Abstract.With the use of a NaI scintillation detector, bursts of radiation with energies in excess of I MeV were recorded at a mountain-top observatory immediately before three, nearby cloud-to-ground, negative lightning strikes. Coincident recordings of the electric field changes due to the discharges showed that, in each case, the bursts began between I and 2 milliseconds before and continued until the onset of the first return stroke. This radiation was associated with approaching stepped-leaders and may have influenced their development.

No abstract

[1] Narrow bipolar events (NBE) are the electromagnetic signature of a distinct class of impulsive and energetic intracloud discharge that occurs in some thunderstorms. NBE are characterized by strong VHF RF emissions and bipolar waveforms when observed by broadband field-change antennas at large distances. These discharges may occur in isolation or precede and perhaps initiate conventional intracloud flashes. When observed at close range, NBE waveforms exhibit electrostatic field changes in addition to the bipolar radiation field change. At extremely close range, the induction and electrostatic fields dominate in our measurements. Using close-range observations in conjunction with the radiation-field measurements, I calculate that on average, an NBE transfers 0.3 C of charge over a distance of 3.2 km and that the discharge wave front propagates at a speed equal to one-half the speed of light.

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 ' ' ......'-intensity of about region of nlgn c•ectnc field " at an strengtn, which time increase in X ray 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.

Since 1998 the Los Alamos Sferic Array (LASA) has recorded electric field change signals from lightning in support of radio frequency (RF) and optical observations by the Fast On‐orbit Recording of Transient Events (FORTE) satellite. By “sferic” (a colloquial abbreviation for “atmospheric”), we refer to a remote measurement of the transient electric field produced by a lightning flash. LASA consisted of five stations in New Mexico in 1998 and was expanded to 11 stations in New Mexico, Texas, Florida, and Nebraska in 1999. During the 2 years of operation described in this paper, the remote stations acquired triggered 8‐ or 16‐ms duration, 12‐bit waveforms and GPS‐based sferic time tags 24 hours per day year‐round. Source locations were determined daily using differential time of arrival techniques, and the waveforms from all geolocated events were transferred to Los Alamos National Laboratory (LANL), where they have been archived for further analysis, including event classification and characterization. We evaluated LASA location accuracy by comparing temporally coincident (occurring within 100 μs) LASA and National Lightning Detection Network (NLDN) event locations. Approximately one half of the locations agreed to within 2 km, with better agreement for events that occurred within the confines of LASA subarrays in New Mexico and Florida. Of the ∼900,000 events located by the sferic array in 1998 and 1999, nearly 13,000 produced distinctive narrow bipolar field change pulses resembling those previously identified as intracloud discharges.