Steve and the Color Purple

Posted on April 24, 2017 by Curtis_Seaman

It’s not often that a new discovery takes place that baffles the minds of lifelong scientists. This is a story about one that seems to have gone viral over the last few days. The abbreviated version (summarized from this article, this article, and this article, and many others like it) is as follows:

A group of dedicated aurora photographers noted a particular type of aurora that was different from what we normally think of. Instead of a rapidly changing curtain of light glowing green or red, it is a single arc of light, “purple” in color, with less apparent motion than a normal aurora. It doesn’t appear to move with the Earth’s magnetic field. The picture that accompanies every article about it is this one:

Photograph credited to Dave Markel Photography

The early guess was that it’s an example of a “proton arc” – a type of aurora caused by high energy protons rather than electrons. (Do a Google Image Search for “proton arc” and you’ll see many other examples.) However, the plot thickened when an expert on the aurora, Prof. Eric Donovan at the University of Calgary, debunked that guess based on the fact that proton arcs are not visible to the human eye. This was backed up by a graduate student at the University of Alaska-Fairbanks. Not knowing what else to call it, the dedicated aurora photographers named it Steve. No joke. (It comes from the animated movie, Over the Hedge.) The name has caught on, and now the internet is full of photographic examples of “Steve”. Here’s a time lapse video.

The Aurorasaurus Project has compiled a list of things we know about Steve. Our expert aurora professor matched up a known time and location of a Steve photograph with an overpass of the European Space Agency’s Swarm satellites and found this out:

“As the satellite flew straight though Steve, data from the electric field instrument showed very clear changes. The temperature 300 kilometres (185 miles) above Earth’s surface jumped by 3,000°C (5,400 degrees Fahrenheit) and the data revealed a 25 kilometre (15.5 mile) wide ribbon of gas flowing westwards at about 6 km/s (3.7 miles per second) compared to a speed of about 10 m/s (32.8 feet per second) either side of the ribbon.”

So, while we don’t exactly know what causes “Steve”, we do know that it is relatively common. (Do that Google Image Search for “proton arc” again for proof.) And we know it’s not a proton arc. Of course, the question that is relevant to us on this blog is: Can the VIIRS Day/Night Band see Steve?

There was a significant geomagnetic storm 22-23 April 2017 that may provide the answer. One of the Alberta Aurora Chasers (our dedicated group of aurora photographers) took this picture and, in the comments, noted the location (Lake Minnewanka, Alberta) and approximate time (“maybe 12:30” AM on the 22nd). Compare that with the nearest Day/Night Band image:

VIIRS Day/Night Band image (08:12 UTC 22 April 2017)

I put a gold star on there to indicate the location of Lake Minnewanka. Don’t see it? Here’s a close-up:

VIIRS Day/Night Band image above zoomed-in on Lake Minnewanka. The gold star indicates the location of the lake.

Unfortunately, Lake Minnewanka is outside the VIIRS swath. But, Aurorasaurus says Steve is often hundreds or thousands of miles long, and oriented east-west, so it should extend into the VIIRS swath. Now, this VIIRS image was taken at about 2:15 AM local time, almost two hours after the photograph was taken. Aurorasaurus also says Steve is visible on the order of minutes, “up to 20 minutes or more”. So, maybe Steve disappeared in the time between the two images. I certainly don’t see any straight or smooth arc of light near the star that resembles Steve. Although, just north of Calgary (the closest city within the VIIRS swath to Lake Minnewanka) there is faint evidence of aurora light, and it is on the equator-ward side of the aurora, which is consistent with previous observations.

The streaks of light visible near Calgary (and general streakiness across the whole aurora) are due to the way the VIIRS instrument scans the scene and the high-temporal variability of the aurora, which we’ve discussed before. But, as I mentioned, these streaks don’t extend for hundreds or thousands of miles.

Maybe, VIIRS had better luck on the next overpass (~3:55 AM local time):

VIIRS Day/Night Band image (09:53 UTC 22 April 2017)

Again, nothing jumps out to say, “Aha! That’s Steve!” So, was Steve there and VIIRS failed to see it? Or, was Steve not there at the time of the VIIRS overpass? The answer to that depends in part on the definition of “purple”.

Is Steve really “purple” as people describe? Or, is it violet? Wikipedia actually has a good section on this (at least, until someone edits it). There’s also the page discussing the “Line of Purples“. The problem stems from the fact that violet is a color similar to purple, but is physically very different. Violet is the name given to a specific wavelength range of light, specifically the visible portion of the spectrum less than 450 nm. Purple is a combination of blue and red wavelengths – blue being wavelengths between ~450 nm and ~495 nm and red being anything visible above ~620 nm. Violet and purple look similar to us because the cone cells in our eyes have a similar response to both colors. However, in the RGB color space of the computer you’re viewing this on, and in the color cameras used to take pictures of Steve, violet is impossible to duplicate. This is because violet is not a combination of red, green and blue – it’s its own wavelength. The red, green and blue light emitting diodes (or phosphors on a plasma screen) don’t emit violet wavelengths. Your camera stores the information it collects in RGB color space, too, and has to approximate violet the same way your computer does – by making it a bluer shade of purple. Depending on the camera, the detectors used may not even be sensitive to violet light.

So, what does this mean for VIIRS? The Day/Night Band is not sensitive to radiation at wavelengths shorter than ~500 nm, which includes blue and violet. But, it is sensitive to red and beyond – up to ~900 nm. So, if Steve really is purple, the Day/Night Band will only be sensitive to the red component of it. (It would be more faint, but VIIRS would likely be sensitive to it, given that it is sensitive to airglow, which is much more faint than the aurora.) If Steve is really violet, than the Day/Night Band won’t see it at all.

So, can the Day/Night Band detect Steve? I can’t answer that based on this information. We will have to wait for another dedicated aurora photographer to take a picture of Steve at a time and place when VIIRS is directly overhead. Feel cheated by that? Just enjoy the images of the aurora above. And, here are a few more from this event:

VIIRS Day/Night Band image (11:34 UTC 22 April 2017)

VIIRS Day/Night Band image (07:53 UTC 23 April 2017)

VIIRS Day/Night Band image (09:34 UTC 23 April 2017)

Don’t forget to click on them to see the full resolution!

UPDATE (13 October 2017): Over the years, I have looked at a number of Day/Night Band images of the aurora. During that time, I’ve noticed some “auroras” that appear to be very “Steve”-like. One example is shown in the image below from 17 January 2015.

VIIRS Day/Night Band image (13:09 UTC 17 January 2015)

The question is: is this an example of Steve? Or, just a less active aurora?

Of course, being over a remote part of northern Alaska, it’s unlikely anyone got a photograph to prove it was Steve. We’ll still have to wait for the perfect alignment of Steve, Steve-hunters and VIIRS to know if the Day/Night Band can (or cannot) detect them.

When Canada Looks Like China

Posted on July 30, 2014 by Curtis_Seaman

No, I’m not talking about Chinatown in Vancouver. Or Chinatown in Toronto. Or any other Chinatown in Canada. I’m talking about this. Or, more exactly, this. Poor air quality is making it difficult to breathe in Canada and elsewhere.

Unlike the situation in China, you can’t really blame the Canadians for their poor air quality. (Unless, of course, some serial arsonist is wreaking havoc unfettered.) You see, it has been an active fire season in western Canada, to put it mildly. Here’s a not-so-mild way to put it. That article, from 3 July 2014, put the number of fires in the Northwest Territories alone at 123, with most of them caused by lightning. But, after a check of the Northwest Territories’ Live Fire Map on 30 July 2014 it looks like there are more than that:

"Live Fire Map" from NWTFire, acquired 17:00 UTC 30 July 2014. This is a static image, not an interactive map.

I estimated 160-170 fires in that image (assuming I didn’t double count or miss any). How many fires can you count?

At one point earlier in July, it was estimated that battling the fires was costing $1 million per day! The fires have been impacting power plants, causing power outages, impacting cellular and Internet service, closing the few roads that exist that far north, and doubling the number of respiratory illnesses reported in Yellowknife, the territory’s capital.

It’s no secret that this area is sparsely populated. At last count, the territory had roughly 41,000 residents in 1.3 million km². (Fun fact: the Northwest Territories used to make up 75% of the land area of Canada. It has since been split up among 5 provinces and into two other territories. With the formation of Nunavut in 1999, it was reduced to being only twice the size of Texas.) If so few people live there, why should we care if they have a few fires?

If you are so heartless as to ask that question, you are also short-sighted and selfish. For one, I already explained the damage that the fires are doing. For two, fires like these impact more than just the immediate area and more than just Canada. Let me explain that but, first, let me show you the fires themselves – as seen by VIIRS – over the course of the last month.

Animation of VIIRS Fire Temperature RGB images 24 June - 25 July 2014

You will have to click on the above image, then on the “933×700” link below the banner to see the animation at full resolution. It is 15 MB, so it may take a while to load if you have limited bandwidth. What you are looking at is the Fire Temperature RGB in the area of Great Slave Lake, the area hardest hit by this fire season. There are a lot of fires visible over the course of the month!

See how the larger fires spread out? They look like the large scale version of an individual flame spreading out on a piece of paper. (Don’t try to replicate it at home. I don’t want you catching your house on fire!) Of course, the spread of the fires is dependent on the winds, humidity, moisture content in the vegetation, and the firefighters – if they’re doing their job.

Now, these weren’t the only fires in Canada during this time. Check out this Fire Temperature RGB image from 15 July 2014 and see how many (rather large) fires there are in British Columbia and Saskatchewan:

VIIRS Fire Temperature RGB composite of channels M-10, M-11 and M-12, taken 21:08 UTC 15 July 2014

Make sure to click through to the full resolution version. I counted 9 large fires in British Columbia, 1 in Alberta (partially obscured by clouds) and 6 in Saskatchewan. If you look closely, you might also spot 3 small fires in Washington plus more small fires in Oregon. (“Small” here is compared to the fires in Canada.)

Now, all these fires means there must be smoke and, because VIIRS has channels in the blue and green portions of the visible spectrum, we can see the smoke clearly. This is one of the benefits of the True Color RGB (in addition to what we discussed last time). If I tried to create another animation, like I did above, showing the extent of the smoke plumes it would be so large it might crash the Internet. Instead, here are some of the highlights (or low-lights, depending on your point of view) from the last month.

On 6 July 2014, the smoke is largely confined to the area around Great Slave Lake:

VIIRS True Color RGB composite of channels M-3, M-4 and M-5, taken 20:35 UTC 6 July 2014

The very next day (7 July 2014) the smoke is blown down into Alberta and Saskatchewan (almost as far south as Calgary and Saskatoon):

VIIRS True Color RGB composite of channels M-3, M-4 and M-5, taken 20:16 UTC 7 July 2014

One day later (8 July 2014) smoke is visible down into Montana, North Dakota and beyond the edge of the image in South Dakota (a distance of over 2000 km [1200 miles] from the source!):

VIIRS True Color RGB composite of channels M-3, M-4 and M-5, taken 19:57 UTC 8 July 2014

On the 12th of July, you could see a single smoke plume stretching from Great Slave Lake all the way into southwestern Manitoba (plus smoke over British Columbia from their fires):

VIIRS True Color RGB composite of channels M-3, M-4 and M-5, taken 20:23 UTC 12 July 2014

When the fires really get going in British Columbia a few days later, the smoke covers most of western Canada. On 15 July 2014, smoke is visible from the state of Washington to the southern reaches of Nunavut and Hudson Bay:

VIIRS True Color RGB composite of channels M-3, M-4 and M-5, taken 19:27 UTC 15 July 2014

One day later (16 July 2014), and it appears that smoke covers 2/3 of Alberta, nearly all of Saskatchewan, all of western Manitoba, southern Nunavut, southeastern Northwest Territories, and most of Montana and North Dakota. There is also smoke over Washington, Oregon and northern Idaho:

VIIRS True Color RGB composite of channels M-3, M-4 and M-5, taken 20:48 UTC 16 July 2014

A quick estimate puts the area of smoke in the above image at 2.5 million km², which is roughly a third the size of the contiguous 48 states!

With renewed activity in the fires in the Northwest Territories last week, the smoke was still going strong over Canada, impacting Churchill, Manitoba (home of polar bears and beluga whales):

VIIRS True Color RGB composite of channels M-4, M-4 and M-5, taken 20:17 UTC 23 July 2014

I guess if the melting polar ice caps don’t kill off the polar bears, they can still get cancer from all this smoke. Maybe the “world’s saddest polar bear” will want to stay in Argentina.

I should add that some of my colleagues at CIRA and I have sensitive noses and were able to smell smoke right here in town (Fort Collins, Colorado) earlier this month. Plus, there were a few smoky/hazy sunsets. (Although it should be clarified that we don’t know if it was from the fires in Canada or the fires in Washington and Oregon. There weren’t any fires in Colorado at the time.) Nevertheless, the areal coverage and extent of the smoke from fires like these is immense, and can have impacts thousands of miles away from the source. And, it’s all carbon entering our atmosphere.

UPDATE (8/1/2014): Colleagues at CIMSS put together this image combining two orbits of data over North America from yesterday (31 July 2014), where you can see smoke stretching from Nunavut all the way down to Indiana, Ohio and West Virginia. There may even be some smoke over Kentucky and Tennessee. Witnesses at CIMSS reported very hazy skies across southern Wisconsin as a result.

JPSS (SNPP and NOAA-20)

VIIRS Imagery and Visualization Team Blog

Tag Archives: Alberta

Steve and the Color Purple

When Canada Looks Like China