Having spoken of cyclones, we shall now direct our attention to anticyclones. In the daily weather charts we sometimes see but two or three isobars, and these are a considerable distance apart, and extend over a large area. The pressure is highest in the centre, and gradually diminishes outwards. The air is calm and cold in the central area, but on the outskirts the wind blows in the direction of the hands of a watch. These are the special features of an anticyclone. The weather in an anticyclone is almost the opposite of that in a depression; that in the latter being wet and unsettled, while that in the former is usually settled and fine, with more or less haze in the air. Another great difference is that while depressions are generally rapid in their movements, anticyclones are nearly stationary; and it is for this reason that they are associated with “settled” fine weather. In the area of high pressure the characteristic features are largely modified by what is termed “radiation” weather, as determined by diurnal and seasonal variations; and as the pressure is nearly stationary, these diurnal and seasonal variations are the chief features of anticyclonic weather.
We shall now give the prognostics due to the variations in some detail, Fig. 5. The sky being generally clear and the air calm, the temperature is high in the day and low at night. In summer brilliant sun shine prevails during the day, and at night there is heavy dew, and in low-lying places mist.
Heavy dews in hot weather indicate a continuance of fair weather, and no dew after a hot day foretells rain.
If mist rises in low ground and soon vanish, expect fair weather.
Thin, white, fleecy, broken mists, slowly ascending the sides of a mountain whose top is uncovered, predicts a fair day.
When the mist creeps up the hill,
Fisher out and try your skill.
When in the morning the dew is heavy and remains long on the grass, when the fog in the valleys is slowly dissipated and lingers on the hill-side, when the clouds seem to be taking a higher place, and when a few loose cirro-strati float gently along, serene weather may confidently be expected for the greater part of that day.
Fig. 5.—Anticyclone Prognostics.