Worldwide character of the 1991 geomagnetic jerk

Local time features of geomagnetic jerks

“…While it is confirmed that the occurrences of the jerks in the southern hemisphere a few years after those of the 1969 and 1978 jerks in the northern hemisphere as pointed out by Alexandrescu et al (1996) and De Michelis et al (1998), it is also found that the occurrence of the jerk in the southern hemisphere is a few years after that of the 1991 jerk in Europe. Taking these time lags in occurrence epochs of the jerks into account, the 1969, 1978, and 1991 jerks are confirmed to be global phenomena as suggested by previous papers.…”

“…The 1969 and 1978 jerks are confirmed to be global phenomena by many papers (e.g., Le Mouël et al, 1982;Alexandrescu et al, 1996), and the 1991 jerk has worldwide character (e.g., De Michelis et al, 1998;Le Huy et al, 1998. It was also reported that the occurrences of the jerks in the southern hemisphere are a few years after those of the 1969 and 1978 jerks in the northern hemisphere (e.g., Alexandrescu et al, 1996), and the occurrence of the jerks in North and South America is a few years before that of the 1991 jerk in other regions (e.g., De Michelis et al, 1998). These commonly observed time lags in occurrence epochs could be evidences, which indicate that the jerks are of internal origin.…”

“…Alexandrescu et al (1996) showed that the jerks occurred in the southern hemisphere a few years after the occurrences of the 1969 and 1978 jerks in the northern hemisphere. De Michelis et al (1998) showed that the jerk occurred in North and South America a few years before the occurrence of the 1991 jerk in other regions. The result of our analysis on this topic obtained from 0000-0100 LT data shown in Fig.…”

The time-varying geomagnetic field of Southern Africa

“…Results obtained prior to 1980 show that the secular variation for declination over southern Africa is predominantly in an eastward direction, except for a small eastern coastal region. During 1980During -1985 Another global sudden change in the secular variation of the geomagnetic field has been reported around 1991 (MacMillan, 1996;De Michelis et al, 1998). This tendency has also been observed at Hermanus, Hartebeesthoek and Tsumeb during the early 1990's.…”

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

“…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).…”