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Before 1979, scientists didn’t have accurate data on the total amount of solar energy that reaches Earth. They were aware of the Sun’s fluctuations, but getting an accurate measurement of solar variation was difficult before the space age. In fact, it wasn’t until the launch of Nimbus-7 satellite in 1978 that a spacecraft was able to get accurate reading above the protective layer of Earth’s atmosphere.

Today scientists use the number 1,368 watts per square meter (W/m2) to denote the “solar constant.” This is an averaged value of solar energy emitted by the Sun. During the Sun’s 11-year solar cycle, this output can vary as much as 1.4 W/m2. Again, the solar constant is only an average, and by itself, it doesn’t inform us in the variations in electromagnetic radiation (energetic waves), solar wind, and magnetic field intensity. (For more information on all of these terms, you can do some exploring at: http://science.howstuffworks.com/sun.htm) But as we shall see, even short term variation in solar energy output has tangible effects on and near Earth.

Our Dynamic Star

The Sun is a very active body: Prominences and flares routinely erupt, sunspots move across the surface in a period fluctuation, and radiation and particles pour out of the Sun in varying intensities. Under the protection of Earth’s magnetic field and atmosphere, these changes are harder to perceive. But, as we learned in Part I, satellites are able to monitor changes of solar output with much greater accuracy. However, even without the orbiting sentinels, we sometimes become aware of the awesome power of our local star.

The Sun is constantly cycling through periods of increasing and decreasing intensity. Scientists trace the approximately 11-year cycle through the monitoring of Sunspots. During peak output times (called the solar maximum) there is a much greater chance for phenomena such as Coronal Mass Ejections (CMEs), which are intense solar wind storms. CMEs erupt from the Sun and can carry up to 100 billion tons of electrified gas toward the Earth at speeds as high as 2000 kilometers per second!

Effects on our Technology and Space Missions

For many of the smaller Coronal Mass Ejections, we notice little or no affect near the Earth’s surface. The Earth’s magnetosphere shields us from solar storms. Oftentimes, much of the material from CMEs is deflected away from our planet by its magnetic field. However, increasing intensity of CMEs can have more profound effects. Sometimes, the events can simply be beautiful; anyone who has seen an auroral display at higher latitudes can attest to this.

There are, however, dangers to consider when eruptions occur during times of solar maximum. For instance, microelectronics onboard satellites are especially susceptible. When high velocity ions plow through a satellite, control systems can be turned on or off, circuits can be burned out, and semiconductor material can be degraded. Solar power panels are especially sensitive to degradation from solar storms. The GOES satellite solar panels lost six years of operating time due to a solar event in 1989. For more on satellites and space weather, you can peruse Windows to the Universe’s Satellites and Space Weather site.

Disruptions to our technology are not limited to satellites. Astronauts are especially vulnerable to solar storms. High frequency radiation and fast moving particles are very damaging to living cells. These fast moving waves and particles have enough energy to knock electrons out of human cells, creating ions. These “ionizing” effects disrupt the normal cell functioning; the most severe damage results when DNA is affected. Space walks leave astronauts with very little protection to solar events. Although spacecraft walls (i.e. onboard the International Space Station or Shuttle) do offer some degree of protection, it is impossible to shield the explorers completely from radiation and particles. But even without solar storms, astronauts are exposed to increased levels of radiation, and it is assumed that they will be exposed to certain “tolerable” levels of radiation during their careers in space.

Effects from geomagnetic storms are not limited to the space faring. During the largest magnetic storms, intense currents can flow from the ionosphere to Earth’s surface. 1989 marked the year of the HydroQuebec Blackout, when ground currents induced from a magnetic storm caused a collapse of an entire power grid in Canada. In this event, 6 million people lost power for more than 9 hours. On a less grand scale, ground induced currents can be carried through pipelines, causing corrosion. In addition, radio waves can be completely disrupted for a few minutes of a few hours during solar flare bursts.

Near Term and Future Concerns

Intense solar storms are obviously a cause for concern. Even though we are often protected from effects of high energy solar output, our technology is not. Moreover, space explorers have a recurrent concern for CMEs and other high energy events. Between the Apollo 16 and 17 missions, the Earth experienced one of the largest “solar proton events” in recorded history. Fortunately, when the storm arrived, the astronauts were under the protective cover of Earth’s atmosphere. Computer simulations have demonstrated that even inside the Apollo Spacecraft astronauts would have absorbed lethal doses of radiation within 10 hours! Active monitoring missions help predict and prepare us for the largest solar events. Since solar wind travels much slower than the speed of light (about 2000 kilometers per second vs. 300,000 kilometers per second), we often have a window of time to prepare for the most violent outbursts. For more on space weather and the monitoring of solar storms, check out: http://www.spaceweather.com.

In the final installment of Solar Influence, we will examine the climatological effects that can occur from solar variability. Part III will cull information from the geologic record to look at long-term historical changes in solar output; it will also examine nearer-term variations and their effects on our environment.