D. A. Kotovsky

Triggered lightning sky waves, return stroke modeling, and ionosphere effective height

Ground waves and sky waves measured 209 km and 250 km south of six triggered lightning flashes containing 30 strokes that occurred in the half-hour before sunset on 27 August 2015 are presented and analyzed. We use a cross-correlation technique to find the ionospheric effective reflection height and compare our results to previous techniques that calculate effective height based on the time delay between ground wave and sky wave time domain features. From the first flash to the last flash there is, on average, a 1.6 km increase in effective ionospheric height, whereas no change in effective ionospheric height can be discerned along the individual strokes of a given flash. We show to what extent the triggered lightning radiation source can be described (using channel-base current, channel geometry, and channel luminosity versus time and height) and speculate that a well-characterized source could allow a more accurate determination of the electromagnetic fields radiated toward the ionosphere than has been done to date. We show that both channel geometry and the change in return stroke current amplitude and waveshape with channel height (inferred from measured channel luminosity versus height and time) determine the waveshape of the ground wave (and presumably the upward propagating wave that results in the sky wave) and that the waveshape of the ground wave does not appear to be related to the current versus time waveform measured at the channel base other than a roughly linear relationship between the two peak values.

Evaluation of ENTLN Performance Characteristics Based on the Ground Truth Natural and Rocket‐Triggered Lightning Data Acquired in Florida

The performance characteristics of the Earth Networks Total Lightning Network (ENTLN) were evaluated by using as ground-truth natural cloud-to-ground (CG) lightning data acquired at the Lightning Observatory in Gainesville (LOG) and rocket-triggered lightning data obtained at Camp Blanding (CB), Florida, in 2014 and 2015. Two ENTLN processors (data processing algorithms) were evaluated. The old processor (P2014) was put into use in June 2014 and the new one (P2015) has been operational since August 2015. Based on the natural-CG-lightning dataset (219 flashes containing 608 strokes), the flash detection efficiency (DE), flash classification accuracy (CA), stroke DE, and stroke CA for the new processor were found to be 99%, 97%, 96%, and 91%, respectively, and the corresponding values for the old processor were 99%, 91%, 97%, and 68%. The stroke DE and stroke CA for first strokes are higher than those for subsequent strokes. Based on the rocket-triggered lightning dataset (36 CG flashes containing 175 strokes), the flash DE, flash CA, stroke DE, and stroke CA for the new processor were found to be 100%, 97%, 97%, and 86%, respectively, while the corresponding values for the old processor were 100%, 92%, 97%, and 42%. The median values of location error and absolute peak current estimation error were 215 m and 15% for the new processor, and 205 m and 15% for the old processor. For both natural and triggered CG lightning, strokes with higher peak currents were more likely to be both detected and correctly classified by the ENTLN.

Do cosmic ray air showers initiate lightning? : A statistical analysis of cosmic ray air showers and lightning mapping array data

It has been argued in the technical literature, and widely reported in the popular press, that cosmic ray air showers (CRASs) can initiate lightning via a mechanism known as relativistic runaway electron avalanche (RREA), where large numbers of high energy and low energy electrons can, somehow, cause the local atmosphere in a thundercloud to transition to a conducting state. In response to this claim, other researchers have published simulations showing that the electron density produced by RREA is far too small to be able to affect the conductivity in the cloud sufficiently to initiate lightning. In this paper, we compare 74 days of cosmic ray air shower data collected in north central Florida during 2013, 2014, and 2015, the recorded CRASs having primary energies on the order of 1016 eV to 1018 eV and zenith angles less than 38 degrees, with Lightning Mapping Array (LMA) data, and we show that there is no evidence that the detected cosmic ray air showers initiated lightning. Furthermore, we show that the average probability of any of our detected cosmic ray air showers to initiate a lightning flash can be no more than 5 percent. If all lightning flashes were initiated by cosmic ray air showers, then about 1.6 percent of detected CRASs would initiate lightning, therefore we do not have enough data to exclude the possibility that lightning flashes could be initiated by cosmic ray air showers.

Nonlinear multi-beam interactions in the D-region ionosphere

Summary form only given. This paper presents experimental observations of ELF/VLF wave generation performed during multi-beam HF heating experiments at the High-frequency Active Auroral Research Program (HAARP) observatory. The primary objective of these experiments is to advance the scientific understanding of the nonlinear absorption processes occurring within the collisional D-region ionosphere. During the February, May, and August 2012 HAARP campaigns, a series of multi-beam HF transmissions were designed to produce inter-harmonic modulation products in the ELF/VLF range. Experiments were performed using a variety of simultaneous 2- to 6-frequency HF transmissions spaced at ELF/VLF frequencies. For instance, in order to generate the 3-frequency experiment using frequencies of 3,248,485 Hz, 3,251,515 Hz, and 3,250,200 Hz, one half of the array broadcast a synthesized-two-frequency (STF) modulation format centered on 3.25 MHz (X-mode) with a modulation frequency of 1515 Hz while the other half of the array broadcast CW at 3.250200 MHz (X-mode). In the presence of the auroral electrojet, this transmission format generated ELF/VLF tones at 1315 Hz, and 1715 Hz, and 3030 Hz, as expected. Additionally, in order to generate ELF waves by the cubic nonlinearity, one half of the array broadcast at 2,750,250 Hz while the other half broadcast at 5,499,500 Hz, generating ELF waves at 1000 Hz. These experiment were repeated using different HF frequencies, different modulation frequencies, and different HF power levels. During the May and August 2012 experiments, a frequency-time variation was imposed on the transmissions in order to enable time-of-arrival signal processing. Experimental observations are compared with the initial results of a multi-beam HF heating model that accounts for inter-harmonic mixing among the various field components. We demonstrate that not all observations (particularly those for the cubic nonlinearity generation method) can be explained without accounting for the electron temperature oscillations that occur at the second harmonic of the HF waves.