A. Simonyan
Institute of Geophysics and Engineering Seismology of the National Academy of Sciences of the Republic of Armenia, V.Sargsyan 5, Giumry, 377515, Armenia
Examination of the spatial temporal secular variability of the geomagnetic field during the last one and half century temporal interval provided by regular measurements on word-wide net of magnetic observatories approved the hypothesis the jerks may be considered as the "quanta" in the main geomagnetic field short-period variability. Conception on geomagnetic jerks is consecutively developed from the assumption that the jerks are the jump-like changes in constant rate of geomagnetic field accelerations. Despite at any point of geomagnetic observations the neighboring jerks are distanced over a few decades temporal analysis of appearance of all jerk-like phenomena on local points of observations shows that globally the jerks are observed more often. On the basis of analysis from the jerk hypothesis of the secular variation series for extended as long as possible temporal interval the complete series of epochs of global jerks and the central epochs for accelerations field giving the stationary state of geomagnetic field development are obtained. Spherical harmonic modeling both the constant accelerations field and jerks field shows on the globe all they appear through the positive and negative sign regional foci. However the modeled magnitudes are in well agreement with the estimations of accelerations and jerks obtained from the secular variation series only till acceleration map for 1909. More early maps for 1901 and 1983 show non-realistic high magnitudes both for accelerations field and jerk in 1906. Unfortunately the earliest epochs in second half of XIX century are provided by least amount of series of geomagnetic observations and thus made impossible the construction of spatial spherical harmonic models. Despite on the provided longest series jerks in XIX century observed quite evidently when quality and quantity of provided observational series allowed it. Extension of investigations of the jerks on the recently prolonged data series allowed us to obtain the more recent jerk in 1987. So conclusion that jerks stochastic superposition in time and in the space forms the observed spatial temporal pattern of the main geomagnetic field variability in high-frequency spectrum range seems more reasonable when we examine the maximally extended data set. The obtained spatial temporal models of constant accelerations field the Earth's magnetic field were used for construction the consecutive spherical harmonic models for geomagnetic field and its secular variations choosing the central epoch 1980 by means of expansion up to second derivatives. All the models were truncated up to the fourth order and degree. The resulted models given as long as possible after the last 1987 jerk, i.e. from 1996 up to beginning of century were continued to the core-mantle boundary with an approximation mantle-isolator concerning geometrical attenuation only. Solving the hydro-magnetic equation in kynematic approximation for the rapid jerk-like variations the horizontal velocity field on the surface of the Earth's liquid core was assessed. The velocity field was presented through the rotational and divergence components following the pioneer work Kahle et al. (1967). The fourth truncation level of velocity field expansion aimed to get over non-uniqueness of solution obtained. Full spatial temporal description of velocity field allowed construction of movement system accelerations field also. They are kept constant within the experiment accuracy limits for the spans between the jerks and suffer essential value jumps during the jerks epochs. Giving those spatial patterns on the liquid core surface we observe they are distributed through the negative and positive magnitudes foci. Both the divergence and rotational components field rearrangement as the origins of jerk we obtain. Evidently within the core liquid incompressibility constraint used the obtained foci of core fluid movement system rearrangement on its surface may be concerned to the scenario of fluid local upwelling from the deepest layers anywhere and consequent down-flow elsewhere.