From Wikipedia, the free encyclopedia
Three recent solar cycles
Solar maximum is contrasted with solar minimum. Solar maximum is the period when the sun’s magnetic field lines are the most distorted due to the magnetic field on the solar equator rotating at a slightly faster pace than at the solar poles. The solar cycle takes an average of about 11 years to go from one solar maximum to the next with an observed variation in duration of 9 to 14 years for any given solar cycle.
For more detailed explanation of solar cycles, see Solar variation.
The unreliability of solar maxima predictions is demonstrated in that NASA had previously predicted the solar maximum for 2010/2011 and possibly to occur as late as 2012. Previously, on March 10, 2006, NASA researchers had announced that the next solar maximum would be the strongest since the historic maximum in 1958 in which the northern lights could be seen as far south as Rome, approximately 42° north of the equator.
- ^ http://earthobservatory.nasa.gov/IOTD/view.php?id=37575
- ^ "New Solar Cycle Prediction", Science@NASA, 09 May 2006, Accessed 26 Mar. 2010
- ^ "Solar Cycle Process and Prediction", NOAA/Space Weather Center, 9 May 2009, Accessed 22 Mar. 2010
- ^ "Solar Storm Warning", Science@NASA, 10 March 2006, Accessed 26 Mar. 2010
SATURDAY, AUGUST 28, 2010
Twice over the past few months I’ve written about the concerns that FEMA and NASA, along with a host of other agencies and governments, have voiced about potential damage a severe solar storm might cause to our high-tech infrastructure.
While sounding a bit like science-fiction, in truth large and potentially disruptive solar storms do occur on rare occasions – usually at the time of a solar maximum.
The next solar maximum is due in 2012-2013, and some scientists have suggested this could be a particularly active cycle.
Some have gone so far as to suggest we could see a flare as big as 1859’s `Carrington Event’ (described here), or the somewhat lesser event of 1921.
Both were strong enough, that were they to happen today, would likely cause serious damage to parts of our electrical infrastructure.
NASA, while admitting that a serious solar storm could happen practically anytime, also cautions that the next big one could be many decades away. It is a genuine threat, they say, but the timing is impossible to predict.
In 2009 the National Academy of Sciences produced a 134 page report on the potential damage that another major solar flare could cause in Severe Space Weather Events—Understanding Societal and Economic Impacts.
You can read it for free online at the above link.
Typical is the report from news.com.au that proclaims:
Admittedly, these sorts of disaster headlines sound a bit like a `Scarrington’ event to me, but the point is to draw the reader’s attention to the story, and here I suppose the headline succeeds admirably.
The body of the article is a bit more grounded, and provides an entertaining and interesting overview of the concerns being voiced by some astronomers about the upcoming solar max.
As you might imagine, this threat has been picked up and greatly amplified by a number of prophesy/ Mayan 2012/ End-of-the-World websites, which tends to dilute it’s legitimacy in many circles.
But astronomers know that our sun is a variable star, and it goes through many major, and minor cycles. The best documented of these is the 11-year/22-year sunspot cycle.
Roughly every 11 years (it runs anywhere from 9 to 14 years), the sun experiences a magnetic pole shift at the time of solar maximum – a period of high sunspot and solar flare activity.
Every 22 years, the cycle completes, and the poles return to their `original’ position.
Our sun has, since 2006, been in a solar minimum or quiescent phase. Very few sunspots and solar flares.
The next solar maximum was predicted to occur in 2012, but the sun’s sunspot activity remains low, and so now NASA is looking more towards 2013.
This from science.nasa.gov.
June 4, 2010: Earth and space are about to come into contact in a way that’s new to human history. To make preparations, authorities in Washington DC are holding a meeting: The Space Weather Enterprise Forum at the National Press Club on June 8th.
Many technologies of the 21st century are vulnerable to solar storms. [more]
Solar flares the size of 1859’s `Carrington Event’ don’t happen very often, and in order to affect earth, the flare or CME (coronal mass ejection) must be pointed towards our planet (or where the earth will be when it arrives 2-3 days later).
Still, in 1989 a geomagnetic storm fried several large power transformers in Quebec, causing a province-wide blackout.
And in 2003, a number of satellites were severely damaged by an extremely powerful CME which also caused some power outages in Europe.
Over the past couple of decades we’ve become increasingly dependant upon computers, the Internet, cell phones, electronic devices, and of course . . . the electrical grid.
Systems that are considered vulnerable to unusually severe geomagnetic storms.
While imbued with a certain degree of hyperbole, the media reports this week aren’t without scientific merit, although the immediacy of the threat is far less certain.
As I’ve stated before, another `Carrington Event’ may not happen in our lifetime, or it could happen within the next few years.
No one knows.
Since National Preparedness Month (NPM10) is just a week away, it is a good time to remind my readers that:
If you are well prepared for an earthquake, ahurricane, or a pandemic . . . you are automatically in a better position to weather the disruptions caused any disaster . . . including something as rare as a catastrophic a solar storm.
Preparing is easy. Worrying is hard.
Some resources to get you started on the road to `all threats’ preparedness include:
AMERICAN RED CROSS http://www.redcross.org/
Solar Storm Warning
March 10, 2006: It’s official: Solar minimum has arrived. Sunspots have all but vanished. Solar flares are nonexistent. The sun is utterly quiet.
Like the quiet before a storm.
This week researchers announced that a storm is coming–the most intense solar maximum in fifty years. The prediction comes from a team led by Mausumi Dikpati of the National Center for Atmospheric Research (NCAR). "The next sunspot cycle will be 30% to 50% stronger than the previous one," she says. If correct, the years ahead could produce a burst of solar activity second only to the historic Solar Max of 1958.
That was a solar maximum. The Space Age was just beginning: Sputnik was launched in Oct. 1957 and Explorer 1 (the first US satellite) in Jan. 1958. In 1958 you couldn’t tell that a solar storm was underway by looking at the bars on your cell phone; cell phones didn’t exist. Even so, people knew something big was happening when Northern Lights were sighted three times in Mexico. A similar maximum now would be noticed by its effect on cell phones, GPS, weather satellites and many other modern technologies.
Right: Intense auroras over Fairbanks, Alaska, in 1958. [More]
Dikpati’s prediction is unprecedented. In nearly-two centuries since the 11-year sunspot cycle was discovered, scientists have struggled to predict the size of future maxima—and failed. Solar maxima can be intense, as in 1958, or barely detectable, as in 1805, obeying no obvious pattern.
The key to the mystery, Dikpati realized years ago, is a conveyor belt on the sun.
We have something similar here on Earth—the Great Ocean Conveyor Belt, popularized in the sci-fi movieThe Day After Tomorrow. It is a network of currents that carry water and heat from ocean to ocean–see the diagram below. In the movie, the Conveyor Belt stopped and threw the world’s weather into chaos.
Above: Earth’s "Great Ocean Conveyor Belt." [More]
The sun’s conveyor belt is a current, not of water, but of electrically-conducting gas. It flows in a loop from the sun’s equator to the poles and back again. Just as the Great Ocean Conveyor Belt controls weather on Earth, this solar conveyor belt controls weather on the sun. Specifically, it controls the sunspot cycle.
Solar physicist David Hathaway of the National Space Science & Technology Center (NSSTC) explains: "First, remember what sunspots are–tangled knots of magnetism generated by the sun’s inner dynamo. A typical sunspot exists for just a few weeks. Then it decays, leaving behind a ‘corpse’ of weak magnetic fields."
Enter the conveyor belt.
"The top of the conveyor belt skims the surface of the sun, sweeping up the magnetic fields of old, dead sunspots. The ‘corpses’ are dragged down at the poles to a depth of 200,000 km where the sun’s magnetic dynamo can amplify them. Once the corpses (magnetic knots) are reincarnated (amplified), they become buoyant and float back to the surface." Presto—new sunspots!
Right: The sun’s "great conveyor belt." [Larger image]
All this happens with massive slowness. "It takes about 40 years for the belt to complete one loop," says Hathaway. The speed varies "anywhere from a 50-year pace (slow) to a 30-year pace (fast)."
When the belt is turning "fast," it means that lots of magnetic fields are being swept up, and that a future sunspot cycle is going to be intense. This is a basis for forecasting: "The belt was turning fast in 1986-1996," says Hathaway. "Old magnetic fields swept up then should re-appear as big sunspots in 2010-2011."
Like most experts in the field, Hathaway has confidence in the conveyor belt model and agrees with Dikpati that the next solar maximum should be a doozy. But he disagrees with one point. Dikpati’s forecast puts Solar Max at 2012. Hathaway believes it will arrive sooner, in 2010 or 2011.
"History shows that big sunspot cycles ‘ramp up’ faster than small ones," he says. "I expect to see the first sunspots of the next cycle appear in late 2006 or 2007—and Solar Max to be underway by 2010 or 2011."
Who’s right? Time will tell. Either way, a storm is coming.
Coronal mass ejection
From Wikipedia, the free encyclopedia
A coronal mass ejection in time-lapse imagery. The Sun (center) is obscured by the coronagraph’s mask. (September 30 – October 1, 2001)
Coronal mass ejections are often associated with other forms of solar activity, most notably solar flares, but a causal relationship has not been established. Most ejections originate from active regions on Sun’s surface, such as groupings of sunspots associated with frequent flares. CMEs occur during both, the solar maxima and the solar minima of sun activity, albeit with decreased frequency during the minima.
Arcs rise above an active region on the surface of the Sun.
Coronal mass ejections release huge quantities of matter, magnetic fields and electromagnetic radiation into space above the sun’s surface, either near the corona or farther into the planet system or beyond (interplanetary CME). The ejected material is a plasma consisting primarily of electrons and protons, but may contain small quantities of heavier elements such as helium, oxygen, and even iron. It is associated with enormous changes and disturbances in the coronal magnetic field.
Coronal mass ejections are usually observed with a white-light coronagraph.
Recent scientific research has shown that the phenomenon of magnetic reconnection is responsible for CME and solar flares. Magnetic reconnection is the name given to the rearrangement of magnetic lines of force when two oppositely directed magnetic fields are brought together. This rearrangement is accompanied with a sudden release of energy stored in the original oppositely directed fields.
On the sun, magnetic reconnection may happen on solar arcades—a series of closely occurring loops of magnetic lines of force. These lines of force quickly reconnect into a low arcade of loops, leaving a helix of magnetic field unconnected to the rest of the arcade. The sudden release of energy in this reconnection causes the solar flare. The unconnected magnetic helical field and the material that it contains may violently expand outwards forming a CME.
This also explains why CMEs and solar flares typically erupt from what are known as the active regions on the sun where magnetic fields are much stronger on average.
Impact on Earth
When the ejection is directed towards the Earth and reaches it as an interplanetary CME (ICME), the shock wave of the traveling mass of Solar Energetic Particles causes a geomagnetic storm that may disrupt the Earth’s magnetosphere, compressing it on the day side and extending the night-side magnetic tail. When the magnetosphere reconnects on the nightside, it releases power on the order of terawatt scale, which is directed back toward the Earth’s upper atmosphere.
This process can cause particularly strong auroras in large regions around Earth’s magnetic poles. These are also known as the Northern Lights (aurora borealis) in the northern hemisphere, and the Southern Lights (aurora australis) in the southern hemisphere. Coronal mass ejections, along with solar flares of other origin, can disrupt radio transmissions and cause damage to satellites and electrical transmission line facilities, resulting in potentially massive and long-lasting power outages.
Humans in space or at high altitudes, for example, in airplanes, risk exposure to intense radiation. Short-term damage might include skin irritation. Long-term consequences might include an increased risk of developing skin cancer.
A Video of the series of CMEs in August 2010
A typical coronal mass ejection may have any or all of three distinctive features: a cavity of low electron density, a dense core (the prominence, which appears as a bright region on coronagraph images embedded in this cavity), and a bright leading edge.
Most ejections originate from active regions on the surface, such as groupings of sunspots associated with frequent flares. These regions have closed magnetic field lines, in which the magnetic field strength is large enough to contain the plasma. These field lines must be broken or weakened for the ejection to escape from the sun. However, CMEs may also be initiated in quiet surface regions, although in many cases the quiet region was recently active. During solar minimum, CMEs form primarily in the coronal streamer belt near the solar magnetic equator. During solar maximum, they originate from active regions whose latitudinal distribution is more homogeneous.
Coronal mass ejections reach velocities between 20km/s to 3200km/s with an average speed of 489km/s, based on SOHO/LASCO measurements between 1996 and 2003. The average mass is1.6×1012kg. The values are only lower limits, because coronagraph measurements provide only two-dimensional data analysis. The frequency of ejections depends on the phase of the solar cycle: from about one every other day near the solar minimum to 5–6 per day near the solar maximum. These values are also lower limits because ejections propagating away from Earth (backside CMEs) can usually not be detected by coronagraphs.
Current knowledge of coronal mass ejection kinematics indicates that the ejection starts with an initial pre-acceleration phase characterized by a slow rising motion, followed by a period of rapid acceleration away from the Sun until a near-constant velocity is reached. Some balloon CMEs, usually the slowest ones, lack this three-stage evolution, instead accelerating slowly and continuously throughout their flight. Even for CMEs with a well-defined acceleration stage, the pre-acceleration stage is often absent, or perhaps unobservable.
Association with other solar phenomena
Coronal mass ejections are often associated with other forms of solar activity, most notably:
- solar flares
- eruptive prominence and X-ray sigmoids
- coronal dimming (long-term brightness decrease on the solar surface)
- EIT and Moreton waves
- coronal waves (bright fronts propagating from the location of the eruption)
- post-eruptive arcades.
The association of a CME with some of those phenomena is common but not fully understood. For example, CMEs and flares are normally closely related, but there was confusion about this point caused by the events originating beyond the limb. For such events no flare could be detected. Most weak flares do not have associated CMEs; most powerful ones do. Some CMEs occur without any flare-like manifestation, but these are the weaker and slower ones. It is now thought that CMEs and associated flares are caused by a common event (the CME peak acceleration and the flare impulsive phase generally coincide). In general, all of these events (including the CME) are thought to be the result of a large-scale restructuring of the magnetic field; the presence or absence of a CME during one of these restructures would reflect the coronal environment of the process (i.e., can the eruption be confined by overlying magnetic structure, or will it simply break through and enter the solar wind).
At first, it was thought that CMEs might be driven by the heat of an explosive flare. However, it soon became apparent that many CMEs were not associated with flares, and that even those that were, often began before the flare. Because CMEs are initiated in the solar corona (which is dominated by magnetic energy), their energy source must be magnetic. Only flares could provide enough heat energy to drive the CME, and flares get their energy from the magnetic field anyway.
Because the energy of CMEs is so high, it is unlikely that their energy could be directly driven by emerging magnetic fields in the photosphere (although this is still a possibility). Therefore, most models of CMEs assume that the energy is stored up in the coronal magnetic field over a long period of time and then suddenly released by some instability or a loss of equilibrium in the field. There is still no consensus on which of these release mechanisms is correct, and observations are not currently able to constrain these models very well.
Illustration of a coronal mass ejection moving beyond the planets towards theheliopause.
CMEs typically reach Earth one to five days after the eruption from the Sun. During their propagation, CMEs interact with the solar wind and the Interplanetary Magnetic Field (IMF). As a consequence, slow CMEs are accelerated toward the speed of the solar wind and fast CMEs are decelerated toward the speed of the solar wind. Fast CMEs (faster than about 500 km s−1) eventually drive a shock. This happens when the speed of the CME in the frame moving with the solar wind is faster than the local fast magnetosonic speed. Such shocks have been observed directly by coronagraphs in the corona and are related to type II radio bursts. They are thought to form sometimes as low as 2 Rs (solar radii). They are also closely linked with the acceleration of Solar Energetic Particles.
NASA mission Stereo
On 25 October 2006, NASA launched the Solar TErrestrial RElations Observatory (STEREO), two near-identical spacecraft which from widely separated points in their orbits will produce the first stereoscopic images of CMEs and other solar activity measurements. The spacecraft will orbit the Sun at distances similar to that of the Earth, with one slightly ahead of Earth and the other trailing. Their separation will gradually increase so that after four years they will be almost diametrically opposite each other in orbit.
The largest recorded geomagnetic perturbation, resulting presumably from a CME, coincided with the first-observed solar flare, on 1 September 1859, and now referred to as the solar storm of 1859. The flare was independently observed by R. C. Carrington and R. Hodgson. The geomagnetic storm was observed with the recording magnetograph at Kew Gardens. The same instrument recorded a crotchet, an instantaneous perturbation of the Earth’s ionosphere by ionizing soft X-rays. This could not easily be understood at the time because it predated the discovery of X-rays by Röntgen and the recognition of the ionosphere by Kennelly and Heaviside.
First clear detections
The first detection of a CME as such was made on December 14, 1971, by R. Tousey (1973) of the Naval Research Laboratory using the Seventh Orbiting Solar Observatory (OSO-7). The discovery image (256 × 256 pixels) was collected on a Secondary Electron Conduction (SEC) vidicon tube, transferred to the instrument computer after being digitized to 7 bits. Then it was compressed using a simple run-length encoding scheme and sent down to the ground at 200 bps. A full, uncompressed image would take 44 minutes to send down to the ground. The telemetry was sent to ground support equipment (GSE) which built up the image onto Polaroid print. Mr. David Roberts, an electronics technician working for NRL who had been responsible for the testing of the SEC-vidicon camera, was in charge of day to day operations. He thought that his camera had failed because certain areas of the image were much brighter than normal. But on the next image the bright area had moved away from the Sun and he immediately recognized this as being unusual and took it to his immediate superior, Dr. Guenter Brueckner, and then to the solar physics branch head, Dr. Tousey. Earlier observations of coronal transients or even phenomena observed visually duringsolar eclipses are now understood as essentially the same thing.
On 1 August 2010, during solar cycle 24, scientists at the Harvard-Smithsonian Center for Astrophysics (CfA) observed a series of four large CMEs emanating from the Earth-facing hemisphere. The initial CME was generated by an eruption on August 1 associated with sunspot 1092, a sunspot which was large enough to be seen without the aid of a solar telescope. The event produced significant aurorae on August 4.
- Orbiting Solar Observatory
- Geomagnetic storm
- Magnetic cloud
- Space weather
- Aurora (astronomy)
- 1859 solar superstorm
- Forbush decrease
- Moreton wave
- ^ Coronal Mass Ejections (at nasa.gov)
- ^ "The Mysterious Origins of Solar Flares", Scientific American, April 2006
- ^ Baker, Daniel N., et al. (2008). Severe Space Weather Events – Understanding Societal and Economic Impacts: A Workshop Report. National Academies Press. p. 77. ISBN 978-0-309-12769-1. "These assessments indicate that severe geomagnetic storms pose a risk for long-term outages to major portions of the North American grid. John Kappenman remarked that the analysis shows “not only the potential for large-scale blackouts but, more troubling, … the potential for permanent damage that could lead to extraordinarily long restoration times.”"
- ^ How Stuff Works: solar flares
- ^ Andrews, M. D., A search for CMEs associated with big flares, in Solar Physics, 218, pp 261–279, 2003
- ^ Vourlidas, A., Wu, S.T., Wang, A. H., Subramanian, P., Howard, R. A. "Direct Detection of a Coronal Mass Ejection-Associated Shock in Large Angle and Spectrometric Coronagraph Experiment White-Light Images" in the "Astrophysical Journal", 598, 2, 1392–1402, 2003
- ^ Manchester, W. B., IV, T. I. Gombosi, D. L. De Zeeuw, I. V. Sokolov, ;, Roussev I., I., K. G. Powell, J. Kóta, G. Tóth, and T. H. Zurbuchen (2005). Coronal Mass Ejection Shock and Sheath Structures Relevant to Particle Acceleration. The Astrophysical Journal, Volume 622, Issue 2, pp. 1225–1239. 622 2: 1225–1239.
- ^ Spacecraft go to film Sun in 3D BBC news, 2006-10-26
- ^ R.A. Howard, A Historical Perspective on Coronal Mass Ejections
- ^ Obit with brief bio for Dr. Brueckner
Natchimuthukonar Gopalswamy, Richard Mewaldt, Jarmo Torsti, Editors, Solar Eruptions and Energetic Particles, Am. Geophys. Union Geophys. Mongraph Series Vol 165, ISBN 0-87590-430-0, 2006.
Wikimedia Commons has media related to: Coronal mass ejection
- NASA—Carrington Super Flare NASA May 6, 2008
- NASA—Cartwheel CME NASA May 27, 2008
- Coronal Mass Ejection Prediction Page
- 2008 Scientific American article on CMEs
- Cluster captures the impact of CMEs
- NOAA/NWS Space Weather Prediction Center