Real-time prediction of geomagnetic storms using Solar Orbiter as a far upstream solar wind monitor

TL;DR

This work demonstrates the feasibility of real-time CME forecasting using Solar Orbiter as a far-upstream monitor, delivering actionable lead times for geomagnetic impact by combining (i) ELEvo-based arrival predictions constrained by upstream in situ data, (ii) magnetic-field scaling and temporal stretching to predict the L1 field, and (iii) the Temerin & Li geomagnetic model to forecast SYM-H with ensemble uncertainty. The two March 2024 CME events show that upstream measurements can reproduce near-Earth magnetic structure and yield substantial lead times (up to ~34 hours before storm peaks), though arrival-time errors remain several hours and magnitude predictions can be limited by missing plasma data and complex CME evolution. Key insights include the dominance of radial evolution over longitudinal differences at separations up to ~10°, the value of using simple, observation-constrained propagation schemes, and the substantial benefit of continuous upstream plasma and field measurements for improving forecast reliability. The results support the strategic value of future dedicated upstream missions and data assimilation for enhanced space weather prediction and preparedness.

Abstract

We present the first real-time predictions of coronal mass ejection (CME) magnetic structure and resulting geomagnetic impact at Earth for two events using far-upstream observations from Solar Orbiter during March 2024. While our approach assumes idealized conditions for CME propagation and scaling, in situ magnetic field data from upstream monitors still produced realistic predictions despite the large heliocentric distance between Solar Orbiter and L1 (0.53 and 0.60 au). Geomagnetic index predictions were made 15.3 and 4.3 hours before the CME shock arrival at L1, and 33.9 and 10.3 hours ahead of peak storm time; a large improvement over current L1-based nowcasting capabilities. Analysis reveals that simple drag-based models, when observationally constrained by upstream in situ observations, improved arrival time estimates, comparable to more complex models, though arrival time errors of several hours persist. Our results show that good predictions of CME magnetic structure and geomagnetic indices with actionable lead-times can be made with far upstream spacecraft, even with longitudinal separations up to 10° from the Sun-Earth line, over heliocentric distance ranges where radial evolution effects dominate over longitudinal effects. Limitations include different expansion behaviors for individual CMEs and regions within. Future missions providing continuous data, including solar wind plasma parameters alongside magnetic field measurements, could account for preexisting disturbed conditions and improve geomagnetic prediction accuracy. Our findings demonstrate the substantial value of real-time upstream solar wind measurements for enhancing geomagnetic forecasting accuracy at Earth and provide critical validation for future dedicated upstream space weather missions.

Figures (6)

• Figure 1: a) SDO/AIA 211, 193, and 171 Å composite image showing the CME source region (outlined by the black rectangle) at 2024-03-17 03:30 UT. Panel (i) presents a zoomed view of the source region, highlighting the skewed post-eruption arcades, with white ‘+’ symbols marking the filament footpoints. b) SOHO LASCO C3 image at 2024-03-17 9:30 UT of the CME directed towards the South with arrows marking the shock and CME.
• Figure 2: Snapshot of the ELEvo model visualization at 2024 March 19 17:00 UT. Left: A top-down view of the solar equatorial plane with the spacecraft locations of Solar Orbiter (orange), BepiColombo (blue), Parker Solar Probe (black), STEREO-A (red) and Earth (green) shown in Heliocentric Earth Equatorial (HEEQ) coordinates. Their trajectories over the two-week window of this study (March 12--25) are indicated by the dashed lines in the corresponding color to the spacecraft marker. The heliocentric distance (R), longitude (lon), and latitude (lat) of Solar Orbiter and Earth are listed, showing that Solar Orbiter is well aligned with the Sun-Earth line during measurement of the CME and located $\sim~$0.56 au upstream of Earth. The propagation of the CME launched 2024 March 17 03:36 UT is represented by the elliptical fronts, where the shaded areas indicate the $\pm 1 \sigma$ uncertainties of the arrival time. The two fronts displayed correspond to two different arrival time predictions: The blue elliptical CME front represents the propagation of the CME using only DONKI kinematics producing predicted arrival times at both Solar Orbiter and L1. The orange front represents the second arrival time prediction, where the observed arrival time at Solar Orbiter is used to constrain the ELEvo model ensemble, producing an updated arrival time prediction at L1. Right: In situ magnetic field data in Geocentric Solar Magnetospheric (GSM) coordinates at Solar Orbiter (top panel) and the real-time solar wind (RTSW) data produced by NOAA at L1, available at the time the snapshot was taken (black vertical line). The predicted CME arrival times corresponding to the modeled fronts are represented by the blue (initial prediction) and orange (updated prediction) vertical lines.
• Figure 3: In situ CME and geomagnetic indices observations and predictions. Top: a timeline indicating when the steps of the real-time procedure were performed (times are also listed in Table \ref{['tab:timeline_event_1']}). a) the observed Solar Orbiter magnetometer data, displayed in Geocentric Solar Magnetospheric (GSM) coordinates with the x, y, and z components in red, green and blue, respectively. The initial Solar Orbiter data is presented by the full color lines, with the data received later represented by fainter color lines. Purple, orange and light blue vertical dashed lines delineate the CME shock front, leading and trailing edge of the CME, respectively. b) the predicted magnetic field at L1 using scaled ($\alpha$ = -1.64) Solar Orbiter MAG observations as described in Section \ref{['sec:pred_structure']}, in the same format as panel a. The associated shaded regions correspond to the uncertainty range, calculated by scaling the data using $\alpha$ = -2 for the lower bound and $\alpha$ = -1.2 for the upper bound. The same dashed vertical lines as panel a indicate where the predicted CME shock front, leading and trailing edge of the CME will occur at L1. These dashed vertical lines are carried through other panels to indicate the predicted CME boundaries where appropriate. The purple shaded region around the estimated time of arrival represents the model uncertainty. c) the observed real-time magnetic field data provided by the NOAA RTSW data product. Purple, orange and light blue vertical solid lines delineate the observed CME shock front, leading and trailing edge of the CME, respectively. These vertical lines are carried through other panels to indicate the observed boundaries where appropriate. d) the predicted SYM-H index produced by the Temerin & Li model is shown by the green line, where the shaded green region represents the uncertainty of the model. The real-time D$_{ST}$ index is shown in black. e) the observed real-time solar wind speed and f) the real-time proton density provided by the NOAA RTSW data product, with dashed lines corresponding to the plasma profiles input to the Temerin & Li model.
• Figure 4: a) Composite SDO/AIA 211, 193, and 171 Å image at 03:40 UT showing the source regions of the CMEs, where the black rectangle outlines the AR 3614 located around N25E07 (the source of the first and faster CME). Panel (i) presents a zoomed view of AR 3614 highlighting the skewed post-eruption loop system at 03:40 UT. Panel (ii) presents the SDO/HMI LOS magnetogram at 00:09 UT and the corresponding pre-eruption photospheric magnetic field context, with the polarity inversion line (PIL) traced in blue. The same PIL is overlaid in panel (i). The b)SOHO LASCO C3 image at 2024-03-23 03:42 UT of the halo CME eruption where arrows indicate the shock and CME.
• Figure 5: Snapshot of the ELEvo model visualization at 2024 March 23 23:00 UT presented in the same format as Figure \ref{['fig:elevo_17march']}. The spacecraft positions show that Solar Orbiter is located at a heliocentric distance of 0.38 au with a longitudinal separation of 11.1$^{\circ}$ with respect to the Sun-Earth line at the time of the snapshot.