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O
is for…
Observation:
Meteorological observations are the
cornerstone of weather forecasting.
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Measuring
the weather
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At
weather stations all over the globe, records are made each hour
of the current weather conditions,
either automatically or by a trained Observer.
The elements measured include temperature,
air pressure, cloud amount and type, visibility, any precipitation
etc. Every hour the data is fed into computer models, which then
generate global and regional forecasts.
Occluded
front, or occlusion: An occlusion is a type of weather
front which develops within a depression, or low, towards the end
of it’s life cycle. It happens when the cold front catches up with
the preceding warm front. The
warm air in between these two fronts is then lifted away from the
earth’s surface.
An
occlusion is marked by a belt of cloud and precipitation, which
may extend ahead of the front in the case of a "warm occlusion"
, or behind it in the case of a "cold occlusion". In Europe, warm
types are more usual during the winter months, the cold type in
summer.
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| Measuring
Oktas |
Okta:
This is a unit used in measuring cloud amount. An observer will
mentally divide the sky into eighths, each of which is called an
okta.
If
half the sky is covered by cloud there is said to be 4 oktas of
cover, if it is completely covered there is 8 oktas cover.
Orographic
cloud and rainfall: This is cloud or rainfall which is caused
when moist air is forced to rise up over high ground. The rising
air experiences a reduction in pressure, and cools, producing condensation,
in the form of water droplets, which then form clouds. These can
be stratus, cumulus or cirrus, and lenticular or wave clouds are
common in this situation too. If the uplift is sufficient, rainfall
can be produced, or enhanced, from these orographic clouds.
Ozone:
Normally, in the atmosphere, oxygen exists as two atoms joined together
in an O2 molecule. This is the form of oxygen we breathe. However,
when oxygen is subjected to ultra-violet light, it can exist as
3 atoms joined together in an O3 molecule, known as ozone.
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| Ozone
can be destroyed by man-made chemicals |
At
about 20km high, in the atmosphere, a layer of ozone exists, protecting
the earth’s surface from the sun’s excess ultra-violet radiation,
which can damage plant and animal life.
Ozone
concentrations vary naturally over space and time, but it can also
be destroyed by man-made chemicals. Thus the "hole" in the ozone
layer, which occurs near the southern pole in autumn, has been a
cause of widespread concern.
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