Forecasting Space Weather
Ben - We hope to see lots of the Sun in our weather forecasts here in the UK - but out in space that may not in fact be the case. Here's Dr Jim Wild, from Lancaster University...
Jim - Well, space weather is the changes in the space environment quite close to the earth that result from primarily solar activity. So, obviously everything on earth is driven - all energy sources on earth ultimately start off at the sun. But the sun's quite dynamic on a lot of timescales. So from minute to minute or hour to hour, year to year, century to century, the amount of activity can change. It's shorter term time scales that we refer to as space weather, in the same way that changes in the atmosphere in the amount of rain from our own day to day we think of as weather on the ground. So space weather is usually driven by the sun, for example, if you have a large flare or coronal mass ejection, that energy is transported through space and will arrive at the earth some time later in a variety of different forms and interact with the space environment around the earth, the magnetic field of the earth, the atmosphere of the earth, and it will produce some effects on the ground or in earth's orbit that we can measure. Actually, we tend to think of space weather as affecting man-made technology, so space weather kind of presents a bit of a hazard to man-made technology on and above the surface of the earth.
Ben - Just like with normal weather, do we try and predict it?
Jim - We do try and predict it. In fact, the ultimate goal would be to be able to predict it. It is quite difficult. Just like it is with normal weather, it's a bit easier the closer to the present that you get. So at the moment, we're kind of at the stage where human beings can do what we call "Nowcasting." Instead of forecasting what's coming, can we actually just say what the status of things is now? So the "nowcasting" at the moment as we're sitting here on this bench in sunny Glasgow is that it's sunny and it's not raining, and a "nowcast" globally would be able to say that to about the entire surface of the earth for the regular weather. If we think about space weather, the "nowcast" would be how much radiation is coming from the sun, how many energetic particles are coming from the sun, what's the status of the earth's atmosphere, the upper ionosphere that we use for radio communications, the radiation belts, how energised are they, how much energy is coming in to the auroral zones that causes the northern lights. All those kind of effects.
So, "nowcasting" is the first stage and we can sort of do that. We can make measurements in real time even from spacecrafts that are upstream of the earth. So, we have sentinel spacecrafts that are located about 250 earth radii upstream of the earth and they sit there and sample solar wind that's on its way towards us from the sun. So we know what's coming and that gives about an hour's warning. We can take pictures of the sun, so that can tell us about things that are going to take about three days to arrive at the earth. So we can start to forecast but it's still quite crude. We're at the stage of being able to say in the summer, it will be generally warmer than the winter and there's probably a big storm due in a few days but it may or may not strike. We're not quite sure yet. So it's still quite ballpark at the moment.
Ben - So how is it studied? What tools do we need to use?
Jim - There's really a whole suite of tools. So, we start all the way from upstream of the earth. So if you imagine you have the sun 93 million miles away. The material leaving the surface of the sun, so physical material, charged gases that we call plasma, that generally takes a few days to get to the earth. So we have a spacecraft that's upstream of the earth that's sitting in this solar wind that can taste and smell if you like. It can see the composition of the solar wind, how energetic it is, how much of the sun's magnetic field that solar wind is dragging out with it. so we have space-based tools that are quite a long way from the earth. Then coming a bit closer, we have an international flotilla of satellites orbiting the earth right down through radiation belts and then getting to quite low altitudes above the surface of earth to a few hundred kilometres above the surface of the earth. And then on the ground, we have whole suites of radars that study the atmosphere, the upper atmosphere, and the ionosphere so that's the electrically charged parts of the upper atmosphere. That's typically from a few 10s to a few hundreds of kilometres. Then right on the ground itself, we have magnetometers. So they're measuring small changes in the earth's magnetic field that are being imposed by the interaction of the earth's magnetic field with the space environment. And so, we have everything from little boxes on the ground that cost a couple of hundred quid to multi-billion pound satellite missions which are 250 planetary radar upstream of the earth.
Ben - If one of the things we're hoping to monitor or prevent or at least be prepared for is damage to our technology by the space weather, isn't it a bit of a risk, putting a multimillion pound satellite between the sun and us?
Jim - Certainly, the satellites that are upstream and monitoring the space weather environment, they are outside of the earth's protective magnetic field to begin with and the protective barriers of the earths atmosphere. So they are in quite harsh radiation environments and they're built to withstand some of this. But you can certainly see when we have large events that the spacecraft do take a bit of a kicking.
There is a very famous event, or to scientists, it's very famous. In October 2003, there was a large flare and accompanying that flare was a coronal mass ejection, a big explosion on the solar surface which stream out about a billion tons of energised electrical charged plasmas, these electrical charged gas which travelled towards the earth at about a million miles an hour. So it took a few days to arrive at the earth.
So when it arrived, it was about October 31st. It was a Halloween storm. Scientists are wonderfully imaginative when it comes to naming these things. But that passed by several spacecrafts on the way and you could see this thing coming, you could see it coming in the images, you could see the blast, and then you could see huge amounts of noise and radiation damage to the spacecrafts. So actually, the spacecraft's solar cells which are obviously designed to absorb radiation and create electricity actually absorbed huge amounts of damaging radiation, and it knocked a couple of months of the expected lifetime of those solar cells. So yeah, they're in quite an extreme environment, but it's kind of like, you have to have a thermometer to put in to that jug of hot water to measure how hot the water is, so you need to build something that'll last.
Ben - How do you adapt a spacecraft to be able to cope with those conditions?
Jim - The ones that go upstream, they're generally built to be radiation hard so the components they used are built to withstand radiation environments. So they're quite different to the kind of components you would buy if you were building a radio set yourself. They're radiation hardened bits of kit. For stuff that's a bit closer to the earth, what you tend to find is that they get some shielding naturally from the earth, but they can still be exposed to damaging radiation doses and especially electrically charged particles because these blitz through semi-conductor chips and they change ones into zeros which can be a very bad thing in a circuit if it controls a computer onboard a spacecraft. So what we can do is those spacecraft can be put into much more safe modes, they can be powered down for example or told to disregard any strange commands in the next few hours or shunted into even slightly different orbits in extreme cases. But of course, the trick there is knowing these things are coming and that's where the forecasting and nowcasting comes in because we really want to be able to study what's coming and be able to say, "Okay, spacecraft needs to be a bit aware now that something interesting is going to happen."
And as well, it's not just spacecraft in orbit, going back to a very common earth analogy, you wouldn't launch a ship - a brand new ship - into a typhoon in the same way that a spacecraft - whether it's a communication satellite or a scientific mission, you wouldn't launch that into a very damaging or extreme space environment. So what you generally want to know is, is it quiet at the moment and is it likely to stay quiet for the next couple of days, so my spacecraft can get launched into some regularised orbit before any bad weather hits.