The characteristics of magnetic signals observed at lulin elf station and their association with earthquakes in Taiwan

Abstract

A data survey reveals multiple periodic variations in auroral hemispheric power (HP) and thermospheric composition (O/N2) in 2006. The periods include 27, 13 - 14, 9, and 6.7 days. These periods of 13 - 14, 9 and 6.7 days are essentially the harmonics of the 27-day solar rotation. Similar multi-periodicities were found in the dayside magnetic merging rate (MMR) (Newell et al. 2007) which depends upon solar wind speed (V), magnitude (BT) and clock angle (θc) of interplanetary magnetic field (IMF). A high correlation coefficient (0.93) between MMR and HP indicates MMR is the driver of the periodic variations. While high solar wind speed associated with coronal holes plays an important role in the HP variations, IMF BT is equally important. The term [BT2/3sin8/3(θc /2)] is even more important as its correlation coefficient with HP is higher than that for BT or solar wind speed. Nevertheless, MMR has the highest correlation with HP. Similar results were seen in the 2005 data where the 9-day variation is dominant. These results indicate that both solar wind speed and IMF conditions are required for accurate specification of periodic variations in aurora hemispheric power and thermosphere composition.