Satellite observations of lightning-induced electron precipitation

Lightning-induced electron precipitation (LEP) from the Earth's radiation belt has been observed on numerous occasions with detectors on the low-altitude S81-1/SEEP satellite. A sequence of seven LEP events on September 9, 1982, and eight events on October 20, 1982, are correlated on a one-to-one basis with one-hop whistlers at Palmer, Antarctica. The temporal profile within a LEP burst has a remarkable fine structure. It is shown to be associated with bunches of magnetically guided and focused 100-to-200 keV electrons that are repeatedly scattered by the atmosphere and bounce between the northern and southern hemispheres. The delay time between the lightning sferic and the arrival of the first electron bunch increases with increasing L as predicted by the first-order gyroresonance theory. The global distribution of strong LEP events observed with the SEEP payload correlates with lightning activity and shows a preferred distribution at 2 < L < 3. This L shell range corresponds to the slot region in the electron radiation belt. A single LEP burst (10−3 erg s−1 cm−2) in the slot region is estimated to deplete ∼0.001% of the particles in the region covered by the burst magnetic field lines. The evidence supports the production of structured LEP by ducted rather than nonducted whistlers. It is found that ducted whistlers can be an important pitch angle diffusion mechanism for 100–250 keV electrons in the 2 < L < 3 range although a number of uncertainties in the various parameters remain to be resolved; It is suggested that observations of LEP can be a new tool to measure the presence and transverse dimensions of plasmaspheric whistler mode ducts.