Wavelet Analysis Applied to Magnetometers from Different Longitudes during High Intensity, Long Duration, Continuous Auroal Activity (HILDCAA).

Abstract:

Around the solar maximum, the dominant structures emanating from the sun are sporadic coronal mass ejection (CMEs) and their interplanetary counterparts (ICMEs). In the descending and minimum phases of solar cycle, the geomagnetic activities are mostly influenced by corotating high speed streams. These high speed streams are embedded with highly fluctuated Alfven waves.When these fluctuation of Alfven waves in IMF (Bz) diminish, the storm starts its long recovery phase. The Earth's equatorial magnetic field monitored by the Dst (disturbed storm time) index found to be below than its quiet day value for days. This phenomena is called high-intensity, long duration, continuous AE activity or HILDCAA. In this work, we discuss the ground magnetometers signatures obtained from five longitudinal stations during three HILDCAA events of different interplanetary causes. The concepts of wavelet analysis (CWT, DWT and modulus correlation) have been used in order to get some common signatures on these stations. The CWT is an integral transform, it explores time frequency representation of the horizontal component of geomagnetic field. The objective of DWT is to highlight the disturbances associated during HILDCAA.The Daubechies orthogonal wavelet transform of order 2 with wavelet coefficient magnitudes at seven levels have been studied. In terms of wavelet coefficients the fluctuations present in the horizontal component of geomagnetic field have been analyzed. Both CWT and DWT have proved to be a useful tool in order to get some common features on these stations during the events . We also used wavelet modulus correlation to study the correlation between H-component from five longitudinal stations with IMF-Bz. These results show that the H-component for all stations are highly correlated with IMF-Bz during HILDCAAs.