The relation between the mean barometric pressure anomaly at Jakarta and the length of the period of the Southern Oscillation

Summary The barometric pressure curve at Jakarta is presumed to consist of two components. The first is the basic air pressure, which shows a relaxation oscillation during a periodt ₁. The value oft ₁ may differ for the successive periods. The second component is the Southern Oscillation proper, which is superimposed on the basic air pressure. This system of two kinds of oscillations may be expressed in the form of a differential equation. The solution of the equation depends on the value of a certain constant. If the value is greater than zero, the solution shows a S.O. the amplitude and period of oscillation of which decreases in time. If the value is less than zero, the solution shows a S.O. the amplitude of which decreases in time and the period of oscillation of which increases in time. As an example of the first contingency the values of the constants occurring in the solution were determined for the period 1868–1876 so that a good approximation to the existing air pressure curve could be attained. It was possible to establish a relationship between the basic air pressure level and the period of oscillation of the S.O. The air pressure curve at Jakarta during the years 1876–1884 was reconstructed from this relationship. The two trains of 3-year waves in 1885–1891 and 1896–1905 may be regarded as an example of the second contingency.