Abstract. A numerical model has been developed which is capable of simulating all phases of the life cycle of metallic ions, and results are described and interpreted herein for the typical case of Fe + ions. This cycle begins with the initial deposition of metallics through meteor ablation and sputtering, followed by conversion of neutral Fe atoms to ions through photoionization and charge exchange with ambient ions. Global transport arising from daytime electric ®elds and poleward/ downward diusion along geomagnetic ®eld lines, localized transport and layer formation through descending convergent nulls in the thermospheric wind ®eld, and ®nally annihilation by chemical neutralization and compound formation are treated. The model thus sheds new light on the interdependencies of the physical and chemical processes aecting atmospheric metallics. Model output analysis con®rms the dominant role of both global and local transport to the ion's life cycle, showing that upward forcing from the equatorial electric ®eld is critical to global movement, and that diurnal and semidiurnal tidal winds are responsible for the formation of dense ion layers in the 90±250 km height region. It is demonstrated that the assumed combination of sources, chemical sinks, and transport mechanisms actually produces F-region densities and E-region layer densities similar to those observed. The model also shows that zonal and meridional winds and electric ®elds each play distinct roles in local transport, whereas the ion distribution is relatively insensitive to reasonable variations in meteoric deposition and chemical reaction rates.

Nighttime zonal plasma drifts in the equatorial region are calculated from a simplified expression involving Pedersen conductivity, geomagnetic field strength, and zonal neutral wind, integrated along flux tubes between apex altitudes of 250–1500 km. The ambient conditions correspond to solar maximum at equinox over the American sector with vertical electron density profiles derived from average drift measured over Jicamarca. Plasma drift outputs from four neutral wind models are evaluated for overall consistency and compared to similar data from the DE 2 satellite collected during solar cycle 21 from 1.5 to 3 years after the solar maximum peak. Drift velocities are displayed to compare model output against the DE 2 measurements. Model inputs of solar maximum with vertical electron drift reduced to one‐half average strength and a heuristically derived wind are found to give very good agreement with the DE 2 results. The implicit conclusion is that this final model is most representative of actual thermospheric winds for the conditions of near‐solar maximum at equinox in the nighttime sector.