Global Characteristic of the Quasi-6-Day Oscillation in Sq-EEJ Current System

Abstract:

Day-to-day variations in the Sq-EEJ current system using dense geomagnetic field observational sites along 210° geomagnetic longitude chain composed of MAGDAS (Global Geomagnetic Observation Network) and observational sites operated by Geospatial Information Authority of Japan (GSI) were analyzed for a comprehensive understanding of the three-dimensional atmosphere-ionosphere-magnetosphere coupled system. In this study, we focus on the quasi-6-day oscillation excited by atmospheric waves from below.

The quasi-6-day wave (Q6DW), one of the atmospheric waves, is excited in the lower atmosphere and propagates into the mesosphere and thermosphere. Using CHAMP, Swarm and Aura satellites, Yamazaki et al. showed that the quasi-6-day oscillation in the EEJ occurs when the Q6DW in the mesosphere is enhanced. This suggests that the quasi-6-day oscillation in the EEJ is caused by the Q6DW propagated from below.

However, the longitudinal and latitudinal dependences of the quasi-6-day oscillation in the Sq-EEJ system are not well known.

To understand the global distribution of the quasi-6-day oscillation in the Sq-EEJ current system, we analyzed H components of magnetic field data of MAGDAS and GSI during 2007.

We used Principal component analysis to eliminate disturbance components at each station. Also, we used Bandpass filter to extract components of the quasi-6-day variations from H components and compare the global variation of the amplitude of the quasi-6-day oscillation in the H components.

Our results indicate that the quasi-6 day oscillation in the Sq-EEJ current system has strong longitudinal and latitudinal dependences, although the Q6DW is a planetary-scale wave. The excitation mechanism of the quasi-6 day oscillation in the Sq-EEJ current system is examined using an atmosphere-ionosphere coupled model (GAIA).