[1] The Solar and Heliospheric Observatory (SOHO) mission's white light coronagraphs have observed nearly 7000 coronal mass ejections (CMEs) between 1996 and 2002. We have documented the measured properties of all these CMEs in an online catalog. We describe this catalog and present a summary of the statistical properties of the CMEs. The primary measurements made on each CME are the apparent central position angle, the angular width in the sky plane, and the height (heliocentric distance) as a function of time. The height-time measurements are then fitted to first- and second-order polynomials to derive the average apparent speed and acceleration of the CMEs. The statistical properties of CMEs are (1) the average width of normal CMEs (20° 900 km s−1) show deceleration. Solar cycle variation and statistical properties of CMEs are revealed with greater clarity in this study as compared with previous studies. Implications of our findings for CME models are discussed.

https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2003JA010282

A catalog of white light coronal mass ejections observed by the SOHO spacecraft

In a previous study (Cane and Richardson, J. Geophys. Res.
 108(A4), SSH6-1, 2003), we investigated the occurrence of interplanetary coronal mass ejections in the near-Earth solar wind during 1996 – 2002, corresponding to the increasing and maximum phases of solar cycle 23, and provided a “comprehensive” catalog of these events. In this paper, we present a revised and updated catalog of the ≈300 near-Earth ICMEs in 1996 – 2009, encompassing the complete cycle 23, and summarize their basic properties and geomagnetic effects. In particular, solar wind composition and charge state observations are now considered when identifying the ICMEs. In general, these additional data confirm the earlier identifications based predominantly on other solar wind plasma and magnetic field parameters. However, the boundaries of ICME-like plasma based on charge state/composition data may deviate significantly from those based on conventional plasma/magnetic field parameters. Furthermore, the much studied “magnetic clouds”, with flux-rope-like magnetic field configurations, may form just a substructure of the total ICME interval.

Near-Earth Interplanetary Coronal Mass Ejections During Solar Cycle 23 (1996 - 2009): Catalog and Summary of Properties

Coronal mass ejections (CMEs) are the largest-scale eruptive phenomenon in the solar system, expanding from active region-sized nonpotential magnetic structure to a much larger size. The bulk of plasma with a mass of ∼ 1011,1013 kg is hauled up all the way out to the interplanetary space with a typical velocity of several hundred or even more than 1000 km s−1, with a chance to impact our Earth, resulting in hazardous space weather conditions. They involve many other much smaller-sized solar eruptive phenomena, such as X-ray sigmoids, filament/prominence eruptions, solar flares, plasma heating and radiation, particle acceleration, EIT waves, EUV dimmings, Moreton waves, solar radio bursts, and so on. It is believed that, by shedding the accumulating magnetic energy and helicity, they complete the last link in the chain of the cycling of the solar magnetic field. In this review, I try to explicate our understanding on each stage of the fantastic phenomenon, including their pre-eruption structure, their triggering mechanisms and the precursors indicating the initiation process, their acceleration and propagation. Particular attention is paid to clarify some hot debates, e.g., whether magnetic reconnection is necessary for the eruption, whether there are two types of CMEs, how the CME frontal loop is formed, and whether halo CMEs are special.

/pdf/coronal-mass-ejections-models-and-their-observational-basis-18wrfif7lq.pdf

Coronal Mass Ejections: Models and Their Observational Basis

This paper outlines the current understanding of solar flares, mainly focused on magnetohydrodynamic (MHD) processes responsible for producing a flare. Observations show that flares are one of the most explosive phenomena in the atmosphere of the Sun, releasing a huge amount of energy up to about 1032 erg on the timescale of hours. Flares involve the heating of plasma, mass ejection, and particle acceleration that generates high-energy particles. The key physical processes for producing a flare are: the emergence of magnetic field from the solar interior to the solar atmosphere (flux emergence), local enhancement of electric current in the corona (formation of a current sheet), and rapid dissipation of electric current (magnetic reconnection) that causes shock heating, mass ejection, and particle acceleration. The evolution toward the onset of a flare is rather quasi-static when free energy is accumulated in the form of coronal electric current (field-aligned current, more precisely), while the dissipation of coronal current proceeds rapidly, producing various dynamic events that affect lower atmospheres such as the chromosphere and photosphere. Flares manifest such rapid dissipation of coronal current, and their theoretical modeling has been developed in accordance with observations, in which numerical simulations proved to be a strong tool reproducing the time-dependent, nonlinear evolution of a flare. We review the models proposed to explain the physical mechanism of flares, giving an comprehensive explanation of the key processes mentioned above. We start with basic properties of flares, then go into the details of energy build-up, release and transport in flares where magnetic reconnection works as the central engine to produce a flare.

/pdf/solar-flares-magnetohydrodynamic-processes-44l1zcjlip.pdf

Solar Flares: Magnetohydrodynamic Processes

Coronal mass ejections (CMEs) are routinely identified in the images of the solar corona obtained by the Solar and Heliospheric Observatory (SOHO) mission’s Large Angle and Spectrometric Coronagraph (LASCO) since 1996. The identified CMEs are measured and their basic attributes are cataloged in a data base known as the SOHO/LASCO CME Catalog. The Catalog also contains digital data, movies, and plots for each CME, so detailed scientific investigations can be performed on CMEs and the related phenomena such as flares, radio bursts, solar energetic particle events, and geomagnetic storms. This paper provides a brief description of the Catalog and summarizes the statistical properties of CMEs obtained using the Catalog. Data products relevant to space weather research and some CME issues that can be addressed using the Catalog are discussed. The URL of the Catalog is: http://cdaw.gsfc.nasa.gov/CME_list.

/pdf/the-soho-lasco-cme-catalog-40h3giq5u2.pdf

The SOHO/LASCO CME Catalog

It is known that the weak state of the heliosphere due to diminished solar activity in cycle 24 backreacted on coronal mass ejections (CMEs) to make them appear wider for a given speed. One of the consequences of the weak state of the heliosphere is that more CMEs appear as halo CMEs (HCMEs), and halos are formed at shorter heliocentric distances. Current predictions for the strength of solar cycle (SC) 25 range from half to twice the strength of SC 24. We compare the HCME occurrence rate and other properties during the rise phase of cycles 23, 24, and 25 to weigh in on the strength of SC 25. We find that HCME and solar wind properties in SC 25 are intermediate between SCs 23 and 24, but closer to SC 24. The HCME occurrence rate, normalized to the sunspot number, is higher in SCs 24 and 25 than in SC 23. The solar wind total pressure in SC 25 is ∼35% smaller than that in SC 23. Furthermore, the occurrence rates of high-energy solar energetic particle events and intense geomagnetic storms are well below the corresponding values in SC 23, but similar to those in SC 24. We conclude that cycle 25 is likely to be similar to or slightly stronger than cycle 24, in agreement with polar-field precursor methods for cycle 25 prediction.

G. Michalek

Papers

What Do Halo CMEs Tell Us about Solar Cycle 25?