Confirmation of EMIC wave‐driven relativistic electron precipitation

Abstract

Electromagnetic ion cyclotron (EMIC) waves are believed to be an important source of pitch angle scattering driven relativistic electron loss from the radiation belts. To date, investigations of this precipitation have been largely theoretical in nature, limited to calculations of precipitation characteristics based on wave observations and small‐scale studies. Large‐scale investigation of EMIC wave‐driven electron precipitation has been hindered by a lack of combined wave and precipitation measurements. Analysis of electron flux data from the POES (Polar Orbiting Environmental Satellites) spacecraft has been suggested as a means of investigating EMIC wave‐driven electron precipitation characteristics, using a precipitation signature particular to EMIC waves. Until now the lack of supporting wave measurements for these POES‐detected precipitation events has resulted in uncertainty regarding the driver of the precipitation. In this paper we complete a statistical study comparing POES precipitation measurements with wave data from several ground‐based search coil magnetometers; we further present a case study examining the global nature of this precipitation. We show that a significant proportion of the precipitation events correspond with EMIC wave detections on the ground; for precipitation events that occur directly over the magnetometers, this detection rate can be as high as 90%. Our results demonstrate that the precipitation region is often stationary in magnetic local time, narrow in L, and close to the expected plasmapause position. Predominantly, the precipitation is associated with helium band rising tone Pc1 waves on the ground. The success of this study proves the viability of POES precipitation data for investigating EMIC wave‐driven electron precipitation.

Pitch Angle Scattering of Sub‐MeV Relativistic Electrons by Electromagnetic Ion Cyclotron Waves

“…Only events were included for which there was simultaneous proton precipitation, suggesting EMIC waves as a likely cause because EMIC waves also scatter ring current protons. Hendry et al () showed that the probability was very high, as high as 90%, for EMIC waves to be observed by ground magnetometers at locations mapped to that of the POES. Other case studies have also demonstrated a connection between precipitation events and EMIC waves (Blum et al, ; Clilverd et al, ; Clilverd et al, ; Hendry et al, ; Hendry et al, ; Rodger et al, ).…”

“…Hendry et al () showed that the probability was very high, as high as 90%, for EMIC waves to be observed by ground magnetometers at locations mapped to that of the POES. Other case studies have also demonstrated a connection between precipitation events and EMIC waves (Blum et al, ; Clilverd et al, ; Clilverd et al, ; Hendry et al, ; Hendry et al, ; Rodger et al, ). It is possible that other mechanisms might be responsible for some of the Hendry et al () events (see, e.g., Shekhar et al, ; Smith et al, ; Yahnin et al, ).…”

Magnetic Local Time‐Resolved Examination of Radiation Belt Dynamics during High‐Speed Solar Wind Speed‐Triggered Substorm Clusters

“…Due to the large number of POES spacecraft, and their LEO orbits, there is very good coverage across L and MLT (e.g., Hendry et al, Fig. , . We have combined the observations from multiple satellites into an L and time grid of median flux values with a 0.25 L ‐resolution and a 15‐min time resolution.…”

Signatures of Ultrarelativistic Electron Loss in the Heart of the Outer Radiation Belt Measured by Van Allen Probes

“…Supporting the theoretical findings, a number of observational case studies used VLF transmitter and receiver systems, riometers, balloons, and polar satellites to measure ultrarelativistic electron precipitation associated with simultaneous EMIC wave detection by ground‐based or satellite magnetometers (Blum et al, ; Clilverd et al, , , Miyoshi et al, ; Rodger et al, , ). Using a recently developed algorithm for determination of precipitation events of sub‐MeV and MeV electrons from Polar Orbiting Environmental Satellites (POES) and Meteorological Operational (METOP‐2) satellite (Carson et al, ), Hendry et al () showed that 60% to 90% of precipitation events coincide with the waves detected on the ground. Yet the observational studies of electron precipitation into the atmosphere suggested that sub‐MeV and MeV electrons can be scattered by EMIC waves, such studies consider only the electron population inside the loss cone, leaving aside the effects of the waves on the pitch angle distribution of particles in the heart of the belt.…”