Magnetic fields and particle signatures in the vicinity of nightside geosynchronous altitudes in the first one-minute-interval of p2 onset: a case study

An onset of pi 2 pulsations was detected at 0402 UT on 26 August 1986 in the midnight sector by the fluxgate magnetometer at the dip-equator (Huancayo, Peru; 144 degrees N, 355.9 degrees in geomagnetic coordinates; 12.1 degrees S, 75.2 degrees W in geographic coordinates; L = 1.00). At the same time in the midnight magnetosphere, GOES 6 (L = 6.6, 2128 LT), GOES 5 (L = 6.6, 2306 LT), 1982-019 (L = 6.6, 0133 LT) and AMPTE/CCE (L = 7.1, 0206 LT) were monitoring the magnetic fields and flux of low-energy particles (electrons; 30-200 keV, protons; 63-230 keV). An examination is made here for the initial disturbances in the first 1-min of pi 2 onset as observed by these satellites in the night-time magnetosphere. It is found that the initial disturbances in the vicinity of the geosynchronous altitudes are not confined to narrow longitudes but appear over a wide range of longitudes that may span 21-02 LT. These disturbances are discussed in terms of the plasma filling processes of the flux tubes.