STORM TIME-DEPENDENCE OF EQUATORIAL DISTURBANCE DYNAMO ZONAL ELECTRIC-FIELDS

We use Jicamarca radar observations of F region vertical plasma drifts and auroral electrojet indices during 1968-1988 to study the characte ristics and temporal evolution of equatorial disturbance dynamo zonal electric fields. These electric fields result from the dynamo action o f storm time winds and/or thermospheric composition changes driven by enhanced energy deposition into the high-latitude ionosphere during ge omagnetically active conditions. The equatorial vertical drift perturb ations last for periods of up to 30 hours after large increases in the high-latitude currents. On the average, this process can be described by two basic components with time delays of about 1-12 hours and 22-2 8 hours between the high-latitude current enhancements and the equator ial velocity perturbations. Our data indicate strong coupling between dynamo processes with different timescales. The short-term disturbance dynamo drives upward equatorial drifts (eastward electric fields) at night with largest amplitudes near sunrise and small downward drifts d uring the day. These perturbation drifts are in good agreement with re sults from the Blanc-Richmond disturbance dynamo theory. The dynamo pr ocess with time delays of about a day drives upward drift velocities a t night with largest values near midnight and downward drifts in the s unrise-noon sector, In this case, the amplitudes of the disturbance dr ifts maximize during geomagnetically quiet times preceded by strongly disturbed conditions. We also present results of a new equatorial stor m time dependent empirical model which illustrate the characteristics of the vertical disturbance dynamo drifts.