Arrival Of Interplanetary Shocks Research Articles

Muon Flux Variations Measured by Low‐Cost Portable Cosmic Ray Detectors and Their Correlation With Space Weather Activity

AbstractWe present a comparison of the measured cosmic ray (CR) muon fluxes from two identical portable low‐cost detectors at different geolocations and their sensitivity to space weather events in real time. The first detector is installed at Mount Wilson Observatory, CA, USA (geomagnetic cutoff rigidity Rc ∼ 4.88 GV), and the second detector is running on the downtown campus of Georgia State University in Atlanta, GA, USA (Rc ∼ 3.65 GV). The variation of the detected muon fluxes is compared to the changes in the interplanetary solar wind parameters at the L1 Lagrange point and geomagnetic indexes. In particular, we have investigated the muon flux behavior during three major interplanetary shock events and geomagnetic disturbances that occurred during July and August of 2022. To validate the interpretation of the measured muon signals, we compare the muon fluxes to the measurement from the Oulu neutron monitor (NM, Rc ∼ 0.8 GV). The results of this analysis show that the muon detector installed at Mount Wilson Observatory demonstrates a stronger correlation with a high‐latitude NM. Both detectors typically observe a muon flux decrease during the arrival of interplanetary shocks and geomagnetic storms. Interestingly, the decrease could be observed several hours before the onset of the first considered interplanetary shocks at L1 at 2022‐07‐23 02:28:00 UT driven by the high‐speed Coronal Mass Ejection and related geomagnetic storm at 2022‐07‐23 03:59:00 UT. This effort represents an initial step toward establishing a global network of portable low‐cost CR muon detectors for monitoring the sensitivity of muon flux changes to space and terrestrial weather parameters.

The Dynamics of Earth’s Cusp in Response to the Interplanetary Shock

The Earth’s magnetospheric cusp, a region with an off-equatorial magnetic field minimum, is an important place which directly transports plasma and energy from the solar wind into the magnetosphere and ionosphere. Its magnetic topology and charged particles therein are known to respond to the solar wind and the interplanetary magnetic field. However, its dynamics in response to the interplanetary (IP) shock are still unknown, due to lack of direct spacecraft observations. This study first reports the observations of the cusp’s motion under the drive of an IP shock and both strong electric fields and outflowing energetic ions in the moving cusp. After an IP shock arrival on 7 September 2017, triple cusps were observed by Cluster C4 when it was crossing the high-altitude northern polar region to the sub-solar magnetosphere. The multiple cusps had a one-to-one correspondence with the dayside magnetosphere compression and relaxation detected by THEMIS E, indicating that one cusp moved back and forth three times due to the IP shock’s impact. In the moving cusp, there were strong impulsive electric fields with a peak of up to ∼40 mV/m and an ionospheric source population of upward propagating ions (O+, He+ and H+) with energies extending to MeV. However, the outflowing ions outside the cusp had energies of no more than 1 keV. An enhancement of energetic O+ appeared inside the cusp with the flux ratio of O+/H+ increasing from 10 keV to ∼ MeV, which implies the efficient acceleration of O+. These observations are shown to be consistent with the prompt acceleration by the impulsive electric fields, which is mass-dependent. This finding suggests a new acceleration mechanism for cusp energetic ions, especially for O+.

Simulated Trapping of Solar Energetic Protons for the 8–10 March 2012 Geomagnetic Storm: Impact on Inner Zone Protons as Measured by Van Allen Probes

AbstractSolar energetic protons (SEPs) have been shown to contribute significantly to the inner zone trapped proton population for energies <100 MeV and L > 1.3 (Selesnick et al., 2007, https://doi.org/10.1029/2006sw000275). The Relativistic Electron Proton Telescope (REPT) on the Van Allen Probes launched 30 August 2012 observed a double‐peaked (in L) inner zone population throughout the 7‐year lifetime of the mission. It has been proposed that a strong SEP event accompanied by a CME‐shock in early March 2012 provided the SEP source for the higher L trapped proton population, which then diffused radially inward to be observed by REPT at L ∼ 2. Here, we follow trajectories of SEP protons launched isotropically from a sphere at 7 Re in 15 s cadence fields from an Lyon‐Fedder‐Mobarry coupled to Rice Convection Model global magnetohydrodynamic (MHD) simulation driven by measured upstream solar wind parameters. The timescale of the interplanetary shock arrival is captured, launching a magnetosonic impulse propagating azimuthally along the dawn and dusk flanks inside the magnetosphere, shown previously to produce SEP trapping. The MHD‐test particle simulation uses Geostationary Operational Environmental Satellite (GOES) proton energy spectra to weight the initial radial profile required for the radial diffusion calculation over the following 2 years. GOES proton measurements also provide a dynamic outer boundary condition for radial diffusion. A direct comparison with REPT measurements 20 months following the trapping event in March 2012 supports this novel combination of short‐term and long‐term evolution of the newly trapped protons.

Frequency‐Dependent Responses of Plasmaspheric Hiss to the Impact of an Interplanetary Shock

AbstractPlasmaspheric hiss waves are essential for the pitch‐angle scattering and precipitation of energetic electrons and interplanetary shocks may affect these waves. We present a case study on the responses of plasmaspheric hiss after an interplanetary shock arrival on September 7, 2017. Based on the observation by RBSP‐B, the plasmaspheric hiss in different frequency ranges shows three different responses simultaneously: hiss waves with frequency below 0.08fce are weakened, waves within 0.08–0.18fce are weakened in magnetic power and modulated by the ultra‐low frequency (ULF) waves in the electric power, while waves above 0.18fce are intensified in magnetic power and modulated by the ULF waves. Further analysis suggests that the hiss waves have different sources: low‐frequency (<∼0.18fce) hiss waves are transmitted from chorus outside the plasmasphere, while high‐frequency (>∼0.18fce) hiss waves are locally amplified. Our results provide a comprehensive view of the frequency‐dependent hiss wave behavior after the impact of interplanetary shocks.

Shock Induced Strong Substorms and Super Substorms: Preconditions and Associated Oxygen Ion Dynamics

It is well known that the interaction between interplanetary (IP) shocks and the Earth’s magnetosphere would generate/excite various types of geomagnetic phenomena. Progresses have been made on the Earth’s magnetospheric response to solar wind forcing in recent years in the aspects associated with magnetospheric substorms. Strong substorms and super substorms could be triggered externally by sudden changes of solar wind dynamic pressures. When a strong substorms (AE > 1000 nT) or super substorms (AE > 2000 nT) occurs, singly charged oxygen ions escaped from the Earth’s ionosphere are found to be a dominated ion population in the magnetotail and in the inner magnetosphere—ring current region. The products of a strong substorms or super substorms- plasmoid, burst bulk flows are also found to contain significant oxygen ions, even substorm injections can be dominated by oxygen ions. Thus, the magnetospheric dynamic must consider the contributions from the heavy oxygen ions. Also, the IP shock induced super substorms associated electromagnetic pulses (dB/dt) would shift the energetic particle (injections) inward and accelerate existing population significantly. Extensive attempts have also been made to understand how the solar wind energy couples with the magnetosphere to excite magnetospheric substorms. The statistical analysis shows that strong substorms (AE > 1000 nT) and super substorms (AE > 2000 nT) triggered by interplanetary shocks are most likely to occur under the southward interplanetary magnetic field (IMF) and fast solar wind pre-conditions. In addition, strong substorms after the IP shock arrival are more likely to occur when IMF points toward (away from) the Sun around spring (autumn) equinox, which can be ascribed to the Russell-McPherron effect. Thus, the southward IMF precondition of an interplanetary shock and the Russell-McPherron effect can be considered as precursors of a strong substorm and/or super substorm triggered by IP shocks. Moreover, the average duration of CME sheath region which is just behind the interplanetary shock are found to be about 7 hours. This indicates that southward IMF compressed by shock could last at least 7 hours long in the downstream of the interplanetary shock (sheath region) if a southward IMF pre-condition is present, which explains why the largest substorm often occur in the CME sheath.

The Intense Substorm Incidence in Response to Interplanetary Shock Impacts and Influence on Energetic Electron Fluxes at Geosynchronous Orbit

AbstractThe interaction between interplanetary (IP) shocks and the Earth's magnetosphere would generate/excite various types of geomagnetic phenomena. In order to analyze what kind of IP shock is more likely to trigger intense substorms (SME/AE > 1,000 nT) and how the energetic electrons response to intense substorms at geosynchronous orbit, we perform a systematic survey of 246 IP shock events using SuperMag and LANL observations between 2001 and 2013. The statistical analysis shows that intense substorms (SME > 1,000 nT) triggered by IP shocks are most likely to occur under the southward interplanetary magnetic field (IMF) and fast solar wind preconditions. Besides, intense substorms after the IP shock arrival are much more likely to occur when IMF points toward (away from) the Sun around spring (autumn) equinox, which can be ascribed to the Russell‐McPherron effect. Thus, the IMF Bs precondition of an IP shock and the Russell‐McPherron effect can be considered as precursors of an intense substorm. Furthermore, after the shock arrival associated with intense substorms, low‐energy (<200 keV) electron fluxes increase significantly at geosynchronous orbit, and high‐energy (>200 keV) electron fluxes decrease. The spectral index becomes softer with intense substorms and remains almost unchanged with moderate substorms no matter whether the IMF precondition is southward or northward.

Statistical study on interplanetary drivers behind intense geomagnetic storms and substorms

Geomagnetic storms and substorms play a central role in both the daily life of mankind and in academic space physics. The profiles of storms, especially their initial phase morphology and the intensity of their substorms under different interplanetary conditions, have usually been ignored in previous studies. In this study, 97 intense geomagnetic storms (Dstmin ≤ –100 nT) between 1998 and 2018 were studied statistically using the double superposed epoch analysis (DSEA) and normalized superposed epoch analysis (NSEA) methods. These storms are categorized into two types according to different interplanetary magnetic field (IMF) Bz orientations: geomagnetic storms whose IMF is northward, both upstream and downstream relative to the interplanetary shock, and geomagnetic storms whose upstream and downstream IMF is consistently southward. We further divide these two types into two subsets, by different geomagnetic storm profiles: Type I/Type II — one/two-step geomagnetic storms with northward IMF both upstream and downstream of the interplanetary shock; Type III/TypeIV — one/two-step geomagnetic storms with southward IMF both upstream and downstream of the interplanetary shock. The results show that: (1) geomagnetic storms with northward IMF both upstream and downstream of the interplanetary shock have a clear initial phase; geomagnetic storms with southward IMF in both upstream and downstream of the interplanetary shock do not; (2) the IMF is an important controlling factor in affecting the intensity characteristics of substorms. When Bz is positive before and after the interplanetary shock arrival, the Auroral Electrojet (AE) index changes gently during the initial phase of geomagnetic storms, the median value of AE index is maintained at 500–1000 nT; (3) when Bz is negative before and after the interplanetary shock arrival, the AE index rises rapidly and reaches its maxmum value about one hour after storm sudden commencements (SSC), although the time is scaled between reference points and the maximum value of AE is usually greater than 1,000 nT, representing intense substorms; (4) for most cases, the Dst0 usually reaches its minimum at least one hour after Bz. These results are useful in improving contemporary space weather models, especially for those that address geomagnetic storms and substorms.

The Characteristic Response of Whistler Mode Waves to Interplanetary Shocks

AbstractMagnetospheric whistler mode waves play a key role in regulating the dynamics of the electron radiation belts. Recent satellite observations indicate a significant influence of interplanetary (IP) shocks on whistler mode wave power in the inner magnetosphere. In this study, we statistically investigate the response of whistler mode chorus and plasmaspheric hiss to IP shocks based on Van Allen Probes and THEMIS satellite observations. Immediately after the IP shock arrival, chorus wave power is usually intensified, often at postmidnight to prenoon sector, while plasmaspheric hiss wave power predominantly decreases near the dayside but intensifies near the nightside. We conclude that chorus wave intensification outside the plasmasphere is probably associated with the suprathermal electron flux enhancement caused by the IP shock. Through a simple ray tracing modeling assuming the scenario that plasmaspheric hiss is originated from chorus, we find that the solar wind dynamic pressure increase changes the magnetic field configuration to favor ray penetration in the nightside and promote ray refraction away from the dayside, potentially explaining the magnetic local time‐dependent responses of plasmaspheric hiss waves following IP shock arrivals.

The aurorae of Uranus past equinox

AbstractThe aurorae of Uranus were recently detected in the far ultraviolet with the Hubble Space Telescope (HST) providing a new, so far unique, means to remotely study the asymmetric Uranian magnetosphere from Earth. We analyze here two new HST Uranus campaigns executed in September 2012 and November 2014 with different temporal coverage and under variable solar wind conditions numerically predicted by three different MHD codes. Overall, the HST images taken with the Space Telescope Imaging Spectrograph reveal auroral emissions in three pairs of successive images (one pair acquired in 2012 and two in 2014), hence 6 additional auroral detections in total, including the most intense Uranian aurorae ever seen with HST. The detected emissions occur close the expected arrival of interplanetary shocks. They appear as extended spots at southern latitudes, rotating with the planet. They radiate 5–24 kR and 1.3‐8.8 GW of ultraviolet emission from H2, last for tens of minutes and vary on timescales down to a few seconds. Fitting the 2014 observations with model auroral ovals constrains the longitude of the southern (northern) magnetic pole to 104 ± 26° (284 ± 26°) in the Uranian Longitude System. We suggest that the Uranian near‐equinoctial aurorae are pulsed cusp emissions possibly triggered by large‐scale magnetospheric compressions.

Electron dropout echoes induced by interplanetary shock: Van Allen Probes observations

AbstractOn 23 November 2012, a sudden dropout of the relativistic electron flux was observed after an interplanetary shock arrival. The dropout peaks at ∼1 MeV and more than 80% of the electrons disappeared from the drift shell. Van Allen twin Probes observed a sharp electron flux dropout with clear energy dispersion signals. The repeating flux dropout and recovery signatures, or “dropout echoes”, constitute a new phenomenon referred to as a “drifting electron dropout” with a limited initial spatial range. The azimuthal range of the dropout is estimated to be on the duskside, from ∼1300 to 0100 LT. We conclude that the shock‐induced electron dropout is not caused by the magnetopause shadowing. The dropout and consequent echoes suggest that the radial migration of relativistic electrons is induced by the strong dusk‐dawn asymmetric interplanetary shock compression on the magnetosphere.

Interplanetary shocks and the resulting geomagnetically induced currents at the equator

AbstractGeomagnetically induced currents (GICs) caused by interplanetary shocks represent a serious space weather threat to modern technological infrastructure. The arrival of interplanetary shocks drives magnetosphere and ionosphere current systems, which then induce electric currents at ground level. The impact of these currents at high latitudes has been extensively researched, but the magnetic equator has been largely overlooked. In this paper, we investigate the potential effects of interplanetary shocks on the equatorial region and demonstrate that their magnetic signature is amplified by the equatorial electrojet. This local amplification substantially increases the region's susceptibility to GICs. Importantly, this result applies to both geomagnetic storms and quiet periods and thus represents a paradigm shift in our understanding of adverse space weather impacts on technological infrastructure.

INFLUENCE OF A CME’S INITIAL PARAMETERS ON THE ARRIVAL OF THE ASSOCIATED INTERPLANETARY SHOCK AT EARTH AND THE SHOCK PROPAGATIONAL MODEL VERSION 3

Predicting the arrival times of coronal mass ejections (CMEs) and their related waves at Earth is an important aspect of space weather forecasting. The Shock Propagation Model (SPM) and its updated version (SPM2), which use the initial parameters of solar flare-Type II burst events as input, have been developed to predict the shock arrival time. This paper continues to investigate the influence of solar disturbances and their associated CMEs on the corresponding interplanetary (IP) shock's arrival at Earth. It has been found that IP shocks associated with wider CMEs have a greater probability of reaching the Earth, and the CME speed obtained from coronagraph observations can be supplementary to the initial shock speed computed from Type II radio bursts when predicting the shock's arrival time. Therefore, the third version of the model, i.e., SPM3, has been developed based on these findings. The new version combines the characteristics of solar flare-Type II events with the initial parameters of the accompanying CMEs to provide the prediction of the associated IP shock's arrival at Earth. The prediction test for 498 events of Solar Cycle 23 reveals that the prediction success rate of SPM3 is 70%-71%, which is apparently higher than that of the previous SPM2 model (61%-63%). The transit time prediction error of SPM3 for the Earth-encountered shocks is within 9 hr (mean-absolute). Comparisons between SPM3 and other similar models also demonstrate that SPM3 has the highest success rate and best prediction performance.

Transit time of CME/shock associated with four major geo-effective CMEs in solar cycle 24

The kinematics of coronal mass ejection (CME) in the interplanetary medium is very important in the concept of space-weather. Main aim of this paper is to study the propagation of four major geo-effective CMEs and their associated shocks observed in solar cycle 24. The arrival of interplanetary shocks and CMEs of these events near the Earth is seen from the ACE/wind in situ data available in OMNI data base. The CMEs considered in this study have a wide range of initial speeds 500–1900km/s in the LASCO field of view, comprising of two slow CMEs (V∼500km/s), one fast CME (V∼1800km/s) and one moderate speed CME (V∼800km/s). The observed transit time of these events are compared with transit time estimated using the empirical shock arrival model (ESA). Especially, we utilize (i) different acceleration – speed equations reported in the literature from the observations made in the last few decades and (ii) various acceleration cessation distances (Acd) In addition, we compared the estimated and observed transit time with that from the Drag Based Model (DBM). From the result of this analysis, we demonstrated that each CME behaves in its own way in the interplanetary medium and their propagation is governed by the CME initial speed, interplanetary acceleration and acceleration cessation distances. In the present paper, we found (i) which acceleration equation is better for the transit time calculations (ii) importance of the CME acceleration cessation distances (iii) reducing the transit time error in CME forecasting. Based on these results and on Zhao and Dryer (2014) review (that included physics-based models), the realistic statistics should be based on real-time studies, not on post-mortem case studies.

The far magnetotail response to an interplanetary shock arrival

We present a study of the impact of the December 7, 2003 fast forward interplanetary (IP) shock on the distant tail of the Earth׳s magnetosphere. Using the data from the several spacecraft located in the solar wind/magnetosheath upstream to the Earth, we monitor a propagation of the IP shock from the L1 point to the magnetosphere. A behavior of the far magnetotail is inferred from the Wind observations at XGSM≈−230RE. Shortly after the shock arrival, Wind crossed consequentially southern and northern lobes and observed a flux rope and the tailward fast plasma flow (≈780km/s) within the plasmasheet. Moreover, a change of the solar wind VZ component across the shock creates a huge kink of the tail magnetosphere that propagates down the tail with the IP shock.

Multi-instrument study of the Jovian radio emissions triggered by solar wind shocks and inferred magnetospheric subcorotation rates

The influence of solar wind conditions on the Jovian auroral radio emissions has long been debated, mostly because it has always been difficult to get accurate solar wind and radio observations at the same time. We present here a study of Jupiter׳s radio emissions compared to solar wind conditions using radio (RPWS) and magnetic (MAG) data from the Cassini spacecraft from October to December 2000, just before its flyby of Jupiter. The spacecraft was then in the solar wind and could record both the radio emissions coming from the Jovian magnetosphere and the solar wind magnetic field (IMF). With these data, we found a good correspondence between the arrival of interplanetary shocks at Jupiter and the occurrence of radio storms. Our results confirm those from the previous studies showing that fast forward shocks (FFS) trigger mostly dusk emissions, whereas fast reverse shocks (FRS) trigger both dawn and dusk emissions. FFS-triggered emissions are found to occur 10–30h after the shock arrival when the IMF is weak (below 2nT), and quasi-immediately after shock arrival when the IMF is strong (above 2nT). FRS-triggered emissions are found to occur quasi-immediately even when the IMF is weak. We show and discuss in depth the characteristic morphologies of the radio emissions related to each type of shock and their implications.We also used simultaneous radio observations from the ground-based Nançay decameter array and from the Galileo radio instrument (PWS). From the comparison of these measurements with Cassini׳s, we deduce the regions where the radio storms occur, as well as the radio source subcorotation rates. We show that FFS-triggered emissions onset happens in a sector of local time centered around 15:00 LT, and that all the shock-triggered radio sources sub-corotate with a subcorotation rate of ~50% when the IMF is below 2nT and of ~80% when it is above 2nT. These rates could correspond to the extended and compressed states of the Jovian magnetosphere.

Forecast of the arrival of interplanetary shocks by measuring cosmic ray fluctuations in the interplanetary medium

Here we present a method to forecast the arrival of an interplanetary shock to the Earth's orbit in advance of up to one day, using cosmic ray fluctuations and solar wind parameters measured onboard the ACE spacecraft. The method is based on our previous results [1]. By means of continuous monitoring of the interplanetary space state since April 2010, we conclude that not all shocks can be reliably forecasted by the method. Only those interplanetary shocks, for which a large flux of low-energy particles (10 keV − 10 MeV) of solar or interplanetary origin exists in the upstream region, can be forecasted. This is typically related to quasi-parallel shocks. In the absence of such particles, a forecast cannot be made. This is a typical situation for quasi-perpendicular shocks. Our analysis shows that, on average, an interplanetary shock can be forecasted for several hours up to one day, with the probability about 70%.

Inner magnetosphere plasma characteristics in response to interplanetary shock impacts

[1] In order to characterize plasma (0.03–45 keV) properties in response to interplanetary (IP) shock impact at the geosynchronous orbit, we have examined 95 shock events from 1997 to 2004. These shock events have been categorized into two groups: shock fronts associated with southward interplanetary magnetic field (IMF; 47 cases) and with northward IMF (48 cases). Our results show that under southward IMF, the plasma becomes denser and hotter following the IP shock arrival. The proton (0.1–45 keV) and electron (0.03–45 keV) number densities have peaks of 1.8 and of 2.5 cm−3 at the duskside, respectively (the typical tail plasma sheet density is about 0.7 cm−3). After the IP shock impact, the plasma (proton and electron) temperature anisotropy increases remarkably at the noon sector, decreases toward dawn and dusk, and minimizes at midnight, suggesting that both electromagnetic ion cyclotron and whistler waves can be stimulated mainly at the dayside magnetosphere. In addition, there are more oxygen ions injecting into the inner magnetosphere, and the density of ionospheric oxygen ions is comparable to proton density. However, for IP shocks associated with northward IMF, the plasma density and temperature increases are insignificant, while slight enhancements of the plasma temperature anisotropy are distributed globally.

Solar wind low-energy energetic ion enhancements: A tool to forecast large geomagnetic storms

Predicting the occurrence of large geomagnetic storms more than an hour in advance is an important, yet difficult task. Energetic ion data show enhancements in flux that herald the approach of interplanetary shocks, usually for many hours before the shock arrival. We present a technique for predicting large geomagnetic storms (Kp ⩾ 7) following the arrival of interplanetary shocks at 1 AU, using low-energy energetic ions (47–65 keV) and solar wind data measured at the L1 libration point. It is based on a study of the relationship between energetic ion enhancements (EIEs) and large geomagnetic storms by Smith et al. [Smith, Z., Murtagh, W., Smithtro, C. Relationship between solar wind low-energy energetic ion enhancements and large geomagnetic storms. J. Geophys. Res. 109, A01110, 2004. doi:10.1029/ 2003JA010044] using data in the rise and maximum of solar cycle 23 (February 1998–December 2000). An excellent correlation was found between storms with Kp ⩾ 7 and the peak flux of large energetic ion enhancements that almost always (93% of time in our time period) accompany the arrival of interplanetary shocks at L1. However, as there are many more large EIEs than large geomagnetic storms, other characteristics were investigated to help determine which EIEs are likely to be followed by large storms. An additional parameter, the magnitude of the post-shock total magnetic field at the L1 Lagrangian point, is introduced here. This improves the identification of the EIEs that are likely to be followed by large storms. A forecasting technique is developed and tested on the time period of the original study (the training data set). The lead times, defined as the times from the arrival of the shock to the start of the 3-h interval of maximum Kp, are also presented. They range from minutes to more than a day; the average for large storms is 7 h. These times do not include the extra warning time given when the EI flux cross the high thresholds ahead of the shock. Because the data-stream used in the original study is no longer available, we extended the original study (1998–2000) to 2001, in order to: (a) investigate EIEs in 2001; (b) present a validation of the technique on an independent data set; (c) compare the results based on the original (P1) energy channel to those of the replacement (P1′) and (d), determine new EIE thresholds for forecasting geomagnetic storms using P1′ data. The verification of this P1′ training data set is also presented, together with lead times.

Solar and interplanetary origins of the November 2004 superstorms

During the first half of November 2004, many solar flares and coronal mass ejections (CMEs) were associated with solar active region (AR) 10696. This paper attempts to identify the solar and interplanetary origins of two superstorms which occurred on 8 and 10 November with peak intensities of Dst = −373 nT and −289 nT, respectively. Southward interplanetary magnetic fields within a magnetic cloud (MC), and a sheath + MC were the causes of these two superstorms, respectively. Two different CME propagation models [Gopalswamy, N., Yashiro, S., Kaiser, M.L. et al. Predicting the 1-AU arrival times of coronal mass ejections. J. Geophys. Res. 106, 29207–29219, 2001; Gopalswamy, N.S., Lara, A., Manoharan, P.K. et al. An empirical model to predict the 1-AU arrival of interplanetary shocks. Adv. Space Res. 36, 2289–2294, 2005] were employed to attempt to identify the solar sources. It is found that the models identify several potential CMEs as possible sources for each of the superstorms. The two Gopalswamy et al. models give the possible sources for the first superstorm as CMEs on 2330 UT 4 November 2004 or on 1454 UT 5 November 2004. For the second superstorm, the possible solar source was a CME that on 0754 UT 5 November 2004 or one that occurred on 1206 UT 5 November 2004. We note that other propagation models sometimes agree and other times disagree with the above results. It is concluded that during high solar/interplanetary activity intervals such as this one, the exact solar source is difficult to identify. More refined propagation models are needed.

Operational validation of HAFv2's predictions of interplanetary shock arrivals at Earth: Declining phase of Solar Cycle 23

This is the third in a series of papers showing the performance of the Hakamada‐Akasofu‐Fry version 2 (HAFv2) model in predicting, in the operational environment, the arrival of interplanetary shocks at Earth. The first and second studies covered the time of the rise and maximum of Solar Cycle 23. This study covers the declining phase, through December 2006. The prediction of shock arrivals is important in space weather applications because these events are often followed by geomagnetic disturbances that disrupt human technologies. The HAFv2 uses, for input, a continuously updating background solar wind onto which transient events (interplanetary shocks) are superimposed whenever near‐real‐time observations are reported of a metric type II radio burst and/or a halo or partial halo coronal mass ejection (CME). Supporting inputs are obtained from GOES 1–8 Å X‐ray data and solar images. We present the performance of the model in standard meteorological forecast metrics and compare the accuracy of the three phases of Solar Cycle 23. We find that the accuracy of the model is consistent between the three periods. For this third phase, we show the added confidence in model predictions provided by the presence of halo/partial halo observations. Halo/partial halo CMEs were found to accompany approximately one half of the events. The predictions of this subset of events have a higher level of confidence and success. Thus the observation of a large CME should not be a requirement for a forecast but rather an indication that when one is observed, the confidence in the prediction is greatly increased.