STRUCTURE OF AURORAL-ZONE PHENOMENA FROM THE DATA OF MERIDIONAL CHAINS OF STATIONS - THE LOWER IONOSPHERE DURING THE EXPANSION PHASE OF MAGNETOSPHERIC SUBSTORMS

The distribution of anomalous ionization in the lower ionosphere during the expansion phase of magnetospheric substorms was examined on the basis of ionospheric and magnetic data along the meridian 90-degrees-E for more than 70 substorms in the winter of 1982-1983. It is shown that the behaviour of the lower ionosphere near locations of maximum eastward and westward electrojets is different for isolated and for prolonged substorms. For isolated substorms diffuse precipitation dominates in the eastward electrojet area and discrete (arc associated) precipitation is usual in the westward electrojet area. For prolonged substorms discrete precipitation is observed at the polar and equatorial edges of the eastward electrojet while the auroral absorption significantly increases in the westward electrojet area. This means the auroral precipitation becomes harder during prolonged substorms. The difference in the features of isolated and prolonged substorms is in good agreement with satellite observations made during magnetospheric substorms.