Instability of secular variations in the horizontal components of the geomagnetic field: quasi-periodic fluctuations and jerks

Two types of fluctuations, with a short period (SPFs, 3 ± 0.15 years) and with a long period (LPFs, 10-70 years), have previously been found in the secular variation rate (SVR) of the horizontal component H, the vertical component Z, and the inclination I of the geomagnetic field (GMF). The fluctuations of SVR for the horizontal components of the GMF (X, Y, and D) and the periods and amplitudes of their SPFs are estimated in this study. The SVR fluctuations for Y and D are synchronous and have identical phases, and the SVR fluctuations for X are opposite to them in phase, except the areas near the magnetic poles. The SPF periods for X, Y, and D are almost the same (2.80 ± 0.14 years). Jerks in the SVR of Y, especially significant in Europe in 1969 and 1978, were studied. It is shown that jerks are a component of long-period fluctuations in the SVR of Y; they appear at the coincidence of extrema of the same sign in LPFs and SPFs. Jerks need not be considered a special phenomenon because they can be presented as the sum of quasi-periodic LPFs and SPFs.