Propagation Teepee: A Possible High‐Frequency (15–30 MHz) Remote Lightning Signature Identified by Citizen Scientists

Abstract

A high‐frequency spectral feature is identified in ground‐based spectrograph data at 15–30 MHz. The feature, likely of terrestrial origin, is often recorded by a group of citizen scientists (the Spectrograph User Group) whose main interest is to observe Jupiter's radio emissions. The feature appears as radio band noise enhancement in which the frequency of enhancement increases and then decreases with time, forming a “triangular spectral feature.” The teepee tent shape leads to its name (TP for short). TPs usually have well‐defined leading and trailing edges. While some TPs occur in isolation, they are often seen in groups, distributed either in time or in apex frequency. While most TPs appear diffuse, close‐up views of a few TPs reveal that they actually consist of discrete bursts, highly suggestive of lightning strokes as possible radiation sources. Here, we investigate the possible generation of TPs by ionospheric reflection of radiation from remote lightning storms.

Using Broadband Radio Noise From Power‐Lines to Map and Track Dense Es Structures

“…We note that the overall shape of the dynamic spectra bears a striking resemblance to spectra reported recently by Fung et al. (2020). Here the authors describe spectra that have a “tent” like shape, where the observed emissions increase as function of frequency and then later decrease.…”

“…We note that by removing local lightning, we would also be removing non‐local lightning, where the distant lightning emissions could be reflecting off of the same E s structures or as Fung et al. (2020) suggest, the F region. Certainly if we are able to observe the RF noise from a distant city, then distant lightning may also be observable.…”

“…Fung et al. (2020) discount changing properties of the ionosphere because there “is no a priori reason to favor particular phase of the changes” of their tent like structures. Yet the authors fail to consider the fact that two of their reported observations occurred during days of geomagnetic activity, during which the ionosphere is highly dynamic, even at midlatitudes.…”

“…Based on an occasional appearance of burst‐like emission, Fung et al. (2020) also claim that RF emission is most likely coming from distant lightning storms, and provide a geometrical argument for this. However, it is difficult to judge the validity of this hypothesis given the lack of comparison to actual lightning data, which is readily available.…”

Jupiter radio emission probability tool

“…The Radio Sky Publishing 2 team developed tools to help the preparation of Jupiter radio observation, in the frame of the RadioJOVE citizen science project (Thieman et al, 2006;Fung et al, 2020). The Radio Jupiter Pro application 3 specifically provides Io Phase-CML probability map, plots indicating the elevation of Jupiter and the Sun at the observer's location, as well as their location within the antenna beam, when this information is configured.…”