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DIURNAL AND SEMI-DIURNAL CHANGES IN PRESSURE
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The barogram of a quiet week in equatorial regions, showing the semi-diurnal osillations in pressure. The maximum at 12 o’clock is due to clock time instead of solar time.
practically forms the crest of the wave of greatest warmth. During the coldest hours of the day a reverse movement takes place and forms a corresponding trough of pressure. This diurnal maximum and minimum of pressure is practically a raising and lowering of the center of mass. As a result, a greater mass means greater pressure, and vice versa.
The semi-diurnal maximum and minimum is very regular and obtains in every part of the earth. It is best studied from the barogram, a strip of paper attached to the revolving drum of a recording barometer. The line drawn by the barograph pen shows a slight rise above mean pressure at 10 o’clock, morning and night, followed by a depression at
