A convection enhancement event observed with the Polar Patrol Balloon #4

A convection enhancement event was observed with the Polar Patrol Balloon #4 which was launched at Syowa Station on December 26,1992. This event occurred during 1700-1900 UT on December 28,1992,when the balloon located in the afternoon sector of the sub-auroral zone. During this period, the amplitude of the southward electric field (E_S) increased from about 20mV/m to 50mV/m and then decreased to 20mV/m again. The northward component of the magnetic field variation (B_H) also increased from 200nT to 600nT, and then decreased to about 100nT. The maximum time of E_S lagged about 12 min after the B_H maximum time (t_). We could estimate the height integrated ionospheric electric conductivity from these horizontal electric field and magnetic field data. Before t_ Hall conductivity (σ_H) was about two times greater than Pedersen conductivity (σ_P), and after t_ σ_H decreased monotonously to become smaller than σ_P, while σ_P maintained a nearly constant value. Around t_ both σ_H and σ_P were enhanced by about 1.5 times in about 10min, and energetic particle precipitation was observed with the on-board X-ray counter. We could summarize this event as follows : there was stable enough particle precipitation to maintain σ_H before t_ : As E_S increased, the ionospheric Hall current increased, and B_H increased. Around t_ a large quantity of particles precipitated above the balloon, ionospheric conductivities and Hall current reached a maximum value, and thus the B_H reached a maximum value. After t_ σ_H and B_H decreased because the energy spectrum of the precipitation became softer, while E_S continued to increase. E_S reached a maximum value about 12min after t_. From the ground-based data in the southern and northern hemispheres and also satellite IMF data, it was concluded that this event was not an isolated disturbace confined just around the balloon location, but was a global feature of the ionospheric convection variation corresponding to the IMF fluctuation