Nacreous Clouds, Sweden Sweden saw spectacular nacreous clouds
on 12th and 13th January. Richard Blaine took these images of
the rare stratospheric clouds from Åre 340 miles NW of
Stockholm. Above: Nacreous clouds blaze 5 minutes after sunset
on 13th. Dark ragged lower tropospheric clouds frame the
picture's base. ©Richard Blaine, shown with permission.
Nacreous clouds are very high, 9-16 miles (15 – 25 km) in the
stratosphere.   They catch sunlight long before ground level
sunrise and after sunset to glow eerily with unbelievably bright
electric colours.   They twist, stretch and curl majestically as
lower dark tropospheric clouds hurry beneath.    Their tiny ice
crystals diffract sunlight to give the iridescent hues.    They
need an unusually cold stratosphere (less than -85 Celsius) and
are therefore rare winter occurrences.   They tend to form in
very windy weather and downwind of mountains. The resulting
tropospheric disturbances possibly loft necessary water vapour
into the lower stratosphere.   The