Solar Mass Ejection Research Articles

Study of CME Propagation in the Inner Heliosphere: SOHO LASCO, SMEI and STEREO HI Observations of the January 2007 Events

We are investigating the geometric and kinematic characteristics of interplanetary coronal mass ejections (ICMEs) using data obtained by the LASCO coronagraphs, the Solar Mass Ejection Imager (SMEI), and the SECCHI imaging experiments on the STEREO spacecraft. The early evolution of CMEs can be tracked by the LASCO C2 and C3 and SECCHI COR1 and COR2 coronagraphs, and the HI and SMEI instruments can track their ICME counterparts through the inner heliosphere. The HI fields of view (4 – 90°) overlap with the SMEI field of view (> 20° to all sky) and, thus, both instrument sets can observe the same ICME. In this paper we present results for ICMEs observed on 24 – 29 January 2007, when the STEREO spacecraft were still near Earth so that both the SMEI and STEREO views of large ICMEs in the inner heliosphere coincided. These results include measurements of the structural and kinematic evolution of two ICMEs and comparisons with drive/drag kinematic, 3D tomographic reconstruction, the HAFv2 kinematic, and the ENLIL MHD models. We find it encouraging that the four model runs generally were in agreement on both the kinematic evolution and appearance of the events. Because it is essential to understand the effects of projection across large distances, that are not generally crucial for events observed closer to the Sun, we discuss our analysis procedure in some detail.

SMEI observations of previously unseen pulsation frequencies in $\sf \gamma$ Doradus

Aims. As g-mode pulsators, gamma-Doradus-class stars may naively be expected to show a large number of modes. Taking advantage of the long photometric time-series generated by the solar mass ejection imager (SMEI) instrument, we have studied the star gamma Doradus to determine whether any other modes than the three already known are present at observable amplitude. Methods. High-precision photometric data from SMEI taken between April 2003 and March 2006 were subjected to periodogram analysis with the PERIOD04 package. Results. We confidently determine three additional frequencies at 1.39, 1.87, and 2.743 d -1 . These are above and beyond the known frequencies of 1.320, 1.364, and 1.47 d -1 . Conclusions. Two of the new frequencies, at 1.39 and 1.87 d -1 , are speculated to be additional modes of oscillation, with the third frequency at 2.743 -1 a possible combination frequency.

Interplanetary coronal mass ejections that are undetected by solar coronagraphs

From February 2003 to September 2005 the Solar Mass Ejection Imager on the Coriolis spacecraft detected 207 interplanetary coronal mass ejections (ICME) in the inner heliosphere. We have examined the data from the Large Angle Spectroscopic Coronagraph (LASCO) on the SOHO spacecraft for evidence of coronal transient activity that might have been the solar progenitor of the Solar Mass Ejection Imager (SMEI) events, taking into account the projected speed of the SMEI event and its position angle in the plane of the sky. We found a significant number of SMEI events where there is either only a weak or unlikely coronal mass ejection (CME) detected by LASCO or no event at all. A discussion of the effects of projection across large distances on the ICME measurements is made, along with a new technique called the Cube‐Fit procedure that was designed to model the ICME trajectory more accurately than simple linear fits to elongation‐time plots. Of the 207 SMEI events, 189 occurred during periods of full LASCO data coverage. Of these, 32 or 17% were found to have a weak or unlikely LASCO counterpart, and 14 or 7% had no apparent LASCO transient association. Using solar X‐ray, EUV and Hα data we investigated three main physical possibilities for ICME occurrence with no LASCO counterpart: (1) Corotating interaction regions (CIRs), (2) erupting magnetic structures (EMS), and (3) flare blast waves. We find that only one event may possibly be a CIR and that flare blast waves can be ruled out. The most likely phenomenon is investigated and discussed, that of EMS. Here, the transient erupts in the same manner as a typical CME, except that they do not have sufficient mass to be detected by LASCO. As the structure moves outward, it accumulates and concentrates solar wind material until it is bright enough to be detected by SMEI.

The period and amplitude changes of Polaris ( UMi) from 2003 to 2007 measured with SMEI

We present an analysis of 4.5 years of high precision (0.1%) space-based photometric measurements of the Cepheid variable Polaris, obtained by the broad band Solar Mass Ejection Imager (SMEI) instrument on board the Coriolis satellite. The data span from April 2003 to October 2007, with a cadence of 101 minutes and a fill factor of 70%. We have measured the mean peak to peak amplitude across the whole set of observations to be 25 mmag. There is, however, a clear trend that the size of the oscillations has been increasing during the observations, with peak to peak variations less than 22 mmag in early 2003, increasing to around 28 mmag by October 2007, suggesting that the peak to peak amplitude is increasing at a rate of 1.39± 0.12 mmag yr 1 . Additionally, we have combined our new measurements with archival measurements to measure a rate of period change of 4.90±0.26 s yr 1 over the last 50 years. However, there is some suggestion that the period of Polaris has undergone a recent decline, and combined with the increased amplitude, this could imply evolution away from an overtone pulsation mode into the fundamental or a double pulsation mode depending on the precise mass of Polaris.

Analysis of Plasma‐Tail Motions for Comets C/2001 Q4 (NEAT) and C/2002 T7 (LINEAR) Using Observations from SMEI

Comets C/2001 Q4 (NEAT) and C/2002 T7 (LINEAR) passed within � 0.3 AU of Earth in April and May of 2004. Their tails were observed by the Earth-orbiting Solar Mass Ejection Imager (SMEI) during this period. A time series of photometric SMEI sky maps displays the motions and frequent disruptions of the comet plasma tails. Ephemerides are used to unfold the observing geometry; the tails are often seen to extend � 0.5 AU from the comet nuclei. Having selected 12 of the more prominent motions as ‘‘events’’ for further study, we introduce a new method for determining solar wind radial velocities from these SMEI observations. We find little correlation between these and the changing solar wind parameters as measured close to Earth, or with coarse three-dimensional reconstructions using interplanetary scintillation data. A likely explanation is that the transverse sizes of the solar wind perturbations responsible for these disruptions are small, P0.05 AU. We determine the radial velocities of these events during the disruptions,usingatechniqueonlypossiblewhentheobservedcomettailsextendoverasignificantfractionof anAU. We find typical radial velocities during these events of 50Y100 km s � 1 lower than before or afterward. Time durations of such events vary, typically from 3 to 8 hr, and correspond to comet traversal distances � 10 6 km (0.007 AU). We conclude that these large disturbances are primarily due to ubiquitous solar wind flow variations, of which these measured events are a subset. Subject headingg comets: individual (C/2001 Q4 (NEAT), C/2002 T7 (LINEAR), C/2004 F4 (Bradfield)) — solar wind — Sun: coronal mass ejections (CMEs)

Observations of a comet tail disruption induced by the passage of a CME

The Solar Mass Ejection Imager observed an extremely faint interplanetary coronal mass ejection (ICME) as it passed Comet C/2001 Q4 (NEAT) on 5 May 2004, apparently causing a disruption of its plasma tail. This is the first time that an ICME has been directly observed interacting with a comet. SMEI's nearly all‐sky coverage and image cadence afforded unprecedented coverage of this rarely observed event. The onset first appeared as a “kink” moving antisunward that eventually developed knots within the disturbed tail. These knots appeared to be swept up in the solar wind flow. We present the SMEI observations as well as identify a likely SOHO/LASCO progenitor of the CME. SMEI observed two other comets (C/2002 T7 [LINEAR] and C/2004 F4 [Bradfield]) and at least five similar events during a 35‐d period encompassing this observation. Although these had similar morphologies to the 5 May NEAT event, SMEI did not observe any ICMEs in these cases. Three of these were observed close to the heliospheric current sheet indicating that a magnetic boundary crossing may have contributed to the disruptions. However, there are no discernable causes in the SMEI observations for the remaining two events.

Three‐dimensional reconstructions of the early November 2004 Coordinated Data Analysis Workshop geomagnetic storms: Analyses of STELab IPS speed and SMEI density data

Combined interplanetary scintillation (IPS) and Solar Mass Ejection Imager (SMEI) remote‐sensing observations provide a view of the solar wind at almost all heliographic latitudes and covering distances from the Sun between 0.1 AU and 3.0 AU. They are used to study the development of the solar wind and coronal transients as they move out into interplanetary space, and also the inner heliospheric response to the passage of corotating solar structures and coronal mass ejections (CMEs). The observations take place in both radio scintillation level and speed for IPS, and in Thomson‐scattered white light brightness for SMEI. With colleagues at the Solar Terrestrial Environment Laboratory (STELab), Nagoya University, Japan, we have developed a data analysis system for the STELab IPS data which can also be applied to SMEI white light data. This employs a three‐dimensional (3‐D) reconstruction technique that obtains perspective views from solar corotating plasma and outward flowing solar wind as observed from the Earth by iterative fitting of a kinematic solar wind model to the data. This 3‐D modeling technique permits reconstructions of the density and speed of CMEs and other interplanetary transients at relatively coarse spatial and temporal resolutions. For the time‐dependent model (used here), these typically range from 5° to 20° in latitude and longitude, with a 1/2 to 1 day time cadence. For events during early November 2004 we compare these reconstructed structures with in situ measurements from the ACE and Wind (near‐Earth) spacecraft to validate the 3‐D tomographic reconstruction results and provide input to the ENLIL 3‐D magnetohydrodynamic (MHD) numerical model.

Simulated Solar Mass Ejection Imager and “Solar Terrestrial Relations Observatory‐like” views of the solar wind following the solar flares of 27–29 May 2003

The three‐dimensional Hakamada‐Akasofu‐Fry (HAFv.2) kinematic solar wind model can be extended to predict what the Solar Terrestrial Relations Observatory (STEREO) spacecraft might expect in observing large‐scale plasma clouds ejected from the Sun. In order to demonstrate this capability, the HAFv.2 model was used to simulate the first observations of a halo coronal mass ejection (CME) from the Solar Mass Ejection Imager (SMEI) instrument on the Coriolis spacecraft, acquired after the solar events of 27–29 May 2003. Projections of the Thomson‐scattered white light intensity on the plane of sky, as observed by the SMEI cameras, were calculated from the three‐dimensional simulations. These simulations of the background solar wind and two shock fronts compare favorably with the white light observations of plasma clouds by the SMEI instrument. The method thus developed is then applied to hypothetical locations of the STEREO spacecraft in a later phase of the STEREO mission. It is shown that the model can be a valuable aid and guide in the identification of multiple shock‐induced variations of the solar wind.

Solar Mass Ejection Imager 3‐D reconstruction of the 27–28 May 2003 coronal mass ejection sequence

The Solar Mass Ejection Imager (SMEI) has recorded the inner‐heliospheric response in white‐light Thomson scattering for many hundreds of interplanetary coronal mass ejections (ICMEs). Some of these have been observed by the Solar and Heliospheric Observatory (SOHO) Large‐Angle Spectroscopic Coronagraph (LASCO) instruments and also in situ by near‐Earth spacecraft. This article presents a low‐resolution three‐dimensional (3‐D) reconstruction of the 27–28 May 2003 halo CME event sequence observed by LASCO and later using SMEI observations; this sequence was also observed by all in situ monitors near Earth. The reconstruction derives its perspective views from outward flowing solar wind. Analysis results reveal the shape, extent, and mass of this ICME sequence as it reaches the vicinity of Earth. The extended shape has considerable detail that is compared with LASCO images and masses for this event. The 3‐D reconstructed density, derived from the remote‐sensed Thomson scattered brightness, is also compared with the Advanced Composition Explorer (ACE) and Wind spacecraft in situ plasma measurements. These agree well in peak and integrated total value for this ICME event sequence when an appropriately enhanced (∼20%) electron number density is assumed to account for elements heavier than hydrogen in the ionized plasma.

Comparison of the extent and mass of CME events in the interplanetary medium using IPS and SMEI Thomson scattering observations

The Solar-Terrestrial Environment Laboratory (STELab), Japan, interplanetary scintillation (IPS) g-level and velocity measurements can be used to give the extent of CME disturbances in the interplanetary medium arising from the scattering of the radio waves from distant point-like natural sources through the intervening medium. In addition, white-light Thomson-scattering observations from the Solar Mass Ejection Imager (SMEI) have recorded the inner heliospheric response to several hundred CMEs. The work described here compares and details the difference in three-dimensional (3D) reconstructions for these two data sets for the well-observed 28 October 2003 halo CME seen in LASCO; this passed Earth on 29 October in the SMEI data at the same elongations as IPS g-level observations. The SMEI data analysis employs a 3D tomographic reconstruction technique that obtains perspective views from outward-flowing solar wind as observed from Earth, iteratively fitting a kinematic solar wind density model, and when av...

Asteroseismology of red giants: photometric observations of Arcturus by SMEI

Abstract We present new results on oscillations of the K1.5 III giant Arcturus (α Boo), from analysis of just over 2.5 yr of precise photometric observations made by the Solar Mass Ejection Imager on board the Coriolis satellite. A strong mode of oscillation is uncovered by the analysis, having frequency 3.51 ± 0.03 μHz. By fitting its mode peak, we are able to offer a highly constrained direct estimate of the damping time (τ= 24 ± 1 d). The data also hint at the possible presence of several radial-mode overtones, and maybe some non-radial modes. We are also able to measure the properties of the granulation on the star, with the characteristic time-scale for the granulation estimated to be ∼0.50 ± 0.05 d.

V arc interplanetary coronal mass ejections observed with the Solar Mass Ejection Imager

Since February 2003, the Solar Mass Ejection Imager (SMEI) has been observing interplanetary coronal mass ejections (ICMEs) at solar elongation angles ε > 20°. The ICMEs generally appear as loops or arcs in the sky, but five show distinct outward concave shapes that we call V arcs. We expect to observe some V arcs, formed by trailing edges of ICME flux ropes or by leading ICME edges sheared by solar wind (SW) speed gradients at the heliospheric current sheet. We characterize the properties of these V arcs and compare them with average properties of all SMEI ICMEs. The typical V arc speeds argue against a slow MHD shock interpretation for their structures. We estimate the V arc solar source locations and their opening angle dynamics as tests for SW shearing. The first test contradicts but the second supports the SW shearing explanation. The implications of the small number of V arcs observed with SMEI is considered. The point P approximation used to determine the V arc locations and inferred solar source regions is critically examined in Appendix A.

Extraction of Halo Coronal Mass Ejection Asymmetry Information from LASCO Coronagraph Images

A method for quantifying the asymmetry attributes of coronal mass ejections (CMEs) is described. The technique developed is applied to a set of full-halo CMEs observed from 1997 to the end of 2000 by the Large Angle Spectrometric Coronagraph (LASCO) instrument on board the Solar and Heliospheric Observatory (SOHO) spacecraft. A cross section of events is examined, with the progression of asymmetry characteristics as the ejecta proceeds outward illustrated for a symmetrical full-halo CME, an asymmetrical full-halo CME, and multiple CMEs. A control sample for a day with minimal solar activity is presented for comparison. A qualitative evaluation of the results with visual inspection of the coronagraph data is discussed. Relationships between the asymmetry parameters derived from the data are examined, and good correlations are found among the asymmetry magnitudes, the average sector pixel intensities, and the frontal CME speeds. This computerized method can also be designed to automatically detect and measure the asymmetry and relative brightness of any CME. We compare the results with storms at Earth to demonstrate that the calculated asymmetry magnitude by itself indicates the geoeffectiveness of a CME, with any associated solar surface activity helping to determine whether the CME is aimed Earthward or not. Thus, this test suggests that our technique is useful as a forecast tool for space weather applications. With modifications, the algorithm is applicable to analyses of the data returned from the Solar Mass Ejection Imager (SMEI) aboard the Coriolis spacecraft and the Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI) coronagraph and heliospheric imagers aboard the two Solar Terrestrial Relations Observatory (STEREO) spacecraft.

Solar Mass Ejection Imager (SMEI) observations of coronal mass ejections (CMEs) in the heliosphere

The Solar Mass Ejection Imager (SMEI) on the Coriolis spacecraft has been obtaining white light images of nearly the full sky every 102 minutes for three years. We present statistical results of analysis of the SMEI observations of coronal mass ejections (CMEs) traveling through the inner heliosphere; 139 CMEs were observed during the first 1.5 years of operations. At least 30 of these CMEs were observed by SMEI to propagate out to 1 AU and beyond and were associated with major geomagnetic storms at Earth. Most of these were observed as frontside halo events by the SOHO LASCO coronagraphs.

Tracking halo coronal mass ejections from 0–1 AU and space weather forecasting using the Solar Mass Ejection Imager (SMEI)

The Solar Mass Ejection Imager (SMEI) has been tracking coronal mass ejections (CMEs) from the Sun to the Earth and beyond since it came online in February 2003. This paper presents some results from the first 19 months of data from SMEI, when over 140 transients of many kinds were observed in SMEI's all‐sky cameras. We focus specifically on 20 earthward directed transients, and compare distance‐time plots obtained from the SMEI transients with those observed in halo CMEs by Large‐Angle Spectrometric Coronograph (LASCO) aboard Solar and Heliospheric Observatory (SOHO), and the arrival time of the shock observed by ACE at 0.99 AU. The geometry of one particular transient is compared using both LASCO and SMEI images in a first attempt to investigate geometry evolution as the transient propagates through the interplanetary medium. For some events, the halo CME, SMEI transient, and shock at 0.99 AU do not match, suggesting that some transients may not correspond to a halo CME. Finally, an evaluation of the potential of SMEI to be used as a predictor of space weather is presented, by comparing the transients observed in SMEI with the 22 geomagnetic storms which occurred during this timeframe. A transient was observed in 14 cases, and distance‐time profiles would have allowed a prediction of the arrival time at ACE within 2 hours of its actual arrival for three events, and within 10 hours for eight events. Of these eight events, seven were detected by SMEI more than 1 day before the transient's arrival at the Earth.

Preliminary three‐dimensional analysis of the heliospheric response to the 28 October 2003 CME using SMEI white‐light observations

The Solar Mass Ejection Imager (SMEI) has recorded the inner heliospheric response in white‐light Thomson scattering to the 28 October 2003 coronal mass ejection (CME). This preliminary report shows the evolution of this particular event in SMEI observations, as we track it from a first measurement at approximately 20° elongation (angular distance) from the solar disk until it fades in the antisolar hemisphere in the SMEI 180° field of view. The large angle and spectrometric coronagraph (LASCO) images show a CME and an underlying bright ejection of coronal material that is associated with an erupting prominence. Both of these are seen by SMEI in the interplanetary medium. We employ a three‐dimensional (3‐D) reconstruction technique that derives its perspective views from outward flowing solar wind to reveal the shape and extent of the CME. This is accomplished by iteratively fitting the parameters of a kinematic solar wind density model to both SMEI white‐light observations and Solar‐Terrestrial Environment Laboratory (STELab), interplanetary scintillation (IPS) velocity data. This modeling technique separates the true heliospheric signal in SMEI observations from background noise and reconstructs the 3‐D heliospheric structure as a function of time. These reconstructions allow separation of the 28 October CME from other nearby heliospheric structure and a determination of its mass. The present results are the first utilizing this type of 3‐D reconstruction with the SMEI data. We determine an excess‐over‐ambient mass for the southward moving ejecta associated with the prominence material of 7.1 × 1016 g and a total mass of 8.9 × 1016 g. Preliminary SMEI white‐light calibration indicates that the total mass of this CME including possible associated nearby structures may have been as much as ∼2.0 × 1017 g spread over much of the earthward facing hemisphere.

Observations of Coronal Mass Ejections from the Solar Mass Ejection Imager and Space Weather Implications

The Solar Mass Ejection Imager (SMEI) was launched into a Sun-synchronous orbit in January 2003. Its mission objective is to detect and track coronal mass ejections (CMEs) from the Sun in order to improve space weather forecasts. In the three years since launch, over 200 CMEs, about 30 of which were Earth-directed, have been observed by SMEI. We have been able to track several of these CMEs from the SOHO LASCO coronagraphs () out to 0.5 AU and beyond, and to observe the morphology and evolution of distinctive features over this wide distance range. We report on comparisons of measurements of CME parameters made in the inner heliosphere with the more typical measurements made nearer the Sun with coronagraphs. We illustrate SMEI's capabilities and present key statistical results on basic CME parameters and the use of SMEI-type data in space weather forecasting models. For example, timely observations by SMEI of CMEs en route to Earth could be input to DoD's operational Hakamada-Akasofu-Fry solar wind model to correct or refine its real-time forecasts of approaching disturbances.

A Search for Early Optical Emission at Gamma‐Ray Burst Locations by theSolar Mass Ejection Imager(SMEI)

The Solar Mass Ejection Imager (SMEI) views nearly every point on the sky once every 102 minutes and can detect point sources as faint as R~10th magnitude. Therefore, SMEI can detect or provide upper limits for the optical afterglow from gamma-ray bursts in the tens of minutes after the burst when different shocked regions may emit optically. Here we provide upper limits for 58 bursts between 2003 February and 2005 April.

Coronal mass ejection kinematics deduced from white light (Solar Mass Ejection Imager) and radio (Wind/WAVES) observations

White‐light and radio observations are combined to deduce the coronal and interplanetary kinematics of a fast coronal mass ejection (CME) that was ejected from the Sun at about 1700 UT on 2 November 2003. The CME, which was associated with an X8.3 solar flare from W56°, was observed by the Mauna Loa and Solar and Heliospheric Observatory (SOHO) Large‐Angle Spectrometric Coronograph (LASCO) coronagraphs to 14 R⊙. The measured plane‐of‐sky speed of the LASCO CME was 2600 km s−1. To deduce the kinematics of this CME, we use the plane‐of‐sky white light observations from both the Solar Mass Ejection Imager (SMEI) all‐sky camera on board the Coriolis spacecraft and the SOHO/LASCO coronagraph, as well as the frequency drift rate of the low‐frequency radio data and the results of the radio direction‐finding analysis from the WAVES experiment on the Wind spacecraft. In agreement with the in situ observations for this event, we find that both the white light and radio observations indicate that the CME must have decelerated significantly beginning near the Sun and continuing well into the interplanetary medium. More specifically, by requiring self‐consistency of all the available remote and in situ data, together with a simple, but not unreasonable, assumption about the general characteristic of the CME deceleration, we were able to deduce the radial speed and distance time profiles for this CME as it propagated from the Sun to 1 AU. The technique presented here, which is applicable to mutual SMEI/WAVES CME events, is expected to provide a more complete description and better quantitative understanding of how CMEs propagate through interplanetary space, as well as how the radio emissions, generated by propagating CME/shocks, relate to the shock and CME. This understanding can potentially lead to more accurate predictions for the onset times of space weather events, such as those that were observed during this unique period of intense solar activity.

Very high altitude aurora observations with the Solar Mass Ejection Imager

The Solar Mass Ejection Imager (SMEI) is a sensitive scanning instrument mounted on the Coriolis satellite that assembles an approximately all‐sky image of the heliosphere in red‐biased visible light once per orbit. Its lines of sight pass obliquely through the topside ionosphere and magnetosphere. We present serendipitous observations of a visual phenomenon detected at high altitudes (≥840 km) over the auroral zones and polar caps. The phenomenon is observed in two basic forms. The first, and more common, are periods of brief (1–3 min), nearly uniform illumination of the imager's field of view, which we interpret as transits of the satellite through a luminous medium. The second appear as localized filamentary structures, which we interpret as columns of luminous material, viewed from a distance, possibly extending to visible altitudes of 2000 km or higher. More than 1000 occurrences of these phenomena were recorded during the first full year of operations. These observations are well correlated in brightness and frequency with periods of enhanced geomagnetic activity.