# If Steve is at 300 km, and SWARM is >440km, how did SWARM measure Steve's temperature?

How did ESA measure Steve's temperature using the SWARM spacecraft? Please explain how the measurement is really done, don't just mention an instrument's acronym.

I did a quick dump of TLEs for Satcats 39451, 39452 and 39453, and estimated their semimajor axes and then altitudes and got the plot below, to double check that SWARM hasn't dipped down to 300km.

All of the reports mention that Steve's ion temperature is 3000C.

This ESA News Release says:

Prof. Donovan said, “As the satellite flew straight though Steve, data from the electric field instrument showed very clear changes.

“The temperature 300 km above Earth’s surface jumped by 3000°C and the data revealed a 25 km-wide ribbon of gas flowing westwards at about 6 km/s compared to a speed of about 10 m/s either side of the ribbon. (emphasis added)

How did one or more of the three SWARM spacecraft above 440km measure the plasma temperature of Steve?

Seven things to know about Steve: http://blog.aurorasaurus.org/?p=449

We are are still learning more about Steve, but here are seven things we think we know so far:

1. Steve appears ~10-20° (in latitude) closer to the equator (south in the Northern hemisphere) than where the normal green aurora is overhead. This means it could be overhead at latitudes similar to Calgary, Canada.

2. Steve is a very narrow arc aligned East-West and extending for hundreds or thousands of miles.

3. Steve emits light in mostly purple-ish colors. It is quite faint but is usually photographed with 5-10 second exposures.

4. Sometimes, it is accompanied by a rapidly evolving green short-lived picket fence structure.

5. Steve can last 20 min or even longer.

6. Steve appears to have a season. For instance, it has not been observed by citizen scientists from October 2016 to February 2017.

7. This phenomena has been reported from the UK, Canada, Alaska, northern US states, and even New Zealand.

http://gizmodo.com/what-the-hell-is-this-beautiful-thing-1794528895

more? (they used to call it a proton arc for lack of a better name. It isn't one!) http://spaceweathergallery.com/index.php?title=proton

Opening of SWARM and CryoSat Science Meeting - Extremely Interesting, Eric Donovan talking about how Steve was "discovered by scientists" by listening to amateur astronomers and aurora photographers who had been watching it for a while! Start to talk about Steve after 01:16:00 https://livestream.com/ESA/earthexplorer2017/videos/152430872

Thanks to @Roger's information here here is an ESA link for the video of the talk. (same time code)

Also, here is some amazing footage!

• I think they correlated the SWARM IR photo with photos taken from Earth. knowing the locations and direction the photos were taken, you can determine the position of the temperature anomaly shown in the IR photos. Apr 25, 2017 at 16:07
• @Hobbes IR camera and thermal imaging are two different things, and IR thermometry is different still. Is there an actual instrument that can measure temperature of plasma of such a low number density? How does it work? Does it have a name?
– uhoh
Apr 25, 2017 at 16:18
• I hope they keep the name "Steve" for this phenomenon, if only to make space.stackexchange questions more entertaining. May 8, 2017 at 14:59

I want to offer some input to the above ---

I'm thrilled in the level, depth, and knowledge reflected in the questions and discussion. This has been eye opening for me.... Citizen Scientist has a new meaning for me!

Regarding 300 km vs 450 km. In my research I deploy, operate, and use data from scientific cameras. The data I was using for Steve came from a "redline" camera.Those emissions typically peak below 300 km. The Swarm measurements were made at ~450 km, on the magnetic field lines that also go through (below) the glowing region below. The temp/velocity measurements were at 450 km... and I presume that all the way down to 100 km, the velocity is fast and the temperature is high, on those field lines.

The Swarm data is from the Electric Field Instrument (EFI) on one of the three European Space Agency (ESA) Swarm satellites. These instruments were developed at UCalgary by Professor David Knudsen and his team, and built by Canadian industry (COM DEV which is now Honeywell).

• Welcome to SXSE, and thank you for taking the time to post here! Let me see if I understand. Since this particular measurement is happening at a high magnetic latitude (~60 degrees versus geographical ~50 degrees) ions will be following the magnetic field lines almost vertically. So while the light observed and photographed is produced at about 300 km altitude where there is sufficient number density, those sub-eV ions (protons?) will naturally be trapped in cyclotron orbits about the magnetic field lines, bringing them to much higher altitudes where they can be sampled by passing spacecraft?
– uhoh
May 11, 2017 at 1:25
• I'm going to assume my interpretation is basically correct, since the physics seems right and it nicely explains the disparities in altitudes. "Vertical" is used loosely.
– uhoh
May 16, 2017 at 6:03

In a later (independent) interview with Eric Donovan, he states the height was 450km. I suspect that in the presentation to the ESA meeting he should have said "300 miles", which is 482 km; that is very close to the altitude of the SWARM A satellite at the time, rather than 300 km. All the online articles, including Wikipedia, appear to be clones of the ESA presentation and 'press release', so may all reflect the same error if I am correct.

• Thanks for your thoughts! In order to be a good stackexchange answer, it would be better if you could add a link or two, and possibly include some research on newer reports that can resolve your hypothesis of a mistake in units followed by repeated quotes of the error. Has this been resolved in newer reports or publications?
– uhoh
Oct 3, 2017 at 0:12

Editor's note: I'm maintaining here information from user Roger until he decides to migrate on his own.

Answer to the question: "Can you add a link or citation that confirms that the temperature of Steve's ions was actually measured by the TII?"

Have a look at the presentation from Eric Donovan at the 4th Swarm science meeting in Banff: http://www.esa.int/spaceinvideos/Videos/2017/03/Opening_of_Swarm_and_CryoSat_Science_Meetings around the time 1:22:14 -> after almost 25 seconds the actual Swarm data are shown (from top to bottom: ion velocity, magnetic anomaly, ion temperature and electron density).

Answer to the question "how did the ESA probe measure Steve's temperature?": The ion temperature is measured by an Thermal Ion Imager (see http://efi.phys.ucalgary.ca/)

• He does say verbally in the video that one of the SWARM satellites flies through Steve, and that would be necessary because TII needs to be exposed directly to the plasma particles. It's not a remote sensing device, the protons have to go directly into it for their temperature to be recorded. It really measures their kinetic energy and you can deduce a temperature from that later. The problem is that with Steve at 300km and only a few tens of km thick vertically at most, and SWARM at 440km or more, this could not have happened this way. These things are mutually inconsistent
– uhoh
May 8, 2017 at 14:41
• So I'm waiting either for at least a preprint if not a peer-reviewed article saying that Steve suddenly jumped up to 440km, or SWARM secretly dipped down to 300km, or something else. The video is not really clear and on the slides that show data I don't see any clear statements about Steve's altitude and the SWARM satellite's altitude. As it stands right now something isn't adding up.
– uhoh
May 8, 2017 at 14:49
• I hope it's not something silly like confusing miles and kilometers, but then how did the signal appear?
– uhoh
May 9, 2017 at 9:44