Non-magnetic aspect sensitive auroral echoes from the lower E region observed at 50 MHz

• Main Authors: R. Ruè Ster, K. Schlegel
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 1999
• Subjects: Alomar; Farley; Norway; EISCAT
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.371.8159; http://hal.archives-ouvertes.fr/docs/00/31/66/82/PDF/angeo-17-1284-1999.pdf

Abstract. Backscatter from E-region irregularities was observed at aspect angles close to 90 ° (almost parallel to the direction of the magnetic ®eld) using the ALOMAR SOUSY radar at Andoya/Norway. Strong electric ®elds and increased E-region electron temperatures simultaneously measured with the incoherent scatter facility EISCAT proved that the Farley-Buneman plasma instability was excited. In addition, strong particle precipitation was present as inferred from EISCAT electron densities indicating that the gradient drift instability may have been active, too. Backscatter at such large aspect angles was not expected and has not been observed before. The characteristics of the observed echoes, however, are in many aspects completely di€erent from usual auroral radar results: the Doppler velocities are only of the order of 10 m/s, the half-width of the spectra is around 5 m/s, the echoes originate at altitudes well below 100 km, and they seem to be not aspect-sensitive with respect to the magnetic ®eld direction. We, therefore, conclude that the corresponding irregularities are not caused by the mentioned instabilities and that other mechanism have to be invoked. Key words. Ionosphere (plasma waves and instabilities; ionosphere irregularities; particle precipitaion) á Meteorology and atmospheric dynamics (middle atmosphere dynamics) 1