Indirect Experimental Evidence for the Existence of Hall and Pedersen Currents in the Auroral E Region

Measurements of the afternoon radio aurora at 1295 MHz

“…All of these items have corresponding features in the radar measurements. The dip latitude range of the observations in Figure 10 is 65ø-70øN and [Newell and Abel, 1968]. It is also to be noted that the strongest echoes occur at the same heights as the largest currents and that the strongest echoes at a given elevation angle occur where both the height dependence and aspect sensitivity are optimum in the same volume of space, namely near 330 ø and 0 ø azimuth.…”

“…However, the theory assumes that the ions are at rest whereas in practice, ion-neutral collisions are likely to transmit the velocity the neutral particles to the observed waves. As noted elsewhere [Newell and Abel, 1968] Another aspect of the two-stream theory is that it predicts wave growth only if the electron-ion relative velocity is somewhat greater than the ion acoustic speed. The relative velocity has been estimated from the computed currents and the observed electron concentration and is shown in Figure 13.…”

On auroral electrojet curvature and the interpretation of azimuth‐scan, radar Doppler data

“…According to data presented by Newell and Abel [ 1968], the azimuth of zero-Doppler crossing occurs at progressively more westerly azimuths at higher altitudes in an eastward electrojet. This effect has been explained as due to an increasing Pedersen current with increasing altitude [Newell and Abel, 1968] and was partly predicted by Gadsden [ 1967]. If we assume that the irregularities actually drift with the electron-ion relative velocity, Ve --V•, we can derive equivalent forms of (6) and (9).…”

“…The electric field and electron velocity reverse sign in a westward electrojet, and therefore the azimuth of zero-Doppler crossing will also move westward by probing progressively higher altitudes in a westward electrojet. For example, assume that the part of the auroral oval observed from Millstone Hill (42.6øN, 71.5øW) by Newell and Abel [1968]…”

“…Note that if a is equal to unity, (21) reduces to (3) or (6), and the Doppler velocity is independent of any ion motion. Since ion motion effects apparently have been observed [Newell and Abel, 1968;Tsunoda, 1975Tsunoda, , 1976], a must not be equal to unity (at least at the higher frequencies). If we follow the same derivation procedure for the curved-line current approximation and use (14) in ( The scaling factor, a, is dependent on the nature of the scattering mechanism.…”