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May 10, 2013
NASA EDGE: Understanding Aurora with VISIONS


Doug Rowland, Heliophysicist at NASA Goddard Space Flight Center


CHRIS: So Doug, why do we use sounding rockets to study the auroras?

DOUG: Sounding rockets have many advantages. They’re sort of complimentary to satellites. The satellites usually have a very extensive instrumentation. They’re very expensive, very complex and they have a lot of capability. What they do is fly, more or less, horizontally through the region. One advantage of a sounding rocket is it’s suborbital, which means it doesn’t orbit. It goes up and it comes down. If you want to get a vertical profile of what’s happening in a region, you might use a sounding rocket, because you can say I want to launch from here and I’m going to go up and I want to come back down. I want to measure as a function of height what’s going on.

CHRIS: Right.

DOUG: The satellite gives you a complimentary view, what’s happening as a function of horizontal distance.

CHRIS: Just give me a slice?

DOUG: A slice, exactly.

CHRIS: Do you ever launch a sounding rocket and have a satellite going over the region at the same time?

DOUG: People do that. Tom Woods at the University of Colorado does that with the SDO. They’ve got an instrument on SDO that needs calibration. If they’re looking at the sun, they’re making the same measurement with the sounding rocket to try to get a good calibration. There have been other attempts to have a satellite go by and maybe not exactly at the same moment but near by in time to do an under flight. We want to do more of those experiments.

CHRIS: You just had a successful mission just recently called VISIONS. What’s the VISIONS project all about?

DOUG: Well VISIONS, we like to have these acronyms. VISIONS is an acronym that tells you what the mission is. It’s using imaging as opposed to direct measurement along the trajectory to measure a phenomenon that we’ve known about for a long time but never have had pictures of. That phenomenon is called the auroral wind.

CHRIS: The auroral wind, wow!

DOUG: The auroral wind. You’ve heard of the solar wind.

CHRIS: The solar wind, yeah.

DOUG: The auroral wind is a wind of gas or ions that come out of our atmosphere and they’re driven out by the aurora. The aurora comes in, heats the atmosphere, gets it energized and boils this atmosphere off. It’s a pretty weak, thin stream of gas but it turns out to be very important because space around Earth is so empty. The magnetosphere is so empty that having this gas, this oxygen flow out, can dominate, at least temporarily, what’s happening out in the magnetosphere. What drives it out is the magnetosphere itself. It’s a feedback loop where the magnetosphere drives the aurora. The aurora takes the oxygen and the auroral wind out and that regulates or feeds back on the magnetosphere itself.

CHRIS: Is it a certain level of storm before you launch that sounding rocket?

DOUG: We launch into a pretty minor sub storm.

CHRIS: Okay.

DOUG: One advantage of the rocket program in addition to this vertical profile is you can wait. You can sit there and wait for ten nights in a row and wait for hours each night to try to get the perfect time. With a satellite, if you zip through and then something happens you miss it. We can wait until there’s an aurora right in our path and right at the right time then go.

CHRIS: What kind of instrumentation do you have on board to be able to make those measurements?

DOUG: Some things you will be familiar to. We have a four-channel camera where we have four different colors of light that we’re looking down. We’re taking pictures from above looking down on the aurora so we can see where the aurora is intense and where it might be driving this oxygen wind out. Our other major instrument is something called the MILENA instrument. MILENA stands for Miniaturized Low-Energy Neutral Atom imagery. MILENA, what it does is it makes pictures by looking at where atoms come from. Instead of looking at light to take a picture, it counts how many oxygen atoms are coming at every point. It spins around. It’s a catcher’s mitt and it looks over there and says I’ve got so many oxygen atoms. It looks over here and says I’ve so many oxygen atoms. It makes a map as it spins around; builds up where those pictures are coming from. We want to check how are they increasing as we go up in altitude? How are they corresponding to bright points in the aurora? We have this camera looking down and saying there’s a bright aurora over there, is there also oxygen coming from that region. We also know that not all auroras are created equally. Some are very energetic and penetrate very low in the atmosphere. Those are usually green.

CHRIS: Right.

DOUG: We have some that are less energetic and they penetrate to a higher altitude and they’re red. We have some evidence that the red aurora is a little better at energizing this atmosphere. So, we use our green and red channel from the camera to say where are those oxygen atoms likely to be coming from. We want to check our theory by looking at where they’re actually coming from.

CHRIS: And of course, when you’re launching these sounding rockets, you’re just not launching them just anywhere in the country, you’re trying to get into the auroral zone up by the Arctic Circle?

DOUG: That’s right. Yeah. Fairbanks is a famous place to study the aurora. We have all kinds of tourists from all over the world, mostly from Japan, actually go there because that’s a very good place, where the skies are clear. It’s cold but not too windy and the aurora is very common, every other night, every third night. It’s a great place to look at the aurora. It’s also the only land-based rocket range in the U.S. It’s operated by the University of Alaska for NASA. It’s got this great down range facility where you can put cameras and magnetometers. On an ocean range like Wallops you can’t really instrument under where the rockets fly because it’s the ocean. But up there you can put the instruments under the rocket trajectory and really get a good picture from cameras looking up as well.

CHRIS: I guess it would be hard to launch from Wallops because we’re so far south.

DOUG: That’s right, yeah. We do lots of great launches from Wallops. We do have interest in the atmospheric physics over Wallops. There’s a lot of interesting stuff that happens here. But to study the aurora, you go to basically Alaska, Norway or Sweden.

CHRIS: Right. You had a successful launch. Can you share some of the data you received?

DOUG: Sure. We saw that we had great electrons coming down. We saw the aurora was very strong. And we saw that our auroral cameras were working well. The MELINA instrument is a new instrument so we’re still learning how it works but we’ve already seen that fact that the altitude dependence of the oxygen atoms is very distinct. As we’re below a certain altitude, the oxygen atoms don’t travel very far. They, sort of, run into each other. As we go above a certain height, they can start to travel long distances and we can start to make these pictures. We’ve already seen directionality to that where we can say there are hot spots in these oxygen atoms. We haven’t yet made the mapping of how those hot spots map to the auroral features but that will be our next step .

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