Statistical analysis of EMIC waves in plasmaspheric plumes from Cluster observations

Abstract

[1] Recently, electromagnetic ion cyclotron (EMIC) wave generation in plasmaspheric plumes has been the subject of extensive discussion. Theory predicts that regions of detached cold, dense plasma immersed in relatively low background magnetic field should aid EMIC wave growth and may provide conditions for interaction between the EMIC waves and relativistic (MeV) electrons, leading to energetic particle loss into the atmosphere. Since plasmaspheric plumes are specific to disturbed geomagnetic conditions, the link between EMIC waves and plumes may be especially important for radiation belt dynamics during magnetic storms. In this work, we present an in situ survey of EMIC waves in plasmaspheric plumes using data from the Cluster satellites and will address the question of whether plumes are important for EMIC wave generation from a statistical perspective. We used a survey of plasmaspheric plumes between 2001 and 2006 identified from the Waves of High frequency and Sounder for Probing of Electron density by Relaxation (WHISPER) sounder measurements. We further identified EMIC waves from simultaneous (with WHISPER) magnetic field measurements by the fluxgate magnetometer instruments and investigated the relationship between these two data sets. Only 10% of the time when Cluster-observed plumes along its orbit did we also observe EMIC waves. The wave occurrence outside plumes is further significantly reduced and is~20 times lower in immediately adjacent regions than inside plumes. We found that cold plasma density was not a good predictor of EMIC occurrence inside the plumes and that the absolute density does not affect the EMIC probability. On the other hand, enhanced solar wind dynamic pressure significantly increases EMIC wave occurrence rate inside the plumes.

Quantification of Energetic Electron Precipitation Driven by Plume Whistler Mode Waves, Plasmaspheric Hiss, and Exohiss

“…Quantification of energetic Electron precipitation driven by plume whistler mode waves, Plasmaspheric hiss, and exohiss. Plasma waves in plumes are particularly interesting, because a plume is a unique region where total plasma density is typically high, but energetic particles (>tens keV) are accessible, thus providing favorable conditions for various types of wave generation (Chan & Holzer, 1976;Hayakawa et al, 1986;Ma et al, 2014;Tsurutani et al, 2015;Usanova et al, 2013;Woodroffe et al, 2017). 1029/ 2019GL082095 et al, 1996Goldstein et al, 2004;Grebowsky, 1970;Weiss et al, 1997) and are often associated with large density fluctuations (Borovsky & Denton, 2008;Goldstein et al, 2004;Moldwin et al, 2004;Spasojević et al, 2003).…”

EMIC waves and plasmaspheric and plume density: CRRES results

“…A plasma plume should provide the necessary background magnetic field and cold plasma density to grow EMIC waves in the region of the outer radiation belts, L ≥4. This region in the dusk sector is where the highest occurrence rates of EMIC waves are observed to overlap with the radiation belts [ Anderson et al , ; Fraser and Nguyen , ; Halford et al , ; Yuan et al , ; Usanova et al , ]. These waves are also potentially able to resonate with the lower energy, ≤1.5 MeV, radiation belt electrons [e.g., Meredith et al , ; Ukhorskiy et al , ; Silin et al , ; Li et al , , and A. Hendry et al, “Lower Energy cut‐off limits of EMIC‐driven energetic electron precipitation” submitted to Journal of Geophysical Research , 2015].…”

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

“…With density enhancements of cold ions, the anisotropic RC proton distributions can become unstable so as to easily excite EMIC waves (Gary et al, 1995). Therefore, EMIC waves in the inner magnetosphere may occur in the region of overlap between the plasmasphere and ring currents (Fraser and Nguyen, 2001;Yuan et al, 2010Yuan et al, , 2012aUsanova et al, 2013), and in regions of high cold plasma density (Yahnin et al, 2002;Halford et al, 2015). In addition, the density structure with the negative gradient of radial electron densities at the plasmapause or plasmaspheric plumes can guide EMIC waves, leading to a small wave normal angle and an order of enhancement of the wave strength (Chen et al, 2009).…”

“…EMIC waves are usually observed in regions of higher cold plasma density such as, but necessarily in the plasmapause or plasmaspheric plumes (Anderson et al, 1992;Fraser and Nguyen, 2001;Chen et al, 2010;Yuan et al, 2012a;Usanova et al, 2013;Halford et al, 2015), because cold dense ions can lead to lower instability threshold for the EMIC wave excitation (Gary et al, 1995). 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).…”