DOWNWARD MAPPING OF QUASI-STATIC IONOSPHERIC ELECTRIC-FIELDS AT LOW LATITUDES DURING FAIR WEATHER

The problem of downward mapping of equatorial ionospheric electric fields is studied in two dimensions employing the finite elements and finite differences numerical techniques. The solutions obtained for low latitudes are compared with known results for high latitudes. It is found that equatorial ionospheric electric fields of scale lengths of the order of 100 km or more reach balloon heights (30-40 km) without undergoing noticeable attenuation. However, in the case of equatorial ionospheric electric fields of scale lengths of a few tens of kilometers it is found that these fields reach balloon heights with severe attenuation. The corresponding attenuation factors are significantly larger than those known for high latitudes. It is also shown that the presence of mountains with a fairly large height as well as of a large-scale conductivity irregularity in the middle atmosphere, such as that expected in the South Atlantic Magnetic Anomaly (SAMA) region during energetic electron precipitation events, can considerably distort the mapped ionospheric electric fields at the middle atmosphere.