Featured Research

from universities, journals, and other organizations

Some Coronal Mass Ejections Are Caused By Shock Waves From Solar Flares In Other Regions Of The Sun

Date:
April 5, 2000
Source:
American Geophysical Union
Summary:
Scientists have discovered that some CMEs are caused by solar flares not directly under them. Shock waves from the flares cross an interconnecting loop of solar material, causing it to eject hot X-rays that form a major part of the CME.

WASHINGTON - Scientists have discovered a new source for some of the large scale eruptions on the Sun known as coronal mass ejections, or CMEs. These eruptions are a key ingredient of strong geomagnetic storms that can cause bright auroras, damage sensitive satellite instruments in space, and even disrupt power generation and transmission by inducing strong electric currents below the surface of the Earth.

Writing in the April 15 issue of Geophysical Research Letters, Dr. Josef I. Khan of University College, London (UK), and Dr. Hugh S. Hudson of the Solar Physics Research Corporation in Tucson, Arizona (USA), report that shock waves launched from solar flares can cause CMEs elsewhere in the solar corona. They found that such mass ejections do not emanate from structures directly above the eruptive flare, a more common pattern, but rather from off to one side.

Khan and Hudson are both currently based at Japan's Institute of Space and Astronautical Science (ISAS) in Kanagawa, where they conducted their investigations using the Yohkoh ("sunbeam") satellite. Studying X-ray images of the Sun, they examined very large hot loops of solar material that sometimes connect sunspot regions in the Sun's northern and southern hemispheres. They found that such loops, known as interconnecting X-ray loops, can simply disappear suddenly, ejecting huge amounts of material.

In particular, Khan and Hudson found three similar disappearances on May 6, 8, and 9, 1998. All of the observed interconnecting X-ray loops disappeared and were followed by looplike CMEs. Each CME event could be tracked far out into the corona via images obtained from another instrument, the Large Angle Spectroscopic Coronagraph (LASCO) on the Solar and Heliospheric Observatory (SOHO) satellite.

The researchers say the association between these disappearing loops and solar flares is novel and interesting. Scientists debate the relationship between CMEs and other phenomena, including solar flares and prominence eruptions. Solar flares release large amounts of energy across the electromagnetic spectrum, while prominence eruptions are the ejection of large suspensions of cool material in the Sun's hot outer atmosphere, or corona. Some, but not all, prominence eruptions and CMEs are associated with flares.

There is, however, a clear relationship between prominence eruptions and CMEs on the one hand and X-ray brightenings seen in the corona below these ejections. The question before scientists is what causes what, and which therefore is the more important phenomenon physically. Khan and Hudson found that for the events they studied, and contrary to the normal pattern, the flare is not located directly below the CME. It is, rather, located off to one side, in a sunspot region outside the structures that erupt to become part of the CME. Put another way, the mass ejected in the CME does not come from the structures directly above the flare.

Khan and Hudson, studying Yohkoh X-ray images, were able to determine fairly accurately the timing of the disappearance of the interconnecting loops. They found that the solar flare occurs before the loops disappear and, therefore, before the start of the coronal mass ejection. Further, by studying these X-ray data and simultaneous data from radio telescopes, they found evidence for shock waves. In every instance they examined, they found that the interconnecting loops disappear when the shocks cross their vicinity.

These observations led to a new scenario Khan and Hudson have put forward to explain some CMEs. A shock wave generated by the flare crosses a large interconnecting loop, causing it to become unstable and erupt. This ejects hot X-ray material, which becomes a significant fraction of the coronal mass ejection. The researchers acknowledge that this hypothesis requires further exploration, and they recognize that it does not apply to all CMEs, only the type they reported.

Yokoh is a mission of the Institute of Space and Astronautical Science (ISAS) of Japan. SOHO is a joint mission of ESA and NASA, stationed at 1.5 million kilometers (930,000 miles) from the Earth, near the so-called Lagrange point L1, where the gravity of Earth and Sun balance each other.

The research for this paper was supported by grants from the Particle Physics and Astronomy Research Council (PPARC) of the United Kingdom and NASA.


Story Source:

The above story is based on materials provided by American Geophysical Union. Note: Materials may be edited for content and length.


Cite This Page:

American Geophysical Union. "Some Coronal Mass Ejections Are Caused By Shock Waves From Solar Flares In Other Regions Of The Sun." ScienceDaily. ScienceDaily, 5 April 2000. <www.sciencedaily.com/releases/2000/04/000404122024.htm>.
American Geophysical Union. (2000, April 5). Some Coronal Mass Ejections Are Caused By Shock Waves From Solar Flares In Other Regions Of The Sun. ScienceDaily. Retrieved September 17, 2014 from www.sciencedaily.com/releases/2000/04/000404122024.htm
American Geophysical Union. "Some Coronal Mass Ejections Are Caused By Shock Waves From Solar Flares In Other Regions Of The Sun." ScienceDaily. www.sciencedaily.com/releases/2000/04/000404122024.htm (accessed September 17, 2014).

Share This



More Space & Time News

Wednesday, September 17, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Boeing, SpaceX to Send Astronauts to Space Station

Boeing, SpaceX to Send Astronauts to Space Station

AFP (Sep. 17, 2014) — NASA selected Boeing and SpaceX on Tuesday to build America's next spacecraft to carry astronauts to the International Space Station (ISS) by 2017, opening the way to a new chapter in human spaceflight. Duration: 01:13 Video provided by AFP
Powered by NewsLook.com
East Coast Treated To Rare Meteor Sighting

East Coast Treated To Rare Meteor Sighting

Newsy (Sep. 16, 2014) — Numerous residents along the East Coast reported seeing a bright meteor flash through the sky Sunday night. Video provided by Newsy
Powered by NewsLook.com
Space Race Pits Bezos Vs Musk

Space Race Pits Bezos Vs Musk

Reuters - Business Video Online (Sep. 16, 2014) — Amazon CEO Jeff Bezos' startup will team up with Boeing and Lockheed to develop rocket engines as Elon Musk races to have his rockets certified. Fred Katayama reports. Video provided by Reuters
Powered by NewsLook.com
NASA Picks Boeing and SpaceX to Ferry Astronauts

NASA Picks Boeing and SpaceX to Ferry Astronauts

AP (Sep. 16, 2014) — NASA is a giant step closer to launching Americans again from U.S. soil. It has announced it has picked Boeing and SpaceX to transport astronauts to the International Space Station in the next few years. (Sept. 16) Video provided by AP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins