The implementation and first results of the new space weather forecasting-targeted inner heliosphere model “European heliospheric forecasting information asset” (EUHFORIA) are presented. EUHFORIA consists of two major components: a coronal model and a heliosphere model including coronal mass ejections. The coronal model provides data-driven solar wind plasma parameters at 0.1 AU by constructing a magnetic field model of the coronal large-scale magnetic field and employing empirical relations to determine the plasma state such as the solar wind speed and mass density. These are then used as boundary conditions to drive a three-dimensional time-dependent magnetohydrodynamics model of the inner heliosphere up to 2 AU. CMEs are injected into the ambient solar wind modeled using the cone model, with their parameters obtained from fits to imaging observations. In addition to detailing the modeling methodology, an initial validation run is presented. The results feature a highly dynamic heliosphere that the model is able to capture in good agreement with in situ observations. Finally, future horizons for the model are outlined.
Context. Coronal Mass Ejections (CMEs) are the primary source of strong space weather disturbances at Earth. Their geoeffectiveness is largely determined by their dynamic pressure and internal magnetic fields, for which reliable predictions at Earth are not possible with traditional cone CME models. Aims. We study two well-observed Earth-directed CMEs using the EUropean Heliospheric FORecasting Information Asset (EUH-FORIA) model, testing for the first time the predictive capabilities of a linear force-free spheromak CME model initialised using parameters derived from remote-sensing observations. Methods. Using observation-based CME input parameters, we perform magnetohydrodynamic simulations of the events with EUH-FORIA, using the cone and spheromak CME models.Results. Simulations show that spheromak CMEs propagate faster than cone CMEs when initialised with the same kinematic parameters. We interpret these differences as result of different Lorentz forces acting within cone and spheromak CMEs, which lead to different CME expansions in the heliosphere. Such discrepancies can be mitigated by initialising spheromak CMEs with a reduced speed corresponding to the radial speed only. Results at Earth evidence that the spheromak model improves the predictions of B (B z ) up to 12-60 (22-40) percentage points compared to a cone model. Considering virtual spacecraft located within ±10 • around Earth, B (B z ) predictions reach 45-70% (58-78%) of the observed peak values. The spheromak model shows inaccurate predictions of the magnetic field parameters at Earth for CMEs propagating away from the Sun-Earth line.Conclusions. The spheromak model successfully predicts the CME properties and arrival time in the case of strictly Earth-directed events, while modelling CMEs propagating away from the Sun-Earth line requires extra care due to limitations related to the assumed spherical shape. The spatial variability of modelling results and the typical uncertainties in the reconstructed CME direction advocate the need to consider predictions at Earth and at virtual spacecraft located around it.
Abstract. In this paper we study the occurrence rate and solar origin of interplanetary coronal mass ejections (ICMEs) using data from the two Solar TErrestrial RElation Observatory (STEREO) and the Wind spacecraft. We perform a statistical survey of ICMEs during the late declining phase of solar cycle 23. Observations by multiple, well-separated spacecraft show that even at the time of extremely weak solar activity a considerable number of ICMEs were present in the interplanetary medium. Soon after the beginning of the STEREO science mission in January 2007 the number of ICMEs declined to less than one ICME per month, but in late 2008 the ICME rate clearly increased at each spacecraft although no apparent increase in the number of coronal mass ejections (CMEs) occurred. We suggest that the near-ecliptic ICME rate can increase due to CMEs that have been guided towards the equator from their high-latitude source regions by the magnetic fields in the polar coronal holes. We consider two case studies to highlight the effects of the polar magnetic fields and CME deflection taking advantage of STEREO observations when the two spacecraft were in the quadrature configuration (i.e. separated by about 90 degrees). We study in detail the solar and interplanetary consequences of two CMEs that both originated from high-latitude source regions on 2 November 2008. The first CME was slow (radial speed 298 km/s) and associated with a huge polar crown prominence eruption. The CME was guided by polar coronal hole fields to the equator and it produced a clear flux rope ICME in the near-ecliptic solar wind. The second CME (radial speed 438 km/s) originated from an active region 11007 at latitude 35° N. This CME propagated clearly north of the first CME and no interplanetary consequences were identified. The two case studies suggest that slow and elongated CMEs have difficulties overcoming the straining effect of the overlying field and as a consequence they are guided by the polar coronal fields and cause in-situ effects close to the ecliptic plane. The 3-D propagation directions and CME widths obtained by using the forward modelling technique were consistent with the solar and in-situ observations.
Aims.We introduce a new model for coronal mass ejections (CMEs) that has been implemented in the magnetohydrodynamics (MHD) inner heliosphere model EUHFORIA. Utilising a linear force-free spheromak (LFFS) solution, the model provides an intrinsic magnetic field structure for the CME. As a result, the new model has the potential to predict the magnetic components of CMEs at Earth. In this paper, we present the implementation of the new model and show the capability of the new model. Methods. We present initial validation runs for the new magnetised CME model by considering the same set of events as used in the initial validation run of EUHFORIA that employed the Cone model. In particular, we have focused on modelling the CME that was responsible for creating the largest geomagnetic disturbance (Dst index). Two scenarios are discussed: one where a single magnetised CME is launched and another in which we launch all five Earth-directed CMEs that were observed during the considered time period. Four out of the five CMEs were modelled using the Cone model. Results. In the first run, where the propagation of a single magnetized CME is considered, we find that the magnetic field components at Earth are well reproduced as compared to in-situ spacecraft data. Considering a virtual spacecraft that is separated approximately seven heliographic degrees from the position of Earth, we note that the centre of the magnetic cloud is missing Earth and a considerably larger magnetic field strength can be found when shifting to that location. For the second run, launching four Cone CMEs and one LFFS CME, we notice that the simulated magnetised CME is arriving at the same time as in the corresponding full Cone model run. We find that to achieve this, the speed of the CME needs to be reduced in order to compensate for the expansion of the CME due to the addition of the magnetic field inside the CME. The reduced initial speed of the CME and the added magnetic field structure give rise to a very similar propagation of the CME with approximately the same arrival time at 1 au. In contrast to the Cone model, however, the magnetised CME is able to predict the magnetic field components at Earth. However, due to the interaction between the Cone model CMEs and the magnetised CME, the magnetic field amplitude is significantly lower than for the run using a single magnetised CME. Conclusions. We have presented the LFFS model that is able to simulate and predict the magnetic field components and the propagation of magnetised CMEs in the inner heliosphere and at Earth. We note that shifting towards a virtual spacecraft in the neighbourhood of Earth can give rise to much stronger magnetic field components. This gives the option of adding a grid of virtual spacecrafts to give a range of values for the magnetic field components.
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