Search

An interval of exceptional solar activity was registered in early September 2017, late in the decay phase of solar cycle 24, involving the complex Active Region 12673 as it rotated across the western hemisphere with respect to Earth. A large number of eruptions occurred between 4-10 September, including four associated with X-class flares. The X9.3 flare on 6 September and the X8.2 flare on 10 September are currently the two largest during cycle 24. Both were accompanied by fast coronal mass ejections and gave rise to solar energetic particle (SEP) events measured by near-Earth spacecraft. In particular, the partially-occulted solar event on 10 September triggered a ground level enhancement (GLE), the second GLE of cycle 24. A further, much less energetic SEP event was recorded on 4 September. In this work we analyze observations by the Advanced Composition Explorer (ACE) and the Geostationary Operational Environmental Satellites (GOES), estimating the SEP event-integrated spectra above 300 keV and carrying out a detailed study of the spectral shape temporal evolution. Derived spectra are characterized by a low-energy break at few/tens of MeV; the 10 September event spectrum, extending up to ~1 GeV, exhibits an additional rollover at several hundred MeV. We discuss the spectral interpretation in the scenario of shock acceleration and in terms of other important external influences related to interplanetary transport and magnetic connectivity, taking advantage of multi-point observations from the Solar Terrestrial Relations Observatory (STEREO). Spectral results are also compared with those obtained for the 17 May 2012 GLE event., Comment: Accepted for publication in Space Weather; 24 pages, 10 figures, 1 table

The Wind spacecraft, launched on November 1, 1994, is a critical element in NASA’s Heliophysics System Observatory (HSO) – a fleet of spacecraft created to understand the dynamics of the sun‐Earth system. The combination of its longevity ( > 25 years in service), its diverse complement of instrumentation, and high resolution and accurate measurements has led to it becoming the “standard candle” of solar wind measurements. Wind has over 55 selectable public data products with over ∼1100 total data variables (including OMNI data products) on SPDF/CDAWeb alone. These data have led to paradigm shifting results in studies of statistical solar wind trends, magnetic reconnection, large‐scale solar wind structures, kinetic physics, electromagnetic turbulence, the Van Allen radiation belts, coronal mass ejection topology, interplanetary and interstellar dust, the lunar wake, solar radio bursts, solar energetic particles, and extreme astrophysical phenomena such as gamma‐ray bursts. This review introduces the mission and instrument suites then discusses examples of the contributions by Wind to these scientific topics that emphasize its importance to both the fields of heliophysics and astrophysics.

A sequence of discrete solar wind structures within the sheath region of an interplanetary coronal mass ejection on November 6, 2015, caused a series of compressions and releases of the dayside magnetosphere. Each compression resulted in a brief adiabatic enhancement of ions (electrons) driving bursts of electromagnetic ion cyclotron (EMIC; whistler mode chorus) wave growth across the dayside magnetosphere. Fine‐structured rising tones were observed in the EMIC wave bursts, resulting in nonlinear scattering of relativistic electrons in the outer radiation belt. Multipoint observations allow us to study the spatial structure and evolution of these sheath structures as they propagate Earthward from L1 as well as the spatio‐temporal characteristics of the magnetospheric response. This event highlights the importance of fine‐scale solar wind structure, in particular within complex sheath regions, in driving dayside phenomena within the inner magnetosphere., Key Points A sequence of discrete structures within an interplanetary coronal mass ejection sheath are tracked via multipoint measurementsEach structure results in magnetospheric compression, adiabatic enhancement of ions and electrons, and cyclotron wave growthThis event highlights the importance of fine‐scale solar wind structure and sheath regions for driving dayside magnetospheric phenomena

We present a new empirical model to predict solar energetic particle (SEP) event-integrated and peak intensity spectra between 10 and 130 MeV at 1 AU, based on multi-point spacecraft measurements from the Solar TErrestrial RElations Observatory (STEREO), the Geostationary Operational Environmental Satellites (GOES), and the Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA) satellite experiment. The analyzed data sample includes 32 SEP events occurring between 2010 and 2014, with a statistically significant proton signal at energies in excess of a few tens of MeV, unambiguously recorded at three spacecraft locations. The spatial distributions of SEP intensities are reconstructed by assuming an energy-dependent 2D Gaussian functional form, and accounting for the correlation between the intensity and the speed of the parent coronal mass ejection (CME), and the magnetic-field-line connection angle. The CME measurements used are from the Space Weather Database Of Notifications, Knowledge, Information (DONKI). The model performance, including its extrapolations to lower/higher energies, is tested by comparing with the spectra of 20 SEP events not used to derive the model parameters. Despite the simplicity of the model, the observed and predicted event-integrated and peak intensities at Earth and at the STEREO spacecraft for these events show remarkable agreement, both in the spectral shapes and their absolute values.

We suggest an analogy between energetic particle and magnetic field observations made by the Voyager 1 spacecraft in the distant heliosheath at 122 AU in August 2012, and those made in the distant geomagnetic tail by the ISEE 3 spacecraft in 1982–1983, despite large differences in the time and distance scales. The analogy suggests that in August, 2012, Voyager 1 may not have moved from the anomalous cosmic ray (ACR)-dominated heliosheath into the interstellar medium but into a region equivalent to the “lobes” of the geomagnetic tail, composed of heliospheric field lines which have reconnected with the interstellar medium beyond the spacecraft and so are open to the entry of cosmic rays, while heliospheric particles (e.g., ACRs) are free to escape, and which maintain a ∼Parker spiral configuration. The heliopause, analogous to the magnetopause forming the outer boundary of the lobes, may then lie beyond this so-called “heliocliff”. Even if this analogy is incorrect, the remarkable similarities between the energetic particle and magnetic field observations in these very different regions are worth noting.

This is a companion to Savani et al. (2015) that discussed how a first-order prediction of the internal magnetic field of a coronal mass ejection (CME) may be made from observations of its initial state at the Sun for space weather forecasting purposes (Bothmer-Schwenn scheme (BSS) model). For eight CME events, we investigate how uncertainties in their predicted magnetic structure influence predictions of the geomagnetic activity. We use an empirical relationship between the solar wind plasma drivers and Kp index together with the inferred magnetic vectors, to make a prediction of the time variation of Kp (Kp(BSS)). We find a 2σ uncertainty range on the magnetic field magnitude (|B|) provides a practical and convenient solution for predicting the uncertainty in geomagnetic storm strength. We also find the estimated CME velocity is a major source of error in the predicted maximum Kp. The time variation of Kp(BSS) is important for predicting periods of enhanced and maximum geomagnetic activity, driven by southerly directed magnetic fields, and periods of lower activity driven by northerly directed magnetic field. We compare the skill score of our model to a number of other forecasting models, including the NOAA/Space Weather Prediction Center (SWPC) and Community Coordinated Modeling Center (CCMC)/SWRC estimates. The BSS model was the most unbiased prediction model, while the other models predominately tended to significantly overforecast. The True skill score of the BSS prediction model (TSS = 0.43 ± 0.06) exceeds the results of two baseline models and the NOAA/SWPC forecast. The BSS model prediction performed equally with CCMC/SWRC predictions while demonstrating a lower uncertainty.

Despite the progress made over the past decades, the physical mechanisms underlying the origin of solar energetic particles (SEPs) are still debated. The largest uncertainties concern the most energetic ($\gtrsim$500 MeV) SEP events, which are difficult to characterize due to the relatively few and indirect observations such as those made by neutron monitors. The Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA) satellite experiment has recently offered a unique opportunity to study SEPs with energies between 80 MeV and few GeV, including their energy spectra, composition and pitch angle distributions. In particular, PAMELA has measured for the first time with good accuracy the spectral features at moderate and high energies for 26 SEP events occurring between 2006 December and 2014 September, providing important constraints for current SEP models. Reported spectral shapes exhibit a high-energy rollover that can be attributed to particles escaping the shock region during acceleration, as a consequence of its limited extension and lifetime. PAMELA observations also allow the relationship between low-energy SEPs detected by in-situ spacecraft and the high-energy SEPs registered by the worldwide network of neutron monitors during the rare ground-level enhancements (GLEs) to be investigated. No qualitative distinction between the spectra of GLE and non-GLE events was observed, suggesting that GLEs are not a separate class, but rather are a subset of a continuous distribution of SEP events that are more intense at high energies. In this work we combine data from PAMELA and other near-Earth spacecraft in order to determine the SEP spectral shapes at 1 AU from tens of keV to a few GeV.

Long Duration Gamma-Ray Flares (LDGRFs) are characterized by delayed and long-duration gamma-ray emission above $\sim$50 MeV. Despite dozens of observations in the last decade with $\it{Fermi}$/LAT, the nature of this emission has been a challenge to explain. The highest energy emission has generally been attributed to the decay of pions produced by the interaction of high-energy protons with ambient solar material. The fact that the $\gamma$-ray emission is delayed from the onset of the initial eruption and that the emission is, in some cases, unusually long in duration suggests that particle acceleration occurs within large volumes extending to high altitudes, either by stochastic acceleration within large coronal loops or by back-precipitation from CME-driven shocks. We have tested these models by a making direct comparisons between the properties of the accelerated ion population at the flare derived from the observations of $\it{Fermi}$/LAT and those of solar energetic particles detected at Earth by PAMELA at comparable high energies. We investigated 27 high-energy gamma ray events (from \cite{ref:SHARE2018}), and for 14 events we compare the two populations (SEPs in space and the interacting population at the Sun) and discuss the implications in terms of potential sources of the LDGRFs.

Little is known about the origin of the high-energy and sustained emission from solar Long-Duration Gamma-Ray Flares (LDGRFs), identified with the Compton Gamma Ray Observatory (CGRO), the Solar Maximum Mission (SMM), and now Fermi. Though Fermi/Large Area Space Telescope (LAT) has identified dozens of flares with LDGRF signature, the nature of this phenomenon has been a challenge to explain both due to the extreme energies and long durations. The highest-energy emission has generally been attributed to pion production from the interaction of >300 MeV protons with the ambient matter. The extended duration suggests that particle acceleration occurs over large volumes extending high in the corona, either from stochastic acceleration within large coronal loops or from back precipitation from coronal mass ejection driven shocks. It is possible to test these models by making direct comparison between the properties of the accelerated ion population producing the gamma-ray emission derived from the Fermi/LAT observations, and the characteristics of solar energetic particles (SEPs) measured by the Payload for Matter-Antimatter Exploration and Light Nuclei Astrophysics (PAMELA) spacecraft in the energy range corresponding to the pion-related emission detected with Fermi. For fourteen of these events we compare the two populations -- SEPs in space and the interacting particles at the Sun -- and discuss the implications in terms of potential sources. Our analysis shows that the two proton numbers are poorly correlated, with their ratio spanning more than five orders of magnitude, suggesting that the back precipitation of shock-acceleration particles is unlikely the source of the LDGRF emission., Accepted for publication in ApJ

This study compares the designation of different solar wind flow regimes (transient, coronal hole, and streamer belt) according to two algorithms derived from observations by the Solar Wind Ion Composition Spectrometer, the Solar Wind Electron Proton Alpha Monitor, and the Magnetometer on the ACE spacecraft, with a similar regime determination performed on board the Genesis spacecraft. The comparison is made for the interval from late 2001 to early 2004 when Genesis was collecting solar wind ions for return to Earth. The agreement between hourly regime assignments from any pair of algorithms was less than two thirds, while the simultaneous agreement between all three algorithms was only 49%. When the results of the algorithms were compared to a catalog of interplanetary coronal mass ejection events, it was found that almost all the events in the catalog were confirmed by the spacecraft algorithms. On the other hand, many short transient events, lasting 1 to 13 h, that were unanimously selected as transient like by the algorithms, were not included in the catalog.

Trapped electrons in Earth's outer Van Allen radiation belt are influenced profoundly by solar phenomena such as high-speed solar wind streams, coronal mass ejections (CME), and interplanetary (IP) shocks. In particular, strong IP shocks compress the magnetosphere suddenly and result in rapid energization of electrons within minutes. It is believed that the electric fields induced by the rapid change in the geomagnetic field are responsible for the energization. During the latter part of March 2015, a CME impact led to the most powerful geomagnetic storm (minimum Dst = −223 nT at 17 March, 23 UT) observed not only during the Van Allen Probe era but also the entire preceding decade. Magnetospheric response in the outer radiation belt eventually resulted in elevated levels of energized electrons. The CME itself was preceded by a strong IP shock whose immediate effects vis-a-vis electron energization were observed by sensors on board the Van Allen Probes. The comprehensive and high-quality data from the Van Allen Probes enable the determination of the location of the electron injection, timescales, and spectral aspects of the energized electrons. The observations clearly show that ultrarelativistic electrons with energies E > 6 MeV were injected deep into the magnetosphere at L ≈ 3 within about 2 min of the shock impact. However, electrons in the energy range of ≈250 keV to ≈900 keV showed no immediate response to the IP shock. Electric and magnetic fields resulting from the shock-driven compression complete the comprehensive set of observations that provide a full description of the near-instantaneous electron energization.

The current understanding of the characteristics of solar and inner heliospheric electron events is inferred almost entirely from observations made by spacecraft located at 1 astronomical unit (au). Previous observations within 1 au of the Sun, by the Helios spacecraft at ∼0.3–1 au, indicate the presence of electron events that are not detected at 1 au or may have merged during transport from the Sun. Parker Solar Probe’s close proximity to the Sun at perihelion provides an opportunity to make the closest measurements yet of energetic electron events. We present an overview of measurements of electrons with energies between ∼17 keV and ∼1 MeV made by the Parker Solar Probe Integrated Science Investigation of the Sun (IS⊙IS) instrument suite during Encounter 2 (2019 March 31–April 10 with perihelion of ∼0.17 au), including several small electron events. We examine these events in the context of the electromagnetic and solar wind environment measured by the FIELDS and SWEAP instruments on Parker Solar Probe. We find most of these electron enhancements to be associated with type III radio emissions that reach the local plasma frequency and one enhancement that appears to be primarily associated with abrupt changes in the local magnetic field. Together, these associations suggest that these are indeed the first measurements of energetic electron events within 0.2 au.

During early November 2013, the magnetosphere experienced concurrent driving by a coronal mass ejection (CME) during an ongoing high-speed stream (HSS) event. The relativistic electron response to these two kinds of drivers, i.e., HSS and CME, is typically different, with the former often leading to a slower buildup of electrons at larger radial distances, while the latter energizing electrons rapidly with flux enhancements occurring closer to the Earth. We present a detailed analysis of the relativistic electron response including radial profiles of phase space density as observed by both Magnetic Electron and Ion Sensor (MagEIS) and Relativistic Electron Proton Telescope instruments on the Van Allen Probes mission. Data from the MagEIS instrument establish the behavior of lower energy (

The process by which the Sun affects the terrestrial environment on short timescales is predominately driven by the amount of magnetic reconnection between the solar wind and Earth's magnetosphere. Reconnection occurs most efficiently when the solar wind magnetic field has a southward component. The most severe impacts are during the arrival of a coronal mass ejection (CME) when the magnetosphere is both compressed and magnetically connected to the heliospheric environment. Unfortunately, forecasting magnetic vectors within coronal mass ejections remain elusive. Here we report how, by combining a statistically robust helicity rule for a CME's solar origin with a simplified flux rope topology, the magnetic vectors within the Earth-directed segment of a CME can be predicted. In order to test the validity of this proof-of-concept architecture for estimating the magnetic vectors within CMEs, a total of eight CME events (between 2010 and 2014) have been investigated. With a focus on the large false alarm of January 2014, this work highlights the importance of including the early evolutionary effects of a CME for forecasting purposes. The angular rotation in the predicted magnetic field closely follows the broad rotational structure seen within the in situ data. This time-varying field estimate is implemented into a process to quantitatively predict a time-varying Kp index that is described in detail in paper II. Future statistical work, quantifying the uncertainties in this process, may improve the more heuristic approach used by early forecasting systems.

This paper focuses on the interactions between the fast solar wind from coronal holes and the intervening slower solar wind, leading to the creation of stream interaction regions that corotate with the Sun and may persist for many solar rotations. Stream interaction regions have been observed near 1 AU, in the inner heliosphere (at \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\sim 0.3$$\end{document}∼0.3–1 AU) by the Helios spacecraft, in the outer and distant heliosphere by the Pioneer 10 and 11 and Voyager 1 and 2 spacecraft, and out of the ecliptic by Ulysses, and these observations are reviewed. Stream interaction regions accelerate energetic particles, modulate the intensity of Galactic cosmic rays and generate enhanced geomagnetic activity. The remote detection of interaction regions using interplanetary scintillation and white-light imaging, and MHD modeling of interaction regions will also be discussed.

The physical parameters of the solar wind observed in-situ near 1 AU have been studied for several decades, and relationships between them, such as the positive correlation between the solar wind plasma temperature, $T$ , and velocity, $V$ , and the negative correlation between density, $N$ , and velocity, $V$ , are well known. However, the magnetic field intensity, $B$ , does not appear to be well correlated with any individual plasma parameter. In this article, we discuss previously under-reported correlations between $B$ and the combined plasma parameters $\sqrt{N V^{2}} $ as well as between $B$ and $\sqrt{NT}$ . These two correlations are strong during periods of corotating interaction regions and high-speed streams, and moderate during intervals of slow solar wind. The results indicate that the magnetic pressure in the solar wind is well correlated both with the plasma dynamic pressure and the thermal pressure.

New results on the short-term galactic cosmic-ray (GCR) intensity variation (Forbish decrease) in 2006 December measured by the PAMELA instrument are presented. Forbush decreases are sudden suppressions of the GCR intensities, which are associated with the passage of interplanetary transients such as shocks and interplanetary coronal mass ejections (ICMEs). Most of the past measurements of this phenomenon were carried out with groundbased detectors such as neutron monitors or muon telescopes. These techniques allow only the indirect detection of the overall GCR intensity over an integrated energy range. For the first time, thanks to the unique features of the PAMELA magnetic spectrometer, the Forbush decrease, commencing on 2006 December 14 and following a CME at the Sun on 2006 December 13, was studied in a wide rigidity range (0.4-20 GV) and for different species of GCRs detected directly in space. The daily averaged GCR proton intensity was used to investigate the rigidity dependence of the amplitude and the recovery time of the Forbush decrease. Additionally, for the first time, the temporal variations in the helium and electron intensities during a Forbush decrease were studied. Interestingly, the temporal evolutions of the helium and proton intensities during the Forbush decrease were found to be in good agreement, while the low rigidity electrons (

Despite the significant progress achieved in recent years, the physical mechanisms underlying the origin of solar energetic particles (SEPs) are still a matter of debate. The complex nature of both particle acceleration and transport poses challenges to developing a universal picture of SEP events that encompasses both the low-energy (from tens of keV to a few hundreds of MeV) observations made by space-based instruments and the GeV particles detected by the worldwide network of neutron monitors in ground-level enhancements (GLEs). The high-precision data collected by the Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA) satellite experiment offer a unique opportunity to study the SEP fluxes between $\sim$80 MeV and a few GeV, significantly improving the characterization of the most energetic events. In particular, PAMELA can measure for the first time with good accuracy the spectral features at moderate and high energies, providing important constraints for current SEP models. In addition, the PAMELA observations allow the relationship between low and high-energy particles to be investigated, enabling a clearer view of the SEP origin. No qualitative distinction between the spectral shapes of GLE, sub-GLE and non-GLE events is observed, suggesting that GLEs are not a separate class, but are the subset of a continuous distribution of SEP events that are more intense at high energies. While the spectral forms found are to be consistent with diffusive shock acceleration theory, which predicts spectral rollovers at high energies that are attributed to particles escaping the shock region during acceleration, further work is required to explore the relative influences of acceleration and transport processes on SEP spectra., Comment: 26 pages, 13 figures, 2 tables

We study the latitudinal distribution of geomagnetic activity in 1966–2009 with local geomagnetic activity indices at 26 magnetic observatories. Using the principal component analysis method we find that more than 97% of the variance in annually averaged geomagnetic activity can be described by the two first principal components. The first component describes the evolution of the global geomagnetic activity, and has excellent correlation with, e.g., the Kp/Ap index. The second component describes the leading pattern by which the latitudinal distribution of geomagnetic activity deviates from the global average. We show that the second component is highly correlated with the relative (annual) fraction of high-speed streams (HSS) in solar wind. The latitudinal distribution of the second mode has a high maximum at auroral latitudes, a local minimum at subauroral latitudes and a low maximum at midlatitudes. We show that this distribution is related to the difference in the average location and intensity between substorms related to coronal mass ejections (CMEs) and HSSs. This paper demonstrates a new way to extract useful, quantitative information about the solar wind from local indices of geomagnetic activity over a latitudinally extensive network.

Previous studies have discussed the identification of interplanetary coronal mass ejections (ICMEs) near the Earth based on various solar wind signatures. In particular, methods have been developed of identifying regions of anomalously low solar wind proton temperatures (T p) and plasma compositional anomalies relative to the composition of the ambient solar wind that are frequently indicative of ICMEs. In this study, similar methods are applied to observations from the Ulysses spacecraft that was launched in 1990 and placed in a heliocentric orbit over the poles of the Sun. Some 279 probable ICMEs are identified during the spacecraft mission, which ended in 2009. The identifications complement those found independently in other studies of the Ulysses data, but a number of additional events are identified. The properties of the ICMEs detected at Ulysses and those observed near the Earth and in the inner heliosphere are compared.

In this study we synthesize the results of four previous studies on the global energetics of solar flares and associated coronal mass ejections (CMEs), which include magnetic, thermal, nonthermal, and CME energies in 399 solar M and X-class flare events observed during the first 3.5 years of the Solar Dynamics Observatory (SDO) mission. Our findings are: (1) The sum of the mean nonthermal energy of flare-accelerated particles ($E_{\mathrm{nt}}$), the energy of direct heating ($E_{\mathrm{dir}}$), and the energy in coronal mass ejections ($E_{\mathrm{CME}}$), which are the primary energy dissipation processes in a flare, is found to have a ratio of $(E_{\mathrm{nt}}+E_{\mathrm{dir}}+ E_{\mathrm{CME}})/E_{\mathrm{mag}} = 0.87 \pm 0.18$, compared with the dissipated magnetic free energy $E_{\mathrm{mag}}$, which confirms energy closure within the measurement uncertainties and corroborates the magnetic origin of flares and CMEs; (2) The energy partition of the dissipated magnetic free energy is: $0.51\pm0.17$ in nonthermal energy of $\ge 6$ keV electrons, $0.17\pm0.17$ in nonthermal $\ge 1$ MeV ions, $0.07\pm0.14$ in CMEs, and $0.07\pm0.17$ in direct heating; (3) The thermal energy is almost always less than the nonthermal energy, which is consistent with the thick-target model; (4) The bolometric luminosity in white-light flares is comparable with the thermal energy in soft X-rays (SXR); (5) Solar Energetic Particle (SEP) events carry a fraction $\approx 0.03$ of the CME energy, which is consistent with CME-driven shock acceleration; and (6) The warm-target model predicts a lower limit of the low-energy cutoff at $e_c \approx 6$ keV, based on the mean differential emission measure (DEM) peak temperature of $T_e=8.6$ MK during flares. This work represents the first statistical study that establishes energy closure in solar flare/CME events., 35 pages, 10 Figures, accepted for publication in The Astrophysical Journal

We present evidence that $>25~\mbox{MeV}$ solar proton events show a clustering in time at intervals of about six months that persisted during the rising and peak phases of Solar Cycle 24. This phenomenon is most clearly demonstrated by considering events originating in the northern or southern solar hemispheres separately. We examine how these variations in the solar energetic particle (SEP) event rate are related to other phenomena, such as hemispheric sunspot numbers and areas, rates of coronal mass ejections, and the mean solar magnetic field. Most obviously, the SEP event rate closely follows the sunspot number and area in the same hemisphere. The variations of about six months are associated with features in many of the other parameters we examine, indicating that they are just one signature of the episodic development of Cycle 24. They may be related to periodicities of about 150 days reported in various solar and interplanetary phenomena during previous solar cycles. The clear presence of periodicities of about six months in Cycle 24 that evolve independently in each hemisphere contradicts a scenario suggested by McIntosh et al. (Nature Com. 6, 6491, 2015) for the variational timescales of solar magnetism.

In the current paradigm for the modulation of galactic cosmic rays (GCRs), diffusion is taken to be the dominant process during solar maxima while drift dominates at minima. Observations during the recent solar minimum challenge the pre-eminence of drift: at such times. In 2009, the approx.2 GV GCR intensity measured by the Newark neutron monitor increased by approx.5% relative to its maximum value two cycles earlier even though the average tilt angle in 2009 was slightly larger than that in 1986 (approx.20deg vs. approx.14deg), while solar wind B was significantly lower (approx.3.9 nT vs. approx.5.4 nT). A decomposition of the solar wind into high-speed streams, slow solar wind, and coronal mass ejections (CMEs; including postshock flows) reveals that the Sun transmits its message of changing magnetic field (diffusion coefficient) to the heliosphere primarily through CMEs at solar maximum and high-speed streams at solar minimum. Long-term reconstructions of solar wind B are in general agreement for the approx. 1900-present interval and can be used to reliably estimate GCR intensity over this period. For earlier epochs, however, a recent Be-10-based reconstruction covering the past approx. 10(exp 4) years shows nine abrupt and relatively short-lived drops of B to < or approx.= 0 nT, with the first of these corresponding to the Sporer minimum. Such dips are at variance with the recent suggestion that B has a minimum or floor value of approx.2.8 nT. A floor in solar wind B implies a ceiling in the GCR intensity (a permanent modulation of the local interstellar spectrum) at a given energy/rigidity. The 30-40% increase in the intensity of 2.5 GV electrons observed by Ulysses during the recent solar minimum raises an interesting paradox that will need to be resolved.

In a previous study (Cane and Richardson, J. Geophys. Res. 108(A4), SSH6-1, 2003), we investigated the occurrence of interplanetary coronal mass ejections in the near-Earth solar wind during 1996 – 2002, corresponding to the increasing and maximum phases of solar cycle 23, and provided a “comprehensive” catalog of these events. In this paper, we present a revised and updated catalog of the ≈300 near-Earth ICMEs in 1996 – 2009, encompassing the complete cycle 23, and summarize their basic properties and geomagnetic effects. In particular, solar wind composition and charge state observations are now considered when identifying the ICMEs. In general, these additional data confirm the earlier identifications based predominantly on other solar wind plasma and magnetic field parameters. However, the boundaries of ICME-like plasma based on charge state/composition data may deviate significantly from those based on conventional plasma/magnetic field parameters. Furthermore, the much studied “magnetic clouds”, with flux-rope-like magnetic field configurations, may form just a substructure of the total ICME interval.

Using a serendipitous configuration of the ACE and Wind spacecraft, we monitor the response of the distant geomagnetic tail (∼ −220 R E ) to an abrupt, approx. fivefold pressure drop (from ∼19.0 to ∼3.5 nPa) at the front boundary of a magnetic cloud (MC) on November 20, 2003. The interplanetary data are from ACE in orbit around the L1 point. The far-tail observations are from Wind, which was nominally in the magnetosheath, separated from the Sun–Earth line by ∼ 40 R E . The magnetic field in the innermost sheath region of the MC had a large B y ( ∼ 30 nT ) and substantial and variable flows lateral to the Sun–Earth line. There was also a significant northward field (∼35 nT), unique in the vicinity of this MC. These extreme values are reached in a filament forming the earliest relic of material accreted by the MC en route to Earth. The effects resulting from these on the far geomagnetic tail are: (1) expansion, (2) tail twisting, and (3) tail tilting. These extreme conditions were in part responsible for a crossing by Wind of a neutral sheet which is tilted by ∼85° to the ecliptic. Further, Wind made two successive excursions deep into the geomagnetic tail, in the first of which a tailward flow burst of ∼1200 km/s was observed. The dayside part of the interaction of the sudden and large dynamic pressure drop with the bow shock is studied with a local 3D MHD simulation. This work is a contribution to the area ICME/MC-sheaths–magnetosheath interactions.

Using observations from the High Energy Telescopes (HETs) on STEREO A and B and similar observations from SoHO, near-Earth, we have identified ~250 individual solar energetic particle events that include >14 MeV protons since the beginning of the STEREO mission [1]. Between the end of December 2009, when the STEREO A and B spacecraft were, respectively, ahead and behind Earth by ~ 65° in ecliptic longitude, and the end of December 2013, 43 different events were clearly detected at all three locations. The observed intensities of such an event are usually assumed to be Gaussian distributed as a function of the longitudes of the Parker Spiral footpoints at the Sun for each observer. This neglects the fact that the interplanetary magnetic field may have large deviations from Parker Spirals, e.g. due to coronal mass ejections from prior events. Nonetheless, we have fit Gaussians to the peak intensities observed simultaneously at three spacecraft for all 43 events. The Gaussian peak intensity is poorly correlated with the corresponding CME speed and the FWHM is uncorrelated with the CME speed. Surprisingly, however, there appear to be distinctly non-random variations of the FWHM values from event to event.

Ensemble modeling of CMEs provides a probabilistic forecast of CME arrival time which includes an estimation of arrival time uncertainty from the spread and distribution of predictions and forecast confidence in the likelihood of CME arrival. The real-time ensemble modeling of CME propagation uses the WSA-ENLIL+Cone model installed at the CCMC and executed in real-time. The current implementation evaluates the sensitivity of WSA-ENLIL+Cone model simulations of CME propagation to initial CME parameters. We discuss the results of real-time ensemble simulations for a total of 35 CME events between January 2013 - July 2014. For the 17 events where the CME was predicted to arrive at Earth, the mean absolute arrival time prediction error was 12.3 hours, which is comparable to the errors reported in other studies. For predictions of CME arrival at Earth the correct rejection rate is 62% and the false-alarm rate is 38%. The arrival time was within the range of the ensemble arrival predictions for 8 out of 17 events. The Brier Score for CME arrival predictions is 0.15 (where 1 is a perfect forecast), indicating that on average, the predicted likelihood of CME arrival is fairly accurate. The reliability of ensemble CME arrival predictions is heavily dependent on the initial distribution of CME input parameters, particularly the median and spread. Preliminary analysis of the probabilistic forecasts suggests undervariability, indicating that these ensembles do not sample a wide enough spread in CME input parameters. Prediction errors can also arise from ambient model parameters, the accuracy of the solar wind background derived from coronal maps, or other model limitations. Finally, predictions of the Kp geomagnetic index differ from observed values by less than one for 11 out of 17 of the ensembles and Kp prediction errors computed from the mean predicted Kp show a mean absolute error of 1.3., 37 pages, 22 figures

This report assesses the current status of research relating the origin at the Sun, the evolution through the inner heliosphere and the effects on the inner heliosphere of the interplanetary counterparts of coronal mass ejections (ICMEs). The signatures of ICMEs measured by in-situ spacecraft are determined both by the physical processes associated with their origin in the low corona, as observed by space-borne coronagraphs, and by the physical processes occurring as the ICMEs propagate out through the inner heliosphere, interacting with the ambient solar wind. The solar and in-situ observations are discussed as are efforts to model the evolution of ICMEs from the Sun out to 1 AU.

The heliospheric counterparts of coronal mass ejections (CMEs) at the Sun, interplanetary coronal mass ejections (ICMEs), can be identified in situ based on a number of magnetic field, plasma, compositional and energetic particle signatures as well as combinations thereof. We summarize these signatures and their implications for understanding the nature of these structures and the physical properties of coronal mass ejections. We conclude that our understanding of ICMEs is far from complete and formulate several challenges that, if addressed, would substantially improve our knowledge of the relationship between CMEs at the Sun and in the heliosphere.

This paper reviews three important effects on energetic particles of corotating interaction regions (CIRs) in the solar wind that are formed at the leading edges of high-speed solar wind streams originating in coronal holes. A brief overview of CIRs and their important features is followed by a discussion of CIR-associated modulations in the galactic cosmic ray intensity, with an emphasis on observations made by spacecraft particle telescope 'anti-coincidence' guards. Such guards combine high counting rates (hundreds of counts/s) and a lower rigidity response than neutron monitors to provide detailed information on the relationship between cosmic ray modulations and CIR structure. The modulation of Jovian electrons by CIRs is then described. Finally, the acceleration of ions to energies of ∼ 20 MeV/n in the vicinity of CIRs is reviewed. Corotating interaction regions (CIRs) are regions of compressed plasma formed at the leading edges of corotating high-speed solar wind streams originating in coronal holes as they interact with the preceding slow solar wind. They are par- ticularly prominent features of the solar wind during the declining and minimum phases of the 11-year solar cycle, but may also be present at times of higher solar activity, interspersed with slow solar wind and transient flows associated with coronal mass ejections (CMEs) (e.g., Richardson, Cane, and Cliver, 2002). This paper reviews three important effects of CIRs on energetic particles in the heliosphere. The first effect is the tendency for the galactic cosmic ray intensity to be depressed temporarily ('modulated') during the passage of a CIR and high- speed stream. This phenomenon has been studied for many years, typically using ground-based neutron monitors. However, the emphasis in this review is on obser- vations made in the inner heliosphere and near the Earth by the 'anti-coincidence' guards of certain spacecraft particle telescopes. Such guards combine a large de- tector volume and integral energy response (> several tens of MeV) to give high counting rates (hundreds of counts/s) which can provide detailed information on the relationship between cosmic ray modulations and CIR structure. The observa

Using a recent classification of the solar wind at 1 AU into its principal components (slow solar wind, high-speed streams, and coronal mass ejections [CMEs]) for 1972-2000, we show that the monthly averaged Galactic cosmic-ray intensity is anticorrelated with the percentage of time that the Earth is embedded in CME flows. We suggest that this anticorrelation results primarily from a CME-related change in the tail of the distribution function of hourly averaged values of the solar wind magnetic field (B) between solar minimum and solar maximum. The number of high B-values (≥10 nT) increases by a factor of ~3 from minimum to maximum (from 5% of all hours to 17%), with about two-thirds of this increase due to CMEs. On an hour-to-hour basis, average changes of cosmic-ray intensity at Earth become negative for solar wind magnetic field values ≥10 nT.

We analyze one of the first solar energetic particle (SEP) events of solar cycle 24 observed at widely separated spacecraft in order to assess the reliability of models currently used to determine the connectivity between the sources of SEPs at the Sun and spacecraft in the inner heliosphere. This SEP event was observed on 2010 August 14 by near-Earth spacecraft, STEREO-A (∼80° west of Earth) and STEREO-B (∼72° east of Earth). In contrast to near-Earth spacecraft, the footpoints of the nominal magnetic field lines connecting STEREO-A and STEREO-B with the Sun were separated from the region where the parent fast halo coronal mass ejection (CME) originated by ∼88° and ∼47° in longitude, respectively. We discuss the properties of the phenomena associated with this solar eruption. Extreme ultraviolet and white-light images are used to specify the extent of the associated CME-driven coronal shock. We then assess whether the SEPs observed at the three heliospheric locations were accelerated by this shock or whether transport mechanisms in the corona and/or interplanetary space provide an alternative explanation for the arrival of particles at the poorly connected spacecraft. A possible scenario consistent with the observations indicates that the observation of SEPs at STEREO-B and near Earth resulted from particle injection by the CME shock onto the field lines connecting to these spacecraft, whereas SEPs reached STEREO-A mostly via cross-field diffusive transport processes. The successes, limitations, and uncertainties of the methods used to resolve the connection between the acceleration sites of SEPs and the spacecraft are evaluated.

A solar ejection passed the Wind spacecraft between December 23 and 26, 1996. On closer examination, we find a sequence of ejecta material, as identified by abnormally low proton temperatures, separated by plasmas with typical solar wind temperatures at 1 AU. Large and abrupt changes in field and plasma properties occurred near the separation boundaries of these regions. At the one boundary we examine here, a series of directional discontinuities was observed. We argue that Alfvenic fluctuations in the immediate vicinity of these discontinuities distort minimum variance normals, introducing uncertainty into the identification of the discontinuities as either rotational or tangential. Carrying out a series of tests on plasma and field data including minimum variance, velocity and magnetic field correlations, and jump conditions, we conclude that the discontinuities are tangential. Furthermore, we find waves superposed on these tangential discontinuities (TDs). The presence of discontinuities allows the existence of both surface waves and ducted body waves. Both probably form in the solar atmosphere where many transverse nonuniformities exist and where theoretically they have been expected. We add to prior speculation that waves on discontinuities may in fact be a common occurrence. In the solar wind, these waves can attain large amplitudes and low frequencies. We argue that such waves can generate dynamical changes at TDs through advection or forced reconnection. The dynamics might so extensively alter the internal structure that the discontinuity would no longer be identified as tangential. Such processes could help explain why the occurrence frequency of TDs observed throughout the solar wind falls off with increasing heliocentric distance. The presence of waves may also alter the nature of the interactions of TDs with the Earth's bow shock in so-called hot flow anomalies.

We determine the solar wind structures (coronal mass ejection (CME)-related, corotating high-speed streams, and slow solar wind) driving geomagnetic storms of various strength over nearly three solar cycles (1972–2000). The most intense storms (defined by Kp) at both solar minimum and solar maximum are almost all (∼97%) generated by transient structures associated with CMEs. Weaker storms are preferentially associated with streams at solar minimum and with CMEs at solar maximum, reflecting the change in the structure of the solar wind between these phases of the solar cycle. Slow solar wind generates a small fraction of the weaker storms at solar minimum and maximum. We also determine the size distributions of Kp for each solar wind component.

We examine a 3-hour long interval on December 24, 1996, containing a magnetic hole associated with an interplanetary magnetic cloud. Two sets of perturbations are observed by the Wind spacecraft at 1 AU. In the first, the field and flow rotate at constant field strength, and the plasma is accelerated to the local Alfven speed. We show this to be a rotational discontinuity. In the second, observed 25 min later, the plasma is heated and the field decreases. We show this to be a slow shock. The whole structure is in pressure balance. We interpret the observations as MHD discontinuities arriving with varying delays from a reconnection site closer to the Sun. Energetic particle observations suggest further that ejecta material is present for many hours prior to the magnetic cloud observation and separated from it by the layer. This suggests that reconnection took place between field lines of a CME of which the magnetic cloud formed a part.

We assess the contribution of various types of solar wind structures (coronal mass ejections (CMEs), high-speed streams, and slow solar wind) to averages of the aa geomagnetic activity index ( ) during the solar cycle. We used solar wind plasma, magnetic field, and energetic particle data to identify the flow types present in the near-Earth solar wind during 1972–1986 (encompassing the decline of solar cycle 20 and all of cycle 21). Corotating high-speed streams contribute ∼ 70% of outside of solar maximum and ∼ 30% at solar maximum (1978–1982). CME-related structures (shocks/postshock flows/ejecta) account for ∼ 50% of at solar maximum and

Evidence is presented for a 22-year cycle in the amplitude of recurrent, near-Earth, near-Ecliptic, galactic cosmic ray modulations during the solar minimum periods in the mid-1950s to mid-1990s. These modulations are ∼50% larger during A > 0 epochs than during A 0 epochs. A change in the latitudinal GCR gradient in successive epochs is unlikely to be the sole reason for the change in depression size since (1) the proportionality constant between the recurrent depressions and latitudinal gradient depends on A, and (2) the cosmic ray density is not organized by crossings of the heliospheric current sheet.

We show that the variations of the interplanetary magnetic field strength (B) over a 22-year period are tracked by the inverted profile of the cosmic ray density measured by neutron monitors. We suggest that global changes in the Sun's magnetic field are more important for long-term modulation than magnetic field enhancements resulting from the merging of high-speed flows and coronal mass ejections in the outer heliosphere. The unexpectedly close relationship that we find between the “tilt angle” of the heliospheric current sheet and the cosmic ray density away from solar minimum for both polarity states of the solar magnetic field may be accounted for by the anticorrelation between the cosmic ray density and field strength variations.

We discuss the structure and evolution of CIRs and their successors in the outer helio- sphere. These structures undergo significant evolution as they are convected to greater heliocentric distances. A progression of different types of structure are observed at increasing distance from the Sun. Similar structures are observed at similar heliocentric distance at different portions of the solar cycle. CIRs and their successors are associated with many important physical processes in the outer heliosphere. We discuss the relationship between these structures and recurrent phenomena such as cosmic ray variations, and review some of the associated theoretical models on the role of corotating structures and global merged interaction regions (GMIRs) in global cosmic ray modulation. We also discuss some outstanding questions related to the origin of non-dispersive quasi-periodic particle enhancements associated with CIRs and their successors in the outer heliosphere.

Corotating Interaction Regions (CIRs) form as a consequence of the compression of the solar wind at the interface between fast speed streams and slow streams. Dynamic interaction of solar wind streams is a general feature of the heliospheric medium; when the sources of the solar wind streams are relatively stable, the interaction regions form a pattern which corotates with the Sun. The regions of origin of the high speed solar wind streams have been clearly identified as the coronal holes with their open magnetic field structures. The origin of the slow speed solar wind is less clear; slow streams may well originate from a range of coronal configurations adjacent to, or above magnetically closed structures. This article addresses the coronal origin of the stable pattern of solar wind streams which leads to the formation of CIRs. In particular, coronal models based on photospheric measurements are reviewed; we also examine the observations of kinematic and compositional solar wind features at 1 AU, their appearance in the stream interfaces (SIs) of CIRs, and their relationship to the structure of the solar surface and the inner corona; finally we summarise the Helios observations in the inner heliosphere of CIRs and their precursors to give a link between the optical observations on their solar origin and the in-situ plasma observations at 1 AU after their formation. The most important question that remains to be answered concerning the solar origin of CIRs is related to the origin and morphology of the slow solar wind.

We report on the finding of a 153-day periodicity in the magnetic field strength and solar wind speed measured at 1 AU during the years 1978–1982. The period and the occurence epoch are consistent with the “154-day” periodicity previously reported for events occurring at the Sun. In particular, the variations in the field strength and the occurence rate of energetic (tens of MeV) solar particle events are in phase. The similar periodicities in the interplanetary field and solar phenomena are consistent with a global phenomenon. Whereas this periodicity is quite strong for the magnetic field magnitude, there is only a weak periodicity for the individual field components. The field magnitude shows essentially no periodicity at this period during the previous and following solar maxima. The lack of persistence, and of significant harmonic components of the observed periodicity, does not support the proposal of a solar “clock” mechanism. The most significant variations in the complete near-earth magnetic field data base (1963–1997) with periods of less than 200 days occur at 166 and 146 days.

Using energetic ion data obtained by the EPAS experiment on the ICE spacecraft we investigate the three dimensional ion bulk flow in the mass loading region around the comet P/Giacobini-Zinner. We find relatively abrupt changes in flow speed (∼ 100 km s−1) at the boundaries between the pickup and mass loading regions. Flow deflections away from the comet tail of ∼15° are observed at the boundaries with peaks upto ∼30° inside the mass loading region. Ion energies of ∼300 keV are found inside the mass loading region which suggest the need to consider other ion acceleration mechanisms in addition to solar wind pickup.

We investigate the magnetic field topology of ejecta (the interplanetary manifestations of solar mass ejections) by using observations of energetic particle anisotropies made by the Goddard Space Flight Center instruments on the ISEE 3, Helios 1, and Helios 2 spacecraft at ≤1 AU from the Sun. In particular, we investigate particle flows observed following the onsets of 39 solar energetic particle events which occurred when the observing spacecraft was located in a preexisting ejecta. To infer when the spacecraft was located in an ejecta, we examine a wide range of indicators of the presence of ejecta, including magnetic cloud signatures, bidirectional energetic ion flows, bidirectional solar wind electron heat fluxes, and depressed proton plasma temperatures. We find that inside ejecta, the particle arrival direction in the ecliptic plane varies widely from event to event, with at least 30% of the events showing flows from the east of the Sun. In contrast, in 60 similar events observed outside ejecta, the particle arrival directions are consistent with flows from the Sun along near-Parker spiral field lines in >90% of cases. We also discuss multiple-spacecraft observations of three particle events which illustrate the contrasting particle flows observed during the same event by spacecraft in different solar wind structures. We conclude that the observations are consistent with the presence of nonspiral magnetic fields, including looped magnetic field lines connected to the Sun, in at least a subset of ejecta.

Brief ( 80%) of electron bursts in the plasma sheet and plasma sheet boundary layer (PSBL) were associated with AL intensifications and/or particle injections observed at geosynchronous orbit, indicative of a relationship with substorm onsets. Bursts were detected following less than 50% of apparent substorms, presumably because a burst was detected only if the spacecraft was located within the region of field lines reconnected at the substorm neutral line. In the deep tail (∼ 200 RE from Earth), peak energetic electron intensities were typically observed near the outer edge of the PSBL closely following substorm onset. This finding suggests that the electrons were accelerated on newly reconnected field lines and lost rapidly from the tail. Unlike low-energy (tens of keV) ions, energetic electrons (at least with intensities above the detector background) were not a general feature of the PSBL or the plasma sheet outside times of enhanced substorm activity. Most plasmoids (∼80%) in the deep tail were not associated with enhanced energetic electron fluxes, a suggestion that electrons accelerated at the substorm neutral line during disconnection of the plasmoid may leak out from the plasmoid. This possibility is consistent with flux-rope-like magnetic structures in plasmoids which connect to open field lines at the flanks of the tail. Electron anisotropies can be examined during the more intense bursts. These show either weak flows consistent with trapping on closed field lines connected to the Earth or stronger, tailward flows which suggest flow away from an acceleration region earthward of the spacecraft. Weak flows were observed in the plasma sheet within ∼90 RE from Earth, consistent with previous ISEE 3 studies suggesting that this is the typical location of the distant neutral line. We confirm earlier observations that electron bursts in the magnetosheath are found predominantly close to the magnetopause, are associated with low-energy ion enhancements, and show strong tailward flows. Since most of these bursts were detected within ∼90 RE of Earth, the region where intense plasma sheet electron bursts were also observed, this finding suggests that the plasma sheet may be source of the magnetosheath bursts.

Brief 0.2-2 MeV electron bursts were detected in the plasma sheet, tail lobes and magnetosheath by the Goddard Space Flight Center Medium Energy Cosmic Ray Experiment during the ISEE 3 geotail mission in 1982-3. We summarize the main features of these data and their implications for the structure and dynamics of the geomagnetic tail. Sharp falls in the intensity and occurrence rate of plasma sheet events at ∼90 Re from Earth suggest a change from predominantly closed field lines Earthward of this location to predominantly open field lines at greater distances downtail. The electron anisotropies and associated plasma flows support this proposal which is also consistent with other ISEE 3 observations suggesting that the tail neutral line typically lies at around this distance. Electron bursts in the tail are closely association with substorm activity onsets as indicated by AL intensifications and particle injections at geosynchronous orbit. Signatures of plasmoid ejection down the tail may be observed following electron bursts. In the deep tail, energetic electron enhancements tend to be observed close to the time of substorm onset and are not generally present in the plasma sheet and plasma sheet boundary layer at other times. This suggests that the electrons are accelerated at the substorm neutral line rather than along the current sheet, and are lost rapidly from the tail along open field lines.

Using a classification of near-Earth solar wind flows into corotating high-speed streams, slow interstream solar wind, and transients originating with coronal mass ejections at the Sun, we determine the drivers of geomagnetic storms of various sizes from 1964 to 2011 based on the Kp index, encompassing more than four solar cycles. We also briefly discuss storm occurrence rates since the beginning of Kp in 1932.

Using observations of solar wind plasma and magnetic field parameters and additional data (e.g., geomagnetic indicies, energetic particle and cosmic ray observations), we have classified the near-Earth solar wind during 1963 to 2011 into three basic flow types: high-speed streams associatedwith coronal holes at the Sun, slow, inter-stream flows, and transient ("CME-related") flows. We discuss the cycle-to-cycle variations in solar wind parameters and structures, and geomagnetic activity, over this period, encompassingmore than four solar cycles.

This paper reviews several aspects of the interaction of the solar wind with the Earth’s magnetosphere, which is dominated by structures that include enhancements in the southward component of the solar wind magnetic field.

The phase scintillation index was obtained from L1 GPS data collected with the Canadian High Arctic Ionospheric Network (CHAIN) during years of extended solar minimum 2008-2010. Phase scintillation occurs predominantly on the dayside in the cusp and in the nightside auroral oval. We set forth a probabilistic forecast method of phase scintillation in the cusp based on the arrival time of either solar wind corotating interaction regions (CIRs) or interplanetary coronal mass ejections (ICMEs). CIRs on the leading edge of high-speed streams (HSS) from coronal holes are known to cause recurrent geomagnetic and ionospheric disturbances that can be forecast one or several solar rotations in advance. Superposed epoch analysis of phase scintillation occurrence showed a sharp increase in scintillation occurrence just after the arrival of high-speed solar wind and a peak associated with weak to moderate CMEs during the solar minimum. Cumulative probability distribution functions for the phase scintillation occurrence in the cusp are obtained from statistical data for days before and after CIR and ICME arrivals. The probability curves are also specified for low and high (below and above median) values of various solar wind plasma parameters. The initial results are used to demonstrate a forecasting technique on two example periods of CIRs and ICMEs.

[1] During Corotating Interaction Region (CIR)-driven storms, relativistic electron fluxes in the outer radiation belt decrease in the main phase, followed by a gradual increase in the recovery phase. Recent studies have shown that whistler mode chorus waves play an important role in accelerating the seed electron population to relativistic energies in the outer radiation belt. However, the evolution of chorus waves and their source electrons responsible for the wave excitation during storm various phases is not well understood. In this study we select 72 CIR-driven storm periods over the interval 2007–2011 to perform superposed epoch analysis of the evolution of chorus waves and source electrons in the L* and MLT range extensively observed by THEMIS during various phases of CIR-driven storms. The wave amplitudes and the occurrence of chorus waves substantially increase and peak in the main phase and gradually decrease in the following recovery phase at L*