Observations made using NASA's Aeronomy of Ice in the Mesosphere (AIM) spacecraft have revealed that this year, the noctilucent cloud
season in the Antarctic began earlier than usual - an observation that some scientists believe is a sign of the impact the inexorable build-up of greenhouse gases is having on Earth's climate.
Around the summer solstice is usually the best time for observing noctilucent clouds
but they can often be seen all through the summer months.
The noctilucent cloud
season was just starting and members were reminded to keep a look out for them in morning and evening twilight.
"The noctilucent clouds
remain lit by the sun because of their great height, whereas weather clouds remain in silhouette against the twilit summer evening sky."
Some experts believe the recent expansion of noctilucent clouds
from northern to mid-latitudes may have been caused by global warming - also blamed by some for extreme weather and flooding.
Dr Gary Burns from the Australian Antarctic Division in Hobart, and colleagues, John French, Karen French and Pene Greet, are investigating a possible link between noctilucent clouds
and climate change.
Greenhouse gases will enhance noctilucent clouds
in two ways.
June usually bring us the start of several displays of high-altitude noctilucent clouds
, which are usually seen about an hour or so after sunset and before sunrise.
in Earth's high-latitude upper mesosphere form at temperatures below 150 K (Rapp and Thomas 2006) and it has been suggested that they are composed of cubic ice (Murray and Plane 2003a,b, 2005; Murray and Jensen 2010).
- They are the highest clouds in the Earth's atmosphere forming above 200,000 ft.
The eerie glow, which appeared to change colour and hang above the horizon, has been confirmed as a phenomenon known as noctilucent clouds
- the highest clouds in the Earth's atmosphere at 50 miles above the ground.
Jay Brausch is a dedicated amateur observer of the aurora borealis and noctilucent clouds
residing at Glen Ullin, North Dakota, USA, 46[degrees]48'N, 101[degrees]46'W.