Equatorial noise emissions observed by the DEMETER spacecraft during geomagnetic storms. Issue 10 (19th October 2016)

• Record Type: Journal Article
• Authors: Němec, F.; Parrot, M.; Santolík, O.
• Is Part Of: Journal of geophysical research. Volume 121:Issue 10(2016:Oct.)
• Page Start: 9744
• Page End: 9757
• Publication Date: 2016-10-19
• Subjects: equatorial noise -- DEMETER; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1002/2016JA023145
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: Equatorial noise emissions are electromagnetic waves routinely observed in the equatorial region of the inner magnetosphere at frequencies between the proton cyclotron frequency and the lower hybrid frequency. Their observations are, however, typically limited to radial distances larger than about 2 R E . We use the data measured by the low‐altitude DEMETER spacecraft (altitude of about 700 km) to confirm that during periods of enhanced geomagnetic activity, these emissions penetrate down to low radial distances and eventually become a dominant wave emission close to the proton cyclotron frequency in the equatorial region. Wave data obtained during six intense geomagnetic storms ( Dst <− 100 nT) are analyzed. It is shown that during the analyzed time intervals, the daytime wave activity within about 20° from the geomagnetic equator is significantly enhanced, while the nightside wave activity shows a weaker increase at lower frequencies. Multicomponent wave data allow us to determine dayside wave propagation parameters. It is shown that the waves are nearly linearly polarized and their wave vector directions are almost perpendicular to the ambient Earth's magnetic field, as it has been previously observed for equatorial noise emissions. Finally, we analyze the dependence of the equatorial wave intensity at the proton cyclotron frequency on Dst and A E geomagnetic indices, and we demonstrate that the dayside wave intensity increases by as much as 3 orders of magnitude during severely disturbed periods. Key Points: During periods of enhanced geomagnetic activity equatorial noise emissions penetrate down to DEMETER altitudes (700 km) Daytime wave activity within 20 degrees from the equator is significantly enhanced; the nighttime wave activity increase is weaker Wave intensity increases by as much as 3 orders of magnitude during severely disturbed periods