To help us stay vigilant against the Sun’s dangerous eruptions of plasma and radiation, a small fleet of spacecraft stand watch directly in the line of fire, 1.5 million kilometers from Earth at the L1 point. After that, we have no more warning until the storm actually hits. L1 is our first and only chance to stick our proverbial finger into the wind—we have to use a model to forecast when the storm front will actually arrive.
Scientists are constantly trying to improve these forecasts with more accurate simulations of the solar wind. However, in a recent study of one such promising upgrade, Cash et al. found that the hoped-for gains did not materialize.
The team was investigating a way to improve how models handle the orientation of the approaching storms. The model currently used by NOAA’s Space Weather Prediction Center assumes that the shock fronts of solar storms intersect Earth like a putter squarely hitting a golf ball. In reality, these shock fronts can be tilted, more like a wild swing from a 9-iron. Thus, the storm’s leading edge might pass above or below Earth, and we may not feel the storm until the swept-back portion of the front strikes us. Conversely, the storm’s leading edge may slip past our scout satellites at L1 but take dead aim at us—slamming us earlier than we expect. Our forecasts are frequently off by as much as 15 minutes.
Determining an approaching storm’s tilt from a single observation point (L1) is difficult, but several papers over the past 15 years have proposed increasingly refined methods to do so. These methods are based on the changes in the ambient magnetic field that our satellites at L1 detect when the storm front washes past them. The authors modified the latest version of this technique, proposed in 2008, to run in real time, continuously, with real-time solar wind data.
However, when they tested their new model on an archive of 97 past solar storms, they found that it made no improvement to the forecast arrival times—both gave errors on average of about 4.5 minutes. Evidently, calculating the orientation of the boundaries in the solar wind magnetic field isn’t as important to better forecasts as accurate measurements of how the magnetic field and solar wind vary with time. The team recommends retaining the flat-plane assumption in NOAA’s model, as there’s no point in complicating things when the cruder method works just as well. (Space Weather, doi:10.1002/2015SW001321, 2016)
—Mark Zastrow, Freelance Writer
Citation: Zastrow, M. (2016), New space weather forecast technique fails to improve forecasts, Eos, 97, doi:10.1o29/2016EO046331. Published on 18 February 2016.