Aspect angle dependence of the E region irregularity velocity at large flow angles

We present the Doppler velocity observations of 1-m plasma waves in the auroral E region by the Scandinavian Twin Auroral Radar Experiment (STARE) Norway VHF coherent radar in the context of simultaneous and coincident measurements of electron and ion drift velocities determined by the European Incoherent Scatter (EISCAT) tristatic radar facility. The measurements were performed in the afternoon sector (1500–2000 MLT) at seven locations along the STARE radar beam 2 with different values of the magnetic off-perpendicular (aspect) angle α between 0.48° and 2.63° and at large angles with respect to the electron background drift ( = 55°–90°). It is demonstrated that the STARE line-of-sight velocity, normalized to the EISCAT-derived electron drift speed at large flow angles, exhibits a decrease with increasing aspect angle, and the rate of decrease is investigated as a function of the flow angle. We also compare the STARE velocity with the electron and ion drift velocity components along the STARE radar beam look direction and show that, at large aspect angles, the E region velocity is correlated (anticorrelated) with the ion (electron) drift velocity component. The results are discussed in the contexts of the linear fluid theory of the modified two-stream plasma instability and the theory of anomalous collisions

A study of aspect angle effects in the E-region irregularity velocity using multi-point electric field measurements

E-region irregularity velocity measured by the STARE Norway VHF radar is considered as a function of magnetic aspect angle α and EISCAT-derived electron drift velocity at 7 locations with α between 0.38° and 2.64°. It is shown that the irregularity line-of-sight (l-o-s) velocity normalized to the electron velocity component V e0 comp exhibits a decrease with an increasing aspect angle for V e0 comp exceeding 500 m/s. The rate of velocity decrease is greater than those reported previously and is close to that predicted by the linear theory of electrojet irregularities without assuming anomalously large collision frequencies