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Register a new userPropagating Conditions and the Time of ICMEs Arrival: A Comparison of the Effective Acceleration Model with ENLIL and DBEM Models
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The Effective Acceleration Model (EAM) predicts the Time-of-Arrival (ToA) of the Coronal Mass Ejection (CME) driven shock and the average speed within the sheath at 1 AU. The model is based on the assumption that the ambient solar wind interacts with the interplanetary CME (ICME) resulting in constant acceleration or deceleration. The upgraded version of the model (EAMv3), presented here, incorporates two basic improvements: (a) a new technique for the calculation of the acceleration (or deceleration) of the ICME from the Sun to 1 AU and (b) a correction for the CME plane-of-sky speed. A validation of the upgraded EAM model is performed via comparisons to predictions from the ensemble version of the Drag-Based model (DBEM) and the WSA-ENLIL+Cone ensemble model. A common sample of 16 CMEs/ICMEs, in 2013-2014, is used for the comparison. Basic performance metrics such as the mean absolute error (MAE), mean error (ME) and root mean squared error (RMSE) between observed and predicted values of ToA are presented. MAE for EAM model was 8.7$pm$1.6 hours while for DBEM and ENLIL was 14.3$pm$2.2 and 12.8$pm$1.7 hours, respectively. ME for EAM was -1.4$pm$2.7 hours in contrast with -9.7$pm$3.4 and -6.1$pm$3.3 hours from DBEM and ENLIL. We also study the hypothesis of stronger deceleration in the interplanetary (IP) space utilizing the EAMv3 and DBEM models. In particularly, the DBEM model perform better when a greater value of drag parameter, of order of a factor of 3, is used in contrast to previous studies. EAMv3 model shows a deceleration of ICMEs at greater distances, with a mean value of 0.72 AU.
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The Wang-Sheeley-Arge (WSA)-ENLIL+Cone model is used extensively in space weather operations world-wide to model CME propagation. As such, it is important to assess its performance. We present validation results of the WSA-ENLIL+Cone model installed at the Community Coordinated Modeling Center (CCMC) and executed in real-time by the CCMC space weather team. CCMC uses the WSA-ENLIL+Cone model to predict CME arrivals at NASA missions throughout the inner heliosphere. In this work we compare model predicted CME arrival-times to in-situ ICME leading edge measurements at STEREO-A, STEREO-B, and Earth (Wind and ACE) for simulations completed between March 2010-December 2016 (over 1,800 CMEs). We report hit, miss, false alarm, and correct rejection statistics for all three locations. For all predicted CME arrivals, the hit rate is 0.5, and the false alarm rate is 0.1. For the 273 events where the CME was predicted to arrive at Earth, STEREO-A, or STEREO-B, and was actually observed (hit event), the mean absolute arrival-time prediction error was 10.4 +/- 0.9 hours, with a tendency to early prediction error of -4.0 hours. We show the dependence of the arrival-time error on CME input parameters. We also explore the impact of the multi-spacecraft observations used to initialize the model CME inputs by comparing model verification results before and after the STEREO-B communication loss (since September 2014) and STEREO-A sidelobe operations (August 2014-December 2015). There is an increase of 1.7 hours in the CME arrival time error during single, or limited two-viewpoint periods, compared to the three-spacecraft viewpoint period. This trend would apply to a future space weather mission at L5 or L4 as another coronagraph viewpoint to reduce CME arrival time errors compared to a single L1 viewpoint.
Magnetic clouds (MCs), as large-scale interplanetary magnetic flux ropes, are usually still connected to the sun at both ends near 1 AU. Many researchers believe that all non-MC interplanetary coronal mass ejections (ICMEs) also have magnetic flux rope structures, which are inconspicuous because the observing spacecraft crosses the flanks of the rope structures. If so, the field lines of non-MC ICMEs should also be usually connected to the Sun on both ends. Then we want to know whether the field lines of most non-MC ICMEs are still connected to the sun at both ends or not. This study examined the counterstreaming suprathermal electron (CSE) signatures of 266 ICMEs observed by the emph{Advanced Composition Explorer} (emph{ACE}) spacecraft from 1998 to 2008 and compared the CSE signatures of MCs and non-MC ICMEs. Results show that only 10 of the 101 MC events ($9.9%$ ) and 75 of the 171 non-MC events ($43.9%$) have no CSEs. Moreover, 21 of the non-MC ICMEs have high CSE percentages (more than $70%$) and show relatively stable magnetic field components with slight rotations, which are in line with the expectations that spacecraft passes through the flank of magnetic flux ropes. So the 21 events may be magnetic flux ropes but the emph{ACE} spacecraft passes through their flanks of magnetic flux ropes. Considering that most other non-MC events have disordered magnetic fields, we suggest that some non-MC ICMEs inherently have disordered magnetic fields, namely have no magnetic flux rope structures.
The propagation of 15 interplanetary coronal mass ejections (ICMEs) from Earths orbit (1 AU) to Mars (~ 1.5 AU) has been studied with their propagation speed estimated from both measurements and simulations. The enhancement of magnetic fields related to ICMEs and their shock fronts cause the so-called Forbush decrease, which can be de- tected as a reduction of galactic cosmic rays measured on-ground. We have used galactic cosmic ray (GCR) data from in-situ measurements at Earth, from both STEREO A and B as well as GCR measurements by the Radiation Assessment Detector (RAD) instrument onboard Mars Science Laboratory (MSL) on the surface of Mars. A set of ICME events has been selected during the periods when Earth (or STEREO A or B) and Mars locations were nearly aligned on the same side of the Sun in the ecliptic plane (so-called opposition phase). Such lineups allow us to estimate the ICMEs transit times between 1 and 1.5 AU by estimating the delay time of the corresponding Forbush decreases measured at each location. We investigate the evolution of their propagation speeds before and after passing Earths orbit and find that the deceleration of ICMEs due to their interaction with the ambient solar wind may continue beyond 1 AU. We also find a substantial variance of the speed evolution among different events revealing the dynamic and diverse nature of eruptive solar events. Furthermore, the results are compared to simulation data obtained from two CME propagation models, namely the Drag-Based Model and ENLIL plus cone model.
The Radiation Assessment Detector (RAD) instrument onboard the Mars Science Laboratory (MSL) missions Curiosity rover has been measuring galactic cosmic rays (GCR) as well as solar energetic particles (SEP) on the surface of Mars for more than 6 years since its landing in August 2012. The observations include a large number of Forbush decreases (FD) caused by interplanetary coronal mass ejections (ICMEs) and/or their associated shocks shielding away part of the GCR particles with their turbulent and enhanced magnetic fields while passing Mars. This study combines MSL/RAD FD measurements and remote tracking of ICMEs using the Solar TErrestrial RElations Observatory (STEREO) Heliospheric Imager (HI) telescopes in a statistical study for the first time. The large data set collected by HI makes it possible to analyze 149 ICMEs propagating toward MSL both during its 8-month cruise phase and after its landing on Mars. We link 45 of the events observed at STEREO-HI to their corresponding FDs at MSL/RAD and study the accuracy of the ICME arrival time at Mars predicted from HI data using different methods. The mean differences between the predicted arrival times and those observed using FDs range from -11 to 5 hr for the different methods, with standard deviations between 17 and 20 hr. These values for predictions at Mars are very similar compared to other locations closer to the Sun and also comparable to the precision of some other modeling approaches.
In this study we use a numerical simulation of an artificial coronal mass ejection (CME) to validate a method for calculating propagation directions and kinematical profiles of interplanetary CMEs (ICMEs). In this method observations from heliospheric images are constrained with in-situ plasma and field data at 1 AU. These data are used to convert measured ICME elongations into distance by applying the Harmonic Mean approach that assumes a spherical shape of the ICME front. We use synthetic white-light images, similar as observed by STEREO-A/HI, for three different separation angles between remote and in-situ spacecraft, of 30{deg}, 60{deg}, and 90{deg}. To validate the results of the method they are compared to the apex speed profile of the modeled ICME, as obtained from a top view. This profile reflects the true apex kinematics since it is not affected by scattering or projection effects. In this way it is possible to determine the accuracy of the method for revealing ICME propagation directions and kinematics. We found that the direction obtained by the constrained Harmonic Mean method is not very sensitive to the separation angle (30{deg} sep: phi = W7; 60{deg} sep: phi = W12; 90{deg} sep: phi = W15; true dir.: E0/W0). For all three cases the derived kinematics are in a relatively good agreement with the real kinematics. The best consistency is obtained for the 30{deg} case, while with growing separation angle the ICME speed at 1 AU is increasingly overestimated (30{deg} sep: Delta V_arr ~-50 km/s, 60{deg} sep: Delta V_arr ~+75 km/s, 90{deg} sep: Delta V_arr ~+125 km/s). Especially for future L4/L5 missions the 60{deg} separation case is highly interesting in order to improve space weather forecasts.
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