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

The problem of downward mapping of equatorial ionospheric electric fie lds is studied in two dimensions employing the finite elements and fin ite differences numerical techniques. The solutions obtained for low l atitudes are compared with known results for high latitudes. It is fou nd that equatorial ionospheric electric fields of scale lengths of the order of 100 km or more reach balloon heights (30-40 km) without unde rgoing noticeable attenuation. However, in the case of equatorial iono spheric electric fields of scale lengths of a few tens of kilometers i t is found that these fields reach balloon heights with severe attenua tion. The corresponding attenuation factors are significantly larger t han 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 c onductivity irregularity in the middle atmosphere, such as that expect ed in the South Atlantic Magnetic Anomaly (SAMA) region during energet ic electron precipitation events, can considerably distort the mapped ionospheric electric fields at the middle atmosphere.