Asymmetric Cone Model Research Articles

Comparison of interplanetary CME arrival times and solar wind parameters based on the WSA‐ENLIL model with three cone types and observations

AbstractWe have made a comparison between coronal mass ejection (CME)‐associated shock propagations based on the Wang‐Sheeley‐Arge (WSA)‐ENLIL model using three cone types and in situ observations. For this we use 28 full‐halo CMEs, whose cone parameters are determined and their corresponding interplanetary shocks were observed at the Earth, from 2001 to 2002. We consider three different cone types (an asymmetric cone model, an ice cream cone model, and an elliptical cone model) to determine 3‐D CME cone parameters (radial velocity, angular width, and source location), which are the input values of the WSA‐ENLIL model. The mean absolute error of the CME‐associated shock travel times for the WSA‐ENLIL model using the ice‐cream cone model is 9.9 h, which is about 1 h smaller than those of the other models. We compare the peak values and profiles of solar wind parameters (speed and density) with in situ observations. We find that the root‐mean‐square errors of solar wind peak speed and density for the ice cream and asymmetric cone model are about 190 km/s and 24/cm3, respectively. We estimate the cross correlations between the models and observations within the time lag of ± 2 days from the shock travel time. The correlation coefficients between the solar wind speeds from the WSA‐ENLIL model using three cone types and in situ observations are approximately 0.7, which is larger than those of solar wind density (cc ∼0.6). Our preliminary investigations show that the ice cream cone model seems to be better than the other cone models in terms of the input parameters of the WSA‐ENLIL model.

Testing the asymmetric cone model for halo CMEs using STEREO/SECCHI coronagraphic observations

Space weather is significantly controlled by halo coronal mass ejections (HCMEs) originating close to the central meridian and directing toward the Earth. Unfortunately, coronagraphic observations (especially for HCMEs) are subject to a projection effect which makes it impossible to determine the true radial velocity and width of CMEs. However, these parameters can be estimated by correcting for the projection effect using the asymmetric cone model (Michalek, 2006). A set of 20 CMEs, observed as halo events in the LASCO field of view and simultaneously as limb events in the STEREO/SECCHI field of view, are used to check the accuracy of the asymmetric cone model. For this purpose, characteristics of the considered CMEs (angular widths and radial speeds) measured in STEREO/SECCHI images are compared with those obtained by the asymmetric cone model. We demonstrate that the widths and speeds determined by both methods are very similar. Correlation coefficients for speeds and angular widths are 0.99 and 0.96, respectively. We have also shown that the projection effect is unpredictable and could sometimes be very significant (up to 100% of the velocity measured in the LASCO field of view). On average, the SOHO/LASCO projected speeds for the HCMEs are 23% smaller than the radial velocities obtained from the STEREO/SECCHI images.

Comparison of Cone Model Parameters for Halo Coronal Mass Ejections

Halo coronal mass ejections (HCMEs) are a major cause of geomagnetic storms, hence their three-dimensional structures are important for space weather. We compare three cone models: an elliptical-cone model, an ice-cream-cone model, and an asymmetric-cone model. These models allow us to determine three-dimensional parameters of HCMEs such as radial speed, angular width, and the angle [γ] between sky plane and cone axis. We compare these parameters obtained from three models using 62 HCMEs observed by SOHO/LASCO from 2001 to 2002. Then we obtain the root-mean-square (RMS) error between the highest measured projection speeds and their calculated projection speeds from the cone models. As a result, we find that the radial speeds obtained from the models are well correlated with one another (R > 0.8). The correlation coefficients between angular widths range from 0.1 to 0.48 and those between γ-values range from −0.08 to 0.47, which is much smaller than expected. The reason may be the different assumptions and methods. The RMS errors between the highest measured projection speeds and the highest estimated projection speeds of the elliptical-cone model, the ice-cream-cone model, and the asymmetric-cone model are 376 km s−1, 169 km s−1, and 152 km s−1. We obtain the correlation coefficients between the location from the models and the flare location (R > 0.45). Finally, we discuss strengths and weaknesses of these models in terms of space-weather application.

Quantitative Measurement of Supersonic Flow Field around an Asymmetric Cone Model with CGBOS Method and 3D-CT Reconstruction

Quantitative Measurement of Supersonic Flow Field around an Asymmetric Cone Model with CGBOS Method and 3D-CT Reconstruction

Is the Asymmetric Cone Model for Halo Coronal Mass Ejections Correct?

A set of 106 limb CMEs which are wide and could be possible halo events, when directed towards Earth, are used to check the accuracy of the asymmetric cone model. For this purpose characteristics of CMEs (widths and radial speeds) measured for the possible halo CMEs are compared with these obtained for halo CMEs using the asymmetric cone model (Michalek, Solar Phys.237, 101, 2006). It was shown that the width and speed distributions for both datasets are very similar and with a probability of p>0.93 (using the Kolmogorov – Smirnov test) were drawn from the same distribution of events. We also determined the accurate relationship between radial (Vrad) and expansion (Vexp) speeds of halo CMEs. This relation for the halo CMEs is simply Vrad=Vexp and could be very useful for space weather application.

Prediction of Space Weather Using an Asymmetric Cone Model for Halo CMEs

Halo coronal mass ejections (HCMEs) are responsible of the most severe geomagnetic storms. A prediction of their geoeffectiveness and travel time to Earth’s vicinity is crucial to forecast space weather. Unfortunately, coronagraphic observations are subjected to projection effects and do not provide true characteristics of CMEs. Recently, Michalek (Solar Phys.237, 101, 2006) developed an asymmetric cone model to obtain the space speed, width, and source location of HCMEs. We applied this technique to obtain the parameters of all front-sided HCMEs observed by the SOHO/LASCO experiment during a period from the beginning of 2001 until the end of 2002 (solar cycle 23). These parameters were applied for space weather forecasting. Our study finds that the space speeds are strongly correlated with the travel times of HCMEs to Earth’s vicinity and with the magnitudes related to geomagnetic disturbances.

An Asymmetric Cone Model for Halo Coronal Mass Ejections

Due to projection effects, coronagraphic observations cannot uniquely determine parameters relevant to the geoeffectiveness of CMEs, such as the true propagation speed, width, or source location. The cone model for Coronal Mass Ejections (CMEs) has been studied in this respect and it could be used to obtain these parameters. There are evidences that some CMEs initiate from a flux-rope topology. It seems that these CMEs should be elongated along the flux-rope axis and the cross section of the cone base should be rather elliptical than circular. In the present paper we applied an asymmetric cone model to get the real space parameters of frontsided halo CMEs (HCMEs) recorded by SOHO/LASCO coronagraphs in 2002. The cone model parameters are generated through a fitting procedure to the projected speeds measured at different position angles on the plane of the sky. We consider models with the apex of the cone located at the center and surface of the Sun. The results are compared to the standard symmetric cone model.