ANTICYCLONE (i.e. opposite to a cyclone), an atmospheric
system in which there is a descending movement of the air and a
relative increase in barometric pressure over the part of the
earth’s surface affected by it. At the surface the air tends to
flow outwards in all directions from the central area of high
pressure, and is deflected on account of the earth’s rotation (see
FErrel’s Law) so as to give a spiral movement in the direction
of the hands of a watch face upwards in the northern
hemisphere, against that direction in the southern hemisphere.
Since the air in an anticyclone is descending, it becomes warmed
and dried, and therefore transmits radiation freely whether from
the sun to the earth or from the earth into space. Hence in
winter anticyclonic weather is characterized by clear air with
periods of frost, causing fogs in towns and low-lying damp areas,
and in summer by still cloudless days with gentle variable airs
and fine weather.
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