Those 'bursts': what did we learn?

During midsummer, I spent more time than usual with my 2-ele 50MHz quad pointed across the Atlantic.  

As well as increasing my DX count to the US and central America a fair bit, I started hearing unusual bursts of propagation, which I dubbed 'metallic bursts', which reasonably captures their quality.  If you listen to this short example, which is beaming and receiving only US signals at the time, you hear a brief burst that one could say is a meteor ping, followed by a much longer burst of propagation of many stations. 

What were the conditions of these bursts?

(1) Occurred frequently (within a few seconds to minutes) during peak midsummer days

(2) The bursts bring propagation from many stations from a wide area of the US simultaneously

(3) Exhibited a metallic quality that suggests Doppler shifting, but could be another effect.

(4) In my case, never heard when the antenna is pointed towards Europe, regardless of strength of Es

(5) Have been heard from Europe by some others (who have provided recordings as evidence)

(6) Occur far less frequently when the peak of midsummer has passed

(7) Did not show a rise in occurrence during the Perseids, which we would certainly expect if the bursts are, as some aggressively assert, simply "meteor scatter, nothing else".  The following recording, where there are no such bursts, is of August 10th, 2020: https://soundcloud.com/user-722868764/50313000-user-u-5

The main - and I think fatal - flaw in the meteor scatter supporters' camp is the last point.  That, plus the fact that a single meteor, at ~100km ablation height, could not provide propagation from the US to the UK. 

At 100km, the maximum propagation for a meteor appearing on the horizon (presumably inaccessible in reality) would be 2 x 1134km, or 2268km - more than 1000km less than the absolute minimum distance between my antenna and Newfoundland - which is about 2000km closer than where the signals were actually coming from (E. coast USA), at well over 5000km distant.  

It is possible that what I expect would have to be at least three meteors could provide the aligned path.  I am not sure what the likelihood of that is, in practice.

I listened carefully for the duration of the Perseids, as did others.  I heard no 'metallic bursts' at all.  I listened to many recordings made by PE4BAS, who provided those without making any claim or judgement, I should point out.  Those recordings show to me that there is (1) a big difference in the rate of bursts heard, even during the largest meteor shower of the year and (2) the bursts are more of a typical meteor scatter ping than midsummer.

Whilst there's a long way to go before any conclusions can be reached, a few facts are worth considering:

(1) The rate of meteoric input into the atmosphere is highest during midsummer (see reference)

(2) The enhanced rate might explain the metallic bursts heard.

(3) The DX path to America, where I heard all my bursts, could exhibit a geometric effect where looking through more atmosphere means 'capturing' more meteor pings. 

(4) There is a lot of activity in the mesosphere at midsummer, creating the quite intimately related phenomena of NLC, PMSE and Es. 

(5) PMSE are bones of contention in the scientific community.  One leading professor working on the mesosphere asserted that PMSE do not contribute to long-distance propagation, although I noted he did not qualify the wavelength he might (or might not) have been thinking about in making that assertion.  Another professor, equally eminent, and working on atmospheric radars daily, said he "would not be surprised" if PMSE did allow such propagation.  

(6) The now well-established openings at 6m between Europe and Japan seem to cluster around the peak midsummer period, as do the 'metallic bursts'.

My working assumption - and I put it no more strongly than that for the moment - is that these peak midsummer bursts might be the product of multiple, shallow and very turbulent reflections by PMSE-like structures.  These kinds of structures are seen visually in NLC, and can be expected to be very similar or identical in PMSE and other reflecting structures at mesospheric height.  Their movement is typically in the several tens and up to 400 metres per second, which allow for a good potential Doppler shift.

An example NLC image below, by no means the best I have in a large collection, is one from 2013, low on the horizon, and shows how a transient, rapidly-moving structure reflects sunlight strongly from one edge, whilst the rest is very diffuse.  Alignments of two or more of these structures could allow RF propagation, which would be quite brief as the alignment broke up.  The reflection would be due to the metallic, charged core of the NLC particle, not the coating of ice as in the case of visible light.

Work that needs to be done - and could be done quite easily - is as follows:

(a) More recordings of these bursts on DX paths, notably on Europe-US and Europe - Japan paths at midsummer, and noting their occurrence across the 24 hour period.

(b) Careful listening during 6m openings in winter, to record the nature and quality of any bursts heard then.

(c) More recordings of 6m bursts, if any, heard during other meteor shower events