Propagation of Coronal Mass Ejections Observed During the Rising Phase of Solar Cycle 24

In this study, we investigate the interplanetary consequences and travel time details of 58 coronal mass ejections (CMEs) in the Sun–Earth distance. The CMEs considered are halo and partial halo events of width \({>}\,120\)°. These CMEs occurred during 2009?–?2013, in the ascending phase of the Solar Cycle 24. Moreover, they are Earth-directed events that originated close to the centre of the solar disk (within about \(\pm30\)° from the Sun’s centre) and propagated approximately along the Sun–Earth line. For each CME, the onset time and the initial speed have been estimated from the white-light images observed by the LASCO coronagraphs onboard the SOHO space mission. These CMEs cover an initial speed range of \({\sim}\,260\,\mbox{--}\,2700~\mbox{km}\,\mbox{s}^{-1}\). For these CMEs, the associated interplanetary shocks (IP shocks) and interplanetary CMEs (ICMEs) at the near-Earth environment have been identified from in-situ solar wind measurements available at the OMNI data base. Most of these events have been associated with moderate to intense IP shocks. However, these events have caused only weak to moderate geomagnetic storms in the Earth’s magnetosphere. The relationship of the travel time with the initial speed of the CME has been compared with the observations made in the previous Cycle 23, during 1996?–?2004. In the present study, for a given initial speed of the CME, the travel time and the speed at 1 AU suggest that the CME was most likely not much affected by the drag caused by the slow-speed dominated heliosphere. Additionally, the weak geomagnetic storms and moderate IP shocks associated with the current set of Earth-directed CMEs indicate magnetically weak CME events of Cycle 24. The magnetic energy that is available to propagate CME and cause geomagnetic storm could be significantly low.     

Statistical Analysis of Solar Events Associated with Storm Sudden Commencements over One Year of Solar Maximum During Cycle 23: Propagation from the Sun to the Earth and Effects

Taking the 32 storm sudden commencements (SSCs) listed by the International Service of Geomagnetic Indices (ISGI) of the Observatory de l’Ebre during 2002 (solar activity maximum in Cycle 23) as a starting point, we performed a multi-criterion analysis based on observations (propagation time, velocity comparisons, sense of the magnetic field rotation, radio waves) to associate them with solar sources, identified their effects in the interplanetary medium, and looked at the response of the terrestrial ionized and neutral environment. We find that 28 SSCs can be related to 44 coronal mass ejections (CMEs), 15 with a unique CME and 13 with a series of multiple CMEs, among which 19 (68%) involved halo CMEs. Twelve of the 19 fastest CMEs with speeds greater than 1000 km?s^?1 are halo CMEs. For the 44 CMEs, including 21 halo CMEs, the corresponding X-ray flare classes are: 3 X-class, 19 M-class, and 22 C-class flares. The probability for an SSC to occur is 75% if the CME is a halo CME. Among the 500, or even more, front-side, non-halo CMEs recorded in 2002, only 23 could be the source of an SSC, i.e. 5%. The complex interactions between two (or more) CMEs and the modification of their trajectories have been examined using joint white-light and multiple-wavelength radio observations. The detection of long-lasting type IV bursts observed at metric–hectometric wavelengths is a very useful criterion for the CME–SSC events association. The events associated with the most depressed Dst values are also associated with type IV radio bursts. The four SSCs associated with a single shock at L1 correspond to four radio events exhibiting characteristics different from type IV radio bursts. The solar-wind structures at L1 after the 32 SSCs are 12 magnetic clouds (MCs), 6 interplanetary coronal mass ejections (ICMEs) without an MC structure, 4 miscellaneous structures, which cannot unambiguously be classified as ICMEs, 5 corotating or stream interaction regions (CIRs/SIRs), one CIR caused two SSCs, and 4 shock events; note than one CIR caused two SSCs. The 11 MCs listed in 3 or more MC catalogs covering the year 2002 are associated with SSCs. For the three most intense geomagnetic storms (based on Dst minima) related to MCs, we note two sudden increases of the Dst, at the arrival of the sheath and the arrival of the MC itself. In terms of geoeffectiveness, the relation between the CME speed and the magnetic-storm intensity, as characterized using the Dst magnetic index, is very complex, but generally CMEs with velocities at the Sun larger than 1000 km?s^?1 have larger probabilities to trigger moderate or intense storms. The most geoeffective events are MCs, since 92% of them trigger moderate or intense storms, followed by ICMEs (33%). At best, CIRs/SIRs only cause weak storms. We show that these geoeffective events (ICMEs or MCs) trigger an increased and combined auroral kilometric radiation (AKR) and non-thermal continuum (NTC) wave activity in the magnetosphere, an enhanced convection in the ionosphere, and a stronger response in the thermosphere. However, this trend does not appear clearly in the coupling functions, which exhibit relatively weak correlations between the solar-wind energy input and the amplitude of various geomagnetic indices, whereas the role of the southward component of the solar-wind magnetic field is confirmed. Some saturation appears for Dst values \(< -100\) nT on the integrated values of the polar and auroral indices.     

The Association of Solar Flares with Coronal Mass Ejections During the Extended Solar Minimum

We study the association of solar flares with coronal mass ejections (CMEs) during the deep, extended solar minimum of 2007?–?2009, using extreme-ultraviolet (EUV) and white-light (coronagraph) images from the Solar Terrestrial Relations Observatory (STEREO). Although all of the fast (v>900 km?s^?1), wide (θ>100^°) CMEs are associated with a flare that is at least identified in GOES soft X-ray light curves, a majority of flares with relatively high X-ray intensity for the deep solar minimum (e.g. ?1×10^?6 W?m^?2 or C1) are not associated with CMEs. Intense flares tend to occur in active regions with a strong and complex photospheric magnetic field, but the active regions that produce CME-associated flares tend to be small, including those that have no sunspots and therefore no NOAA active-region numbers. Other factors on scales similar to and larger than active regions seem to exist that contribute to the association of flares with CMEs. We find the possible low coronal signatures of CMEs, namely eruptions, dimmings, EUV waves, and Type III bursts, in 91 %, 74 %, 57 %, and 74 %, respectively, of the 35 flares that we associate with CMEs. None of these observables can fully replace direct observations of CMEs by coronagraphs.     

The Interplanetary Responses to the Great Solar Activities in Late October 2003

Based on the observations of the Sun and the interplanetary medium, a series of solar activities in late October 2003 and their consequences are studied comprehensively. Thirteen X-ray flares with importance greater than M-class, six frontside halo coronal mass ejections (CMEs) with span angle larger than 100 and three associated eruptions of filament materials are identified by examining lots of solar observations from October 26 to 29. All these flares were associated with type III radio bursts, all the frontside halo CMEs were accompanied by type II or type II-like radio bursts. Particularly, among these activities, two major solar events caused two extraordinary enhancements (exceeding 1000 particles/(cm²s^–1sterMev^–1) of solar energetic particle (SEP) flux intensity near the Earth, two large ejecta with fast shocks preceding, and two great geomagnetic storms with Dst peak value of –363 and –401 nT, respectively. By using a cross correlation technique and a force-free cylindrical flux rope model, the October 29 magnetic cloud associated with the largest CME are analyzed, including its orientation and the sign of its helicity. It is found that the helicity of the cloud is negative, contrary to the regular statistical pattern that negative- and positive-helical interplanetary magnetic clouds would be expected to come from northern and southern solar hemisphere. Moreover, the relationship between the orientation of magnetic cloud and associated filament is discussed. In addition, some discussion concerning multiple-magnetic-cloud structures and SEP events is also given.     

A Study of the Earth-Affecting CMEs of Solar Cycle 24

Using in situ observations from the Advanced Composition Explorer (ACE), we have identified 70 Earth-affecting interplanetary coronal mass ejections (ICMEs) in Solar Cycle 24. Because of the unprecedented extent of heliospheric observations in Cycle 24 that has been achieved thanks to the Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI) instruments onboard the Solar Terrestrial Relations Observatory (STEREO), we observe these events throughout the heliosphere from the Sun to the Earth, and we can relate these in situ signatures to remote sensing data. This allows us to completely track the event back to the source of the eruption in the low corona. We present a summary of the Earth-affecting CMEs in Solar Cycle 24 and a statistical study of the properties of these events including the source region. We examine the characteristics of CMEs that are more likely to be strongly geoeffective and examine the effect of the flare strength on in situ properties. We find that Earth-affecting CMEs in the first half of Cycle 24 are more likely to come from the northern hemisphere, but after April 2012, this reverses, and these events are more likely to originate in the southern hemisphere, following the observed magnetic asymmetry in the two hemispheres. We also find that as in past solar cycles, CMEs from the western hemisphere are more likely to reach Earth. We find that Cycle 24 lacks in events driving extreme geomagnetic storms compared to past solar cycles.     

PARTICLE ACCELERATION IN GEOSPACE AND ITS ASSOCIATION WITH SOLAR EVENTS

Particle acceleration is a prominent feature of the geomagnetic storm, which is the prime dynamic process in Geospace – the near-Earth space environment. Magnetic storms have their origin in solar events, which are transient disturbances of the solar atmosphere and radiation that propagates as variations of the solar wind fields and particles through interplanetary space to the Earth's orbit. During magnetic storms, ions of both solar wind origin and terrestrial origin are accelerated and form an energetic ring current in the inner magnetosphere. This current has global geomagnetic effects, which have both physical and technical implications. Recently, it has been shown that large magnetic storms, which exhibit an unusually energized ionospheric plasma component, are closely associated with coronal mass ejections (CMEs). This implies a cause/effect chain connecting solar events through CMEs and the solar wind with the acceleration of terrestrial ion populations which eventually constitute the main source of global geomagnetic disturbances. Here we present spacecraft observations related to storm-time particle acceleration and assess the observations within the framework of causes and effects of solar-terrestrial relationships.     

The 2015 Summer Solstice Storm: One of the Major Geomagnetic Storms of Solar Cycle 24 Observed at Ground Level

We report on the 22?–?23 June 2015 geomagnetic storm that occurred at the summer solstice. There have been fewer intense geomagnetic storms during the current solar cycle, Solar Cycle 24, than in the previous cycle. This situation changed after mid-June 2015, when one of the largest solar active regions (AR 12371) of Solar Cycle 24 that was located close to the central meridian, produced several coronal mass ejections (CMEs) associated with M-class flares. The impact of these CMEs on the Earth’s magnetosphere resulted in a moderate to severe G4-class geomagnetic storm on 22?–?23 June 2015 and a G2 (moderate) geomagnetic storm on 24 June. The G4 solstice storm was the second largest (so far) geomagnetic storm of Cycle 24. We highlight the ground-level observations made with the New-Tupi, Muonca, and the CARPET El Leoncito cosmic-ray detectors that are located within the South Atlantic Anomaly (SAA) region. These observations are studied in correlation with data obtained by space-borne detectors (ACE, GOES, SDO, and SOHO) and other ground-based experiments. The CME designations are taken from the Computer Aided CME Tracking (CACTus) automated catalog. As expected, Forbush decreases (FD) associated with the passing CMEs were recorded by these detectors. We note a peculiar feature linked to a severe geomagnetic storm event. The 21 June 2015 CME 0091 (CACTus CME catalog number) was likely associated with the 22 June summer solstice FD event. The angular width of CME 0091 was very narrow and measured \({\sim}\, 56^{\circ }\) degrees seen from Earth. In most cases, only CME halos and partial halos lead to severe geomagnetic storms. We perform a cross-check analysis of the FD events detected during the rise phase of Solar Cycle 24, the geomagnetic parameters, and the CACTus CME catalog. Our study suggests that narrow angular-width CMEs that erupt in a westward direction from the Sun–Earth line can lead to moderate and severe geomagnetic storms. We also report on the strong solar proton radiation storm that began on 21 June. We did not find a signal from this SEP at ground level. The details of these observations are presented.     

Solar Sources of Interplanetary Coronal Mass Ejections During the Solar Cycle 23/24 Minimum

We examine solar sources for 20 interplanetary coronal mass ejections (ICMEs) observed in 2009 in the near-Earth solar wind. We performed a detailed analysis of coronagraph and extreme ultraviolet (EUV) observations from the Solar Terrestrial Relations Observatory (STEREO) and Solar and Heliospheric Observatory (SOHO). Our study shows that the coronagraph observations from viewpoints away from the Sun–Earth line are paramount to locate the solar sources of Earth-bound ICMEs during solar minimum. SOHO/LASCO detected only six CMEs in our sample, and only one of these CMEs was wider than 120^°. This demonstrates that observing a full or partial halo CME is not necessary to observe the ICME arrival. Although the two STEREO spacecraft had the best possible configuration for observing Earth-bound CMEs in 2009, we failed to find the associated CME for four ICMEs, and identifying the correct CME was not straightforward even for some clear ICMEs. Ten out of 16 (63 %) of the associated CMEs in our study were “stealth” CMEs, i.e. no obvious EUV on-disk activity was associated with them. Most of our stealth CMEs also lacked on-limb EUV signatures. We found that stealth CMEs generally lack the leading bright front in coronagraph images. This is in accordance with previous studies that argued that stealth CMEs form more slowly and at higher coronal altitudes than non-stealth CMEs. We suggest that at solar minimum the slow-rising CMEs do not draw enough coronal plasma around them. These CMEs are hence difficult to discern in the coronagraphic data, even when viewed close to the plane of the sky. The weak ICMEs in our study were related to both intrinsically narrow CMEs and the non-central encounters of larger CMEs. We also demonstrate that narrow CMEs (angular widths ≤?20^°) can arrive at Earth and that an unstructured CME may result in a flux rope-type ICME.     

A Major Geoeffective CME from NOAA 12371: Initiation,CME–CME Interactions,and Interplanetary Consequences

In this article, we present a multi-wavelength and multi-instrument investigation of a halo coronal mass ejection (CME) from active region NOAA 12371 on 21 June 2015 that led to a major geomagnetic storm of minimum \(\mathrm{Dst} = -204\) nT. The observations from the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory in the hot EUV channel of 94 Å confirm the CME to be associated with a coronal sigmoid that displayed an intense emission (\(T \sim6\) MK) from its core before the onset of the eruption. Multi-wavelength observations of the source active region suggest tether-cutting reconnection to be the primary triggering mechanism of the flux rope eruption. Interestingly, the flux rope eruption exhibited a two-phase evolution during which the “standard” large-scale flare reconnection process originated two composite M-class flares. The eruption of the flux rope is followed by the coronagraphic observation of a fast, halo CME with linear projected speed of 1366 km?s^?1. The dynamic radio spectrum in the decameter-hectometer frequency range reveals multiple continuum-like enhancements in type II radio emission which imply the interaction of the CME with other preceding slow speed CMEs in the corona within \(\approx10\)?–?\(90~\mbox{R} _{\odot}\). The scenario of CME–CME interaction in the corona and interplanetary medium is further confirmed by the height–time plots of the CMEs occurring during 19?–?21 June. In situ measurements of solar wind magnetic field and plasma parameters at 1 AU exhibit two distinct magnetic clouds, separated by a magnetic hole. Synthesis of near-Sun observations, interplanetary radio emissions, and in situ measurements at 1 AU reveal complex processes of CME–CME interactions right from the source active region to the corona and interplanetary medium that have played a crucial role towards the large enhancement of the geoeffectiveness of the halo CME on 21 June 2015.     

High Speed Stream Properties and Related Geomagnetic Activity During the Whole Heliosphere Interval (WHI): 20 March to 16 April 2008

We study the interplanetary features and concomitant geomagnetic activity of the two high-speed streams (HSSs) selected by the Whole Heliosphere Interval (WHI) campaign participants: 20 March to 16 April 2008 in Carrington rotation (CR) 2068. This interval was chosen to perform a comprehensive study of HSSs and their geoeffectiveness during this ??deep?? solar minimum. The two HSSs within the interval were characterized by fast solar-wind speeds (peak values >?600 km?s^?1) containing large-amplitude Alfvénic fluctuations, as is typical of HSSs during normal solar minima. However, the interplanetary magnetic field (IMF) magnitude [B _o] was exceptionally low (??3??C?5 nT) during these HSSs, leading to lower than usual IMF B _z values. The first HSS (HSS1) had favorable IMF polarity for geomagnetic activity (negative during northern Spring). The average AE and Dst for the HSS1 proper (HSS1P) were +?258 nT and ??21 nT, respectively. The second HSS (HSS2) had a positive sector IMF polarity, one that is less favorable for geomagnetic activity. The AE and Dst index averages were +?188 nT and ??7 nT, both lower than corresponding numbers for the first event, as expected. The HSS1P geomagnetic activity is comparable to, and the HSS2P geomagnetic activity lower than, corresponding observations for the previous minimum (1996). Both events?? geomagnetic activities are lower than HSS events previously studied in the declining phase (in 2003). In general, V _sw was faster for the HSSs in 2008 compared to 1996. The southward IMF B _z was lower in the former. The product of these two parameters [V _sw and IMF B _z ] comprises the solar-wind electric field, which is most directly associated with the energy input into the magnetosphere during the HSS intervals. Thus the combined effects led to the solar wind energy input in 2008 being slightly less than that in 1996. A detailed analysis of magnetic-field variances and Alfvénicity is performed to explore the characteristics of Alfvén waves (a central element in the geoeffectiveness of HSSs) during the WHI. The B _z variances in the proto-CIR (PCIR) were ???30 nT² and <?10 nT² in the high speed streams proper.     

A Simultaneous Forbush Decrease Associated with an Earthward Coronal Mass Ejection Observed by STEREO

The intensity?Ctime profile of Forbush decrease (FD) events observed by neutron monitors (NMs) looks like that of a geomagnetic storm as defined by the Dst index. Oh, Yi, and Kim (J.?Geophys. Res. 113, A01103, 2008) and Oh and Yi (J.?Geophys. Res. 114, A11102, 2009) classified FD events based on the amount of overlap and simultaneity of their main phase in Universal Time (UT). Oh and Yi define an FD event as simultaneous if the main phases observed by NMs distributed evenly around the Earth overlap in UT, and nonsimultaneous if they overlap only in the local time of some stations. They suggested that the occurrence mechanisms of two types of FD events may be related to interplanetary (IP) magnetic structures such as IP shocks and magnetic clouds. In their model, the simultaneity of FD events depends on the strength and propagation direction of magnetic structures overtaking the Earth. Recently, the Solar Terrestrial Relations Observatory (STEREO) mission has been able to visualize the emergence and propagation direction of coronal mass ejections (CMEs) in three dimensions in the heliosphere; thus, it is now possible to test the suggested mechanisms. One simultaneous FD event observed on 18 February 2011 may have been caused by a CME heading directly toward the Earth, which was observed on 15 February 2011 by the STEREO mission. Therefore, the simultaneity of FD events is proven to be a useful analysis tool in understanding the geoeffectiveness of solar events such as interplanetary CMEs and IP shocks.     

Analysis of the Properties of Super Solar Proton Events and Associated Phenomena

The solar flares, the speeds of shocks propagated in the solar-terrestrial space and driven by coronal mass ejections (CMEs), the heliographic longitudes and Carrington longitudes of source regions, and the geomagnetic storms, which are accompanied by the super solar proton events with a peak ?ux equal to or exceeding 10 000 pfu, have been studied by using the data of ground-based and space observations. The results show that the heliographic longitudes of source regions of super solar proton events distributed in the range from E30? to W75°. The Carrington longitudes of source regions of super solar proton events distributed in the two longitudinal belts, 130°∼220° and 260°∼320°, respectively. All super solar proton events were accompanied by major solar flares and fast CMEs. The averaged speeds of shocks propagated from the sun to the Earth were greater than 1 200 km/s. Eight super solar proton events were followed by major geomagnetic storms (Dst≤−100 nT), except that one super solar proton event was followed by a geomagnetic storm with the geomagnetic activity index Dst=−96 nT, a little smaller than that of major geomagnetic storms.     

Solar activity during first six years of solar cycle 24 and 23: a comparative study

Attempt to look into the nature of solar activity and variability have increased importance in recent days because of their terrestrial relationships. In the present work we have attempted to compare the solar activity events during first six years (2008–2013) of the ongoing solar cycle 24 with first six years (1996–2001) of solar cycle 23. To that end, we have considered sunspot numbers, F10.7 cm solar flux, halo CMEs and geomagnetic storms as comparison parameters. Sunspot number during the year 2008–2013 varied from 0 to 96.7 while during the year 1996 to 2001 it was observed from 0.9 to 170.1. Solar radio flux (F10.7 cm index) varied from 65 to 190 during the years 2008–2013 while it was observed from 65 to 283 during the years 1996–2001. 197 cases of halo CMEs (width=360^°) in solar cycle 23 (1996–2001) and 177 cases of halo CMEs (width=360^°) in solar cycle 24 (2008–2013) are investigated. 287 and 104 geomagnetic storm cases (Dst varies between ?50 and ?350 nT) are analysed during the half period of solar cycle 23 and 24 respectively. Comparative results indicate that solar cycle 23 was more pronounced in comparison of solar cycle 24.     

Correction to: Solar Temperature Variations Computed from SORCE SIM Irradiances Observed During 2003 – 2020

Forbush decreases (FDs) are sharp reductions of the cosmic-ray (CR) intensity, following intense solar activity such as coronal mass ejections (CMEs) and their corresponding interplanetary shocks. In some cases, shocks create sudden storm commencements (SSCs) at the Earth’s magnetosphere with significant interest for space-weather studies. Preincreases and/or predecreases of CR intensity before the onset of FDs, known as precursory signals, have been widely examined by many authors. In this work, an attempt to define precursory signals that are not related to SSCs is presented. For the present analysis, CR data recorded by the ground-based Neutron Monitor Network as well as data on solar flares, CMEs, solar-wind speed, interplanetary magnetic field, and geomagnetic indices for the years 1969?–?2019 are used. To identify FDs that present precursors, the adopted criteria are mainly the FD amplitude (> 2%) and the equatorial CR anisotropy before the onset time (> 0.8%). The analysis of FDs and the study of their asymptotic-longitude CR distribution for precursors are based on the Global Survey Method and the Ring of Stations Method, respectively. Precursory signals are identified in 17 out of 27 events without SSCs.

     

Propagation Characteristics of CMEs Associated with Magnetic Clouds and Ejecta

We have investigated the characteristics of magnetic cloud (MC) and ejecta (EJ) associated coronal mass ejections (CMEs) based on the assumption that all CMEs have a flux rope structure. For this, we used 54 CMEs and their interplanetary counterparts (interplanetary CMEs: ICMEs) that constitute the list of events used by the NASA/LWS Coordinated Data Analysis Workshop (CDAW) on CME flux ropes. We considered the location, angular width, and speed as well as the direction parameter, D. The direction parameter quantifies the degree of asymmetry of the CME shape in coronagraph images, and shows how closely the CME propagation is directed to Earth. For the 54 CDAW events, we found the following properties of the CMEs: i) the average value of D for the 23 MCs (0.62) is larger than that for the 31 EJs (0.49), which indicates that the MC-associated CMEs propagate more directly toward the Earth than the EJ-associated CMEs; ii) comparison between the direction parameter and the source location shows that the majority of the MC-associated CMEs are ejected along the radial direction, while many of the EJ-associated CMEs are ejected non-radially; iii) the mean speed of MC-associated CMEs (946 km?s^?1) is faster than that of EJ-associated CMEs (771 km?s^?1). For seven very fast CMEs (≥?1500 km?s^?1), all CMEs with large D (≥?0.4) are associated with MCs and the CMEs with small D are associated with EJs. From the statistical analysis of CME parameters, we found the superiority of the direction parameter. Based on these results, we suggest that the CME trajectory essentially determines the observed ICME structure.     

Coronal Mass Ejections and Non-recurrent Forbush Decreases

Coronal mass ejections (CMEs) and their interplanetary counterparts (interplanetary coronal mass ejections, ICMEs) are responsible for large solar energetic particle events and severe geomagnetic storms. They can modulate the intensity of Galactic cosmic rays, resulting in non-recurrent Forbush decreases (FDs). We investigate the connection between CME manifestations and FDs. We used specially processed data from the worldwide neutron monitor network to pinpoint the characteristics of the recorded FDs together with CME-related data from the detailed online catalog based upon the Solar and Heliospheric Observatory (SOHO)/Large Angle and Spectrometric Coronagraph (LASCO) data. We report on the correlations of the FD magnitude to the CME initial speed, the ICME transit speed, and the maximum solar wind speed. Comparisons between the features of CMEs (mass, width, velocity) and the characteristics of FDs are also discussed. FD features for halo, partial halo, and non-halo CMEs are presented and discussed.     

On Fields and Mass Constraints for the Uniform Propagation of Magnetic-Flux Ropes Undergoing Isotropic Expansion

An analytical 3-D magnetohydrodynamic (MHD) solution of a magnetic-flux rope (FR) is presented. This FR solution may explain the uniform propagation, beyond ～?0.05 AU, of coronal mass ejections (CMEs) commonly observed by today’s missions like The Solar Mass Ejection Imager (SMEI), Solar and Heliospheric Observatory (SOHO) and Solar Terrestrial Relations Observatory (STEREO), tracked to tens of times the radius of the Sun, and in some cases up to 1 AU, and/or beyond. Once a CME occurs, we present arguments regarding its evolution based on its mass and linear momentum conservation. Here, we require that the gravitational and magnetic forces balance each other in the framework of the MHD theory for a simple model of the evolution of a CME, assuming it interacts weakly with the steady solar wind. When satisfying these ansätze we identify a relation between the transported mechanical mass of the interplanetary CME with its geometrical parameters and the intensity of the magnetic field carried by the structure. In this way we are able to estimate the mass of the interplanetary CME (ICME) for a list of cases, from the Wind mission records of ICME encountered near Earth, at 1 AU. We obtain a range for masses of ～?10⁹ to 10¹³ kg, or assuming a uniform distribution, of ～?0.5 to 500 cm^?3 for the hadron density of these structures, a result that appears to be consistent with observations.     

Three-Dimensional Evolution of Erupted Flux Ropes from the Sun (2 – 20 R ⊙) to 1 AU

Studying the evolution of magnetic clouds entrained in coronal mass ejections using in-situ data is a difficult task, since only a limited number of observational points is available at large heliocentric distances. Remote sensing observations can, however, provide important information for events close to the Sun. In this work we estimate the flux rope orientation first in the close vicinity of the Sun (2?–?20 R _⊙) using forward modeling of STEREO/SECCHI and SOHO/LASCO coronagraph images of coronal mass ejections and then in situ using Grad–Shafranov reconstruction of the magnetic cloud. Thus, we are able to measure changes in the orientation of the erupted flux ropes as they propagate from the Sun to 1 AU. We present both techniques and use them to study 15 magnetic clouds observed during the minimum following Solar Cycle 23 and the rise of Solar Cycle 24. This is the first multievent study to compare the three-dimensional parameters of CMEs from imaging and in-situ reconstructions. The results of our analysis confirm earlier studies showing that the flux ropes tend to deflect towards the solar equatorial plane. We also find evidence of rotation on their travel from the Sun to 1 AU. In contrast to past studies, our method allows one to deduce the evolution of the three-dimensional orientation of individual flux ropes rather than on a statistical basis.     

On the Origin, 3D Structure and Dynamic Evolution of CMEs Near Solar Minimum

We have conducted a statistical study 27 coronal mass ejections (CMEs) from January 2007 – June 2008, using the stereoscopic views of STEREO SECCHI A and B combined with SOHO LASCO observations. A flux-rope model, in conjunction with 3D triangulations, has been used to reconstruct the 3D structures and determine the actual speeds of CMEs. The origin and the dynamic evolution of the CMEs are investigated using COR1, COR2 and EUVI images. We have identified four types of solar surface activities associated with CMEs: i) total eruptive prominence (totEP), ii) partially eruptive prominence (PEP), iii) X-ray flare, and iv) X-type magnetic structure (X-line). Among the 27 CMEs, 18.5% (5 of 27) are associated with totEPs, 29.6% (8 of 27) are associated with PEPs, 26% (7 of 27) are flare related, and 26% (7 of 27) are associated with X-line structures, and 43% (3 of 7) are associated with both X-line structures and PEPs. Three (11%) could not be associated with any detectable activity. The mean actual speeds for totEP-CMEs, PEP-CMEs, flare-CMEs, and X-line-CMEs are 404 km?s^?1,247 km?s^?1,909 km?s^?1, and 276 km?s^?1, respectively; the average mean values of edge-on and broadside widths for the 27 CMEs are 52 and 85 degrees, respectively. We found that slow CMEs (V≤400 km?s^?1) tend to deflect towards and propagate along the streamer belts due to the deflections by the strong polar magnetic fields of corona holes, while some faster CMEs show opposite deflections away from the streamer belts.