Context.
On 2020 April 19 a coronal mass ejection (CME) was detected in situ by Solar Orbiter at a heliocentric distance of about 0.8 AU. The CME was later observed in situ on April 20 by the Wind ...and BepiColombo spacecraft whilst BepiColombo was located very close to Earth. This CME presents a good opportunity for a triple radial alignment study, as the spacecraft were separated by less than 5° in longitude. The source of the CME, which was launched on April 15, was an almost entirely isolated streamer blowout. The Solar Terrestrial Relations Observatory (STEREO)-A spacecraft observed the event remotely from −75.1° longitude, which is an exceptionally well suited viewpoint for heliospheric imaging of an Earth directed CME.
Aims.
The configuration of the four spacecraft has provided an exceptionally clean link between remote imaging and in situ observations of the CME. We have used the in situ observations of the CME at Solar Orbiter, Wind, and BepiColombo and the remote observations of the CME at STEREO-A to determine the global shape of the CME and its evolution as it propagated through the inner heliosphere.
Methods.
We used three magnetic flux rope models that are based on different assumptions about the flux rope morphology to interpret the large-scale structure of the interplanetary CME (ICME). The 3DCORE model assumes an elliptical cross-section with a fixed aspect-ratio calculated by using the STEREO Heliospheric Imager (HI) observations as a constraint. The other two models are variants of the kinematically-distorted flux rope (KFR) technique, where two flux rope cross-sections are considered: one in a uniform solar wind and another in a solar-minimum-like structured solar wind. Analysis of CME evolution has been complemented by the use of (1) the ELEvoHI model to compare predicted CME arrival times and confirm the connection between the imaging and in situ observations, and (2) the PREDSTORM model, which provides an estimate of the
Dst
index at Earth using Solar Orbiter magnetometer data as if it were a real–time upstream solar wind monitor.
Results.
A clear flattening of the CME cross-section has been observed by STEREO-A, and further confirmed by comparing profiles of the flux rope models to the in situ data, where the distorted flux rope cross-section qualitatively agrees most with in situ observations of the magnetic field at Solar Orbiter. Comparing in situ observations of the magnetic field between spacecraft, we find that the dependence of the maximum (mean) magnetic field strength decreases with heliocentric distance as
r
−1.24 ± 0.50
(
r
−1.12 ± 0.14
), which is in disagreement with previous studies. Further assessment of the axial and poloidal magnetic field strength dependencies suggests that the expansion of the CME is likely neither self-similar nor cylindrically symmetric.
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FMFMET, NUK, UL, UM, UPUK
We examined plasma and magnetic field observations from all three Ulysses polar orbits of the Sun to study the properties of the slow and fast solar wind and interplanetary coronal mass ejections ...(ICMEs). We derived equations to characterize the radial and latitudinal variations for these three types of heliospheric plasma and identify distinguishing features in their spatial variations. Most notably, the slow‐wind proton temperature falls less rapidly with distance than does the fast wind, indicating a source of enhanced heating in the low‐speed wind. After removing the radial variations from the measurements, only minor latitudinal gradients were identified. The fast wind has now been shown to be only weakly dependent on solar latitude for two successive solar minima. The spatial variations in the ICME properties do not differ significantly from the slow and fast solar wind, although the variability in their parameters is much larger. We also investigated solar cycle variations in the fast polar coronal hole (PCH) flows by comparing their properties measured over Ulysses' 1st and 3rd orbits. While the latitudinal gradients were similar, slight differences were observed in the radial dependence for the proton density and magnetic field strength. Also, a slight reduction in the proton speed at 1 AU, along with more significant decreases in the proton temperature, density, dynamic pressure, and magnetic field strength, was observed for the 3rd orbit relative to that for the 1st. These results are consistent with recent observations of weaker PCH flows for the current solar minimum.
Interplanetary coronal mass ejections (ICMEs) observed by the MESSENGER and
Venus Express
spacecraft have been catalogued and analysed. The ICMEs were identified by a relatively smooth rotation of ...the magnetic field direction consistent with a flux rope structure, coinciding with a relatively enhanced magnetic field strength. A total of 35 ICMEs were found in the surveyed MESSENGER data (primarily from March 2007 to April 2012), and 84 ICMEs in the surveyed
Venus Express
data (from May 2006 to December 2013). The ICME flux rope configurations have been determined. Ropes with northward leading edges were about four times more common than ropes with southward leading edges, in agreement with a previously established solar cycle dependence. Ropes with low inclinations to the solar equatorial plane were about four times more common than ropes with high inclinations, possibly an observational effect. Left- and right-handed ropes were observed in almost equal numbers. In addition, data from MESSENGER,
Venus Express
, STEREO-A, STEREO-B and ACE were examined for multipoint signatures of the catalogued ICMEs. For spacecraft separations below 15° in heliocentric longitude, the second spacecraft observed the ICME flux rope in 82 % of cases; this percentage dropped to 49 % for separations between 15 and 30°, to 18 % for separations between 30 and 45°, and to 12 % for separations between 45 and 60°. As the spacecraft separation increased, it became increasingly likely that only the sheath and not the flux rope of the ICME was observed, in agreement with the notion that ICME flux ropes are smaller in longitudinal extent than the shocks or discontinuities that they often drive. Furthermore, this study has identified 23 ICMEs observed by pairs of spacecraft close to radial alignment. A detailed analysis of these events could lead to a better understanding of how ICMEs evolve during propagation.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Aims: To describe the epidemiology of children with traumatic brain injury (TBI) admitted to paediatric intensive care units (PICUs) in the UK. Methods: Prospective collection of clinical and ...demographic information from paediatric and adult intensive care units in the UK and Eire between February 2001 and August 2003. Results: The UK prevalence rate for children (0–14 years) admitted to intensive care with TBI between February 2001 and August 2003 was 5.6 per 100 000 population per year (95% Poisson exact confidence intervals 5.17 to 6.05). Children admitted to PICUs with TBI were more deprived than the population as a whole (mean Townsend score for TBI admissions 1.19 v 0). The commonest mechanism of injury was a pedestrian accident (36%), most often occurring in children over 10. There was a significant summer peak in admissions in children under 10 years. Time of injury peaked in the late afternoon and early evening, a pattern that remained constant across the days of the week. Injuries involving motor vehicles have the highest mortality rates (23% of vehicle occupants, 12% of pedestrians) compared with cyclists (8%) and falls (3%). In two thirds of admissions (65%) TBI was an isolated injury. Conclusions: TBI in children requiring intensive care is more common in those from poorer backgrounds who have been involved in accidents as pedestrians. The summer peak in injury occurrence for 0–10 year olds and late afternoon timing give clear targets for community based injury prevention.
Plasma parcels are observed propagating from the Sun out to the large coronal heights monitored by the Heliospheric Imagers (HI) instruments onboard the NASA STEREO spacecraft during September 2007. ...The source region of these out‐flowing parcels is found to corotate with the Sun and to be rooted near the western boundary of an equatorial coronal hole. These plasma enhancements evolve during their propagation through the HI cameras' fields of view and only becoming fully developed in the outer camera field of view. We provide evidence that HI is observing the formation of a Corotating Interaction Region (CIR) where fast solar wind from the equatorial coronal hole is interacting with the slow solar wind of the streamer belt located on the western edge of that coronal hole. A dense plasma parcel is also observed near the footpoint of the observed CIR at a distance less than 0.1AU from the Sun where fast wind would have not had time to catch up slow wind. We suggest that this low‐lying plasma enhancement is a plasma parcel which has been disconnected from a helmet streamer and subsequently becomes embedded inside the corotating interaction region.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
The presence of contrast enhancement in a brain tumor is often regarded as a sign of malignancy. The authors identified 314 patients with malignant and low-grade supratentorial glial neoplasms in an ...unselected population, 58 of which lacked contrast enhancement on preoperative neuroimaging. Nonenhancing gliomas were malignant in approximately one third of cases, especially in older patients. Histologic confirmation of the diagnosis is therefore important in all patients suspected of harboring a primary glial neoplasm.
The magnetic field structures of two interplanetary coronal mass ejections (ICMEs), each observed by a pair of spacecraft close to radial alignment, have been analysed. The ICMEs were observed
in ...situ
by MESSENGER and STEREO-B in November 2010 and November 2011, while the spacecraft were separated by more than 0.6 AU in heliocentric distance, less than 4° in heliographic longitude, and less than 7° in heliographic latitude. Both ICMEs took approximately two days to travel between the spacecraft. The ICME magnetic field profiles observed at MESSENGER have been mapped to the heliocentric distance of STEREO-B and compared directly to the profiles observed by STEREO-B. Figures that result from this mapping allow for easy qualitative assessment of similarity in the profiles. Macroscale features in the profiles that varied on timescales of one hour, and which corresponded to the underlying flux rope structure of the ICMEs, were well correlated in the solar east–west and north–south directed components, with Pearson’s correlation coefficients of approximately 0.85 and 0.95, respectively; microscale features with timescales of one minute were uncorrelated. Overall correlation values in the profiles of one ICME were increased when an apparent change in the flux rope axis direction between the observing spacecraft was taken into account. The high degree of similarity seen in the magnetic field profiles may be interpreted in two ways. If the spacecraft sampled the same region of each ICME (
i.e.
if the spacecraft angular separations are neglected), the similarity indicates that there was little evolution in the underlying structure of the sampled region during propagation. Alternatively, if the spacecraft observed different, nearby regions within the ICMEs, it indicates that there was spatial homogeneity across those different regions. The field structure similarity observed in these ICMEs points to the value of placing
in situ
space weather monitors well upstream of the Earth.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Interplanetary coronal mass ejections (ICMEs) are a significant feature of the heliospheric environment and the primary cause of adverse space weather at the Earth. ICME propagation and the evolution ...of ICME magnetic field structure during propagation are still not fully understood. We analyze the magnetic field structures of 18 ICME magnetic flux ropes observed by radially aligned spacecraft in the inner heliosphere. Similarity in the underlying flux rope structures is determined through the application of a simple technique that maps the magnetic field profile from one spacecraft to the other. In many cases, the flux ropes show very strong underlying similarities at the different spacecraft. The mapping technique reveals similarities that are not readily apparent in the unmapped data and is a useful tool when determining whether magnetic field time series observed at different spacecraft are associated with the same ICME. Lundquist fitting has been applied to the flux ropes, and the rope orientations have been determined; macroscale differences in the profiles at the aligned spacecraft may be ascribed to differences in flux rope orientation. Assuming that the same region of the ICME was observed by the aligned spacecraft in each case, the fitting indicates some weak tendency for the rope axes to reduce in inclination relative to the solar equatorial plane and to align with the solar east‐west direction with heliocentric distance.
Plain Language Summary
Coronal mass ejections (CMEs) are large eruptions of magnetic field and plasma from the Sun. When they arrive at the Earth, these eruptions can cause significant damage to ground and orbital infrastructure; forecasting this “space weather” impact of CMEs at the Earth remains a difficult task. The impact of individual CMEs is largely dependent on their magnetic field configurations, and an important aspect of space weather forecasting is understanding how CME field configuration changes with distance from the Sun. We have analyzed the signatures of 18 CMEs observed by pairs of lined‐up spacecraft and show that their basic magnetic field structures often display significant self‐similarities, that is, they do not often show significant reordering of field features with heliocentric distance. This similarity points to the general usefulness of placing spacecraft between the Sun and Earth to act as early‐warning space weather monitors. CME signatures observed at such monitors would likely be similar to the signatures subsequently arriving at the Earth and could be used to produce space weather forecasts with longer lead times.
Key Points
Eighteen interplanetary flux ropes observed by radially aligned spacecraft in the inner heliosphere have been examined
Many of the flux ropes showed significant self‐similarities in magnetic field structure at the aligned spacecraft
Macroscale differences in the magnetic field profiles are consistent with the flux ropes displaying different axis orientations
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
The Heliospheric Imager (HI) instruments on board the STEREO spacecraft are used to analyze the solar wind during August and September 2007. We show how HI can be used to image the streamer belt and, ...in particular, the variability of the slow solar wind which originates inside and in the vicinity of the streamer belt. Intermittent mass flows are observed in HI difference images, streaming out along the extension of helmet streamers. These flows can appear very differently in images: plasma distributed on twisted flux ropes, V‐shaped structures, or “blobs.” The variety of these transient features may highlight the richness of phenomena that could occur near helmet streamers: emergence of flux ropes, reconnection of magnetic field lines at the tip of helmet streamers, or disconnection of open magnetic field lines. The plasma released with these transient events forms part of the solar wind in the higher corona; HI observations show that these transients are frequently entrained by corotating interaction regions (CIRs), leading to the formation of larger, brighter plasma structures in HI images. This entrainment is used to estimate the trajectory of these plasma ejecta. In doing so, we demonstrate that successive transients can be entrained by the same CIR in the high corona if they emanate from the same corotating source. Some parts of the streamers are more effective sources of transients than others. Surprisingly, evidence is given for the outflow of a recurring twisted magnetic structure, suggesting that the emergence of flux ropes can be recurrent.
We use observations from the Boolardy Engineering Test Array (BETA) of the Australian Square Kilometre Array Pathfinder (ASKAP) telescope to search for transient radio sources in the field around the ...intermittent pulsar PSR J1107−5907. The pulsar is thought to switch between an ‘off’ state in which no emission is detectable, a weak state and a strong state. We ran three independent transient detection pipelines on two-minute snapshot images from a 13 h BETA observation in order to (1) study the emission from the pulsar, (2) search for other transient emission from elsewhere in the image and (3) to compare the results from the different transient detection pipelines. The pulsar was easily detected as a transient source and, over the course of the observations, it switched into the strong state three times giving a typical time-scale between the strong emission states of 3.7 h. After the first switch it remained in the strong state for almost 40 min. The other strong states lasted less than 4 min. The second state change was confirmed using observations with the Parkes radio telescope. No other transient events were found and we place constraints on the surface density of such events on these time-scales. The high sensitivity Parkes observations enabled us to detect individual bright pulses during the weak state and to study the strong state over a wide observing band. We conclude by showing that future transient surveys with ASKAP will have the potential to probe the intermittent pulsar population.
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