Preliminary report of numerical simulation of Type 2 irregularities in the equatorial electrojet

Experimental studies of the equatorial electrojet have indicated that there are two classes of irregularities associated with the electrojet current. The first (known as type 1) propagates perpendicular to the earth's magnetic field at the ion acoustic velocity and is believed to be caused by the two-stream instability [Farley, 1963; Buneman, 1963]. The second class (type 2) appears to travel at the drift velocity of the electrons, does not have any threshold in the drift velocity, and is more easily excited than type 1 for wavelengths longer than a few meters. It is generally believed that type 2 irregularities are caused by the gradient drift instability [Maeda et al., 1963; Knox, 1964; Reid, 1968; Rogister and D'Angelo, 1970; Whitehead, 1971].