The decomposition of temporal variations of pulsar dispersion measures

The pulsar dispersion measure (DM) accounts for the total electron content between a pulsar and us. High-precision observations for projects of pulsar timing arrays show temporal DM variations of millisecond pulsars. The aim of this paper is to decompose the DM variations of 30 millisecond pulsars using the Hilbert-Huang transform (HHT) method, so that we can determine the general DM trends resulting from interstellar clouds and the annual DM variation curves resulting from the solar wind, interplanetary medium and/or ionosphere. We find that the decomposed annual variation curves of 22 pulsars exhibit quasi-sinusoidal, one-component and double-component features of different origins. The amplitudes and phases of the curve peaks are related to the ecliptic latitude and longitude of pulsars, respectively.