Textbooks rarely give time−domain solutions to antenna problems. For the case of a finite linear antenna along which a fixed current waveform propagates, we present analytical time−domain solutions for the electric and magnetic radiation (far) fields. We also give computer solutions for the total (near and far) fields. The current waveform used as an example in the computer calculations approximates that of a lightning return−stroke, a common geophysical example of the type of radiation source under consideration.

The first wideband dE/dt recordings have been obtained for the narrow bipolar pulses previously identified by Le Vine (1980) as “sources of the strongest RF radiation from lightning.” These dE/dt waveforms are dramatically different from those of other known lightning processes. A burst of high‐frequency “noise” is superimposed on the slower bipolar pattern one might expect from the relatively smooth E waveforms. For 18 such pulses from an isolated thunderstorm cell at known range, the mean peak E and dE/dt, range‐normalized to 100 km, were 8.0±5.3 V/m and 20±15 V/m/μs, respectively. Spectral analysis indicates that the sources of these pulses radiate much more strongly than first‐return strokes at frequencies from 10 MHz to at least 50 MHz. Absolutely calibrated power and energy spectra are presented which are reliable from 200 KHz to perhaps 20 MHz. At 18 MHz the narrow pulses appear to contain nearly 16 dB more spectral energy than first return‐stroke waveforms from the same range. Supporting evidence shows that they generally occur as isolated pulses in intracloud flashes but are not associated with K changes or other known phenomena. They can occur in either polarity.

[1] Four field campaigns were conducted in southern Arizona (AZ) and in northern Texas and southern Oklahoma (TX-OK) in 2003 and 2004 to evaluate the performance of the U.S. National Lightning Detection Network TM (NLDN) in detecting cloud-to-ground (CG) lightning after an upgrade in 2002 and 2003. The 2-year average flash detection efficiency (DE) in AZ was 93% (1024/1097), and the measured (first plus subsequent) stroke DE was 76% (2746/3620). The corresponding values in TX-OK were 92% (338/367) and 86% (755/882), respectively. After correcting for the time resolution of the video camera (16.7 ms), we estimate that the actual NLDN stroke DE and video multiplicities were about 68% and 3.71 in AZ and 77% and 2.80 in TX-OK. The average DE for negative first strokes (92%) was larger than the measured DE for subsequent strokes that produced a new ground contact (81%) and the DE for subsequent strokes that remained in a preexisting channel (67%). The primary cause of the NLDN missing strokes was that the peak of the radiated electromagnetic field was below the NLDN detection threshold. The average estimated peak current (I p ) of negative first strokes and the average multiplicity of negative flashes varied from storm to storm and between the two regions, but this variability did not affect the DE as long as the recording sessions had more than 60 flashes. By analyzing the NLDN locations of subsequent strokes that remained in the same channel as the first stroke we infer that the median random position error of the NLDN was 424 m in AZ and 282 m in TX-OK. An evaluation of the classification of lightning type by the NLDN (i.e., CG stroke versus cloud pulse) showed that 1.4-7% (6/420 to 6/86) of the positive NLDN reports with an I p 10 kA in TX-OK were produced by CG strokes; 4.7-26% (5/106 to 5/19) of the positive reports with 10 kA < I p 20 kA were CGs; and 67-95% (30/45 to 30/32) of the reports with I p ! +20 kA were CG strokes. Some 50-87% (52/104 to 52/60) of the negative, single-stroke NLDN reports in AZ and TX-OK with jI p j 10 kA were produced by CG flashes. Both the upper and lower bounds in these classification studies have observational biases.

The large-amplitude radiation field pulses produced by intracloud lightning discharge processes have been recorded with submicrosecond time resolution. The wave forms are distinctly different from those produced by return strokes in cloud-to-ground lightning, yet they are surprisingly alike within a discharge and in different discharges. The shapes tend to be bipolar, with two or three narrow, fast-rising pulses superimposed on the initial half cycle. Pulses with a positive initial polarity are usually produced in the several tens of milliseconds prior to the first return stroke in a cloud-to-ground discharge. Positive pulses tend to occur at regular intervals and have a mean full width of about 40 + 13 us. Negative pulses are usually produced during isolated cloud discharges at more random intervals and have shapes similar to the positive pulses but with more variability. The implications of the field shapes and polarities for the physics of intracloud discharge processes are discussed.

We present a characterization of Florida lightning return stroke electric and magnetic fields derived from simultaneous measurements of the fields at two separate stations, one station being within 15 km of the lightning, the other at either about 50 or 200 km from the lightning. We give (1) examples of correlated wave forms, (2) typical first and subsequent stroke wave forms over the distance range 1.0–200 km, and (3) the following statistical data from which the typical wave forms were derived: for electric field, rise time, initial peak value, ramp starting time, ramp slope, value at 170 μs, ratio of value at 170 μs to initial peak, zero‐crossing time for 50 and 200 km wave forms; for magnetic fields, time of hump following initial peak, ratio of hump value to initial peak value, zero‐crossing time for 50 and 200 km wave forms. Return stroke electric and magnetic field characteristics appear to be independent of location in Florida.