Solar Radiation – when there’s too much of a good thing

In a previous entry, we covered geomagnetic storms and their potential impact on the power grid and electronic devices here on Earth. To recap, geomagnetic storms are caused by gusts of solar wind interacting with the Earth’s magnetic fields and atmosphere. Depending upon their intensity they can create power blackouts by triggering false alarms in system designed to protect the grid. At their most intense they can actual damage power transmission equipment. At higher levels of intensity, radio transmission suffers, navigation beacons become useless for the duration of the storm – and you can forget that line about “fewest dropped calls.”

Even though geomagnetic storms are very interesting, they are not the only space weather that effects our planet. We also experience the effects of solar radiation storms (which we’ll cover today) and radio blackouts (which we’ll cover in a later entry). Solar radiation storms are spikes in solar radiation emissions from the sun. Radio blackouts are caused disturbances in the ionosphere that result from x-ray emissions from the sun. Both can impact our electronic devices and solar radiation has the ability to impact human life directly as well.

Map of annual average solar radiation

Solar radiation is not necessarily a bad thing. People who depend upon the sun for power, rely upon it. The profitability of companies that install solar power systems, or utilities that generate power for the grid from the sun make their living by knowing how to harness available solar radiation in their regions. Yet, while a spike in solar radiation may sound like a not-so-bad thing for the guys with solar panels on their houses, it can have a detrimental impact. Solar radiation, even though it can be useful, is still radiation. Even moderate solar radiation storms can subject airline passengers flying at higher latitudes to what NOAA calls “elevated radiation  risk” (NOAA, 2005) and solar power equipment can be functionally impaired or permanently damaged.

Average frequency is based on an 11 -year solar cycle. Solar radiation storms also have similar intensity ratings: from S1 (Minor) to S5 (Extreme). Let’s break the intensity scale down.

S1 – Minor Solar Radiation Storm. Happens about 50 times per 11-year cycle – or once every 80 days or so on average. According to NOAA there is virtually no biological impact and no impact on navigation. People using HF radios in the polar regions may notice, but for most of us, it’s a non-event.

S2 – Moderate Solar Radiation Storm. Happens about 25 times per solar cycle – or about once every 160 days. NOAA states that these solar radiation storms subject airline passengers flying at higher latitude to “elevated radiation risk” (NOAA, 2005) and goes on to state, “Pregnant women are particularly susceptible” (NOAA, 2005).  How many pregnant women think to check the space weather forecast before booking an airline ticket? It’s something that most of us don’t even think about. Satellites may experience “single event upsets” (NOAA, 2005) and HF radio signals and navigation in the polar regions will degrade.

S3 – Strong Solar Radiation Storm. Happens about 10 times per solar cycle – or about once every 13 or 14 months. During these events NASA requires astronauts to take radiation exposure precautions. Those airline passengers and crew who were are now exposed to even more greatly elevated risk from radiation exposure. Again, pregnant women are at greatest risk.  NASA says this exposure is roughly the equivalent of getting a single chest x-ray.

S4 – Severe Solar Radiation Storm. Happens maybe 3 times per solar cycle  – or once every 3 – 4 years, give or take. Astronauts on space walks are exposed to “unavoidable radiation hazards”  even when taking precautions (NOAA, 2005).  Satellites will experience imaging noise and memory issues – perhaps even orientation problems. And if the satellites are having issues, all those services we use that depend upon efficient satellite performance are going to be impacted. The problem with your Garmin, may not really be a problem with your Garmin at all. Expect navigation errors. On the ground, solar panel efficiency will decline. Do we even need to mention the radiation risk posed to airline passengers and crew in the higher latitudes?

S5 – Extreme Solar Radiation Storm. Happens on average less than once per solar cycle. Astronauts face unavoidable high radiation exposure risk. Those airline passengers and crew? Even more greatly elevated risks – especially to pregnant women. Satellites can be severely impacted or even “rendered useless” (NOAA, 2005). Navigation using electronic systems will be challenging at best. Expect HF radio trouble, and perhaps complete radio blackouts in polar regions. On the ground, solar panels may suffer permanent damage.

As near as I can tell from my internet research, the last solar radiation storm of any significant intensity was in the summer of 2000 and it was an S3. When are we due from another? Or a bigger one? No one knows for certain. Solar radiation storms are difficult to predict. Currently, about the best we can do is see the event,  and brace ourselves for the impact of the solar radiation storm that will arrive 15 minutes or so later.

While we’re  super careful about exposure to x-ray radiation during pregnancy, most pregnant women who are clear to fly don’t think twice (or even once) about solar radiation.  Even though prediction is dicey, if I were pregnant, I would want to know about the solar radiation forecast before I got on an airplane that would be taking a flight path through a higher latitude.

There are two main points I hope you’re walking away with today.

1) The Earth is part of a solar system that functions within a larger universe. We are not immune to what happens in space, or with our sun. Solar generated events, like geomagnetic storms (covered previously), solar radiation storms (covered today) and radio blackouts (to be covered later) all have an impact on our planet. Sometimes that impact is not limited to our electronic devices, but can extend to our bodies as well.

2) Sunscreen cannot protect you from all wavelengths of solar radiation. It only blocks some of the ultraviolet rays that are responsible for sunburn – and only for a limited amount of time.  If you’re flying through higher latitudes during a solar event, you have no protection at all.  As always: forewarned is forearmed.

As always, thanks for reading.

~ L.


National Oceanic and Atmospheric Administration.  2005. “Solar Radiation Storms”  Retrieved from:

Images: Solar radiation map © 2010


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