Intermittency analysis of geomagnetic storm time-series observed in Brazil

Abstract

In this paper, we present and discuss the results of the statistical analysis applied to the geomagnetic field H-component (temporal resolution 1 min) observed at Vassouras (22.4°S, 43.6°W; dip lat. 18.5°S), Brazil, during the months of July 2000, March 2001, April 2001, April 2002 and May 2002. Each month studied had intense or very intense geomagnetic storm. For |Dst| max between 100 and 200 nT, the geomagnetic storms have been considered as intense, whereas for |Dst| max>200 nT, the geomagnetic storms have been considered very intense. The statistical parameter kurtosis (a measure of intermittency) shows that, the higher values in kurtosis cause the probability density function (PDF) more spiky. Furthermore, the higher values in kurtosis are possibly more efficient for the disturbed geomagnetic system to return to the steady-state conditions. In order to evaluate the importance of this feature in detail, we used the approach of the Hölder exponent applied to one of the periods studied, July 2000, representing respectively the interval of the quiet and post geomagnetically disturbed conditions. The results indicated that the part after the recovery phase had higher Hölder exponent than during quiet conditions. Thus, indicating that the intermittency introduced by disturbance acts more efficiently for return to the steady-state conditions. Analysis performed with Morlet wavelet transform and study of anisotropy in geomagnetic storm time-series show that the disturbances are important source of intermittency having small scales (with periods ≪1 day) and are much more dominant compared with the diurnal variations in geomagnetic field H-component. The present work indicates the importance of the intermittency in the recovery phase of geomagnetic storms.