This makes me think specifric to lightning from cloud to ground, or cloud to ionosphere.
Incidence has been recorded, and I have some doubt of absence of ionosphere closer to the surface than 100 km. I could go along with 80. There is the "D layer" or "D region" of the ionosphere that Wikipedia notes as 50-95 km aloft.
As far as I know, the greatest lightning strikes are "positive giants", less-common items from thundercloud top to ground, unlike more usual of cloud-to-ground lightning being negative-into-ground and having upper end in the middle, maybe lowish-middle of a usual thundercloud.
I suspect "positive giants" to be the main source of the greatest of "whistlers".
A "whistler" is an outburst of broadband upper-audio-frequency electromagnetic radiation from a lightning stroke, typically a cloud-to-ground one, going to the lightning stroke's antipode or coming back to within 1,000 or hundreds of km or-so of its origin. A "whistler" has characteristic of largely-sinewave tone of frequency varying inversely with time. Propagation speed of relevant frequencies of electromagnetic waves between Earth and its ionosphere is less than c, and varies inversely with frequency.
There is such a thing as a "tweet" known before Twitter existed. That's upper-audio-range RF from a typically cloud-to-ground lightnig stroke
100's of km away - this turns up as a quick fraction-of-second brief blip of upper-audio-freq. RF with frequency decreasing as time progresses through the fraction (smallish) of a second where this is heard.