Homepage

Right after pounding the final words of Reading the Weather into my computer, I opened the Aviation Weather Handbook, FAA-H-8083-28 and scrolled to Chapter 23. At first glance, space weather stands tall as a meteorological oxymoron. How can weather—the state of the atmosphere with respect to heat or cold, wetness or dryness, calm or storm, clearness or cloudiness—exist in a vacuum?

It defines Space Weather as “processes occurring on the Sun or in the Earth’s magnetosphere, ionosphere, and thermosphere that could have a potential impact to the near-Earth environment. Space weather phenomena such as solar flares, radiation storms, and geomagnetic storms are some potential concerns for aviation.”

Okay, so why is it important to atmospheric aviators? Oh, because space weather can affect radio communications, GPS navigation, and expose humans and their avionics to radiation. Tell me more.

With its uninterrupted luminescence and solar wind, the sun is the primary source of space weather, especially when it is in an eruptive mood. It cyclically spews coronal mass ejections and flares into the void, potentially causing radio blackouts, magnetic storms, and ionospheric and radiation storms on Earth. Contributing sources of space weather include galactic cosmic rays, charged particles born in distant supernovae. Consider it a steady space weather drizzle.

Unlike an LED bulb, the sun’s energy output changes over time. Sunspots are the handbook’s primary example. Although astronomers have been studying them for centuries, sunspot physics are not fully understood. Their activity waxes and wanes over an 11-year cycle and their activity is “often used for a proxy index for changing space weather conditions.”

When sunspots erupt, galactic gales blow. Coronal mass ejections (CMEs), flares, and galactic cosmic rays from distant supernovae contribute to solar wind, the breeze of charged particles and a magnetic field of plasma that carries the sun’s stormy energy to Earth. Even when the sun isn’t storming, wind’s constant current of plasma fuels Earth’s geomagnetic field, which in turn defines the globe’s geospace, the area influenced by solar wind.

Extending in all directions, Earth’s magnetosphere “forms a cocoon for the planet, protecting it from the flow of solar wind. It deflects most of the wind’s energy, but some of it gets through, especially when the sun is storming.” This is when we are most likely to marvel at the aurora undulating in night skies near the polar regions in the northern and southern hemispheres.

One layer down from the magnetosphere is the ionosphere. It is a shell of plasma where electrons and ions are embedded in the neutral atmosphere of Earth. It begins roughly 80 km above the Earth’s surface. That’s 49.709 miles or 262,467 feet for those without a conversion app close at hand.

The sun erupts mostly where it is most magnetic (the image of a solar zit comes to mind). Flares and CMEs are the most common because they can be seen from Earth (with the appropriate vision-protective filters). Earthlings have known about solar flares for more than a century. These electromagnetic volcanos erupt with a bright flash that lasts a few minutes, or a few hours. Traveling at the speed of light, their energy instantly affect the sunny side of Earth.

We really didn’t know about CMEs until the satellite era. Not as bright as a solar flare, CMEs can mature for hours before they erupt. When a large volume of the sun’s corona (its outer atmosphere) erupts, its energy can equal a large solar flare, but its travel time is slower, one to four days. But a CME plays greater havoc to Earth’s magnetic field and can cause the strongest magnetic storms.

When a geomagnetic storm blows up in the Earth’s magnetic field, the aurora is the only esthetically pleasing consequence. Otherwise, these storms cause nothing but problems for technological systems like aviation’s navigation and communication networks, and they can last for days, with more robust tempests lasting a week.

This deluge of solar particles and electromagnetic radiation can also stir up the ionosphere and magnetosphere, often at the same time. “The symptoms of an ionospheric storm include enhanced currents, turbulence and wave activity, and a nonhomogeneous distribution of free electrons. This clustering of electrons, which leads to scintillation of signals passing through the cluster, is particularly problematic for the Global Navigation Satellite System (GNSS), which includes the United States’ GPS.” These storms can last a few minutes to a few days, and they often mirror the duration of geomagnetic storms.

Space Weather Consequences

The electromagnetics of space weather is what makes it important to Earthly aviation. When line-of-sight VHF communication isn’t possible, as it is over the ocean, airplanes must communicate using High Frequency, which bounces over the horizon, and is usually the first to suffer a solar flare blackout. With some solar storms, this detrimental effect can spill over to 30-300 MHz. That includes the aviation VHF spectrum that spans from 118.000 to 135.975 mHz.

Satellite signals transit the ionosphere, but their frequencies are usually high enough “for the ionosphere to appear transparent.” But when sufficiently stirred, the ionosphere can scintillate a satellite’s signal, causing “a twinkling in both amplitude and phase that can result in loss-of-lock and the inability for the receiver to track a Doppler-shifted radio wave.”

This loss-of-lock is one way space weather affects GPS signals. The other two are an increased error of the computed position, and solar radio noise overwhelming the transmitted GPS signal.

Finally, space weather irradiates pilots, their passengers, and their avionics, especially at higher latitude and flight levels. For the electronic components, the damage comes from “the highly ionizing interactions of cosmic rays, solar particles, and the secondary particles generated in the atmosphere.” And the more modern the avionics, with their ever-shrinking electronic organs, the more susceptible they are to the electronic precipitation from space weather.

Now that space weather has my attention, my next question is, Where does one get a space weather briefing? Hmm, Chapter 26.7, Space Weather Advisory. Let’s see what it has to say. — Scott Spangler, Editor