Solar flares could cause Garmin glitches

Recent solar flares affect satellite communication

Two solar flares captured over a three-day period in 2011

Did you miss that Strava KOM by a second recently? Or has your Garmin taken longer than normal to find a GPS connection in recent days? Solar flares could be to blame.


The largest active sunspot in 24 years has launched six major flares toward Earth recently, according to a report in the Wall Street Journal. The solar flares have temporarily disrupted navigation systems and radio communications in recent weeks.

Solar astronomers are calling the sunspot AR 12192. It is about 20 times the surface area of Earth, the federal Space Weather Prediction Center in Boulder, Colorado, told the WSJ, adding that the largest flares “produced as much energy as a billion thermonuclear weapons”. The blasts of heat can cause increased drag on satellites, the WSJ report said.

For cyclists using Garmins or other GPS computers, the consequences obviously aren’t as important as they are for airline pilots, but there could be tiny anomalies in ride data, experts told BikeRadar.

“All GPS units can be affected,” said Bifford Williams, a research scientist at Global Atmospheric Technology and Sciences. “GPS works by timing signals from multiple satellites to determine your distance from each satellite and triangulate your position. Flares and coronal mass ejections can deposit particles (electrons, ions) in the upper atmosphere concentrated towards the poles that change the index of refraction which can delay or change the angle of the signals. Too strong an ionized layer can block the signals completely.”

Weather can also have a smaller effect on GPS than the ionized particles from flares, Williams said, as atmospheric neutral density changes.

“The effect depends on the accuracy you need, how many satellites are in unobstructed view, and if you can tolerate intermittent dropouts,” Williams said. “Flares will produce effects that are highly variable in time and space, but mostly at higher latitudes.”

At the (US) National Oceanic and Atmospheric Administration, Dr Rodney Viereck is the director of the Space Weather Prediction Testbed. He told BikeRadar that typical solar flares do not have a major impact on single-frequency GPS systems, such as those phone in smart phones and most cycling GPS units.

“The enhancement in the lower ionosphere from a flare will impact high-frequency radio waves and this is what causes problems for airline pilots,” Dr Viereck said. “But even a major enhancement in this lower part of the ionosphere does not change the vertically integrated Total Electron Content (or TEC) by very much and it is this TEC that impacts GPS. The bigger challenge for GPS receivers is just having clear line-of-sight to at least four GPS satellites. Trees, bridges, buildings and hills all block the GPS signal and this is what typically cases the most problems.”

“On rare occasions, a solar flare can include a burst of radio emissions at the same frequencies as the GPS signal. In these cases, the solar radio burst will overwhelm the very weak GPS signal and GPS systems on the sunlit side of Earth will lose lock on the GPS signal and the GPS receiver will stop working. These events are quite rare and may occur only once every 10 or 20 years.”

“So how does space weather affect GPS systems? Solar flares often trigger coronal mass ejections (CMEs) and these create geomagnetic storms, which do have a major impact on the GPS accuracy and availability,” Dr Viereck said, echoing Williams’ point above.

“But CMEs take a day or more to reach Earth. So the impact will be several days after the flare. During major geomagnetic storms, your single-frequency GPS (such as in your cell phone or running device) will simply provide less accurate position information. Normally, if you have good viewing of four or more satellites, your GPS will provide uncertainties of about 2-10m. During geomagnetic storms, the errors can be as large as 60m. Storms can last for hours and mostly affect high latitudes such as the northern part of the US or Canada.  When the storm subsides, your GPS errors will return to normal all on their own. There is no need to reset anything.”

“At the Institute of Navigation (ION) conference last month, there were several sessions on wearable GPS systems for sports and the problems of the accumulated errors, especially during long races,” Dr. Viereck said.

“A mile or two of error during a marathon can be very disheartening. Several companies are working on ways to compensate using internal motion sensors, software, cell towers, etc,  so that your running/riding device does not introduce errors when you go under bridges. Stay tuned; technology will find a solution.”

[Updated Nov. 3 with response from Garmin.] Garmin spokesperson Amy Nouri told BikeRadar that accuracy for the company’s GPS units is “typically better than 3 meters”, and that any solar-flare related issues would only result in “a slight decrease in accuracy for consumer grade GPS units, which is short lived and typically not observable by the consumer”. Garmin has not had any customer-reported issues, Nouri said.

In addition to GPS receivers, some newer Garmin devices also use Glonass, which is a Russian satellite positioning system that is complementary to GPS.


In BikeRadar testing, we have found the dual-channel positioning to offer the tangible benefit of the cycling unit like an Edge 810 or Edge 1000 locking onto a signal faster than an older unit with just GPS. Whether this has improved accuracy, we can’t say.