After the sun hurled out the biggest solar flare in five years, media were abuzz, sometimes hyperbolically, about the prospective solar storm threat. Then, when a mere “minor” storm arrived Thursday with minimal impact, headlines pronounced the storm a fizzler.
But, just as it was presumed dead, geomagnetic storming surged early Friday, reaching the strong levels initially forecast. The twists and turns of this recent solar event illuminate the challenges in forecasting solar activity.
Forecasting space weather has a lot in common with forecasting weather on Earth. It involves analyzing both observed conditions (obtained from satellites) and model simulations, and leveraging forecaster experience to make a prediction. But space weather prediction has a long way to go to match the skill level of today’s terrestrial weather forecasts.
Graphic: Why space weather matters
Let’s explore why forecasting space weather is so difficult.
NOAA’s Space Weather Prediction Center (SWPC) recently placed into operation the first physics-based numerical computer model. It can predict the size and arrival time (plus or minus about 7 hours) of an approaching cloud of plasma, known as a coronal mass ejection (CME), but not its intensity.
Currently, the only capability in predicting CME intensity resides in the subjective experience and expertise of SWPC forecasters who continually monitor conditions (e.g., sunspots, solar flares) on the surface of the sun.
Present-day forecasts for approaching CMEs are not unlike the unreliable weather forecasts beyond a day or so of the 1970s - before the modern era of fairly accurate computer (terrestrial) weather prediction models.
Predicting the intensity of an Earth-bound CME is not the only challenge facing forecasters. There is no capability whatsoever in forecasting the orientation of an incoming CME’s magnetic field. This is critical since the alignment of the Earth’s magnetic field relative to the CME determines whether a severe (G4) to extreme (G5) geomagnetic storm actually materializes.
The strongest and potentially most devastating geomagnetic storm requires the magnetic field of the CME be opposite that of Earth’s. Think of this simply as a pair of bar magnets. When the poles of each magnet are the same (N-N or S-S) when they approach one another they are repulsed, but if opposite poles are brought together, they attract each other.
The only reliable available information on the strength of the CME and magnetic field orientation come from observations available from NASA’s Advanced Composition Explorer (ACE) satellite. But ACE is positioned so close to Earth (relative to the Sun) that only very short term notice (1 hour at most) is possible.
Not having information about the CME’s magnetic field orientation is paralyzing for forecasters said Joe Kunches, space weather scientist at NOAA’s SWPC.
“It’s like predicting a hurricane without knowing the barometic pressure in the center of the storm,” he said.
Kunches also compared forecasting CMEs to watching a pitcher toss a baseball but having no information about how it’s spinning until right when it reaches the catcher
In light of these limitations, on Wednesday when the SWPC predicted a G3-rated (strong) storm arriving Thursday morning (and G3-G4, strong-intense, by NASA), it should have been viewed as nothing more than an educated guess.
Unfortunately, the forecasts issued did not provide sufficient information about their uncertainty (degree of confidence).
Although NOAA’s forecast for a G3-magnitude storm ultimately verified, it occurred later than expected. Under different circumstances, it might have failed.
Most assuredly, as the solar cycle approaches its maximum expected in 2013, and subsequently begins to decline, a continuing spate of solar storms will repeatedly pose threats to Earth’s near space and surface environment (the most intense CMEs tend to occur during the rise and subsequent decline in the solar cycle, not near the maximum). The sun unleashed another strong solar flare last night with an associated CME now headed towards Earth.
As the sun continues erupting and belting out these clouds of plasma towards Earth, the capabilities and especially limitations of existing space weather forecasting must be kept in mind.