Detecção de impulsos na variação secular geomagnética, no observatório magnético de Vassouras

Abstract

The time variations of the Earth's magnetic field have a wide spectrum. Low periods are due to pertubations in the Earth's ionosphere and magnetosphere. The long period, known as secular variation of the geomagnetic field, are related to the generation and maintenance of the field in the core-mantle bondary (CMB). However, the distinction between the inner and outer sources is not always straighforward. There are intermediate periods like the solar cycle with a period of eleven years and shorter periods from one to two years that are probabily generated in the Earth's core. The geomagnetic jerks are examples of this short period variation being identified by the abrupt changes in the geomagnetic secular variation. Several works have been published about the subject, but the origin, definition and characteristics of the geomagnetic jerks remains an open discussion within the scientific community. Even fundamental parametres, like time of occurrence and distribution of the events are not a consensus among the researchers. The main ocurrences identified are 1901, 1913, 1925, 1969, 1978, and more recently in 1992 and 1999. This work idenfies the geomagnetic jerks occurred at Vassouras Observatory between 1915 and 2001 using both classical methods and wavelet analysis. The latter has advantages for this study as they are particularly useful to detect abrupt changes in a particular series. The geomagnetic jerks are discontinuities in an α derivative of the field. Another advantage of that analysis is that it is not necessary to introduce any information a priori about the origin of the geomagnetic jerks.