55694014
Statistical study of coronal mass ejection source locations: Understanding CMEs viewed in coronagraphs
[1] How to properly understand coronal mass ejections (CMEs) viewed in white light coronagraphs is crucial to many relative researches in solar and space physics. The issue is now particularly addressed in this paper through studying the source locations of all the 1078 Large Angle and Spectrometric Coronagraph (LASCO) CMEs listed in Coordinated Data Analysis Workshop (CDAW) CME catalog during 1997–1998 and their correlation with CMEs' apparent parameters. By manually checking LASCO and Extreme Ultraviolet Imaging Telescope (EIT) movies of these CMEs, we find that, except 231 CMEs whose source locations cannot be identified due to poor data, there are 288 CMEs with location identified on the frontside solar disk, 234 CMEs appearing above solar limb, and 325 CMEs without evident eruptive signatures in the field of view of EIT. On the basis of the statistical results of CMEs' source locations, there are four physical issues: (1) the missing rate of CMEs by SOHO LASCO and EIT, (2) the mass of CMEs, (3) the causes of halo CMEs, and (4) the deflections of CMEs in the corona, are exhaustively analyzed. It is found that (1) about 32% frontside CMEs cannot be recognized by SOHO, (2) the brightness of a CME at any heliocentric distance is roughly positively correlated with its speed, and the CME mass derived from the brightness is probably overestimated, (3) both projection effect and violent eruption are the major causes of halo CMEs, and especially for limb halo CMEs the latter is the primary one, and (4) most CMEs deflected toward equator near the solar minimum; these deflections can be classified into three types: the asymmetrical expansion, the nonradial ejection, and the deflected propagation.
41231566
Quantitative Analysis of CME Deflections in the Corona
In this paper, ten CME events viewed by the STEREO twin spacecraft are analyzed to study the deflections of CMEs during their propagation in the corona. Based on the three-dimensional information of the CMEs derived by the graduated cylindrical shell (GCS) model (Thernisien, Howard, and Vourlidas in Astrophys. J.652, 1305, 2006), it is found that the propagation directions of eight CMEs had changed. By applying the theoretical method proposed by Shen et al. (Solar Phys.269, 389, 2011) to all the CMEs, we found that the deflections are consistent, in strength and direction, with the gradient of the magnetic energy density. There is a positive correlation between the deflection rate and the strength of the magnetic energy density gradient and a weak anti-correlation between the deflection rate and the CME speed. Our results suggest that the deflections of CMEs are mainly controlled by the background magnetic field and can be quantitatively described by the magnetic energy density gradient (MEDG) model.
119228154
Full halo coronal mass ejections: Do we need to correct the projection effect in terms of velocity?
[1] The projection effect is one of the biggest obstacles in learning the real properties of coronal mass ejections (CMEs) and forecasting their geoeffectiveness. To evaluate the projection effect, 86 full halo CMEs (FHCMEs) listed in the Coordinated Data Analysis Workshop CME catalog from 1 March 2007 to 31 May 2012 are investigated. By applying the Graduated Cylindrical Shell model, we obtain the deprojected values of the propagation velocity, direction, and angular width of these FHCMEs and compare them with the projected values measured in the plane-of-sky. Although these CMEs look full halo in the view angle of SOHO, it is found that their propagation directions and angular widths could vary in a large range, implying projection effect is a major reason causing a CME being halo, but not the only one. Furthermore, the comparison of the deprojected and projected velocities reveals that most FHCMEs originating within 45° of the Sun-Earth line with a projected speed slower than 900 km s−1 suffer from large projection effect, while the FHCMEs originating far from the vicinity of solar disk center or moving faster than 900 km s−1have small projection effect. Thus, for the latter class of FHCMEs, it is not necessary to correct the measured velocities.
55072733
Source Region of the Decameter–Hectometric Type II Radio Burst: Shock–Streamer Interaction Region
D–H type II radio bursts are widely thought to be caused by coronal mass ejections (CMEs). However, it is still unclear where the exact source of the type IIs on the shock surface is. We identify the source regions of the decameter–hectometric (D–H) type IIs based on imaging observations from SOHO/LASCO and the radio dynamic spectrum from Wind/Waves. The analysis of two well-observed events suggests that the sources of these two events are located in the interaction regions between shocks and streamers, and that the shocks are enhanced significantly in these regions.
119292805
Influence of Coronal Holes on CMEs in Causing SEP Events
The issue of the influence of coronal holes (CHs) on coronal mass ejections (CMEs) in causing solar energetic particle (SEP) events is revisited. It is a continuation and extension of our previous work, in which no evident effects of CHs on CMEs in generating SEPs were found by statistically investigating 56 CME events. This result is consistent with the conclusion obtained by Kahler in 2004. We extrapolate the coronal magnetic field, define CHs as the regions consisting of only open magnetic field lines and perform a similar analysis on this issue for 76 events in total by extending the study interval to the end of 2008. Three key parameters, CH proximity, CH area and CH relative position, are involved in the analysis. The new result confirms the previous conclusion that CHs did not show any evident effect on CMEs in causing SEP events.
115149137
CONTRACTING AND ERUPTING COMPONENTS OF SIGMOIDAL ACTIVE REGIONS
It has recently been noted that solar eruptions can be associated with the contraction of coronal loops that are not involved in magnetic reconnection processes. In this paper, we investigate five coronal eruptions originating from four sigmoidal active regions, using high-cadence, high-resolution narrowband EUV images obtained by the Solar Dynamic Observatory (SDO). The magnitudes of the flares associated with the eruptions range from GOES class B to class X. Owing to the high-sensitivity and broad temperature coverage of the Atmospheric Imaging Assembly (AIA) on board SDO, we are able to identify both the contracting and erupting components of the eruptions: the former is observed in cold AIA channels as the contracting coronal loops overlying the elbows of the sigmoid, and the latter is preferentially observed in warm/hot AIA channels as an expanding bubble originating from the center of the sigmoid. The initiation of eruption always precedes the contraction, and in the energetically mild events (B- and C-flares), it also precedes the increase in GOES soft X-ray fluxes. In the more energetic events, the eruption is simultaneous with the impulsive phase of the nonthermal hard X-ray emission. These observations confirm that loop contraction is an integrated process in eruptions with partially opened arcades. The consequence of contraction is a new equilibrium with reduced magnetic energy, as the contracting loops never regain their original positions. The contracting process is a direct consequence of flare energy release, as evidenced by the strong correlation of the maximal contracting speed, and strong anti-correlation of the time delay of contraction relative to expansion, with the peak soft X-ray flux. This is also implied by the relationship between contraction and expansion, i.e., their timing and speed.
5692175
Effects of correlation between merging steps on the global halo formation
The excursion set theory of halo formation is modified by adopting the fractional Brownian motion, to account for possible correlation between merging steps. We worked out analytically the conditional mass function, halo merging rate and formation time distribution in the spherical collapse model. We also developed an approximation for the ellipsoidal collapse model and applied it to the calculation of the conditional mass function and the halo formation time distribution. For models in which the steps are positively correlated, the halo merger rate is enhanced when the accreted mass is less than similar to 25M*, while for the negatively correlated case this rate is reduced. Compared with the standard model in which the steps are uncorrelated, the models with positively correlated steps produce more aged population in small mass haloes and more younger population in large mass haloes, while for the models with negatively correlated steps the opposite is true. An examination of simulation results shows that a weakly positive correlation between successive merging steps appears to fit best. We have also found a systematic effect in the measured mass function due to the finite volume of simulations. In future work, this will be included in the halo model to accurately predict the three-point correlation function estimated from simulations.
110979284
The R&D program for silicon detectors in CMS
Abstract This paper describes the main achievements in the development of radiation resistant silicon detectors to be used in the CMS tracker. After a general description of the basic requirements for the operation of large semiconductor systems in the LHC environment, the issue of radiation resistance is discussed in detail. Advantages and disadvantages of the different technological options are presented for comparison. Laboratory measurements and test beam data are used to check the performance of several series of prototypes fabricated by different companies. The expected performance of the final detector modules are presented together with preliminary test beam results on system prototypes.
110710115
Readout electronics of the ALICE photon spectrometer
The photon spectrometer (PHOS) in the ALICE experiment at LHC is a PbWO4 crystal based electromagnetic calorimeter, dedicated to measuring photons, π°'s and η's over a broad pT range from about 100 MeV/c to 100 GeV/c with the best possible energy and position resolution. The front-end electronics of the PHOS is thus required to cover a large dynamic range, to achieve a timing resolution better than ~ 2 ns in order to discriminate against 1-2 GeV/c (anti-)neutrons, and to provide high pT trigger to select rare high pT events. In this paper, we present the full PHOS readout system, including the avalanche photo-diode, the low noise charge sensitive preamplifier, the 32 channel front-end electronics card, the trigger region unit and the trigger OR module. Results from PHOS commissioning with beam particles and cosmic rays will also be presented to address the performance of the PHOS readout electronics.
122736493
Cosmic-ray energy spectrum around the knee obtained by the Tibet experiment and future prospects
The observation of the extensive air showers has been carried out since 1990 by Tibet air-shower array to study the origin of the cosmic-rays. In order to investigate the chemical composition around the knee, air-shower core detector was used in two experimental phases aiming to separate light primary elements (proton and helium). In a first phase experiment made in 1996-1999, primary proton and helium spectra were measured using a hybrid detector consisted of Tibet II air-shower array, emulsion chambers, and burst detectors. The result indicated that the fraction of light elements among the all particle spectrum is less than 30%. We performed the second phase experiment in 2002-2005 to measure proton + helium together to confirm the previous result with higher statistics by improving the detection efficiency for the air-shower cores. The P + He spectrum was obtained in a good agreement with previous result by several times higher statistics. The flux of the light elements, together with the all-particle energy spectrum, indicates the dominance of nuclei heavier than helium in the energy range around the knee. We also present the outline of the next phase experiment, which is to measure the heavy elements around the knee, using low threshold air-shower core detector named YAC. (C) 2010 COSPAR. Published by Elsevier Ltd. All rights reserved.
12882522
THE CLUSTERING OF SDSS GALAXY GROUPS: MASS AND COLOR DEPENDENCE
We use a large sample of galaxy groups selected from the SDSS data release 4 with an adaptive halo-based group finder to probe how the clustering strength of groups depends on their masses and colors. In particular, we determine the relative biases of groups of different masses, as well as that of groups with the same mass but with different colors. In agreement with previous studies, we find that more massive groups are more strongly clustered, and the inferred mass dependence of the halo bias is in good agreement with predictions for the ΛCDM concordance cosmology. Regarding the color dependence, we find that groups with red centrals are more strongly clustered than groups of the same mass but with blue centrals. Similar results are obtained when the color of a group is defined to be the total color of its member galaxies. The color dependence is more prominent in less massive groups and becomes insignificant in groups with masses 1014 h−1 M☉. These results are consistent with those obtained by Yang et al. from an analysis of the 2dFGRS, but inconsistent with those obtained by Berlind et al., who also used an SDSS group catalog. We construct a mock galaxy redshift survey from the large Millennium N-body simulation. Applying our group finder to this mock survey, and analyzing the mock data in exactly the same way as the true data, we are able to accurately recover the intrinsic mass and color dependencies of the halo bias in the model. Interestingly, the semianalytical model reveals the same color dependence of the halo bias as we find in our group catalog. We discuss these results in light of the assembly bias of dark matter halos and the star formation histories of galaxies.