Ground Observations Of Earth’s Magnetic Field to Reveal the Screening Effect of the Ionosphere on Geomagnetic Pulsation

Abstract

Ultra-Low Frequency (ULF) waves are plasma waves originate in upstream region of the solar wind encountering earth’s magnetic field obstacle. These waves propagate through earth’s magnetosphere to the ground surface of the earth passing by the ionosphere. However, upstream waves include Pc3-4 frequency range: 7-100 mHz. Accordingly, the ionosphere plays a role in characteristics of these waves that recorded on the ground. This dissertation addresses the effect of the ionosphere on the ULF waves. Here, a simultaneous ground and in situ satellite observations are carried out to detect ULF waves. In situ satellite data were obtained from the space flight mission Cluster; and the signatures of these waves were then observed on data from the ground geomagnetic station (KAG) which belong to the magnetic data acquisition system (MAGDAS) global network of magnetometers. Dynamic spectrum magnetograms of these data have shown corresponding enhancements of Pc3-4 waves amplitudes in both in situ and ground data. The waves in the source at geospace were found to be in the azimuth direction, i.e. in the By component of the data, i.e. (Toroidal) ULF mode; while their corresponding signatures on the ground were observed in the H component of the magnetic data from KAG station. These results reveal the screening effect played by the ionosphere on these ULF waves.