If
current weather forecasts turn out to be right, the weather will be a very
mixed bag in the UK this week. Unseasonably warm temperatures reaching 20C
(68F) are predicted, followed by rain and possibly snow - and all over the next
few days. There is also a possibility of
something called "blood rain" in the South East, but what is it?
"Blood
rain" a term used for rain carrying sand from deserts. When the rain dries
off it leaves a thin layer of dust which can sometimes be a reddish colour,
hence the name. It is capable of coating houses, cars and garden furniture. "It is a rather grandiose term for fine
desert sand particles that are whipped up by winds and mix with the moisture in
clouds," says a Met Office spokesman.
Storms
in the Sahara desert, which is around 2,000 miles away, are usually responsible
for stirring up dust blown towards the UK, say weather experts. Watch Met
Office satellite animation of such dust movement here. The current winds
arriving in the country are part of the band of warm air which is predicted to
bring unseasonably warm temperatures over the next few days, followed by rain
in some areas.
The
rain and the fine layer of dust left after it falls can be reddish, but also
other colours. "The different coloured sands in the Sahara mean the rain
and the coating it leaves can vary in colour," says weather expert Philip
Eden. "It can be reddish, but it is quite rare. It is more likely to be a
sandy colour or brown. It's not as spectacular as it sounds." "Blood
rain" happens a few times a year in the UK, say experts. It is more common
in southern Europe like Spain and the South of France, which are closer to the
Sahara. But it can travel longer distances and fall in areas like Scandinavia.
A
well-documented incident of "blood rain" happened in 2001 in the
southern Indian state of Kerala. In the middle of a monsoon red rain started to
fall and did so intermittently for several weeks. The colour was strong enough
to stain clothes. There were also reports of green, yellow, brown and black
rains.
Investigations
suggested the rain was red because winds had stirred up dust from the Arabian
Peninsula. Although another theory explored even suggested some sort of life
form had fallen from the skies. It was reported at the time that Godfrey Louis,
a physicist at Mahatma Gandhi University in Kottayam, concluded samples left
over from the rains did not contain dust and instead had "a clear
biological appearance". For
"blood rain" to leave a residue it needs to be a brief shower. "This is because there is a higher
concentration of sand in a short shower," says Eden. "Heavier, more
prolonged rainfall simply ends up washing away the residue."
There
are very early recordings of "blood rain" in historical texts. It is
mentioned in Homer's Iliad, thought to have been written in the 8th Century BC.
The 12th Century writer Geoffrey of Monmouth, who made popular the legends of
King Arthur, also referred to it and the 12th Century historian, William of
Newburgh. In earlier times it was
believed the rain was actually blood and it was considered a bad omen. Often it
was used in texts and literature to predict bad events. With the spread of modern scientific method in
the 17th Century, it started to be explained in terms of rational causes. By
the 19th Century, the idea of dust being to blame started to dominate.
BBC News
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