Observations of an extreme storm in interplanetary space caused by successive coronal mass ejections (1405.6088v1)

Abstract: Space weather refers to dynamic conditions on the Sun and in the space environment of the Earth, which are often driven by solar eruptions and their subsequent interplanetary disturbances. It has been unclear how an extreme space weather storm forms and how severe it can be. Here we report and investigate an extreme event with multi-point remote-sensing and in-situ observations. The formation of the extreme storm showed striking novel features. We suggest that the in-transit interaction between two closely launched coronal mass ejections resulted in the extreme enhancement of the ejecta magnetic field observed near 1 AU at STEREO A. The fast transit to STEREO A (in only 18.6 hours), or the unusually weak deceleration of the event, was caused by the preconditioning of the upstream solar wind by an earlier solar eruption. These results provide a new view crucial to solar physics and space weather as to how an extreme space weather event can arise from a combination of solar eruptions.

• The paper reports that the interaction of consecutive CMEs produced an extreme solar storm with record solar wind speeds (2246 km/s) and magnetic field strength (109 nT) at 1 AU.
• The paper utilized multi-point remote sensing and in-situ measurements to capture detailed dynamics of CME-CME interactions in interplanetary space.
• The paper demonstrates that preconditioning of the solar wind by an earlier CME minimized drag, challenging conventional models and underscoring the need for improved forecasting.

Analyzing Extreme Solar Storms Induced by Consecutive Coronal Mass Ejections

The paper presents a detailed analysis of an extreme space weather event observed in interplanetary space on July 23, 2012. This event was characterized by a significant enhancement in solar wind speed and magnetic field strength due to interactions between successive coronal mass ejections (CMEs). The research utilized multi-point remote-sensing and in-situ observations, highlighting novel features and offering a new perspective on the dynamics leading to extreme space weather conditions.

Key Observations and Findings

Central to this paper is the documentation of successive CMEs originating from the Sun and their interaction en route to 1 AU, observed predominantly by STEREO A and B. The initial CME (CME1) followed closely by a second (CME2) resulted in amplified effects due to their interaction. Notably, the paper recorded an unprecedented solar wind speed of approximately 2246 km/s and a magnetic field strength of 109 nT at 1 AU – figures that surpass typical interplanetary CME values and rival historic solar disturbances.

The minimal deceleration of the CME complex was attributed to the preconditioning of the solar wind by a preceding CME. This phenomenon challenges typical expectations of CME speed reduction due to drag effects, suggesting that under specific solar preconditions, a CME can traverse the heliosphere with minimal energy loss, ultimately reaching the Earth with formidable intensity.

Practical and Theoretical Implications

The paper underscores the potential for severe geomagnetic storms resulting from CME-CME interactions, emphasizing the importance of improved forecasting models that can capture these dynamics. The implications for space weather prediction models are notable, particularly in terms of refining the estimates for solar wind speed and magnetic field strength at 1 AU, which conventional models often underestimate.

This research contributes to the understanding of space weather phenomena by illustrating how rare combinations of solar eruptions and interplanetary conditions culminate in significant solar disturbances. The potential impacts on modern society, reliant on space-based and ground-based technological systems, underscore the necessity of refining predictive capabilities to mitigate such high-consequence events.

Prospective Research Directions

Future research should focus on enhancing predictive models by incorporating comprehensive data from multi-point observations to provide detailed insights into CME interactions. Additionally, understanding the solar cycle's role in influencing CME activity—even in weaker cycles—could offer further context for the occurrence of extreme space weather events. The development of simulations capable of accurately reproducing such events will be vital not only for scientific comprehension but perhaps more critically, for developing actionable space weather mitigation strategies.

In conclusion, this paper represents a significant step forward in recognizing the importance of CME interactions in causing extreme space weather, enhancing both the theoretical framework and practical forecasting methodologies in heliophysics.