Coronal Mass Ejections Arrival Time Research Articles

Validation of a priori CME arrival predictions made using real‐time heliospheric imager observations

AbstractBetween December 2010 and March 2013, volunteers for the Solar Stormwatch (SSW) Citizen Science project have identified and analyzed coronal mass ejections (CMEs) in the near real‐time Solar Terrestrial Relations Observatory Heliospheric Imager observations, in order to make “Fearless Forecasts” of CME arrival times and speeds at Earth. Of the 60 predictions of Earth‐directed CMEs, 20 resulted in an identifiable Interplanetary CME (ICME) at Earth within 1.5–6 days, with an average error in predicted transit time of 22 h, and average transit time of 82.3 h. The average error in predicting arrival speed is 151 km s−1, with an average arrival speed of 425km s−1. In the same time period, there were 44 CMEs for which there are no corresponding SSW predictions, and there were 600 days on which there was neither a CME predicted nor observed. A number of metrics show that the SSW predictions do have useful forecast skill; however, there is still much room for improvement. We investigate potential improvements by using SSW inputs in three models of ICME propagation: two of constant acceleration and one of aerodynamic drag. We find that taking account of interplanetary acceleration can improve the average errors of transit time to 19 h and arrival speed to 77 km s−1.

Interplanetary-scintillation observations of coronal mass ejections near the maximum of the 24th solar-activity cycle

The mean velocities of coronal mass ejections (CMEs) detected in 2011–2012 are estimated from interplanetary-scintillation observations carried out with the Pushchino Big Scanning Antenna 111 MHz. The mean velocities are estimated based on the interval between the X-ray burst associated with the birth of the CME and the increase in the observed scintillations. The estimated mean CME velocity within the corona and the region probed by the scintillations at elongations from 40° to 50° is close to the mean velocity between the solar corona and the Earth. In half of the studied events, the estimated accuracy of the CME arrival time to the Earth is several hours. The CME velocities estimated from the delay between the X-ray bursts and the scintillation increase are significantly closer to the real velocities than the velocities estimated from the widths of the temporal spectra of the scintillations.

Quantitative comparison of methods for predicting the arrival of coronal mass ejections at Earth based on multiview imaging

We investigate the performance of six methods for predicting the coronal mass ejection (CME) time of arrival (ToA) and velocity at Earth using a sample of nine Earth‐impacting CMEs between March 2010 and June 2011. The CMEs were tracked continuously from the Sun to near Earth in multiviewpoint imaging data from STEREO Sun‐Earth Connection Coronal and Heliospheric Investigation (SECCHI) and SOHO Large Angle and Spectroscopic Coronagraph (LASCO). We use the Graduate Cylindrical Shell model to estimate the three‐dimensional direction and height of the CMEs in every image out to ∼200R⊙. We fit the derived three‐dimensional (deprojected) height and time (HT) data with six different methods to extrapolate the CME ToA and velocity at Earth. We compare the fitting results with the in situ data from the Wind spacecraft. We find that a simple linear fit above a height of 50R⊙ gives the ToA with an error ±6h for seven (78%) of the CMEs. For the full sample, we are able to predict the ToA to within ±13h. These results are a half day improvement over past CME arrival time methods that only used SOHO LASCO data. We conclude that heliographic height‐time measurements of the CME front made away from the Sun‐Earth line and beyond the coronagraphic field of view are sufficient for reasonably accurate predictions of their ToA.

Estimating Travel Times of Coronal Mass Ejections to 1 AU Using Multi-spacecraft Coronagraph Data

We study the relationship between the speeds of coronal mass ejections (CMEs) obtained close to the Sun and in the interplanetary medium during the low solar-activity period from 2008 to 2010. We use a multi-spacecraft forward-modeling technique to fit a flux-rope-like model to white-light coronagraph images from the STEREO and SOHO spacecraft to estimate the geometrical configuration, propagation in three-dimensions (3D), and the radial speeds of the observed CMEs. The 3D speeds obtained in this way are used in existing CME travel-time prediction models. The results are compared to the actual CME transit times from the Sun to STEREO, ACE, and Wind spacecraft as well as to the transit times calculated using projected CME speeds. CME 3D speeds give slightly better predictions than projected CME speeds, but a large scatter is observed between the predicted and observed travel times, even when 3D speeds are used. We estimate the possible sources of errors and find a weak tendency for large interplanetary CMEs (ICMEs) with high magnetic fields to arrive faster than predicted and small, low-magnetic-field ICMEs to arrive later than predicted. The observed CME transit times from the Sun to 1 AU show a particularly good correlation with the upstream solar-wind speed. Similar trends have not been observed in previous studies using data sets near solar maximum. We suggest that near solar minimum a relatively narrow range of CME initial speeds, sizes, and magnetic-field magnitudes led to a situation where aerodynamic drag between CMEs and ambient solar wind was the primary cause of variations in CME arrival times from the Sun to 1 AU.

Ensemble Modeling of CME Propagation

The current progression toward solar maximum provides a unique opportunity to use multi-perspective spacecraft observations together with numerical models to better understand the evolution and propagation of coronal mass ejections (CMEs). Of interest to both the scientific and forecasting communities are the Earth-directed “halo” CMEs, since they typically produce the most geoeffective events. However, determining the actual initial geometries of halo CMEs is a challenge due to the plane-of-sky projection effects. Thus the recent 15 February 2011 halo CME event has been selected for this study. During this event the Solar TErrestrial RElations Observatory (STEREO) A and B spacecraft were fortuitously located ∼ 90° away from the Sun–Earth line such that the CME was viewed as a limb event from these two spacecraft, thereby providing a more reliable constraint on the initial CME geometry. These multi-perspective observations were utilized to provide a simple geometrical description that assumes a cone shape for a CME to calculate its angular width and central position. The event was simulated using the coupled Wang–Sheeley–Arge (WSA)-Enlil 3D numerical solar corona-solar wind model. Daily updated global photospheric magnetic field maps were used to drive the background solar wind. To improve our modeling techniques, the sensitivity of the modeled CME arrival times to the initial input CME geometry was assessed by creating an ensemble of numerical simulations based on multiple sets of cone parameters for this event. It was found that the accuracy of the modeled arrival times not only depends on the initial input CME geometry, but also on the accuracy of the modeled solar wind background, which is driven by the input maps of the photospheric field. To improve the modeling of the background solar wind, the recently developed data-assimilated magnetic field synoptic maps produced by the Air Force Data Assimilative Photospheric flux Transport (ADAPT) model were used. The ADAPT maps provide a more instantaneous snapshot of the global photospheric field distribution than that provided by traditional daily updated synoptic maps. Using ADAPT to drive the background solar wind, an ensemble set of eight different CME arrival times was generated, where the spread in the predictions was ∼ 13 hours and was nearly centered on the observed CME shock arrival time.

Effect of Solar Wind Drag on the Determination of the Properties of Coronal Mass Ejections from Heliospheric Images

The Fixed-Φ (FΦ) and Harmonic Mean (HM) fitting methods are two methods to determine the “average” direction and velocity of coronal mass ejections (CMEs) from time–elongation tracks produced by Heliospheric Imagers (HIs), such as the HIs onboard the STEREO spacecraft. Both methods assume a constant velocity in their descriptions of the time–elongation profiles of CMEs, which are used to fit the observed time–elongation data. Here, we analyze the effect of aerodynamic drag on CMEs propagating through interplanetary space, and how this drag affects the result of the FΦ and HM fitting methods. A simple drag model is used to analytically construct time–elongation profiles which are then fitted with the two methods. It is found that higher angles and velocities give rise to greater error in both methods, reaching errors in the direction of propagation of up to 15∘ and 30∘ for the FΦ and HM fitting methods, respectively. This is due to the physical accelerations of the CMEs being interpreted as geometrical accelerations by the fitting methods. Because of the geometrical definition of the HM fitting method, it is more affected by the acceleration than the FΦ fitting method. Overall, we find that both techniques overestimate the initial (and final) velocity and direction for fast CMEs propagating beyond 90∘ from the Sun–spacecraft line, meaning that arrival times at 1 AU would be predicted early (by up to 12 hours). We also find that the direction and arrival time of a wide and decelerating CME can be better reproduced by the FΦ due to the cancelation of two errors: neglecting the CME width and neglecting the CME deceleration. Overall, the inaccuracies of the two fitting methods are expected to play an important role in the prediction of CME hit and arrival times as we head towards solar maximum and the STEREO spacecraft further move behind the Sun.

Modeling of coronal mass ejections that caused particularly large geomagnetic storms using ENLIL heliosphere cone model

In our previous paper we reported the results of modeling of 14 selected well‐observed strong halo coronal mass ejection (CME) events using the WSA‐ENLIL cone model combination. Cone model input parameters were obtained from white light coronagraph images of the CME events using the analytical method developed by Xie et al. (2004). This work verified that coronagraph input gives reasonably good results for the CME arrival time prediction. In contrast to Taktakishvili et al. (2009), where we started the analysis by looking for clear CME signatures in the data and then proceeded to model the interplanetary consequences at 1 AU, in the present paper we start by generating a list of observed geomagnetic storm events and then work our way back to remote solar observations and carry out the corresponding CME modeling. The approach used in this study is addressing space weather forecasting and operational needs. We analyzed 36 particularly strong geomagnetic storms, then tried to associate them with particular CMEs using SOHO/LASCO catalogue, and finally modeled these CMEs using WSA‐ENLIL cone model. Recently, Pulkkinen et al. (2010) developed a novel method for automatic determination of cone model parameters. We employed both analytical and automatic methods to determine cone model input parameters. We examined the CME arrival times and magnitude of impact at 1 AU for both techniques. The results of the simulations are compared with the ACE satellite observations. This comparison demonstrated that WSA‐ENLIL model combination with coronagraph input gives reasonably good results for the CME arrival times for this set of “geoeffective” CME events as well.

Wang‐Sheeley‐Arge–Enlil Cone Model Transitions to Operations

http://www.agu.org/journals/sw/swa/news/article/?id=2011SW000669 The National Weather Service's (NWS) Space Weather Prediction Center (SWPC) is transitioning the first large-scale, physics-based space weather prediction model into operations on the NWS National Centers for Environmental Prediction (NCEP) supercomputing system (see also C. Schultz, Space weather model moves into prime time, Space Weather, 9, S03005, doi:10.1029/2011SW000669, 2011). The model is intended to provide 1- to 4-day advance warning of geomagnetic storms from quasi-recurrent solar wind structures and Earth-directed coronal mass ejections (CMEs). A team has been put together at SWPC to bring an advanced numerical model—developed with broad participation of the research community—into operational status. The modeling system consists of two main parts: (1) a semiempirical near-Sun module (Wang-Sheeley-Arge (WSA)) that approximates the outflow at the base of the solar wind; and (2) a sophisticated three-dimensional magnetohydrodynamic numerical model (Enlil) that simulates the resulting flow evolution out to Earth. The former module is driven by observations of the solar surface magnetic field accumulated over a solar rotation and composited into a synoptic map; this input is used to drive a parameterized model of the near-Sun expansion of the solar corona, which provides input for the interplanetary module to compute the quasi-steady (ambient) solar wind outflow. Finally, when an Earth-directed CME is detected in coronagraph images from NASA spacecraft, these images are used to characterize the basic properties of the CME, including speed, direction, and size. This input “cone” representation is injected into the preexisting ambient flow, and the subsequent transient evolution forms the basis for the prediction of the CME's arrival time at Earth, its intensity, and its duration (Figure 1). The system will be delivered to NCEP in fall 2011, to undergo a year of trial operation. During that time, potential improvements to the modeling system will be evaluated, and early assessments of its performance will be undertaken. This transition draws upon contributions from many agencies and institutions, including the Center for Integrated Space Weather Modeling, Community Coordinated Modeling Center, Naval Research Laboratory, National Center for Atmospheric Research, Laboratory for Atmospheric and Space Physics, Office of Naval Research, Air Force Weather Agency (AFWA), and the Air Force Research Laboratory (AFRL). The long-term success of the system will hinge on training (collective experience), the quality of inputs (better interpretation, new observations), customer interactions, and the establishment of an effective operations-to-research (and the reverse) chain, which is critical to the continued improvement of the system. We thank C. Nick Arge for his essential contribution in the development and implementation of the WSA model. Annette Parsons is the AFWA project administrator at SWPC. Douglas Biesecker is the project verification and validation lead at SWPC. Dusan Odstrcil is the Enlil originator and a researcher at George Mason University, Fairfax, Va. George Millward is the project technical lead at SWPC. Steve Hill is the development and transition section lead at SWPC. Vic Pizzo is project scientist at NOAA SWPC, Boulder, Colo.; E-mail: vic.pizzo@noaa.gov

Empirical model of the transit time of interplanetary coronal mass ejections

We study the correlation between near-Earth observations of interplanetary coronal mass ejections (ICMEs) detected by the Wind and ACE spacecrafts and their counterparts of coronal mass ejections (CMEs) observed near the Sun by the SOHO/LASCO coronagraph during 1996–2002. The results have been compared with an empirical model given by Gopalswamy, et al. (2000; 2001) to predict the 1-AU arrival time of CMEs. In this paper, we use an expected data set with a wider range with initial velocities than that considered in previous models. To improve the accuracy of the predicted arrival time, we divided the CME events into two groups according to their effective acceleration and deceleration. The results show that our model works well for events with a negative acceleration in the initial velocity range between 500 and 2500 km/s, while the model described by Gopalswamy is better for events with initial velocities near the solar wind velocity.

Validation of the coronal mass ejection predictions at the Earth orbit estimated by ENLIL heliosphere cone model

Modeling is an important tool in understanding physical processes in the space weather. Model performance studies evaluate the quality of model operation by comparing its output to a measurable parameter of interest. In this paper we studied the performance of the combination of the halo coronal mass ejection (CME) analytical cone model and ENLIL three‐dimensional MHD heliosphere model. We examined the CME arrival time and magnitude of impact at 1 AU for different geoeffective events, including the October 2003 Halloween Storm and the 14 December 2006 storm CMEs. The results of the simulation are compared with the ACE satellite observations. The comparison of the simulation results with the observations demonstrates that ENLIL cone model performs better compared to reference mean velocity and empirical models.

The role of aerodynamic drag in dynamics of coronal mass ejections

AbstractDynamics of coronal mass ejections (CMEs) is strongly affected by the interaction of the erupting structure with the ambient magnetoplasma: eruptions that are faster than solar wind transfer the momentum and energy to the wind and generally decelerate, whereas slower ones gain the momentum and accelerate. Such a behavior can be expressed in terms of “aerodynamic” drag. We employ a large sample of CMEs to analyze the relationship between kinematics of CMEs and drag-related parameters, such as ambient solar wind speed and the CME mass. Employing coronagraphic observations it is demonstrated that massive CMEs are less affected by the aerodynamic drag than light ones. On the other hand, in situ measurements are used to inspect the role of the solar wind speed and it is shown that the Sun-Earth transit time is more closely related to the wind speed than to take-off speed of CMEs. These findings are interpreted by analyzing solutions of a simple equation of motion based on the standard form for the drag acceleration. The results show that most of the acceleration/deceleration of CMEs on their way through the interplanetary space takes place close to the Sun, where the ambient plasma density is still high. Implications for the space weather forecasting of CME arrival-times are discussed.