Scientists have been scratching their heads over late blossoming cloud formations which were seen in the mesosphere – the region in the Earth’s atmosphere between 50 and 80 kilometres above the surface, almost touching space.
The strange thing is not that there has been noctilucent clouds (NLCs) – clouds formed when summertime water vapour rises to the edge of space and forms long streaks of ice crystals in the sky – but that they are appearing so late in the year.
NLCs typically form in May, become intense in June before fading in July.
However, this year, they have reached their peak in late July, heading into August, and exploding “with unusual luminosity”.
Website Space Weather says that reports of NLCs in August have tripled in comparison to the same time last year.
But researchers have stated that this is due to an unexpected surge of water vapour in the mesosphere.
Lynn Harvey of Colorado’s Laboratory for Atmospheric and Space Physics (LASP) said: “There has been an unexpected surge of water vapour in the mesosphere.
“July went out like a lion!”
Still, it remains unclear why there is so much water vapour so late in the year.
One theory is to do with the upcoming solar minimum.
The sun follows cycles of roughly 11 years where it reaches a solar maximum and then a solar minimum.
During a solar maximum, the sun gives off more heat and is littered with sunspots. Less heat in a solar minimum is due to a decrease in magnetic waves.
The sun was not expected to head into a solar minimum until around 2020, but it appears to be heading in early
Space Weather says: “The phenomenon could be linked to solar minimum, now underway. It is notable that the coldest and wettest years in the mesosphere prior to 2018 were 2008-2009–the previous minimum of the 11-year solar cycle.
“Another possibility involves planetary wave activity in the southern hemisphere which can, ironically, boost the upwelling of water vapour tens of thousands of miles away in the north.”