Energy spectra of electron microbursts from 170 keV to 340 keV have been measured by the solid-state detectors aboard the low-altitude (680 km) polar-orbiting Korean STSAT-1 (Science and Technology SATellite). These measurements have revealed two important characteristics unique to the microbursts: (1) They are produced by a fast-loss cone-filling process in which the interaction time for pitch-angle scattering is less than 50 ms and (2) The e-folding energy of the perpendicular component is larger than that of the parallel component, and the loss cone is not completely filled by electrons. To understand how wave-particle interactions could generate microbursts, we performed a test particle simulation and investigated how the waves scattered electron pitch angles within the timescale required for microburst precipitation. The application of rising-frequency whistler-mode waves to electrons of different energies moving in a dipole magnetic field showed that chorus magnetic wave fields, rather than electric fields, were the main cause of microburst events, which implied that microbursts could be produced by a quasi-adiabatic process. In addition, the simulation results showed that high-energy electrons could resonate with chorus waves at high magnetic latitudes where the loss cone was larger, which might explain the decreased e-folding energy of precipitated microbursts compared to that of trapped electrons.

1. INTRODUCTION
 2. OBSERVATION
 3. WAVE AND PARTICLE INTERACTIONS
 4. WAVE-PARTICLE INTERACTIONS IN AUNIFORM MAGNETIC FIELD
 5. WAVE-PARTICLE INTERACTION IN DIPOLE 
MAGNETIC FIELD
 6. TEST PARTICLE SIMULATION IN DIPOLE MAGNETIC FIELD
 7. DISCUSSION AND CONCLUSION
 ACKNOWLEDGMENTS
 REFERENCES

• Jaejin Lee(Korea Astronomy and Space Science Institute, Daejeon 34055, Korea, University of Science and Technology, Daejeon 34113, Korea) Corresponding Author
• Kyung-Chan Kim(Korea Astronomy and Space Science Institute, Daejeon 34055, Korea)
• Jong-Gil Lee(Korea Astronomy and Space Science Institute, Daejeon 34055, Korea, University of Science and Technology, Daejeon 34113, Korea)