International audienceFollowing an earlier study which gives the principles of the method and an example of application to the eastern component of the magnetic field in the European region [Alexandrescu et al., 1995], detection and characterization of geomagnetic jerks using wavelet analysis is generalized to any horizontal component of the field and to a worldwide distribution (involving 97 locations) of observations. This allows for a systematic and global search for such events within the twentieth century and makes it possible to unravel a number of intriguing properties associated with them. Whereas our first study only reveals five such events in Europe, we can now state that seven and only seven events have apparently occurred throughout the world during the present century. Two (1969 and 1978) are unquestionably of global extent, three (1901, 1913, and 1925) being possibly of similar extent, while the remaining two (1932 and 1949) are not seen everywhere at the Earth's surface. We confirm our early result that the events are more singular than previously thought, with a "regularity" systematically closer to 1.5 than to 2, and a common mean value of about 1.6. Furthermore, the 1969 and 1978 events display a two-step spatio-temporal behavior consisting of an "early arrival" in the northern hemisphere, a "late arrival" in the southern hemisphere, and a time lag between the two arrivals of the order of a couple of years. We were also able to show that the 1969 and 1978 events tend to at least partially balance each other. The extent to which this is true remains to be assessed, mainly because our method, although already providing some information about the geometry of the events, does not yet allow the proper recovery of their intensities

Wavelet analysis is applied to detect and characterize singular events, or singularities, or jerks, in the time series made of the last century monthly mean values of the east component of the geomagnetic field from European observatories. After choosing a well‐adapted wavelet function, the analysis is first performed on synthetic series including an “internal”, or “main”, signal made of smooth variation intervals separated by singular events with different “regularities”, a white noise and an “external” signal made of the sum of a few harmonics of a long‐period variation (11 years). The signatures of the main, noise, and harmonic signals are studied and compared, and the conditions in which the singular events can be clearly isolated in the composite signal are elucidated. Then we apply the method systematically to the real geomagnetic series (monthly means of Y from European observatories) and show that five arid only five remarkable events are found in 1901, 1913, 1925, 1969, and 1978. The characteristics of these singularities (in particular, homogeneity of some derived functions of the wavelet transform over a large range of timescales) demonstrate that these events have a single source (of course, internal). Also the events are more singular than was previously supposed (their “regularity” is closer to 1.5 than to 2., indicating that noninteger powers of time should be used in representing the time series between the jerks).

Abstract. Declination (D) and inclination (I) data from the

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Spherical harmonic models of the 1969, 1979 and 1992 geomagnetic jerks are computed using data from about 160 worldwide geomagnetic observatories. The dominance of the internal origin part with respect to the external one confirms again the internal origin of these events. A change of sign is observed between two successive jerks (1969)(1970)(1971)(1972)(1973)(1974)(1975)(1976)(1977)(1978)(1979)(1979)(1980)(1981)(1982)(1983)(1984)(1985)(1986)(1987)(1988)(1989)(1990)(1991)(1992). The acceleration jump of the fluid flow at the core mantle boundary (CMB) generating the three jerks is computed. Striking similarities between the three acceleration maps are observed (within the sign change mentioned above). These results suggest some long time scale memory in the processes that are responsible for the jerks. These processes remain to be elucidated.