Associated Research Papers

AIP_Roussev_2008_Final.pdf - Ilia I. Roussev et al. Global MHD Modeling of CMEs and Related Shocks from Complex Active Regions

ApJL_695_2_171.pdf - C. Jacobs et al. The Internal Structure of Coronal Mass Ejections: Are All Regular Magnetic Clouds Flux Ropes?

ApJ_64491_preprint.pdf – Cohen et al., Enhancement of Photospheric Meridional Flow by Reconnection Processes

ApJL_668_L87.pdf – Roussev et al., New Physical Insight on the Changes in Magnetic Topology During Coronal Mass Ejections: Case Studies for the 2002 April 21 and August 24 Events

Roussev_JCP2008_Published.pdf - Roussev et al., Eruptive events in the solar atmosphere: new insights from theory and 3-D numerical modeling

IAU257_2008_N_Lugaz.pdf – Lugaz et al., IAU Symposium, No. IAU257, 2008,The August 24, 2002 Coronal Mass Ejection: When a Western Limb Event Connects to Earth

ApJ_645_1537.pdf – Cohen et al., Enhancement of Photospheric Meridional Flow by Reconnection Processes

RoussevAGUMonogSeries_2005.pdf - Roussev & Sokolov, Models of Solar Eruptions: Recent Advances from Theory and Simulations

AA_418_L9.pdf – Doyle et al., New Insight into the blinker phenomenon and the dynamics of the solar transition region

JGR_109_A01102.pdf – Manchester et al., Three-dimensional MHD siulation of a flux rope driven CME

ApJ_588_L45.pdf - Roussev et al., A Three-Dimensional Flux Rope Model for Coronal Mass Ejections Based on a Loss of Equilibrium

Research

Introduction to CMEs

What are Coronal Mass Ejections?

Coronal Mass Ejections (CMEs) are the most extreme events occurring in our solar system and are usually defined as large-scale expulsions of plasma observed as bright arcs by coronagraphs. Typically, 10^{12}-10^{13} kg of coronal material is hurled into interplanetary space with a kinetic energy of the order of 10^{24}-10^{25} Joules. CMEs range in speed from 50 to 2500 km/s, and those with speeds in excess of the ambient solar wind (fast CMEs) eventually drive shock waves ahead of them as they propagate away from the Sun. The frequency of eruptions highly depends on the phase of the solar cycle: from 6 a day near solar maximum (2002) to 0.5-0.8 a day near solar minimum The first clear detection was on December 14, 1971 using the 7th Orbiting Solar Observatory (OSO-7). Over 10,000 CMEs have been observed by the different space-based coronagraphs since 1971, allowing a better view of their average properties. However, such a fundamental question as the nature of the CME triggering mechanism is still a matter of debate.

Detection of transient events near Earth was also made possible with space-borne measurements. The association of transients observed in the solar wind at Earth with CMEs observed by coronagraphs was made in 1982, when a magnetic cloud (the simplest and most regular type of solar wind transients) was observed by Helios-1, two days after a CME was observed by SMM in the solar corona. These transients are associated at Earth with geomagnetic storms, which are one of the causes of aurora, etc.

   

Order of magnitude:
An average CME would travel from Honolulu to NYC in 20 seconds, a fast one in 4 seconds.
An average CME contains as much mass as 500 million Hummer H2.
An average CME has as much energy as 20 billion Hiroshima bombs, 200 million nuclear warheads, or about 100,000 times more energy as the largest Earthquake ever recorded.

Right and Left images: SOHO/LASCO (ESA & NASA) (Left image SOHO view of a Coronal Mass Ejection on 2002/01/04.)

Link to an animation of a CME: http://www.nasa.gov/mission_pages/solar-b/solar_mm_001.html

Magnetic topology and CME initiation

The physical causes of coronal mass ejections (CMEs) have been debated by the solar community for over three decades now. The vast majority of proposed models to-date agree that CMEs are the result of catastrophic loss of mechanical equilibrium or stability of the coronal magnetic field. It is argued that the magnetic field in the corona may contain sufficient energy in excess of the potential limit to power an eruption, provided that some critical state is reached. The existing models typically involve idealized physical circumstances with either bipolar or quadrupolar underlying magnetic field geometries (see Figures).

The real Sun, however, demonstrates cases far more sophisticated than those studied in idealized configurations. At the Computational Center for Heliophysics in Hawaii, we study the effect of the magnetic topology of the Sun on the initiation and initial development of solar eruptions and associated phenomena (EUV waves, particle acceleration, etc...) This work is made possible by models of the coronal magnetic field which incorporates solar magnetogram observations to produce a realistic magnetic field topology. We proposed a generalization of the ``breakout'' model of Antiochos et al. and studied this CME initiation mechanism in realistic magnetic configuration. This model is aimed at reproducing one of the consequences in the corona of flux emergence, namely the shearing of opposite polarity spots. In our model, we add a small-scale bipole to the coronal magnetic field at some depth below the solar surface (Figure 1 top) and we move the opposite polarity with a speed of about 60-100 km/s (~< 2% of Alfvénic speed) (Figure 1 bottom). We also impose shearing flows on the solar surface. At the end of the shearing phase, due to current build-up, a pseudo-flux rope formed (Figure 2) and erupts (Figure 3) We argued that due to the reconnection of the bipolar emerging flux with neighboring (active region and quiet Sun) flux, the erupting material is not simply the initial flux of the erupting dipole. The reconnection occurs preferentially at pre-existing null points ( points where the magnetic field vanishes) and quasi-separatrix layer (separating topologically distinct regions of the solar surface, Figure 4, some cool movies too). One associated consequence of the eruption mechanism is that the footprint of the erupting flux is not fixed but move on the solar surface in a jump-like manner in a series of reconnection events. This behavior could have important implications for the production of solar energetic particles in terms of varying seed population.

 

 

 

Figure 1.



Figure 2.



Figure 3.



Figure 4.