ULTRA-LOW-FREQUENCY FLUCTUATIONS OF GEOMAGNETIC FIELD AS MEAS- URED AT THE OBSERVATORY ALMA-ATA [43.25N; 76.95E]

Abstract

The variability of the geomagnetic field in seismic regions is the subject of close at-
tention of geophysicists. Work in this direction is carried out in order to identify geomagnetic data
perturbations of space and lithospheric nature. This paper presents the results of a study of the be-
havior of the magnetic field in the seismic region of the Northern Tien Shan on the basis of data
from the Observatory "Alma-Ata" [43.25N; 76.95E]. The distinctive features of ultra-low-
frequency fluctuations in the magnetically disturbed day (Kp=8) and in the magnetically calm day
(Kp=2) were established. On the perturbed day, the oscillation amplitude is 5-15 NT with periods
from 2 to 5 minutes, whereas on the magnetically calm day the oscillation amplitude is the largest in
the Z-component, they are 0.50.15 NT with periods less than 1 min. The dynamics of the spectral
index β calculated by the method of fast Fourier transform for the midnight values of the geomag-
netic field in the seismic period is studied. It was found that the dynamics of the spectral index β is
determined by the geomagnetic environment, that is, external factors such as solar flare activity,
primarily affect the characteristics of ultra-low-frequency fluctuations of the geomagnetic field. The
presence of seismogenic anomalies is not observed, possibly due to the average intensity of earth-
quakes.