Observation and modeling of a geo-effective event observed on 2011 May 28 from the solar surface to 1au

TL;DR

The study investigates a geo-effective event on 2011 May 28 driven by two filament eruptions from adjacent ARs near a coronal hole. It combines multi-spacecraft remote-sensing and in situ observations with NLFFF flux-rope insertion and hydrodynamic propagation models to Sun–Earth distances, revealing that the coronal hole lowers the flux rope stability threshold and that the two CMEs propagate largely independently within the CH-origin high-speed wind, arriving at Earth with distinct signatures (D_ST ≈ -80 nT). The magnetic models reveal a pre-eruptive null-point/X-point topology and show that CME1 carried larger axial/poloidal flux and helicity than CME2, while both had positive helicity. Overall, the CH–AR topology significantly modulates CME kinematics, interaction likelihood, and geo-effectiveness, and the integrated modeling framework provides a computationally efficient path to track CME evolution from the Sun to 1 au.

Abstract

In this study, we present a comprehensive observational and modeling study of a geo-effective event with D_ST index of -80 nT observed on 2011 May 28 when a coronal hole was bordering an active region. We analyze HMI and EUV images and found that this event involved two filament eruptions ~8 hours apart from two different active region closed to each other. We produce 3D magnetic field configurations for the active regions that are consistent with the observations and employ numerical models to track the CME/ICME propagation up to 1\,au. From our, magnetic models we found that the nearby coronal hole reduced the stability threshold of the flux ropes, with axial flux values approximately three times lower than in comparable cases without coronal holes. A derivative analysis applied to STEREO coronagraph and OMNI database in situ data revealed no evidence of CME-CME interaction during the early stages of their evolution and identified distinct signatures of two CMEs, along with the interacting flow associated with the nearby coronal hole at 1 au. Moreover, we used hydrodynamic simulations constrained by remote sensing and in situ data to track the different structures in the solar wind. We found a good agreement between data and the models. Additionally, we found that the presence of the coronal hole may have suppressed interactions between CMEs, with the transients subsequently propagating along the solar wind streams emerging from the coronal hole.

Figures (17)

• Figure 1: Spacecraft location on 2011 May 25 00:00 UT. The Sun's location is shown in yellow. STEREO-A direction and location are shown in dash line and red circle, STEREO-B is marked in blue and Earth (SDO, SOHO and Wind) in green. STEREO-A/B were separated by about 90$^{\circ}$ from Earth.
• Figure 2: HMI magnetogram showing the eruption locations of two filaments. The rectangular boxes enclose the two active regions: NOAA 11218 ( left) and NOAA 11216 ( right). The red and blue S-shaped lines indicate the locations of the filament eruptions. The grayscale intensity is scaled between $+$100 G ( white) and $-$100 G ( black).
• Figure 3: AIA 193 Å observation snapshots of the filament eruption on 2011 May 25 03:45 and 04:15 UT related to CME 1. In the top left panel, the black arrow is pointing to the filament before launch, and in panels top right, bottom left, and bottom right the eruption evolution. The left dark regions (pointed by the red arrow in top left panel) indicates the coronal hole.
• Figure 4: Same as Figure \ref{['fig:aia193']} but for CME 2. We show AIA 193 Å observation snapshots of the second filament eruption on 2011 May 25 from 12:14 UT to 12:44 UT which is close to the location of the first eruption (pointed by the small blue arrow). In the top left panel, the black arrow points to the S-shaped filament before the eruption and panels (top right, bottom left, and bottom right) show the eruption evolution. The left big regions (pointed by the red arrow in the top left panel) correspond to the coronal hole.
• Figure 5: Example of the construction of the step-function $\Delta SB$ time series from the COR 2 images. Top left: Original $\Delta SB$ time series (shown in black) and its second derivative (in blue). Top right: Histogram of the second derivative with the $\sigma$ value used as a filter to obtain step-functions of the $\Delta SB$) time series. Bottom left: step-function of the $\Delta SB$ time series obtained when consecutive series elements with a lower value than $\sigma$ are averaged.