The difficulty of space weather forecasting

We have plenty of trouble predicting weather here on Earth. What about predicting weather in the vast space between our planet and the sun? Geomagnetic storms in Earth’s atmosphere create enchanting displays of the northern and southern lights.

But they can also damage satellites and spacecraft, disrupt communications systems, cause power outages and, potentially, injure astronauts. David McComas at the Southwest Research Institute in San Antonio, Texas is trying to find a way to predict geomagnetic storms.

David McComas: In the last couple of years, the biggest progress in my opinion is that we have this remote imaging, and so for the first time instead of looking at these individual samples, like individual weather stations on the ground, we’re getting the remote picture just like the satellite image of the cloud tops …

Last fall, McComas and his colleagues used an Earth-orbiting satellite to take the first complete image of what’s called Earth’s plasma sheet. That’s a reservoir of plasma — or ionized gas — stretching out from the night side of our planet. This ionized gas can dump out onto our atmosphere and cause a geomagnetic storm.

If collected regularly, the new satellite information should help scientists predict geomagnetic storms several minutes before they start — enough time for spacecraft to be turned off or pointed in a safe direction.

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Although we call it space weather, the large-scale events that take place between the sun and Earth are very different from weather as we know it here on Earth. Bad weather on Earth snarls traffic and delays flights, but bad weather in space disrupts communications systems, damages satellites and spacecraft, and prompts beautiful displays of the northern lights.

Earth’s plasma sheet is a reservoir of plasma — or ionized gas — streaming out over Earth’s night side. It starts above Earth’s equator and extends for several times the width of Earth. Earth’s magnetic field is stretched into a long tail on Earth’s night side by the solar wind streaming out from the sun. The plasma sheet is enveloped by this tail.

David McComas is the executive director for space science and engineering at the Southwest Research Institute. He’s been working in the field of space weather since it began about a decade ago.

David McComas: “This whole field is really only about 10 years old. That’s about how long we’ve known that we can start to think of it (as,) as a space weather and as a possibly predictive process. So a tremendous amount of progress has been made over the past decade. In the last couple of years, the biggest progress in my opinion is that we have this remote imaging, so for the first time instead of looking at these individual samples, like individual weather stations on the ground, we’re getting the remote picture just like the satellite image of the cloud tops.”

McComas is currently trying to understand better how plasma is put into the plasma sheet from the surrounding solar wind.

One way McComas describes his work is: “Well, the plasma sheet is sort of like a fuel tank. This is where you store all of this material that can get dumped onto the atmosphere and make the Aurora Borealis and a number of these other space storm effects, but our imaging of it is sort of like the fuel gauge, being able to look at that whole reservoir and gauge how much material is in there that could be involved in a big storm.” (8:24)

But how much plasma is in the tank doesnât necessarily determine how severe the storm will be. That depends on a number of factors.

McComas’s latest study demonstrated that when the plasma sheet is full, and the orientation of the interplanetary magnetic field (IMF) is southward, a solar wind event can cause the plasma in the sheet to empty onto Earth’s atmosphere and cause a geomagnetic storm. Scientists had pieced this idea together based on point measurements, but the McComas team took the first remote images of the plasma sheet, allowing them to see the fullness of the sheet over a much larger area.

Their results indicate that the two most important factors to observe in order to monitor and predict such storms are the orientation of the interplanetary magnetic field (IMF) and the amount of material in the plasma sheet. So the remote images of the plasma sheet are an important tool in understanding how to predict severe space weather events.

And predicting these storms is key.

David McComas: “There are very clear practical applications for space weather in particular, because there are such expensive satellite systems and other technological systems which are adversely affected by severe space weather. Being able to better predict them will allow us to be better prepared, there are things you can do on spacecraft to turn off certain subsystems and put them in states which are better able to weather those storms.”

The plasma sheet is part of the tail of Earth’s magnetosphere. It’s a big slab of ionized gas located between the two tail lobes, on the side of Earth that faces away from the sun. It’s not a flat plane, the way we think a sheet should look. It’s more like a blob. There’s a picture at https://www-istp.gsfc.nasa.gov/Education/wtail.html if that helps at all. The plasma sheet has a weaker magnetic field than the rest of the magnetosphere’s tail, which means that the plasma isn’t held in as tightly, so it can slosh around, and crash back in on Earth’s atmosphere to make bad space weather.

McComas and friends used an instrument aboard a NASA satellite to take the very first image of Earth’s plasma sheet in 2002. The instrument is called the Medium-Energy Neutral Atom instrument and it’s on NASA’s Imager for Magnetopause to Aurora Global Exploration (IMAGE) spacecraft. McComas helped develop the sensor concept for the MENA instrument when he was still at Los Alamos.

Of course there’s been lots of remote imaging with satellites through the years, but the cool thing about this type of remote imaging is that it uses the neutral atoms – not photons of light or UV or radio waves. So it’s a whole new technology that’s been developed in the past decade or so. And it allows scientists to see the ionized gas in the Earth’s magnetosphere – previously invisible stuff. Neutral atom imaging was discovered when a researcher using a charged particle instrument found some brightening in his images that he couldn’t explain. He thought it was a problem with the instrument, and he ended up discovering that it was a real effect – a flow of real particles coming from the near-Earth region.

What you have in your mind?