Energetic electron precipitation during high-speed solar wind stream driven storms

Abstract

[1] Electron precipitation from the Earth's inner magnetosphere transmits solar variability to the Earth's upper atmosphere and may affect surface level climate. Here we conduct a superposed epoch analysis of energetic electrons observed by the NOAA POES spacecraft during 42 high-speed solar wind stream (HSS) driven geomagnetic storms to determine the temporal evolution and global distribution of the precipitating flux. The flux of trapped and precipitating E > 30 keV electrons increases immediately following storm onset and remains elevated during the passage of the HSS. In contrast, the trapped and precipitating relativistic electrons (E > 1 MeV) drop out following storm onset and subsequently increase during the recovery phase to levels which eventually exceed the prestorm levels. There is no evidence for enhanced precipitation of relativistic electrons during the MeV flux drop out, suggesting that flux drop outs during the main phase of HSS-driven storms are not due to precipitation to the atmosphere. On average, the flux of precipitating E > 30 keV electrons is enhanced by a factor of ∼10 during the passage of the high-speed stream at all geographic longitudes. In contrast, the precipitating relativistic electron count rate is observed to peak in the region poleward of the South Atlantic Anomaly. During the passage of the high-speed stream, the flux of precipitating E > 30 keV electrons peaks in the region from 2100 to 1200 magnetic local time at low L (4 < L < 7) and in the prenoon sector at high L (7 < L < 9), suggesting that chorus waves are responsible for the precipitation of E > 30 keV electrons in both regions.

Ionization and NO production in the polar mesosphere during high-speed solar wind streams: model validation and comparison with NO enhancements observed by Odin-SMR

“…Although they were qualitatively able to explain the daily variation by the expected daily variation in EEP fluxes (e.g. Meredith et al, 2011), they could not find any evidence of a seasonal variation in EEP and were unable to find an explanation for the seasonal variation in CNA response. They did not attempt to make a quantitative comparison between the CNA response and EEP fluxes.…”

“…Studies of the ionization of the atmosphere in response to EEP, in terms of cosmic-noise absorption (CNA), have indicated an unexplained seasonal variation in HSS-related effects and have suggested possible order-ofmagnitude underestimates of the EEP fluxes by the satellite observations in some circumstances. Here we use a model of ionization by EEP coupled with an ion chemistry model to show that published average EEP fluxes, during HSS events, from satellite measurements (Meredith et al, 2011), are fully consistent with the published average CNA response (Kavanagh et al, 2012). The seasonal variation of CNA response can be explained by ion chemistry with no need for any seasonal variation in EEP.…”

“…This would imply that EEP fluxes and NO production rates are underestimated by 2 orders of magnitude when based on the POES measurements. Since statistical average HSS-related EEP fluxes (Meredith et al, 2011) are below 10 6 cm −2 s −1 sr −1 , it is then not clear whether they represent true conditions or are underestimated by a large factor.…”

“…The availability of direct observations of the solar wind in recent decades has led to an understanding that the arrival of high-speed solar wind streams (HSS) at Earth is a major source of energization, pitch-angle scattering and precipitation of high-energy electrons into the atmosphere (see review by Baker and Li, 2003). Statistical studies of energetic electrons using instruments on the Polar Orbiting Environmental Satellites (POES) have shown that there are large increases in the fluxes of both trapped and precipitating electrons associated with HSS, affecting electron energies from 30 keV to some MeV (the limits of the observations) (Meredith et al, 2011). These can be expected to reach altitudes between 50 and 90 km in geomagnetic latitude bands between about 55-70 • N or S. Further, since the solar coronal holes which cause HSS are more prevalent around the declining phase of the solar sunspot cycle, and HSS occur much more frequently than solar proton events, it has been suggested that the result may be climate forcing which is not exactly in phase with the solar cycle.…”

Relativistic electron response to the combined magnetospheric impact of a coronal mass ejection overlapping with a high‐speed stream: Van Allen Probes observations

“…Statistical studies show that chorus waves are most strong in the premidnight to dawn sector [Li et al, 2011;Meredith et al, 2003]. Chorus waves are also implicated in pitch angle scattering of low-energy electrons [Lam et al, 2010;Meredith et al, 2011], a phenomenon which can be used to characterize these waves. Li et al [2013] have realized a technique to characterize chorus wave amplitudes, using low-energy electron measurements from the POES (Polar Operational Environmental Satellites) spacecraft.…”