Worldwide wavelet analysis of geomagnetic jerks

Abstract

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

Impulses of the geomagnetic secular variation (jerks) at vassouras magnetic observatory detected by wavelet analysis

“…For example, the 1932 jerk is local since it was mostly observed in the southern hemisphere and not seen in any European observatory. Another local jerk was detected in 1949, observed mainly in the Pacific area and in the American region (Alexandrescu et al, 1996). A more recent and local jerk occurring at 2003 was found by Olsen & Mandea (2007) by using satellite data.…”

“…The wavelet analysis is another method that has been applied to identify jerks. Alexandrescu et al (1996) used the continuous wavelet transform and found five events characterized as worldwide jerks, occurred during the last century : 1901: , 1913: , 1925: , 1969: and 1978. Some works point to more recent global jerks at 1991 (De Michelis et al, 1998 and at 1999 (Mandea et al, 2000).…”

“…These three events show a nonsimultaneous behavior. This means that the same event occurs in slightly different times at distinct observatories; usually these jerks appear at a later time in the southern hemisphere, with a time delay of about two years (Alexandrescu et al, 1996;De Michelis et al, 2000;Chambodut & Mandea, 2005).…”

The wavelet response as a multiscale characterization of scattering processes at granular interfaces

“…The geometrical sense of this equation is that the wavelet transform of a homogeneous singularity has the appearance of a cone whose apex points onto the singularity for a ↓ 0 + . Equation (6) indicates that the magnitude of the wavelet transform is ∝ a α when sampled along the cone lines also called the ridge functions (see Alexandrescu et al [1995Alexandrescu et al [ , 1996 and Le Gonidec et al…”

“…Consequently, the interesting properties of the wavelet transform concerning the characterization of abrupt changes in signals [e.g. Mallat and Hwang, 1992;Herrmann, 1994;Alexandrescu et al, 1995Alexandrescu et al, , 1996 are retrieved in the wavelet response which may be used to remotely analyse the multiscale structure of acoustical interfaces [Walden and Hosken, 1986;Herrmann, 1996;Wapenaar, 1998Wapenaar, , 1999Marsan and Bean, 1999].…”