What Are CMEs?

Humans have made significant strides on Earth, encapsulating vast data in tiny pen drives. Yet, certain natural phenomena continue to baffle us. Among these are Coronal Mass Ejections (CMEs), discovered by space scientists, with the potential to alter our reality in a blink. 

What Are CMEs? Coronal Mass Ejections are solar eruptions of billions of tons of molten plasma flying away from the Sun at a million miles per hour. They are the most powerful events in our solar system that we are aware of and could be one of the most significant dangers to life as we humans know it on earth.

Delving into the realm of CMEs unveils a fascinating interplay of celestial dynamics. This article embarks on a journey to unravel the essence, historical discovery, and inherent dynamics of these awe-inspiring phenomena.  

Dynamics: What Causes CMEs?

The initial discovery of CMEs stemmed from an agricultural observation concerning the scarcity of sunspots reaching the Earth and its subsequent impact on wheat production. Further observations revealed that CMEs transpire when there is a disruption in the forces maintaining equilibrium. 

Recommended Reading: How Much Time Do We Have Before a G5 Geomagnetic Storm Hits After a Solar CME?

Specifically, CMEs manifest when the upward forces outweigh the downward forces, with the principal forces identified as gravity and gas pressure. CMEs also reside within a magnetic field, which exerts dominance over the plasma, particularly around the most active regions of the corona at lower altitudes. 

These events lead to the formation of two competing magnetic forces, inducing pressure and tension. A higher degree of pressure prevails in the region possessing the strongest magnetic field, which naturally extends towards the area with a weaker magnetic field. 

An eruption, culminating in what we now recognize as Coronal Mass Ejections, is initiated when a certain factor tips the balance in favor of the gradient of the outward pressure.

The onset of CMEs is attributed to a burgeoning force of imbalance that amplifies over time, rendering the eruption exceedingly violent.

Biggest Acknowledged CME / Geomagnetic Storms of All Time

Here’s The Thing With CME’s

After you follow the NOAA Space Weather Prediction Center for a while, you realize that 99 percent of all Geomagnetic storms that hit the earth are glancing blows and not direct hits.

In a quote from the scientific paper link above, the ”Theory of Coronal Mass Ejections” by James A. Klimchuk and the Space Science Division, Naval Research Laboratory, Washington, DC, first published in January 2001.

The reality of the power of Coronal Mass Ejections (CMEs) becomes clear.

“Coronal mass ejections (CMEs) are the most energetic events in the solar system. They are spectacular displays representing the sudden eruption of up to 10¹⁶ gm of coronal material at speeds of typically several hundred kilometers per second [Hundhausen, 1999; St. Cyr et al, 2000]. In more colloquial terms, they are a billion tons of super heated matter flying away from the Sun at a million miles per hour! 

We now know that CMEs are more than just interesting natural phenomena. They are also the primary cause of the largest and most damaging space weather disturbances [Gosling, 1993; Webb et al., 2000]. Effects include the temporary and sometimes permanent failure of satellites, the degradation or disruption of communication, navigation, and commercial power systems, and the exposure of astronauts and polar-route airline crews to harmful doses of radiation. 

Some of these effects are delayed approximately 3 days, the time it takes a CME to propagate to Earth and interact with the magnetosphere. Others begin almost immediately Space Weather Geophysical after the CME lifts off from the Sun due to the production of solar energetic particles (SEPs) that travel at relativistic speeds. Clearly, there is a need to understand CMEs and ultimately to predict them before they occur. This need will grow even greater as society’s dependence on space and space-based technologies steadily increases over time.”

Klimchuk, J.A. (2001). Theory of Coronal Mass Ejections. In Space Weather (eds P. Song, H.J. Singer and G.L. Siscoe). https://doi.org/10.1029/GM125p0143

Please see some of our other interesting articles like “How Many Watts of Power Do You Need for Emergency Preparedness?” and “Should You Be Worried About Weather-Caused Power Grid Outages?”

The Historical Discovery of Coronal Mass Ejections

Solar-terrestrial relationships have impacted human life in multifarious ways. In 1801, a scientist named William Herschel reported a correlation between high wheat prices in England and the occurrence of five prolonged periods of fewer sunspots.

Herschel’s observations highlighted significant insights that would underpin later discoveries. He noted that fewer sunspots resulted in diminished heat and light from the sun. These conditions led to lower wheat production, thereby increasing the demand for wheat, which consequently sold at exorbitant prices.

At the time, Herschel’s report was met with incredulity. Still, advancements in space science and space weather eventually vindicated his observations. Scientific evidence now indicates the existence of sunspots, around which the sun’s radiation intensifies due to the appearance of brighter facula.

In 1843, the phenomenon associated with sunspots was designated as a geomagnetic storm, a term coined by Alexander von Humboldt. This terminology emerged from a series of synthesized knowledge concerning observable geometric disturbances around the sun.

In 1852, Edward Sabine unearthed more associations, discovering synchronous changes in the number of sunspots and geomagnetic activities around the sun. These incremental discoveries culminated on September 1, 1859, with the observation of a sudden solar brightening, which preceded a major geomagnetic event 17 hours later.

The discovery by Carrington and Hodgson underwent a series of iterative studies before scientists could ascertain with certainty that the geomagnetic event was tied to a solar event. Specifically, it was understood that the sudden brightening around the sun was, in fact, the ejection of a stream of particulate matter, later also identified as a cloud of plasma. This marked the discovery of Coronal Mass Ejections (CMEs). 

CMEs as a New Phenomenon

Numerous studies regard the discovery of CMEs as a relatively recent phenomenon. This realization of heated plasma emanating from the sun occurred in 1971 and has since captivated the research endeavors of various groups striving to comprehend what is deemed the most energetic phenomenon on the sun. 

The intrigue surrounding CMEs also lies in their potential extensive impact within the heliosphere. 

The Morphological Properties of CMEs

Coronal Mass Ejections (CMEs) exhibit a variety of shapes. This characteristic can be anticipated considering these ejections depart from the sun at speeds of about 1900 miles per hour (3056 km/h).

Nonetheless, fundamental differences have led to the categorization of CMEs into what scientists term normal CMEs and those deemed less typical. Normal CMEs possess narrower shapes characterized by closed frontal loops. These types of ejections project from the sun in a jet-like motion along an open magnetic field.

Intriguingly, all CMEs share a three-part structure: a bright frontal loop, a dark cavity, and an embedded bright core. Alternative nomenclature for these features includes the shock, sheath, and ejecta/magnetic cloud (MC). 

This tripartite structure has come to be recognized as the standard morphology of CMEs. However, subsequent observations reveal that only 30% of all CMEs conform to this standard morphology.

Some CMEs manifest without the embedded bright core, a phenomenon scientists attribute to the loss of filament material as it drains onto the solar surface and along the magnetic field. Conversely, other CMEs lose their bright core due to thermal instability, failing to form a filament prior to eruption. 

Observable Features of CMEs

The observable features of CMEs have significantly contributed to their definition. Space scientists identified the existence of CMEs upon observing alterations in the sun’s coronal structure, where the changes exhibited an outward motion.

Subsequent observations disclosed the emergence of a discrete, bright, white-light feature captured within a coronagraph’s field of view. These observable features are not discernible to the naked eye. Using soft X-rays, extreme ultraviolet, and radio wavelengths is requisite for making multi-wavelength observations, achieving a comprehensive understanding of CMEs.

Recent propositions suggest that employing the Ly𝛼 line at ultra-violet (UV) wavelengths would more aptly detect the observable features of CMEs. A notable characteristic of CMEs is the emission of white light from the corona. This white light emanates from photospheric radiation, whose enhanced brightness amplifies the coronal density along the line of sight.

Discerning all features of a CME in a single observation poses a challenge, explaining the continual observations undertaken by different groups over the years. Various observations deploy space-borne coronagraphs, while others are conducted from ground-based stations. 

These concerted efforts have culminated in over ten thousand recordings of CME events, thus explaining the most significant properties of this natural phenomenon.  

Key Takeaways 

Coronal Mass Ejections (CMEs) are natural phenomena that elucidate the relationship between the sun and planet Earth. The Earth relies on the sun for warmth and to facilitate plant growth. Alterations in sunspot activity can affect production.

CMEs arise when there is a disturbance in the forces governing the sun’s magnetic field. This imbalance precipitates violent eruptions that have the potential to alter life on Earth within mere seconds. 

References: 

• AGU Publications: Theory of Coronal Mass Ejections
• Astronomy & Astrophysics: Determination of coronal mass ejection orientation and consequences for their propagation
• NASA: Coronal Mass Ejections: A Summary of Recent Results
• Springer Open: History and development of coronal mass ejections as a key player in solar terrestrial relationship
• SpringerLink: Coronal Mass Ejections: Models and Their Observational Basis
• The Astrophysical Journal: The Lyα Emission in a C1.4 Solar Flare Observed by the Extreme Ultraviolet Imager aboard Solar Orbiter