Update on the higher-HF bands DX of December 01, 2019.

On December 1st, there was a remarkable set of solar minimum openings on 12 and 10m from Europe into the antipodes.

A day later, I commented that this unusual and rare propagation could be related to the approaching austral midsummer.

NLC seen from Dunedin, NZ, on the same day as unusual upper HF DX opened up.  (C) Mirko Harnisch

A few days after the event, I learn from Spaceweather.com that noctilucent clouds were definitively seen from Dunedin, New Zealand - at a latitude of 45 degrees south - on the same day as the propagation event.  This is the only known sighting of NLC so far from the south pole; the equivalent position in the north encompasses, for example, southern France and northern Italy.  NLC are also being seen further from the north pole in the northern hemisphere.

The rather sensationalist claims by the media about the planetary waves boosting NLC are a bit silly.  Planetary waves have been known about for many decades, and are well understood to modulate NLC with various periodicities of one to several days.  The 5-day wave mentioned in the article is one of the strongest and most-easily detected planetary waves.
  
The fact of the unusual EU-VK propagation at higher HF and the sighting of the very extensive NLC from ZL is almost certainly not a coincidence, given that Es, PMSE and related phenomena can all arise from the same underlying mechanism.

That mechanism is one of a warming midsummer troposhere yielding a strongly cooling mesosphere owing to upwelling and gravity wave activity.  NLC form around meteor debris, and the debris-ice particles, just nanometers across, are highly charged surfaces - which is where the radio propagation relationship comes in.

UPDATE (2): Non-summer mesospheric echoes appeared over central Wales today (06/12/2019), as seen by the MST radar near Aberystwyth.  The radar isn't quite working at optimum settings at the moment, but the winter echoes are certainly there, roughly between 10UT and 14UT:

In the northern hemisphere, summer 50MHz propagation from Europe to JA is often seen, and has also been related to NLC/PMSE.

The data from AIM satellite confirms the very northerly extent of part of the NLC formation.  On 08/12/2019, the NLC was continuing to appear at near 50 degrees south.