Cosmic radio noise absorption events associated with equatorward drifting arcs during a substorm growth phase

• Published in: Annales Geophysicae
• Main Authors: J. R. T. Jussila, A. T. Aikio, S. Shalimov, S. R. Marple
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2004
• Subjects: Science; Q; Physics; QC1-999; Geophysics. Cosmic physics; QC801-809; EISCAT
• Online Access: https://doi.org/10.5194/angeo-22-1675-2004; https://doaj.org/article/a15260aeb5b54cb5990cf57122d454ba

Cosmic radio noise absorption (CNA) events associated with equatorward drifting arcs during a substorm growth phase are studied by using simultaneous optical auroral, IRIS imaging riometer and EISCAT incoherent scatter radar measurements. The CNA is generally attributed to energetic particle precipitation in the D-region. However, it has been argued that plasma irregularities or enhanced electron temperature ( T e ) in the E-region could also produce CNA. Both of the latter mechanisms are related to intense electric fields in the ionosphere. We present two events which occur during a substorm growth phase in the evening MLT sector. In both of the events, an auroral arc is drifting equatorward, together with a region of CNA (auroral absorption bay) located on the equatorward side and outside of the arc. Both of the events are associated with enhanced D-region electron density on the equatorward side of the auroral arc, but in the second event, a region of intense electric field and enhanced electron temperature in the E-region is also located on the equatorward side of the arc. We show that in the studied events neither plasma instabilities nor enhanced T e play a significant role in producing the measured CNA, but the CNA in the vicinity of the equatorward drifting arcs is produced by D-region energetic electron precipitation. Key words. Ionosphere (auroral ionosphere; particle precipitation; electric fields and currents)