Plasmaspheric Plumes and EMIC Rising Tone Emissions

Abstract

Due to its polar orbit Cluster spacecraft crossed plasmaspheric plumes out of the magnetic equatorial plane. We study the occurrence of broadband, narrowband, and rising tone emissions in the plume vicinity, below the local proton gyrofrequency. Based on a database of 935 Cluster plumes crossings, reduced to 189 unique plumes, we find that broadband activity is the most common case. We confirm result from a previous study showing that plume vicinity is not a preferred place for observing narrowband emissions. Rising tones are the less frequently observed of these three kinds of emissions. Nevertheless, ElectroMagnetic Ion Cyclotron (EMIC) rising tone occurrence rate is high compared to the narrowband one: Tones are seen in six of 30 plume events (20%) when narrowband emissions are observed. Rising tones are observed at absolute magnetic latitudes larger than 17 ∘ and up to 35 ∘ . We detail the 16 August 2005 plume crossing when a rising tone is observed. Results of a ray tracing analysis agree with a tone triggering process taking place above 15 ∘ of magnetic latitude.

Statistical study and corresponding evolution of plasmaspheric plumes under different levels of geomagnetic storms

“…The structureless hiss waves often arise in high-density plasmaspheric plumes (Meredith et al, 2004;Yuan et al, 2012;Zhang et al, 2018Zhang et al, , 2019. Furthermore, although electromagnetic ion cyclotron (EMIC) waves are not preferentially observed in the highdensity plumes (Usanova et al, 2013;Grison et al, 2018), the plume maybe related to the excitation of EMIC waves (Grison et al, 2018;Yu et al, 2016;Yuan et al, 2010). The electron scattering induced by hiss waves is thought to be a key contributor to the formation of the radiation belt slot region (Su et al, 2015;Shi et al, 2019;Zhang et al, 2019).…”

Periodic Rising and Falling Tone ECH Waves From Van Allen Probes Observations

“…Quasiperiodic rising and falling tone features are commonly observed for chorus (Li et al., 2011) and magnetosonic (MS) waves (Boardsen et al., 2014; N. Liu et al., 2019), and sometimes observed for electromagnetic ion cyclotron (EMIC) waves (Grison et al., 2018) and plume hiss (Shi et al., 2019; Su et al., 2018). However, the typical features of rising and falling tone ECH waves are still not well explored yet.…”

Instantaneous Frequency Analysis on Nonlinear EMIC Emissions: Arase Observation

“…The linear growth theory of the ion cyclotron instability from the temperature anisotropy has been studied (e.g., Gary et al, ). Nonlinear wave growth of the EMIC emissions has been investigated by observations (Grison et al, , ; Nakamura et al, ; Pickett et al, ), theory (Omura et al, ), and simulations (Shoji & Omura, , , ). Both the rising and falling tone emissions are observed (Nakamura et al, ) and reproduced by hybrid code simulations (Shoji & Omura, , ).…”