A rapid, global and prolonged electron radiation belt dropout observed with the Global Positioning System constellation

A rapid loss of energetic (>230 keV) electrons from the outer radiation belt was observed with the GPS constellation between 1430 and 1730 UTC on 7 May 2007. The rapid loss occurred from 4 < L * < 6 over all measured energies above 230 keV. Currently accepted rapid loss mechanisms include magnetopause shadowing and/or outward diffusion, and precipitation to the atmosphere due to wave‐particle interactions. Here the loss timescale is ∼2 hr, and the magnetopause is near L = 8, which requires unrealistically high outward diffusion rates. Current estimates of the loss timescales associated with EMIC waves, plasmaspheric hiss and whistler‐mode chorus are too long, even in combination, to explain the observed losses inside L* ≃ 6.