Ionospheric equivalent current systems of low-latitude Pc3 pulsations

Abstract Ionospheric equivalent current systems of low-latitude Pc3 pulsations observed on 7 June 1980 were studied using data from the AFGL (Air Force Geophysics Laboratory) magnetometer network. The network, which covers four hours in longitude, consists of seven stations: five along 55°N and two along 40°N geomagnetic latitude. Pulsations studied had a period between 11 and 23 s and were observed simultaneously at all seven stations. A cross spectral analysis of the interstation signals showed a phase structure in longitude as well as in latitude. In longitude, the apparent phase propagated eastward or westward, but was not always consistent between the H - and D -components. In latitude, on the other hand, the apparent phase was always poleward for both components. Ionospheric equivalent current systems were drawn by combining the results of the cross spectral analysis of the interstation signals with the phase differences of the H - and D -components at each station. Two different types of the current systems, namely Type A and Type B were found. Type A indicates that either a clockwise (CW) or counterclockwise (CCW) ionospheric current cell appears at the North-East end of the activity Region, moves toward the West, and then disappears at the North-West end of the activity region. This type of event has a spectral peak between 12 and 16 s and is observed between 6:00 and 10:00 M.L.T. Type B consists of two sub-cells moving from North to South independently. This type has a spectral peak between 11 and 23 s, a range much broader than that of Type A and is commonly seen between 7:30 and 15:00 M.L.T. The structure and movement of the current system associated with low-latitude Pc3 pulsations is discussed in relation to the field-line resonance model.