mesosphere. While ascending, the instrument triggered many times on the signals from the electric-field-change instrument, recording the gamma-ray background at those times. A greater than three-fold increase in the gamma-ray flux was observed as the balloon descended through a thunderstorm anvil where a strong electric field was suspected to be present. These observations suggest that gamma-ray production in thunderstorms may not be as uncommon as previously believed.

Balloon‐borne x‐ray spectrometer for detection of x rays produced by thunderstorms

A new balloon‐borne instrument designed by the author detects x rays produced in thunderstorms. The instrument uses a sodium iodide (NaI) scintillation detector, and flies on a small meteorological balloon. A three bin (30 to 60, 60 to 90, and 90 to 120 keV) x‐ray spectrum is acquired every 0.25 s. The deployment of these detectors with electric‐field meters has resulted in several vertical profiles of x‐ray intensity and electric‐field strength. These data support the hypothesis that the electric field generated by the thunderstorm can produce energetic electrons, which in turn emit bremsstrahlung x rays.

Electric‐field changes of lightning observed in thunderstorms

During the Summer and Fall of 1998 we launched five balloon-borne instruments into thunderstorms to observe changes in the vertical component of electric field caused by lightning. Four of these were for measurement of field change only. The fifth was part of a larger package that included a gamma radiation detector and a GPS receiver on board. We have processed electric-field-change data from two of these flights. We discuss examples of field changes observed at altitude and compare them with data from the National Lightning Detection Network (NLDN) for cloud-to-ground lightning flashes that were coincident in time. Limits on time resolution and timing accuracy prevent unambiguous identification of the lightning processes that caused the field changes. It appears that they may have been caused by charge movements relatively near the instruments as compared with the ground-strike location of coincident flashes.

Electrical current along balloon rigging line inside thunderstorms

We have designed a new instrument to measure the current flowing along balloon rigging line during flights through thunderstorms. This instrument was tested in a high voltage facility and used to collect line current data during one balloon flight into a thunderstorm. Using these data, worst-case calculations are made; as such, we claim that they are the upper limits of any alteration .to the measured electric field or particle charge that may occur, and the real number is likely much less. It is postulated the rigging-line current could have two separate effects on the measured . .