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Mostly Sunny with a chance of mass coronal ejection
 --- The art of space weather prediction with NOAA physicist Janet Green

There's nothing like a warm sunny day to lift the mood and make the world look alive and vibrant. The Sun is the benefactor of life on this planet, giving it the energy it needs to survive and grow. Like most things in nature though, it has its good days and its bad. Its angry moods are hidden behind a seemingly calm face of brilliant light, but they are there nonetheless and can be very harmful to our electrical equipment and lifestyles. It’s one of the jobs of NOAA (the National Oceanic and Atmospheric Administration) to observe the Sun’s activity and try to give advance warning of solar storms to operations that can be adversely affected by them.

Someone involved in this work is NOAA physicist Janet Green. We asked her some questions about all of this and she happily provided some illuminating answers.

Q. What is a typical day like for scientists who observe and predict space weather?

NOAA. A scientist at the space weather prediction center has two main roles. One is to promote the transition of space weather models from the research community to forecast tools that will run reliably in an operational setting. The other is to ensure that quality data, on which our forecast products rely, is available from our satellite and ground based instruments.

For example, SWPC is responsible for the Space Environment Monitors onboard NOAA’s five Polar Orbiting Environmental Satellites. These instruments measure energetic protons and electrons that cause the aurora in the polar regions. Scientists check calibrations, monitor the instrument health, and ensure that the data continues to flow to our most popular products and websites http://www.swpc.noaa.gov/pmap/index.html . We also work with the Department of Defense and NASA to develop new instruments and plan for future satellite missions so our products continue to improve. We attend scientific meetings, and meet with researchers from around the world to learn about new techniques and scientific advances that might be beneficial to some of our space weather customers. SWPC is currently working on implementing a new tool that describes the radiation environment near geosynchronous orbit that will help satellite operators manage their space assets more effectively and mitigate the harmful effects of space radiation. Products that make it past a rigorous set of tests and validation are implemented in our forecast center. Forecasters stand watch 24x7 in the center and consolidate the output from data and models into text alerts.

Q. What types of equipment are most vulnerable to solar activity and in what way?

NOAA. Space weather can affect a wide range of equipment and activities including satellite electronics, polar aviation communication, power grid transformers, and the global positioning system.

Satellites, on which our high-tech world has become increasingly dependent on for communication, operate in a hostile environment of very high energy particle radiation. These particles (mostly protons and electrons) are confined by Earth’s magnetic field to orbit in a doughnut shaped region from ~1.5x Re (radius of the Earth) to ~10x Re. Engineers try to design satellites to withstand the constant barrage of particles which can penetrate through solid material. Yet sometimes even the best designs fail. The energetic particles can damage electronics, flip programming bits, or degrade solar cells, diminishing the function of the satellite or sometimes leaving it completely inoperable.

"The loss of one satellite due to space radiation is ~$500 million."

Airline communications are degraded by 2 different space weather phenomena: solar flares and solar energetic particle events. A large solar flare produces X-rays that bathe the dayside of Earth and degrade HF (high-frequency) communication. In response, airlines must rely instead on satellite communication which is more expensive. For those planes not equipped with such technology, they rely on planes leap-frogging information by line of sight. In recent years, major airlines have begun flying polar routes from North America to Asia to reduce flying time for the convenience of passengers and fuel cost savings. Most of the time, these flights operate smoothly. However, on occasion an explosive event at the sun releases a flood of very high energy protons that stream down magnetic field lines into the polar regions. The deluge of particles is enough to disrupt HF signals, the only available form of communication above ~83 degrees latitude. During one of these polar particle events, planes are diverted to lower latitudes often forcing additional fuel stops and delays of more than several hours for passengers.

Electrical power, which most of us take for granted, is delivered through a complex grid that remains stable only through the cooperation and constant maintenance of many different power companies. An unexpected failure of a single component can affect a wide-sweeping area, as was seen during the Northeast power blackout of 2003 which was precipitated by a single station in Ohio. During a geomagnetic storm, large transformers, which connect pieces of the grid at different voltages, are particularly vulnerable. A geomagnetic storm occurs when Earth’s magnetosphere is distorted and shaken up by energetic blobs of plasma, known as coronal mass ejections (CME) that are ejected from the sun. The changes to Earth’s magnetic field can induce large currents in the transformers and heat it to unsafe limits where the transformer performance is degraded or it is completely destroyed. During a geomagnetic storm, power companies will take action to increase power output from many different sources to reduce the load on any one particular component and keep the transformers operating within a safe range.

GPS works by triangulating on the time it takes an electromagnetic signal to reach several orbiting satellites. These signals must travel through Earth’s atmosphere and ionosphere to the satellites. During a geomagnetic storm, the ionosphere becomes disturbed with electron density bubbles and fountains. The changing density can affect how the electromagnetic signals propagate causing significant errors in the GPS locations.

Q. We're currently starting solar cycle #24. Is this cycle starting out with unusually low sunspot activity or is it about normal?

NOAA. It is still too soon to say whether this cycle is starting out with unusually low sunspot activity. The current numbers are not lower than has been observed in previous solar minimums. However, the next 6 months or so will be very telling. If the current low numbers continue, it may be an indication of a less active solar cycle.

Q. I read some predictions last year that this cycle could turn out to be an unusually strong one in terms of solar storms. What are you currently expecting?

NOAA. A solar prediction panel was convened by NASA, NOAA, and ISES last year to reach a consensus on what might be expected from the next solar cycle. A press release was put out on April 25, 2007 that can be found here: http://www.swpc.noaa.gov/SolarCycle/SC24/PressRelease.html. Illustrating the complexity of long term forecasts, the panel was not able to reach a consensus with half the panel favoring a strong solar maximum peaking at ~140 sunspots and the other half favoring a weak solar maximum peaking near 90 sunspots. The researchers are divided because they are uncertain about the basic physics that governs how the magnetic field of the sun changes and how that affects the solar cycle. What is known is that the magnetic field of the sun reverses direction every 11 years from being directed primarily northward to southward and vice versa. The flip is caused by flows of plasma at the sun. Proponents of the weak solar maximum believe that the polar magnetic field of the sun, which can be measured today, is transported equatorward and becomes the background for magnetic activity and sunspots of the next solar maximum. The current polar magnetic field is weak, which leads them to conclude that the next maximum will also have weak activity. The proponents of the strong solar maximum, on the other hand, are basing their arguments on physics based models of solar flows. They argue that the movement of plasma from the polar regions to the equator takes much longer than eleven years. Therefore, the current polar magnetic field has little bearing on the next solar cycles activity.

The panel recently reconvened to determine whether recent observations had swayed opinions. However, the recent sunspot counts and polar magnetic field measurements still had not changed significantly to support or deny either camps theory.

Q. Solar cycles are typically about 11 years in length. Do you also observe longer term trends in solar activity or is the Sun relatively stable and constant beyond the 11-year cycles?

Above: video shows coronal mass ejections of hot plasma
Below: solar flares shaped along curved lines of magnetic flux

NOAA. Other cycles have been identified but only the 11 and 22 year cycles are very strong in the observations. The 11 year cycle describes the variation in the number of sunspots. The 22 year cycle describes the time it takes the Sun’s magnetic field to reverse direction and then return to the initial orientation.

Q. Sunspots are relatively cooler areas of the Sun's surface, yet it seems that the Sun radiates more energy when there are more of them. Can you explain how this works?

NOAA. It seems counterintuitive that sunspots, which are cool and dark, actually cause the Sun to radiate more energy. This phenomenon is explained by the fact that sunspots are typically surrounded by very hot bright fringes called faculae. The brightness of the faculae is enough to compensate for the darkness of the sunspot leading to an overall increase in the amount of energy radiated.

Q. Since the Sun emits both energy traveling at the speed of light, and matter which would travel more slowly, what disturbances can you give advance warning of and which ones can you not?

NOAA. Energy from the Sun travels to Earth on timescales of minutes to days. However, these timescales do not always dictate the advance warning times. For some phenomena, we can increase warning time based on statistical probabilities of events occurring. For example, X-rays, which disrupt HF (high frequency) communication, are emitted when a solar flare erupts from the surface of the sun and reach Earth in ~8 minutes. Cameras onboard NOAA satellites orbiting Earth continuously image the surface of the sun. The SWPC forecasters issue an alert every time a solar flare is observed. In addition, SWPC also provides 3 day advance flare predictions. These predictions are based on statistical probabilities that a sunspot region with a certain size or magnetic characteristic is likely to produce a flare.

High energy solar particles, that also disrupt HF communication over the poles, often follow a solar flare or a coronal mass ejection (CME). They may arrive at Earth in minutes, hours, or not at all. Unlike the X-rays, these particles do not follow a straight direct path to Earth. They are constrained to follow the magnetic field lines of the Sun which flow outward in a spiral similar to a spinning lawn sprinkler. Like, pearls on a string, only those protons that are released on magnetic field lines that thread through Earth will have an impact.

Coronal mass ejections (CME) are the slowest form of energy to arrive and are responsible for the geomagnetic storms that disrupt power grids and reduce GPS accuracy. These are large bubbles of strong magnetic field and energetic plasma that are sometimes ejected from sunspots and active regions on the sun. They may take ~3 days to arrive or they may follow a trajectory that misses Earth completely. They have to push through the ambient magnetic field and plasma between the Sun and Earth making their exact arrival time uncertain. In addition, their release from the sun is difficult to observe because surprisingly, these large energy explosions leave little trace in solar images. Sometimes they are associated with solar flares and sometimes they are not. The best indication that a CME is coming our way is from coronagraphs that image the area around the Sun. A CME coming are way appears as a faint halo or expanding circle. Currently, no NOAA satellites carry coronagraphs that can be used for operations although that may change in the future. The next best warning comes from the ACE satellite which sits upstream of Earth and provides ~60 minute warning.

Q. From time to time solar storms can be strong enough to induce troublesome currents into the electrical power grid. The March 1989 Hydro-Quebec event is one example. How frequently do these events occur, and how do you work with electric utility companies to warn them?

NOAA. Power grids do not often fail completely during magnetic storms. However, recently the power companies have found that even moderate magnetic storms can induce currents that slowly degrade transformers and diminish their lifetime. Geomagnetic storms are ultimately caused by activity at the sun which follows an 11 year cycle. Therefore, the occurrence rate of geomagnetic storms also follows an 11 year cycle. During solar maximum, moderate to large geomagnetic storms occur ~10-20 times per year. During solar minimum that number is reduced to ~5 per year. A storm the size of the March 1989 event is expected to occur about once every 60 years.

Q. NASA is ending its Polar satellite mission which looked at the auroral "crowns" at the Earth's poles. Was anything of major significance learned about the Sun and Earth interaction from that mission?

NOAA. Although the most publicly visible instruments on Polar were the cameras that took incredible images of the aurora, the satellite carried a whole host of instruments to study the physics of Earth’s magnetic field and plasma environment. Of particular interest to space weather, was an electron detector telescope that measured the high energy electron radiation belt particles that are so troublesome to satellites. For decades, scientists have debated how these electrons are accelerated to such devastatingly high energies. They had divided into two camps with one camp arguing that the electrons were pushed Earthward by fluctuating electric fields from a source outside of geosynchronous orbit (6.6 Earth radii). The other camp argued that they were locally accelerated inside of 6.6 Re by very low frequency waves. With Polar, scientists were able to show that indeed, the source had to be inside of 6.6 Re. From the outside, this may seem like a trivial debate. But already, updating data assimilation models to include this new source has greatly improved our predictive capabilities.

Interaction of the solar wind with the Earth's magnetosphere   - SOHO/ NASA

Q. I read a few articles last year that suggested the Earth's magnetic core was shifting somewhat and could reverse at some point. Is the time-scale of that too large for it to be of concern for us now, or could this present significant problems in the future?

NOAA. The Earth’s magnetic field has flipped many times in the last billion years. The flips are captured by ocean ridges where lava is continuously flowing out and cooling. As the lava cools, the direction of the magnetic field is frozen into the rock providing a time history of the field reversals. These flips occur at seemingly random intervals ranging from tens of thousands of years apart to many millions of years apart. A complete reversal typically takes around 10,000 years.

Q. When the Earth's magnetic field "flips" like that does it cause a temporary collapse of the protective magnetosphere, and if so, what consequences could that have in terms of changes to the atmosphere or genetic mutation of life forms from solar wind radiation?

NOAA. When Earth's magnetic field flips, it is likely that the field strength is reduced and the structure becomes more chaotic but the field does not completely go away. Thus, it will still provide some protection from the energetic particles streaming from the sun. Our atmosphere also provides an additional layer of protection stopping the particles from reaching the ground. There is not a clear correlation between magnetic field reversals and extinctions. However, some research suggests that a combination of just the right space weather effects may have led to some extinctions noted in past records. Our atmosphere is continuously bombarded from very high-energy nuclei, known as cosmic rays, that come from astrophysical objects outside our solar system. These particles can effectively reduce the ozone in the atmosphere allowing more UV radiation to penetrate to Earth's surface. One numerical simulation shows that when a magnetic field reversal occurs while our solar system passes through an interstellar cloud, the elevated cosmic rays and reduced magnetic field results in enough UV radiation penetrating to Earth's surface to be harmful to life. These results have yet to be verified with observations.

Q. Does the average individual need to be concerned about space weather? If so, in what way?

NOAA. Space weather impacts many areas of the high-tech infrastructure on which we all rely but there is no space weather umbrella that the average individual can keep in their trunk just in case the sun starts acting up. The costs of space weather are substantial and ultimately impact the tax payers. The loss of one satellite due to space radiation is ~$500 million. The cost of diverting just one polar airplane flight is ~$100K. The cost of delaying or redoing work because of large GPS errors ranges from $10-$100K per day. The cost of a large city losing power is estimated at about $900 M.


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