Forecasting low-latitude radio scintillation with 3-D ionospheric plume models: 1. Plume model

A three‐dimensional model has been developed for the plasma plumes caused by interchange instabilities in the low‐latitude ionosphere to describe the structure and extent of the radio scintillation generated by turbulence in and around the plumes (down to the scale sizes resolvable by the computer model). With the inclusion of the processes that determine the transport of plasma parallel to the geomagnetic field lines as well as transverse to them, the model can predict the extent in latitude of the plumes and their scintillation. To better reflect the day‐to‐day variability of the occurrence of the plumes, the model is closely coupled to a time‐dependent model of the ambient ionosphere to describe the changing conditions under which the plasma instabilities that cause the turbulence must act. Diagnostics presented here will illustrate the density structures found in the models of the plumes, including maps of airglow emissions which show the effect of the density depletions within the plumes. A companion paper presents a phase‐screen calculation of the amplitude scintillation caused by the plumes.