Pc2 EMIC waves generated high off the equator in the dayside outer magnetosphere

Abstract

[1] It is generally accepted that electromagnetic ion cyclotron (EMIC) waves are generated around the equatorial regions and propagate toward the high latitude ionospheres in both hemispheres. Here we describe a prolonged EMIC wave event in the Pc2 (0.1-0.2 Hz) frequency band above the He + cyclotron frequency detected by the four Cluster satellites as they traversed sunward from L $ 13 in the outer magnetosphere to the magnetopause, over 13 -20 magnetic latitude north of the equator and across the high latitude cusp region near local magnetic noon. Wave packet energy propagated dominantly along the geomagnetic field direction, confirming this was a traveling EMIC wave rather than a toroidal field line resonance. The energy packets propagated in alternating directions rather than uni-directionally from the equator, implying the wave source was located in a high latitude region away from the equator, where a minimum in the B field is located. The CIS-CODIF H + ion data provided evidence that the waves were generated locally via the ion cyclotron instability. We believe the off-equatorial minimum magnetic field regions may be important source regions for these waves in the outer magnetosphere. Citation: Liu, Y. H., B. J. Fraser, and F. W. Menk (2012), Pc2 EMIC waves generated high off the equator in the dayside outer magnetosphere, Geophys. Res.

Multiple bidirectional EMIC waves observed by Cluster at middle magnetic latitudes in the dayside magnetosphere

“…The waves are observed at L = 10.7–11.5, MLT = 10.3–10.4, and MLAT = 33.2 ° –48.6 ° . This event is then compared to another event, previously published, observed on 16 February 2004 [ Liu et al ., , ]. In this comparison, we extend the published observations of the 2004 event to investigate two proxies for wave generation and calculate the Poynting vector spectrum.…”

“…Liu et al . [] suggested reflection as an explanation for the 2004 event. However, the linear theory proxy and electron plasma/gyrofrequency ratio suggest that the waves in that event are locally generated, but the possibility that the waves might be reflected at higher latitudes remains possible.…”

“…Plotting the Poynting vector as a spectrum reveals the slight frequency dependence of the propagation direction, which is not seen in Liu et al . [].…”

“…[]. Furthermore, this study provides a comparison between this event and the 16 February 2004 midlatitude EMIC event that was recently published [ Liu et al ., , ].…”

Energetic ions scattered into the loss cone with observations of the Cluster satellite

“…EMIC waves, identified on the ground as Pc1-2 waves, are often excited in the magnetospheric equatorial plane (Anderson et al, 1992;Fraser et al, 2005;Engebretson et al, 2007;Yuan et al, 2012a;Sakaguchi et al, 2008). In the dayside outer magnetosphere, EMIC waves in Pc2 band can also be generated high off the equator and in the regions of the minimum of magnetic field within Shabansky orbits (Liu et al, 2012). Through the wave-particle interactions, EMIC waves can scatter ring current (RC) ions and radiation belt relativistic electrons into the loss cone, leading to loss into the atmosphere (Yahnin et al, 2006;Jordanova, et al, 2007;Sakaguchi et al, 2008;Morley et al, 2009;Yuan et al, 2010Yuan et al, , 2012aYuan et al, , b, 2013Carson et al, 2013;Li et al, 2014;Usanova et al, 2010Usanova et al, , 2014.…”