When the field eventually recuperated, it was pointing in the opposite direction. Here was a real triumph for Glatzmaier and Roberts. Their MHD model had produced a geomagnetic reversal entirely on its own, without any provocation from the experimenters. Our original motivation was not to simulate magnetic field reversals. That seemed too much to hope for.
Lines wrapping around the core in east-west bands indicate the toroidal magnetic field.
Although the model simulations have continued, with one now exceeding 200,000 years in duration, Glatzmaier and Roberts have not witnessed a second reversal. That may be a good sign, since reversals of the actual geomagnetic field usually occur only once every few hundred thousand years and occasionally much less frequently. Still, with only one reversal under their belts, the scientists cannot yet draw many conclusions about what causes the process. T he MHD model garnered even more attention last July, when two seismologists reported that the solid inner core of the actual Earth is spinning faster than the rest of the planet. Xiaodong Song and Paul G. Richards of the Lamont-Doherty Earth Observatory in Palisades, N.Y., who made the discovery, credited the MHD model for stimulating their search.