A model study of how electric field structures affect the polar cap F region

A three‐dimensional time‐dependent ionospheric model was used to study how electric field structures affect the polar F region. The electric field structures are represented by elongated Volland two‐cell models whose dimensions range from tens to 1000 km. These model structures are intended to represent the polar cap electric field for IMF B z northward conditions. A statistical method is used to generate a set of these structures. Their electric field strength and polarity are varied in order to study the F region's dependence on this magnetospheric input. For electric field structures whose size and electric field strengths are consistent with B z northward observations, several ionospheric dependencies were found. The N m F 2 parameter, in general, decreased due to the presence of the higher electric fields associated with the structures. Decreases ranging from a few percent to a factor of 4 were obtained from the simulations. This decrease in N m F 2 was frther complicated by the initial N m F 2 conditions, i.e., past history of the flux tube, being quite different when the structure is present. H m F 2 in the vicinity of a structure can be raised or lowered by up to 100 km, however, this change is not uniquely dependent upon the vertical induced drift. The role of enhanced reaction rates due to elevated ion temperatures is very important. The F region becomes spatially very structured. The modulation of this structure in N m F 2 is up to an order of magnitude in this study.