116 research outputs found
L1 and off Sun-Earth line visible-light imaging of Earth-directed CMEs: An analysis of inconsistent observations
The efficacy of coronal mass ejection (CME) observations as a key input to
space weather forecasting is explored by comparing on and off Sun-Earth line
observations from the ESA/NASA SOHO and NASA STEREO spacecraft. A comparison is
made of CME catalogues based on L1 coronagraph imagery and off Sun-Earth line
coronagraph and heliospheric imager (HI) observations, for the year 2011.
Analysis reveals inconsistencies in the identification of a number of
potentially Earth-directed CMEs. The catalogues reflect our ability to identify
and characterise CMEs, so any discrepancies can impact our prediction of
Earth-directed CMEs. We show that 15 CMEs, which were observed by STEREO, that
had estimated directions compatible with Earth-directed events, had no
identified halo/partial halo counterpart listed in the L1 coronagraph CME
catalogue. In-situ data confirms that for 9 of these there was a consistent L1
Interplanetary CME (ICME). The number of such "discrepant" events is
significant compared to the number of ICMEs recorded at L1 in 2011, stressing
the need to address space weather monitoring capabilities, particularly with
the inclusion of off Sun-Earth line observation. While the study provides
evidence that some halo CMEs are simply not visible in near-Earth coronagraph
imagery, there is evidence that some halo CMEs viewed from L1 are compromised
by preceding CME remnants or the presence of multiple-CMEs. This underlines (1)
the value of multiple vantage point CME observation, and (2) the benefit of off
Sun-Earth line platform heliospheric imaging, and coronagraph imaging, for the
efficient identification and tracking of Earth-directed events.Comment: 36 pages, 6 figures, in press at AGU Space Weather, 202
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Testing the current paradigm for space weather prediction with heliospheric imagers
Predictions of the arrival of four coronal mass ejections (CMEs) in geospace are produced through use of three CME geometric models combined with CME drag modeling, constraining these models with the available Coronagraph and Heliospheric Imager data. The efficacy of these predications is assessed by comparison with the Space Weather Prediction Center (SWPC) numerical MHD forecasts of these same events. It is found that such a prediction technique cannot outperform the standard SWPC forecast at a statistically meaningful level. We test the Harmonic Mean, Self-Similar Expansion, and Ellipse Evolution geometric models, and find that, for these events at least, the differences between the models are smaller than the observational errors. We present a new method of characterizing CME fronts in the Heliospheric Imager field of view, utilizing the analysis of citizen scientists working with the Solar Stormwatch project, and we demonstrate that this provides a more accurate representation of the CME front than is obtained by experts analyzing elongation time maps for the studied events. Comparison of the CME kinematics estimated independently from the STEREO-A and STEREO-B Heliospheric Imager data reveals inconsistencies that cannot be explained within the observational errors and model assumptions. We argue that these observations imply that the assumptions of the CME geometric models are routinely invalidated and question their utility in a space weather forecasting context. These results argue for the continuing development of more advanced techniques to better exploit the Heliospheric Imager observations for space weather forecasting
Reconstructing CMEs with Coordinated Imaging and In Situ Observations: Global Structure, Kinematics, and Implications for Space Weather Forecasting
See the pdf for detailsComment: 45 pages, 16 figures, ApJ, in pres
On Sun-to-Earth Propagation of Coronal Mass Ejections
We investigate how coronal mass ejections (CMEs) propagate through, and
interact with, the inner heliosphere between the Sun and Earth, a key question
in CME research and space weather forecasting. CME Sun-to-Earth kinematics are
constrained by combining wide-angle heliospheric imaging observations,
interplanetary radio type II bursts and in situ measurements from multiple
vantage points. We select three events for this study, the 2012 January 19, 23,
and March 7 CMEs. Different from previous event studies, this work attempts to
create a general picture for CME Sun-to-Earth propagation and compare different
techniques for determining CME interplanetary kinematics. Key results are
obtained concerning CME Sun-to-Earth propagation. Our comparison between
different techniques (and data sets) also has important implications for CME
observations and their interpretations. Future CME observations and space
weather forecasting are discussed based on these results. See detail in the
PDF.Comment: ApJ, in pres
Optimising use of electronic health records to describe the presentation of rheumatoid arthritis in primary care: a strategy for developing code lists
Background
Research using electronic health records (EHRs) relies heavily on coded clinical data. Due to variation in coding practices, it can be difficult to aggregate the codes for a condition in order to define cases. This paper describes a methodology to develop ‘indicator markers’ found in patients with early rheumatoid arthritis (RA); these are a broader range of codes which may allow a probabilistic case definition to use in cases where no diagnostic code is yet recorded.
Methods
We examined EHRs of 5,843 patients in the General Practice Research Database, aged ≥30y, with a first coded diagnosis of RA between 2005 and 2008. Lists of indicator markers for RA were developed initially by panels of clinicians drawing up code-lists and then modified based on scrutiny of available data. The prevalence of indicator markers, and their temporal relationship to RA codes, was examined in patients from 3y before to 14d after recorded RA diagnosis.
Findings
Indicator markers were common throughout EHRs of RA patients, with 83.5% having 2 or more markers. 34% of patients received a disease-specific prescription before RA was coded; 42% had a referral to rheumatology, and 63% had a test for rheumatoid factor. 65% had at least one joint symptom or sign recorded and in 44% this was at least 6-months before recorded RA diagnosis.
Conclusion
Indicator markers of RA may be valuable for case definition in cases which do not yet have a diagnostic code. The clinical diagnosis of RA is likely to occur some months before it is coded, shown by markers frequently occurring ≥6 months before recorded diagnosis. It is difficult to differentiate delay in diagnosis from delay in recording. Information concealed in free text may be required for the accurate identification of patients and to assess the quality of care in general practice
Using coordinated observations in polarized white light and Faraday rotation to probe the spatial position and magnetic field of an interplanetary sheath
Coronal mass ejections (CMEs) can be continuously tracked through a large portion of the inner heliosphere by direct imaging in visible and radio wavebands. White light (WL) signatures of solar wind transients, such as CMEs, result from Thomson scattering of sunlight by free electrons and therefore depend on both viewing geometry and electron density. The Faraday rotation (FR) of radio waves from extragalactic pulsars and quasars, which arises due to the presence of such solar wind features, depends on the line-of-sight magnetic field component B ∥ and the electron density. To understand coordinated WL and FR observations of CMEs, we perform forward magnetohydrodynamic modeling of an Earth-directed shock and synthesize the signatures that would be remotely sensed at a number of widely distributed vantage points in the inner heliosphere. Removal of the background solar wind contribution reveals the shock-associated enhancements in WL and FR. While the efficiency of Thomson scattering depends on scattering angle, WL radiance I decreases with heliocentric distance r roughly according to the expression Ir –3. The sheath region downstream of the Earth-directed shock is well viewed from the L4 and L5 Lagrangian points, demonstrating the benefits of these points in terms of space weather forecasting. The spatial position of the main scattering site r sheath and the mass of plasma at that position M sheath can be inferred from the polarization of the shock-associated enhancement in WL radiance. From the FR measurements, the local B ∥sheath at r sheath can then be estimated. Simultaneous observations in polarized WL and FR can not only be used to detect CMEs, but also to diagnose their plasma and magnetic field properties
Characteristics of Kinematics of a Coronal Mass Ejection during the 2010 August 1 CME-CME Interaction Event
We study the interaction of two successive coronal mass ejections (CMEs)
during the 2010 August 1 events using STEREO/SECCHI COR and HI data. We obtain
the direction of motion for both CMEs by applying several independent
reconstruction methods and find that the CMEs head in similar directions. This
provides evidence that a full interaction takes place between the two CMEs that
can be observed in the HI1 field-of-view. The full de-projected kinematics of
the faster CME from Sun to Earth is derived by combining remote observations
with in situ measurements of the CME at 1 AU. The speed profile of the faster
CME (CME2; ~1200 km/s) shows a strong deceleration over the distance range at
which it reaches the slower, preceding CME (CME1; ~700 km/s). By applying a
drag-based model we are able to reproduce the kinematical profile of CME2
suggesting that CME1 represents a magnetohydrodynamic obstacle for CME2 and
that, after the interaction, the merged entity propagates as a single structure
in an ambient flow of speed and density typical for quiet solar wind
conditions. Observational facts show that magnetic forces may contribute to the
enhanced deceleration of CME2. We speculate that the increase in magnetic
tension and pressure, when CME2 bends and compresses the magnetic field lines
of CME1, increases the efficiency of drag.Comment: accepted for Ap
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