ing the lifetime of these energetic particles and modifying auroral activity. Natural charge-exchange lifetimes for ring current ions are ~ 105 sec, as can be seen from the duration of the recovery phase of a geomagnetic storm. If the ring-current particle lifetimes are significantly shortened by charge exchange interaction with the neutral cloud, auroral activity would be significantly reduced by the following sequence of effects: (a) charge-exchange reaction converts an energetic charged particle into an energetic neutral which immediately escapes geomagnetic confinement; (b) ring current precipitation is enhanced and trapped fluxes are reduced, leading to (c) reduction of strength and duration of geomagnetic storms and ionospheric disturbances. Our purpose in this study is to estimate the effect of neutral-hydrogen exhaust on the ring current by virtue of charge exchange. For this purpose we must calculate the mean density [[spi:math]] of hydrogen atoms around the drift shell of a ring-current ion. For simplicity we consider ions that mirror at the magnetic equator, since it is known that ring current particles are strongly peaked near 90° pitch angle. To evaluate the prompt effects of the neutral exhaust jet, we have devised a model in which the hydrogen density varies inversely as the square of the distance from an equatorial point located R earth radii from the geocenter (see Figure 17). The density vanishes outside a cone of halfangle a, and the axis of the cone lies in the equatorial plane. Moreover, the axis of the cone is tangential to the drift path of a ring-current ion. This conical model of neutral exhaust jet is not unlike the cases discussed in Section II.A. We assume continuous emission of neutrals at a rate [[spi:math]] and velocity u from the point source at geocentric distance R and longitude [[spi:math]]= 0 in a centered-dipole field. The square of the distance from a point on the drift path of a ring-current ion is given by 64
RkJQdWJsaXNoZXIy MTU5NjU0Mg==