engleski

Drag-based Forecast for CME Arrival

The accurate estimation of the CME arrival times at 1 AU is of key importance for space weather forecast. It is a challenging issue, since when a CME expands, it inevitably interacts with the solar corona and the ambient solar wind occupying the interplanetary space. This often results in modification of the CME's plasma properties and propagation path. There are various approaches in use for arrival time prediction - either based on MHD modeling or empirical relations between parameters measured from coronagraphs and in-situ at L1. Here, we investigate the performance of the recent Drag Based Ensemble Model (DBEM, Dumbović et al., 2018 ; Žic et al., 2015) available for users from the ESA Space Situational Awareness Portal (http://swe.ssa.esa.int). DBEM provides an ensemble of probabilistic predictions for CME arrivals based on the Drag-Based Model (DBM, Vršnak et al., 2013) which assumes that the propagation of a CME is dependent solely on the magnetohydrodynamic drag (in analogy to the aerodynamic drag) exerted to the CME from the ambient solar wind. We have selected to test a set of twelve geoeffective Earth-directed fast halo CMEs. For the model runs, we use as input CMEs' shock speed and the velocity of the respective preceding solar wind measured by WIND spacecraft. We perform test runs with values of the drag parameter: (0.1, 0.2 and 0.3)x10-7 km-1. Overall, the model produced a wide distribution of arrival times. The predictions were rather good, being confined in the range of ± 10 h. In addition, the model provides prediction for the CME arrival speeds, which in our case seem to be overestimated for all drag values. The closest predicted arrival time to about -2.5 h on average, was achieved by setting the drag value to 0.2x10-7 km-1. When matching also the predicted to the observed arrival speeds, the best average result was achieved with drag parameter 0.3x10-7 km-1, corresponding to +4.5 h CME arrival time. These drag values are higher than the recommended 0.1x10-7 km-1 for fast CMEs, suggesting that the exerted solar wind drag was higher than anticipated. This implies that further improvement in the CME arrival forecast requires more detailed and precise knowledge of the preconditioning of the interplanetary space through which the CMEs are propagating. References: Dumbović, M., et al., The Drag-based Ensemble Model (DBEM) for Coronal Mass Ejection Propagation. Astrophys. J., 854:180, 2018 Žic, M. et al., Heliospheric Propagation of Coronal Mass Ejections: Drag-based Model Fitting. Astrophys. J. Suppl., 218:32, 2015 Vršnak, B., et al., Propagation of Interplanetary Coronal Mass Ejections: The Drag-Based Model, Solar Phys. 285:295-315, 2013

coronal mass ejections ; interplanetary shocks ; space weather ; forecasts ; models ; Physics - Space Physics

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