Fast Interplanetary Coronal Mass Ejections Research Articles

The Extreme Space Weather Event in 1941 February/March

Abstract Given the infrequency of extreme geomagnetic storms, it is significant to note the concentration of three extreme geomagnetic storms in 1941, whose intensities ranked fourth, twelfth, and fifth within the aa index between 1868–2010. Among them, the geomagnetic storm on 1941 March 1 was so intense that three of the four Dst station magnetograms went off scale. Herein, we reconstruct its time series and measure the storm intensity with an alternative Dst estimate (Dst*). The source solar eruption at 09:29–09:38 GMT on February 28 was located at RGO AR 13814 and its significant intensity is confirmed by large magnetic crochets of ∣35∣ nT measured at Abinger. This solar eruption most likely released a fast interplanetary coronal mass ejection with estimated speed 2260 km s−1. After its impact at 03:57–03:59 GMT on March 1, an extreme magnetic storm was recorded worldwide. Comparative analyses on the contemporary magnetograms show the storm peak intensity of minimum Dst* ≤ −464 nT at 16 GMT, comparable to the most and the second most extreme magnetic storms within the standard Dst index since 1957. This storm triggered significant low-latitude aurorae in the East Asian sector and their equatorward boundary has been reconstructed as 38.°5 in invariant latitude. This result agrees with British magnetograms, which indicate an auroral oval moving above Abinger at 53.°0 in magnetic latitude. The storm amplitude was even more enhanced in equatorial stations and consequently casts caveats on their usage for measurements of the storm intensity in Dst estimates.

Magnetic Cloud and Sheath in the Ground-level Enhancement Event of 2000 July 14. I. Effects on the Solar Energetic Particles

Abstract Ground-level enhancements generally accompany fast interplanetary coronal mass ejections (ICMEs), and ICME-driven shocks are sources of solar energetic particles (SEPs). Observations of the GLE event of 2000 July 14 show that a very fast and strong magnetic cloud (MC) is behind the ICME shock and the proton intensity-time profiles observed at 1 au had a rapid two-step decrease near the sheath and MC. Therefore, we study the effect of sheath and MC on SEPs accelerated by an ICME shock by numerically solving the focused transport equation. The shock is regarded as a moving source of SEPs with an assumed particle distribution function. The sheath and MC are set to thick spherical caps with enhanced magnetic field, and the turbulence levels in the sheath and MC are set to be higher and lower than those of the ambient solar wind, respectively. The simulation results of proton intensity-time profiles agree well with the observations in energies ranging from ∼1 to ∼100 MeV, and the two-step decrease is reproduced when the sheath and MC arrived at the Earth. The simulation results show that the sheath-MC structure reduced the proton intensities for about 2 days after the shock passed through the Earth. It is found that the sheath contributed most of the decrease while the MC facilitated the formation of the second step decrease. The simulation also infers that the coordination of magnetic field and turbulence in sheath-MC structure can produce a stronger reduction of SEP intensities.

Capability of Geomagnetic Storm Parameters to Identify Severe Space Weather

Abstract The paper investigates the capability of geomagnetic storm parameters in the disturbance storm-time (Dst), Kp, and AE indices to distinguish between severe space weather (SvSW) that causes the reported electric power outages and/or telecommunication failures and normal space weather (NSW) that does not cause these severe effects in a 50 yr period (1958–2007). The parameters include the storm intensities DstMin (minimum Dst during the main phase, MP, of the storm), (dDst/dt)MPmax, Kpmax, and AEmax. In addition, the impulsive parameter is derived for the storms that are automatically identified in the Kyoto Dst and USGS is the integral of the modulus of the Dst from onset of the MP (MPO) to the DstMin. T MP is the MP duration from MPO to DstMin. The corresponding mean values and are also calculated. Regardless of the significant differences in the storm parameters between the two Dst indices, the IpsDst in both indices seems to identify four of the five SvSW events (and the Carrington event) in more than 750 NSW events that have been reported to have occurred in 1958–2007, while all other parameters separate one or two SvSWs from the NSWs. Using the Kyoto IpsDst threshold of −250 nT, we demonstrate a 100% true SvSW identification rate with only one false NSW. Using the false NSW event (1972 August 4), we investigate whether using a higher resolution Dst might result in a more accurate identification of SvSWs. The mechanism of the impulsive action leading to large IpsDst and SvSW involves the coincidence that the fast interplanetary coronal mass ejection velocity V contains its shock (or front) velocity and large interplanetary magnetic field Bz southward covering .

A Study of Fluctuations in Magnetic Cloud‐Driven Sheaths

AbstractInterplanetary coronal mass ejections are at the center of the research on geomagnetic activity. Sheaths, highly fluctuating structures, which can be found in front of fast interplanetary coronal mass ejections, are some of the least known geoeffective solar transients. Using Morlet transforms, we analyzed the magnetic fluctuations in a list of 42 well‐identified and isolated magnetic clouds driving a sheath and shock (Masías‐Meza et al., 2016, https://doi.org/10.1051/0004-6361/201628571. We studied the fluctuations inside sheaths by defining two quantities: the power and the anisotropy. With a simple statistical approach we found that sheaths, in particular, those driven by a fast magnetic cloud, encountering a highly turbulent solar wind, and forming a high Alfvén Mach number shock have high levels of turbulent energy (∼10 times compared with the solar wind) as well as a low anisotropy (approximately halved compared with the solar wind) of their fluctuations. On the other hand, the effect of the shock angle and plasma beta in the solar wind are less straightforward: If the shock is quasi‐parallel or the beta in the solar wind is high, both the turbulent energy in the sheaths and the anisotropy of the fluctuations are reduced; but for quasi‐perpendicular shocks or low beta solar wind the turbulent energy and anisotropy can take any value.

Study of Interplanetary CMEs/Shocks During Solar Cycle 24 Using Drag-Based Model: The Role of Solar Wind

In this paper we analyze a set of 27 fast interplanetary coronal mass ejections (ICMEs) observed during the period January 2010 – December 2013 in Solar Cycle 24. The arrivals of interplanetary shocks and CMEs at 1 AU are found from OMNI spacecraft high resolution data and their travel times are compared with Empirical Shock Arrival (ESA; Gopalswamy et al. in Adv. Space Res. 36, 2289, 2005) and Drag Based Model (DBM; Vrsnak et al. in Solar Phys. 285, 295, 2013). The analysis of the transit time, deceleration, and drag parameter is used to examine the role of the solar-wind characteristics in the dynamics of ICMEs. The obtained ICME parameters (deceleration, drag parameter) are compared with the decelerated events (34 of 91 events in Solar Cycle 23) from the study of Manoharan et al. (J. Geophy. Res. 109, A06109, 2004). The interplanetary (IP) deceleration shows similar trend between the cycles. Though the Cycle 24 has weak solar wind, it does not affect the arrival time behavior. It is concluded that the solar-wind behavior is considered to be the same in Cycles 23 and 24 for ICMEs. The IP drag parameter is linearly correlated with CME initial speed. The p-value between CME speed and drag parameter suggests that they are highly significant. The important result of the study is that the solar wind showed a similar kind of drag effect for the propagating CMEs in both cycles.

Solar Wind and Heavy Ion Properties of Interplanetary Coronal Mass Ejections

Magnetic field and plasma properties of the solar wind measured in near-Earth space are a convolution of coronal source conditions and in-transit processes which take place between the corona and near-Earth space. Elemental composition and heavy ion charge states, however, are not significantly altered during transit to Earth and thus such properties can be used to diagnose the coronal source conditions of the solar wind observed in situ. We use data from the Advanced Composition Explorer (ACE) spacecraft to statistically quantify differences in the coronal source properties of interplanetary coronal mass ejections (ICMEs). Magnetic clouds, ICMEs which contain a magnetic flux-rope signature, display heavy ion properties consistent with significantly hotter coronal source regions than non-cloud ICMEs. Specifically, magnetic clouds display significantly elevated ion charge states, suggesting they receive greater heating in the low corona. Further dividing ICMEs by speed, however, shows this effect is primarily limited to fast magnetic clouds and that in terms of heavy ion properties, slow magnetic clouds are far more similar to non-cloud ICMEs. As such, fast magnetic clouds appear distinct from other ICME types in terms of both ion charge states and elemental composition. ICME speed, rather ICME type, correlates with helium abundance and iron charge state, consistent with fast ICMEs being heated through the more extended corona. Fast ICMEs also tend to be embedded within faster ambient solar wind than slow ICMEs, though this could be partly the result of in-transit drag effects. These signatures are discussed in terms of spatial sampling of ICMEs and from fundamentally different coronal formation and release processes.

Superposed epoch study of ICME sub-structures near Earth and their effects on Galactic cosmic rays

Interplanetary coronal mass ejections (ICMEs) are the interplanetary manifestations of solar eruptions. The overtaken solar wind forms a sheath of compressed plasma at the front of ICMEs. Magnetic clouds (MCs) are a subset of ICMEs with specific properties (e.g. the presence of a flux rope). When ICMEs pass near Earth, ground observations indicate that the flux of galactic cosmic rays (GCRs) decreases. The main aims of this paper are to find: common plasma and magnetic properties of different ICME sub-structures, and which ICME properties affect the flux of GCRs near Earth. We use a superposed epoch method applied to a large set of ICMEs observed \insitu\ by the spacecraft ACE, between 1998 and 2006. We also apply a superposed epoch analysis on GCRs time series observed with the McMurdo neutron monitors. We find that slow MCs at 1 AU have on average more massive sheaths. We conclude that it is because they are more effectively slowed down by drag during their travel from the Sun. Slow MCs also have a more symmetric magnetic field and sheaths expanding similarly as their following MC, while in contrast, fast MCs have an asymmetric magnetic profile and a compressing sheath in compression. In all types of MCs, we find that the proton density and the temperature, as well as the magnetic fluctuations can diffuse within the front of the MC due to 3D reconnection. Finally, we derive a quantitative model which describes the decrease of cosmic rays as a function of the amount of magnetic fluctuations and field strength. The obtained typical profiles of sheath/MC/GCR properties corresponding to slow, mid, and fast ICMEs, can be used for forecasting/modelling these events, and to better understand the transport of energetic particles in ICMEs. They are also useful for improving future operative space weather activities.

Simulation of magnetic cloud erosion during propagation

AbstractWe examine a three‐dimensional (3‐D) numerical magnetohydrodynamic (MHD) simulation describing a very fast interplanetary coronal mass ejection (ICME) propagating from the solar corona to 1 AU. In conjunction with its high speed, the ICME evolves in ways that give it a unique appearance at 1 AU that does not resemble a typical ICME. First, as the ICME decelerates far from the Sun in the solar wind, filament material at the back of the flux rope pushes its way forward through the flux rope. Second, diverging nonradial flows in front of the filament transport poloidal flux of the rope to the sides of the ICME. Third, the magnetic flux rope reconnects with the interplanetary magnetic field (IMF). As a consequence of these processes, the flux rope partially unravels and appears to evolve to an entirely unbalanced configuration. At the same time, filament material at the base of the flux rope moves forward and comes in direct contact with the shocked plasma in the CME sheath. We find evidence that such remarkable behavior has actually occurred when we examine a very fast CME that erupted from the Sun on 2005 January 20. In situ observations of this event near 1 AU show very dense cold material impacting the Earth following immediately behind the CME sheath. Charge state analysis shows this dense plasma is filament material. Consistent with the simulation, we find the poloidal flux (Bz) to be entirely unbalanced, giving the appearance that the flux rope has eroded. The dense solar filament material and unbalanced positive IMF Bz produced a number of anomalous features in a moderate magnetic storm already underway, which are described in a companion paper by Kozyra et al. (2014).

Magnetic field and dynamic pressure ULF fluctuations in coronal-mass-ejection-driven sheath regions

Abstract. Compressed sheath regions form ahead of interplanetary coronal mass ejections (ICMEs) that are sufficiently faster than the preceding solar wind. The turbulent sheath regions are important drivers of magnetospheric activity, but due to their complex internal structure, relatively little is known on the distribution of the magnetic field and plasma variations in them. In this paper we investigate ultra low frequency (ULF) fluctuations in the interplanetary magnetic field (IMF) and in dynamic pressure (Pdyn) using a superposed epoch analysis of 41 sheath regions observed during solar cycle 23. We find strongest fluctuation power near the shock and in the vicinity of the ICME leading edge. The IMF and Pdyn ULF power have different profiles within the sheath; the former is enhanced in the leading part of the sheath, while the latter is increased in the trailing part of the sheath. We also find that the ICME properties affect the level and distribution of the ULF power in sheath regions. For example, sheath regions associated with strong or fast ICMEs, or those that are crossed at intermediate distances from the center, have strongest ULF power and large variation in the power throughout the sheath region. The weaker or slower ICMEs, or those that are crossed centrally, have in general considerably weaker ULF power with relatively smooth profiles. The strong and abrupt decrease of the IMF ULF power at the ICME leading edge could be used to distinguish the ICME from the preceding sheath plasma.

Radial Speed Evolution of Interplanetary Coronal Mass Ejections During Solar Cycle 23

We report radial speed evolution of interplanetary coronal mass ejections (ICMEs) detected by the SOHO/LASCO coronagraph, interplanetary scintillation (IPS) at 327 MHz, and in-situ observations. In this study, we analyze solar wind disturbance factor (g-value) data derived from IPS observations during 1997-2009 covering nearly the whole period of Solar Cycle 23. By comparing observations from the SOHO/LASCO, IPS, and in situ, we then identify 39 ICMEs that could be analyzed carefully. Here, we define two speeds V_SOHO and V_bg, which are initial speed of ICME and the speed of the background solar wind, respectively. Examinations of these speeds yield the following results; i) Fast ICMEs (with V_SOHO - V_bg > 500 km/s) rapidly decelerate, moderate ICMEs (with 0 km/s < V_SOHO - V_bg < 500 km/s) show either gradually decelerating or uniform motion, and slow ICMEs (with V_SOHO - V_bg < 0 km/s) accelerate. The radial speeds converge on the speed of background solar wind during their outward propagation. We subsequently find; ii) both the acceleration and deceleration are nearly complete by 0.79 (+/- 0.04) AU, and those are ended when the ICME speed reaches a given speed. We find the value of that to be 480 (+/- 21) km/s. iii) For the fast and moderate ICMEs, a linear equation with a constant coefficient is more appropriate than a quadratic equation to describe their kinematics, because the chi-square for the linear equation satisfies the statistical significance level of 0.05, while the quadratic one is not. These results support the hypothesis that the radial motion of ICMEs is governed by a drag force due to interaction with the background solar wind. These findings also suggest that ICMEs propagating faster than background solar wind are controlled mainly by the hydrodynamic Stokes drag.

MAGNETIC RECONNECTION IN THE SOLAR WIND AT CURRENT SHEETS ASSOCIATED WITH EXTREMELY SMALL FIELD SHEAR ANGLES

Using Wind 3 s plasma and magnetic field data, we have identified nine reconnection exhausts within a solar wind disturbance on 1998 October 18–20 driven by a moderately fast interplanetary coronal mass ejection (ICME). Three of the exhausts within the ICME were associated with current sheets having local field shear angles, θ, ranging from 4° to 9°, the smallest reported values of θ yet associated with reconnection exhausts in a space plasma. They were observed in plasma characterized by extremely low (0.02–0.04) plasma β, and very high (281–383 km s−1) Alfvén speed, VA. Low β allows reconnection to occur at small θ and high VA leads to exhaust jets that are fast enough relative to the surrounding solar wind to be readily identified. Very small-θ current sheets are common in the solar wind at 1 AU, but typically are not associated with particularly low plasma β or high VA. On the other hand, small-θ current sheets should be common in the lower solar corona, a plasma regime of extremely low β and extremely high VA. Our observations lend credence to models that predict that reconnection at small-θ current sheets is primarily responsible for coronal heating.

Interplanetary Coronal Mass Ejections Observed by Ulysses Through Its Three Solar Orbits

An extended Ulysses interplanetary coronal mass ejections (ICMEs) list is used to statistically study the occurrence rate of ICMEs, the interaction of ICMEs with solar wind, and the magnetic field properties in ICMEs. About 43% of the ICMEs are identified as magnetic clouds (MCs). It is found that the occurrence rate of ICMEs approximately follows the solar activity level, except for the second solar orbit; the rate is higher in the southern heliolatitude than in the northern heliolatitude; and it roughly decreases with the increase of ICME speeds. Our results show that the speed difference between the ICME and the solar wind in front of it shows a slight decrease with increasing heliocentric distance for ICMEs preceded by a shock, whereas no such dependence is found for the ICMEs without shock association. It is also found that approximately 23% of the ICMEs are associated with radial field events, in which the interplanetary magnetic field with near-radial direction lasts for many hours, in the Ulysses detected range, and these associated events are not necessarily confined to fast ICMEs or the trailing portions of ICMEs. Nearly all these associated events occur during the period of declining solar wind speed and most of them occur at low heliolatitudes.

A brief review of “solar flare effects” on the ionosphere

The study of solar flare effects (SFEs) on the ionosphere is having a renaissance. The development of GPS ground and satellite data for scientific use has opened up new means for high time resolution research on SFEs. At present, without continuous flare photon spectra (X rays, EUV, UV, and visible) monitoring instrumentation, the best way to model flare spectral changes within a flare is through ionospheric GPS studies. Flare EUV photons can increase the total electron content of the subsolar ionosphere by up to 30% in ∼5 min. Energetic particles (ions) of 10 keV to GeV energies are accelerated at the flare site. Electrons with energies up to several MeV are also created. A coronal mass ejection (CME) is launched from the Sun at the time of the flare. Fast interplanetary CMEs (ICMEs) have upstream shocks which accelerate ions to ∼10 keV to ∼10 MeV. Both sources of particles, when magnetically connected to the Earth's magnetosphere, enter the magnetosphere and the high‐latitude and midlatitude ionosphere. Those particles that precipitate into the ionosphere cause rapid increases in the polar atmospheric ionization, disruption of transpolar communication, and cause ozone destruction. Complicating the picture, when the ICME reaches the magnetosphere ∼1 to 4 days later, shock compression of the magnetosphere energizes preexisting 10–100 keV magnetospheric electrons and ions, causing precipitation into the dayside auroral zone (∼60°–65° MLAT) ionospheres. Shock compression can also trigger supersubstorms in the magnetotail with concomitant energetic particle precipitation into the nightside auroral zones. If the interplanetary sheath or ICME magnetic fields are southwardly directed and last for several hours, a geomagnetic storm will result. A magnetic storm is characterized by the formation of an unstable ring current with energetic particles in the range ∼10 keV to ∼500 keV. The ring current decays away by precipitation into the middle latitude ionosphere over timescales of ∼10 h. A schematic of a time line for the above SFE ionospheric effects is provided. Descriptions of where in the ionosphere and in what time sequence is provided in the body of the text. Much of the terminology presently in use describing solar, interplanetary, magnetospheric, and ionospheric SFE‐related phenomena are dated. We suggest physics‐based terms be used in the future.

Large geomagnetic storms of extreme solar event periods in solar cycle 23

During extreme solar events such as big flares or/and energetic coronal mass ejections (CMEs) high energy particles are accelerated by the shocks formed in front of fast interplanetary coronal mass ejections (ICMEs). The ICMEs (and their sheaths) also give rise to large geomagnetic storms which have significant effects on the Earth’s environment and human life. Around 14 solar cosmic ray ground level enhancement (GLE) events in solar cycle 23 we examined the cosmic ray variation, solar wind speed, ions density, interplanetary magnetic field, and geomagnetic disturbance storm time index ( D st). We found that all but one of GLEs are always followed by a geomagnetic storm with D st ⩽ −50 nT within 1–5 days later. Most(10/14) geomagnetic storms have D st index ⩽ −100 nT therefore generally belong to strong geomagnetic storms. This suggests that GLE event prediction of geomagnetic storms is 93% for moderate storms and 71% for large storms when geomagnetic storms preceded by GLEs. All D st depressions are associated with cosmic ray decreases which occur nearly simultaneously with geomagnetic storms. We also investigated the interplanetary plasma features. Most geomagnetic storm correspond significant periods of southward B z and in close to 80% of the cases that the B z was first northward then turning southward after storm sudden commencement (SSC). Plasma flow speed, ion number density and interplanetary plasma temperature near 1 AU also have a peak at interplanetary shock arrival. Solar cause and energetic particle signatures of large geomagnetic storms and a possible prediction scheme are discussed.

Field-Line Draping Around ICMES

Magnetic field orientations in the sheaths of ten fast interplanetary coronal mass ejections (ICMEs) that cover the solar longitude range roughly from 20° East to 33° West (as determined from the associated flare or filament disruption) are overlain on the MHD-computed magnetic field pattern showing draping in Earth’s magnetosheath. The general draping pattern is evident in the ICME sheath orientations including, most importantly, the east flank where draping causes the greatest distortion of the magnetic field away from the general Parker spiral. Deviations from the general draping pattern are also evident which, we suggest, result from the history of accretion of the inhomogeneous interplanetary magnetic field (IMF) into the ICME sheath over a long stretch of solar wind before arriving at one AU. The profiles of magnetic field intensity between the ICME shock and the nose of the ICME deviate significantly from the corresponding profile in Earth’s magnetosheath. The ICME samples are much more irregular and show no general tendency to increase toward the stagnation point. We suggest that again this difference reflects the history of IMF accretion by the ICME sheath. The long stretch of accreted inhomogeneous field (a significant fraction of one AU) can account for the irregularity, and the weakness of the field close to the body possibly reflects a weaker ICME shock closer to the Sun.

Plasma depletion and mirror waves ahead of interplanetary coronal mass ejections

We find that the sheath regions between fast interplanetary coronal mass ejections (ICMEs) and their preceding shocks are often characterized by plasma depletion and mirror wave structures, analogous to planetary magnetosheaths. A case study of these signatures in the sheath of a magnetic cloud (MC) shows that a plasma depletion layer (PDL) coincides with magnetic field draping around the MC. In the same event, we observe an enhanced thermal anisotropy and plasma beta as well as anticorrelated density and magnetic fluctuations which are signatures of mirror mode waves. We perform a superposed epoch analysis of ACE and Wind plasma and magnetic field data from different classes of ICMEs to illuminate the general properties of these regions. For MCs preceded by shocks, the sheaths have a PDL with an average duration of 6 hours (corresponding to a spatial span of about 0.07 AU) and a proton temperature anisotropy T⊥p/T∥p ≃ 1.2–1.3, and are marginally unstable to the mirror instability. For ICMEs with preceding shocks which are not MCs, plasma depletion and mirror waves are also present but at a reduced level. ICMEs without shocks are not associated with these features. The differences between the three ICME categories imply that these features depend on the ICME geometry and the extent of upstream solar wind compression by the ICMEs. We discuss the implications of these features for a variety of crucial physical processes including magnetic reconnection, formation of magnetic holes, and energetic particle modulation in the solar wind.

Interplanetary coronal mass ejection and ambient interplanetary magnetic field correlations during the Sun‐Earth connection events of October–November 2003

Magnetic field observations made during 28 October to 1 November 2003, which included two fast interplanetary coronal mass ejections (ICMEs), allow a study of correlation lengths of magnetic field parameters for two types of interplanetary (IP) structures: ICMEs and ambient solar wind. Further, they permit the extension of such investigations to the magnetosheath and to a distance along the Sun‐Earth line (X) of about 400 RE. Data acquired by three spacecraft are examined: ACE, in orbit around the L1 point; Geotail, traveling eastward in the near‐Earth solar wind (at R ∼ 30 RE); and Wind, nominally in the distant geomagnetic tail (R ∼ −160 RE) but making repeated excursions into the magnetosheath/solar wind due to the flapping of the tail. Analyses are presented in both time and frequency domains. We find significant differences in the cross‐correlation/coherence properties of the ambient interplanetary magnetic field (IMF) and ICME parameters. For the ambient IMF, we find high coherence to be confined to low frequencies, consistent with other studies. In contrast, ICME magnetic field parameters remain generally coherent up to much higher frequencies. Scale lengths of ICME magnetic field parameters are in excess of 400 RE. High speeds of ∼1700 km s−1 are inferred from the plot of phase difference versus frequency, consistent with that obtained from plasma instruments. To strengthen these results and to extend them to include dependence on the distance perpendicular to the Sun‐Earth line (Y), we examine a 28‐day interval in year 2001 characterized by a sequence of 10 ICMEs and containing roughly equal ambient solar wind and ICME time intervals. ACE‐Wind X and Y separations were ∼220 and ∼250 RE, respectively. We find good coherence/correlation alternating with poor values. In particular, we find that in general ICME coherence/correlation lengths along Y are larger by a factor of 3–5 than those quoted in the literature for ambient solar wind parameters. Our findings are good news for the space weather effort, which depends crucially on predicting the arrival of large events, since they make possible the placement of upstream monitors to give a longer lead time than at L1.

Heliospheric energetic particle observations during the October–November 2003 events

The intense level of solar activity recorded from 19 October to 12 November 2003 led to unusually high energetic particle intensities observed throughout the heliosphere. The fleet of spacecraft distributed in the inner and outer heliosphere offers us the opportunity to study both the effects of these events in different regions of the heliosphere and the evolution of the energetic particle intensities measured at different heliocentric radial distances. Observations at 1 AU by the ACE and GOES‐11 spacecraft show multiple particle intensity enhancements associated with individual injections of solar energetic particles (SEPs) and with the arrival of shocks driven by coronal mass ejections (CMEs), resulting in a long time interval (∼40 days) of elevated low‐energy (&lt;1 MeV) ion and near‐relativistic (&lt;315 keV) electron intensities. Observations from the Ulysses spacecraft at 5.2 AU, 6° north of the ecliptic, and 120–90° west of the Earth also showed elevated low‐energy ion and near‐relativistic electron intensities for more than ∼40 days that were modulated by the effects of recurrent corotating interaction regions (CIRs) and the passage of a fast interplanetary coronal mass ejection (ICME). The Cassini spacecraft at 8.7 AU, 3° south of the ecliptic, and 75–35° west of the Earth saw an intense low‐energy ion and near‐relativistic electron event in association with the passage of an enhanced magnetic field structure formed by the compression of transient solar wind flows and CIRs. The prompt component of the SEP event at Cassini was largely reduced due to the modulating effect of intervening transient flows propagating between the Sun and the spacecraft. The Voyager‐2 spacecraft at 73 AU and 25° south of the ecliptic did not observe these events until April 2004. The arrival of a merged interaction region (MIR) at Voyager‐2 produced a ∼70‐day period with elevated &lt;17 MeV proton and &lt;60 keV electron intensities. Particle fluences computed over the duration of the events at each spacecraft show a radial dependence that decays more slowly than that expected from a simple model assuming adiabatic cooling of an isotropic particle population uniformly distributed in a shell symmetrically expanding at the solar wind speed. Although the SEP events were observed throughout the heliosphere, both (1) the solar particle injections occurring at different times and longitudes, and (2) the marked differences in the interplanetary stream structures propagating toward different longitudes resulted in distinct time‐intensity histories at each spacecraft, and therefore periods with equal particle intensities were not observed by this fleet of spacecraft.

An unusually fast interplanetary coronal mass ejection observed by Ulysses at 5 AU on 15 November 2003

On 15 November 2003, at ∼2030 UT, Ulysses/SWOOPS observed the onset of a large, unusually fast interplanetary coronal mass ejection (ICME) in the solar wind at 5.2 AU. Ulysses measured the peak solar wind flow speed associated with this event, vmax = 993 km s−1, in the turbulent sheath region preceding the ICME. This is the fastest solar wind speed recorded by Ulysses/SWOOPS at this distance since November 1992. On 7 November 2003 at 1554 UT, SOHO/LASCO observed the solar counterpart of this ICME behind the west limb of the Sun; the CME had a plane‐of‐sky speed of 1995 km s−1. We believe this CME originated in AR 0486, the same active region responsible for the extremely fast ICMEs that impacted the Earth on 29 and 30 October 2003. The ICME took at least 4.3 days to propagate past Ulysses and had a radial width of ∼2.1 AU. The ICME was a magnetic cloud, with a depressed proton beta of ∼0.01 and a smooth rotation of the magnetic field polar angle from 43° to −62°. In addition, Ulysses/SWOOPS also observed bidirectional electron streaming throughout the ICME, indicating that even at this distance, closed field lines threaded the entire event. In the days preceding the ICME, Ulysses observed disturbed solar wind conditions, including six shocks from 6 November to 15 November and several small ICMEs, indicating a high degree of solar activity.