Our Sun: The Culprit of Widespread Power Outages
If you’ve been through a storm, you may have gotten your power knocked out at one point or another. However, how often have you seen total power failure for a major part of a continent? Maybe once in a lifetime, such as the 1989 Quebec power outage.
The culprit of many of these widespread electricity flaws is none other than the same thing that allows life to thrive on Earth — the sun.
The sun is capable of putting out huge ejections of plasma into space, and some of these streams incidentally are detected on Earth. These ejections are called Coronal Mass Ejections, (CMEs), and can have devastating effects on the planet if the conditions are just right.
This type of solar activity was first noticed in 1859 and labeled as a flare related to the geomagnetic disturbances on Earth (Carrington, 1859). The storm had overridden some of the lines in the U. S. telegraph network, and this was the most probable reason why it was noticed. The first clear detection of a CME itself was taken in December of 1971 by Richard Tousey.
In order to understand the mechanics of a CME, we must understand the events happening at the sun. When the magnetic fields on the sun are closed, segments of the outer corona are ejected out into interplanetary space. The closed magnetic fields help the ejections keep their shape and intensity by herding them into a powerful stream that escapes the sun, known as CMEs.
Like anything from the sun, a CME takes time to reach Earth due to the vast distance (93 million miles) between the Earth and the Sun. The amount of time varies with some CMEs taking weeks to reach Earth while others less than a day, according to the SOHO LASCO CME CATALOG (Yashiro et al 2004).
The Advanced Composition Explorer (ACE) studies solar particles and detects a wide range of elements in a CME. Scientists use this device’s data to analyze CMEs and their structure in the data before they reach Earth. Using a particular data value from ACE, the Bz (from ACE Real-Time Solar Wind Data), astronomers have found a distinction to CMEs that are detected. In the beginning, before a CME hits, the data will show a “sheath region”, in which the Bz values will furiously toggle between negative and positive values. Then, when the actual CME hits, the Bz will stabilize in either a positive region or a negative value.
This distinction between the positive and negative values of the Bz is the most important to determining if a geomagnetic storm would’ve hit. If the Bz has a positive value, the CME will not do much. On the other hand, if the Bz has a negative value, then the CME will reconnect with the Earth’s magnetic field and have the potential to cause a geomagnetic storm (Gonzalez & Tsurutani, 1987). This is evidenced by the Bz’s close relation to the DST index (Burton et al 1975), with the DST measuring the disturbance of the magnetic field in the Earth’s atmosphere. Usually, as the Bz starts becoming more and more negative, the DST index will follow suit because of the disturbances in the atmosphere (Burton et al 1975).
In order to obtain more information about the CME, scientists study images (such as H-alpha) and simulations (such as those of JHelioviewer) of the sun to detect magnetic fields and solar filaments on its surface and how they may contribute to the negative-positive Bz orientation of the CME. Solar filaments can have chirality, or north-south orientations, distinguished by their placement in the magnetic fields on the surface of the sun (Martin, 1998). Many studies have indicated that the north-south orientation of a solar filament has a strong correlation with the negative-positive orientation of the Bz for a CME (Yurchyshyn 2001), (Palmerio et al 2018). More research is going on to further solidify this claim.
As such, it is very important to study solar weather not just to advance our scientific knowledge about stars and the sun, but also to detect harmful CMEs from the sun and to potentially avert disaster.
~ USAAAO Publicity Team (Kashvi Mundra)
References
Carrington, R.C., 1859. Description of a Singular Appearance seen in the Sun
on September 1, 1859. Monthly Notices of the Royal Astronomical Society
20, 13–15.
Tousey, R., Brueckner, G. E., Koomen, M. J., & Michels, D. J. 1972, Naval Research
Reviews, 25, 8
Stenzel, R.L. & Gekelman, W. (1981). Magnetic field line
reconnection experiments. 1. Field topologies, J. Geophys.
Res. 86, 649–58.
ACE Mission. (1998). Advanced Composition Explorer (ACE). http://www.srl.caltech.edu/ACE/ace_mission.html
Burton, R. K., R. L. McPherron, and C. T. Russell.: 1975, J. Geophys. Res., 80, 4204.
https://doi.org/10.1029/JA080i031p04204
Martin, S. F. (1998). Filament Chirality: A Link Between Fine-Scale and Global Patterns (Review). In D. F. Webb, B. Schmieder, & D. M. Rust (Eds.), Iau colloq. 167: New perspectives on solar prominences (Vols. ASP Conf. Ser., 150, p. 419).
Yurchyshyn, V. B., Wang, H., Goode, P. R., & Deng, Y.
2001, ApJ, 563, 381
Palmerio, E., Kilpua, E. K. J., Mostl, C., Bothmer, V., James, A. W., Green, L. M., Harrison, R. A. (2018). Coronal Magnetic Structure of Earthbound CMEs and In Situ
Comparison. Space Weather , 16 , 442–460. doi: 10.1002/2017SW001767
Gonzalez, W. D., & Tsurutani, B. T. 1987, Planetary and
Space Science, 35, 1101 ,
doi: https://doi.org/10.1016/0032-0633(87)90015-8
Yashiro, S., Gopalswamy, N., Michalek, G., St. Cyr, O.C., Plunkett, S.P., Rich, N.B., Howard, R.A., 2004. A catalog of white light coronal mass ejections observed by the SOHO spacecraft. J. of Geophys. Res. 109, A07105.
