Assessing VBz variations during CME propagation: a preparatory study for the HENON mission using EUHFORIA

Abstract

Coronal mass ejections (CMEs) are among the main drivers of space weather hazards. In this context, HENON is a new space mission designed to carry out observations in the solar wind upstream of the Earth, aiming to provide timely alerts for hazardous perturbations propagating towards the Earth. HENON will orbit Earth on a distant retrograde orbit, approximately 0.082 AU upstream of the Earth when it is on the Sun-Earth line. The measurements taken by HENON will allow us to determine plasma and magnetic field parameters with a lead time of several hours with respect to the Lagrangian point L1. We assess the VB_z parameter variations (the product of solar wind speed V and southward magnetic field B_z) along the HENON orbit. Given its role as a primary driver of geomagnetic activity, we analyse how these measurements change with respect to Earth's position to evaluate HENON's forecasting potential. We used the FRi3D CME model of the EUHFORIA simulation code to characterize the initial properties of the CME. FRi3D allows us to set the CME magnetic field as a magnetic flux rope. From the simulation results, we evaluated the VB_z parameter at nine virtual spacecraft positions along the planned HENON orbit. The heliocentric longitudes of the virtual spacecraft range from about -6.9° to 6.9°, while the geocentric longitudes vary from -60° to +60° in steps of 15°. The initial direction of propagation of the CME central apex is either along the Sun-Earth line or at heliocentric longitudes of {\pm}30°. We find that with the proposed orbital parameters, the values of the VBz parameter along the HENON orbit are sufficiently similar to those measured in the vicinity of the Earth to be useful for space weather forecasts. HENON enables reliable VB_z estimates 2-8 hours in advance, improving space weather forecasting and protection of critical infrastructure and satellites.

Figures (12)

• Figure 1: Dynamical configuration of DRO in the ecliptic plane, from Perozzi17. In both panels, the heliocentric orbit of the Earth is depicted in blue, while the orbit of the satellite is shown in red. In the right panel, the spacecraft's trajectory with respect to the Earth's reference frame is shown in black.
• Figure 2: The HENON spacecraft orbits around the Earth. Key region 1 (KR1) and key region 2 (KR2) are also reported. The spacecraft geocentric longitudes are measured from the Earth-Sun line in the clockwise direction, in agreement with the retrograde motion of HENON. (Figure adapted from Cicalo25)
• Figure 3: RUN1 simulation results at the time of arrival of the CME-driven shock at the HENON virtual spacecraft, indicated as HNN (see legend), positioned directly in front of the Earth, along the Sun-Earth line. Top row: detrended density in the equatorial plane (left) and in the meridional plane (right), with the colorbar on the right-hand side (panel (a)). Bottom row: radial velocity in the equatorial plane (left) and in the meridional plane (right), with the colorbar on the right-hand side (panel (b)). A yellow dot indicates the Earth's position, while green squares indicate the virtual spacecraft locations. In the inset we indicated the geocentric position of the virtual spacecraft in different colors.
• Figure 4: RUN1 simulation results. From top to bottom, the magnetic field components and strength, the plasma density, the bulk velocity components, the plasma temperature, and the $VB_z$ parameter. Left panels: values at the HENON spacecraft upstream of the Earth on the Earth-Sun line; right panels: values at the Earth.
• Figure 5: Variation of the $VB_z$ parameter at the nine virtual spacecraft along KR1, plus at the Earth (solid green line), in the case of positive magnetic helicity. The geocentric longitudes of each spacecraft are indicated in the legend. $VB_z$ is negative just after the shock crossing and then, because of the rotation of the magnetic field inside the flux rope, positive. In this case, $VB_z$ becomes smaller than $-5\;$mV/m for a period longer than 4 hours, implying that a geomagnetic storm is possible. For later times, after the CME passage, $VB_z$ tends towards small values, typical of unperturbed periods. The inset shows a magnified view of the $VB_z$ profiles around the time of the negative peaks, as indicated by the dashed rectangle in the main panel.