Tag Archives: river

Rivers of Ice

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Oh, Yakutsk! It has been a long time – 2012, to be exact – since we last spoke about you (on our sister blog). It was a different time back then, with me still referring to the EUMETSAT Natural Color RGB as “pseudo-true color”. (Now, most National Weather Service forecasters know it as the “Day Land Cloud RGB”). VIIRS was a only a baby with less than one year on the job. Back then, the area surrounding the “Coldest City on Earth” was on fire. This time, we return to talk about ice.

You see, rivers near the Coldest City on Earth freeze during the winter, as do most rivers at high latitudes. Places like the Northwest Territories, the Yukon, Alaska and Siberia use this to their advantage. Rivers that are frozen solid can make good roads, a fact that has often been overly dramatized for TV. Transporting heavy equipment may be better done on solid ice in the winter than on squishy, swampy tundra in the summer. But, that comes with a cost: ice roads only work during the winter.

In remote places like these, with few roads, rivers are the lifeblood of transportation – acting as roads during the winter and waterways for boats during the summer. But, what about the transition period that happens each spring and fall? Every year there is a period of time where it is too icy for boats and not icy enough for trucks. Monitoring for the autumn ice-up is an important task. And, perhaps it is more important to monitor for the spring break-up of the ice, since the break up period is often associated with ice jams and flooding.

We’ve covered the autumn ice up before on this blog, but VIIRS recently captured a great view of the spring break up near Yakutsk, that will be our focus today.

We will start with the astonishing video captured by VIIRS’ geostationary cousin, the Advanced Himawari Imager (AHI) on Himawari-8 from 18 May 2018:

The big river flowing south to north in the center of the frame is the Lena River. (Yakutsk is on that river just south of the easternmost bend.) The second big river along the right side of the frame is the Aldan River, which turns to the west and flows into the Lena in the center of the frame.

Now that you are oriented, take a look at that video again in full screen mode. If you look closely, you will see a snake-like section of ice flowing from the Aldan into the Lena. This is exactly the kind of thing river forecasters are supposed to be watching for during the spring!

Of course, this is a geostationary satellite, which provides good temporal resolution, but not as good spatial resolution. The video is made from 1-km resolution imagery, but we are looking at high latitudes on an oblique angle, so the resolution is more like 3-4 km here. (Note: the scene in the video above is approximately the same latitude as the Yukon River delta, so this acts as a good preview of what GOES-17 and its Advanced Baseline Imager [ABI] will offer.) So, how does this look from the vantage point of VIIRS, which provides similar imagery, but at 375 m resolution? See for yourself:

(You will have to click on the image to get the animation to play.)

Animation of VIIRS Natural Color RGB composite of channels I-1, I-2 and I-3 (18 May 2018)
Animation of VIIRS Natural Color RGB composite of channels I-1, I-2 and I-3 (18 May 2018)

This animation includes both Suomi NPP and NOAA-20 VIIRS. That gives us ~50 min. temporal resolution to go with the sub-kilometer spatial resolution. Eagle-eyed viewers can see how the resolution changes over the course of the animation, as the rivers start out near the left edge of the VIIRS swath (~750 m resolution), then on subsequent orbits, the rivers are near nadir (~375 m resolution) and then on the right edge of the swath (~750 m resolution again). In any case, this is better spatial resolution than AHI can provide (or ABI will provide) at this latitude.

One thing you can do with this animation is calculate how fast the ice was moving. I estimated the leading edge of the big “ice snake” moved about 59 pixels (22.3 km at 375 m resolution) during the 3 hour, 21 minute duration of the animation. That works out to an average speed of 6.7 km/hr (3.6 knots), which doesn’t seem unreasonable. Counting up pixels also indicates our big “ice snake” is at least 65 km long, and the Aldan River is nearly 3 km wide in its lower reaches when it meets the Lena River. That is in the neighborhood of 200 km2 of ice!

That much ice moving at over 3 knots can do a lot of damage. Just look at what the ice on this much smaller river did to this bridge:

(Make sure you watch it all the way to the end!)

Oh, How the Seasons Change!

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The transition between winter and summer happens twice a year. Unless you live in the tropics. Then you don’t really have winter. If there are seasons there, they are “dry” and “wet”. But, at high latitudes, the transition from summer to winter is often abrupt and cannot be mistaken for anything else. It’s hard not to notice when 22 hours of sunlight turns into 2 hours of sunlight and back again the following year. For places like the interior of Alaska, it’s also hard not to notice the temperatures in the 70s F giving way to temperatures below 0 °F. (Of course, here in Colorado, our temperatures went from 70 °F to 10 °F in a period of about 36 hours hours this week. Not to brag or anything.)

Summers are short at high latitudes but, autumns are shorter. So, what can VIIRS tell us about the changing seasons?

We’re going to focus on the “Natural Color” RGB composite. In this composite, the red component is the reflectance at 1.6 µm, the green component is the reflectance at 0.87 µm and the blue component is the reflectance at 0.64 µm (a red visible wavelength). The Natural Color RGB is useful for detecting snow and ice, determining cloud top phase, monitoring vegetation and detecting flooding. So, it’s good to get familiar with it.  Plus, it’s one of the best RGB composites you can make with the high-resolution (375 m) channels on VIIRS.

Here is a Natural Color RGB image of Alaska from 6 September 2014 – at the end of summer:

VIIRS Natural Color RGB composite of channels I-1, I-2 and I-3, taken 22:56 UTC 6 September 2014
VIIRS Natural Color RGB composite of channels I-1, I-2 and I-3, taken 22:56 UTC 6 September 2014.

It’s easy to pick out the ice clouds from the liquid clouds, just as it’s easy to see the snow on the Brooks Range. They appear cyan instead of white (as they would in the True Color RGB composite). If you want to know why snow and ice appear cyan in this composite, click here. But, I want to draw your attention to the third and nineteenth longest rivers in the US. Lower-48ers that didn’t click on the link are probably wondering which rivers I’m referring to. But, of course, Alaskans know which rivers I’m talking about, right?

OK, fine. Just to make sure we’re all on the same page, I’m talking about the Yukon and the Kuskokwim. These rivers are wide enough to be seen by VIIRS. Did you find them in the above image? Click on the image to see it in full resolution and make sure you see them.

Notice how the rivers are almost black. That’s because water is poorly reflective at these three wavelengths. This will come in handy later on. Now, let’s look again at these rivers a month later (7 October 2014):

VIIRS Natural Color RGB composite of channels I-1, I-2 and I-3, taken 23:19 UTC 7 October 2014
VIIRS Natural Color RGB composite of channels I-1, I-2 and I-3, taken 23:19 UTC 7 October 2014.

Why are the rivers surrounded by brown when a month earlier the river valleys were green? Deciduous trees like to hang out in the river valleys of southwestern Alaska, and these trees have already changed color and lost all their leaves over the course of this month, leaving behind only the bare branches and trunks. This is one sign of the changing seasons. (Note, however, that it is just a coincidence that these areas appear brown here. This is a false-color composite. The brown color is due to the reduced reflectivity of the deciduous forests at 0.87 µm caused by the lack of leaves, not because the tree trunks are brown. Read this if you want to learn more.)

Another sign of the changing seasons is the additional snow present. Everywhere north of the Brooks Range is snow covered. Plus, you can see pockets of snow in the Kilbuck and Kuskokwim Mountains, the Aleutian Range and in the hills and mountains surrounding Norton Sound.

Fast forward another month to 4 November 2014:

VIIRS Natural Color RGB composite of channels I-1, I-2 and I-3, taken 22:51 UTC 4 November 2014
VIIRS Natural Color RGB composite of channels I-1, I-2 and I-3, taken 22:51 UTC 4 November 2014.

Now, almost the whole state is covered by snow. But, look at the rivers! They are no longer black – they are cyan, which means they have frozen over. Although, if you look closely, you can see a few pixels suggesting open water on the lower sections of the Yukon, generally between Russian Mission and Mountain Village. Also, look closely where the Kuskokwim River flows into Kuskokwim Bay, downstream from Bethel – there is ice along the shores, but open water in the middle. Ice is also forming in Norton Sound and has covered Baird Inlet.

Two weeks earlier (21 October 2014), there is more of a mix of ice and open water on the Yukon and Kuskokwim:

VIIRS Natural Color RGB composite of channels I-1, I-2, and I-3, taken 23:59 UTC 21 October 2014
VIIRS Natural Color RGB composite of channels I-1, I-2, and I-3, taken 23:59 UTC 21 October 2014.

Identifying ice and open water on the rivers is very important. When the two coexist, ice jams can occur. When an ice jam forms, it blocks the flow of the river, which can flood areas upstream of the jam. When the jam breaks, it can cause a flash flood downstream.

Ice jams, even on small rivers, can show their power:

Imagine what they can do on the third and nineteenth largest rivers in the country!

Sometimes, you don’t have much time to get out of the way. Note: you might not want to watch this one if you are prone to motion sickness:

Who remembers what happened to Crooked Creek on the banks of the Kuskokwim in 2011? Or on the Yukon River at Eagle in 2013?

Of course, once the rivers are completely frozen over, there is no threat of an ice jam or flooding. But, now that you know how to spot ice forming on these rivers in the fall, you’ll hopefully be able to spot the return of open water in the spring, when the threat returns.

To really capture the changing of the seasons, here’s an animation of the relatively cloud-free images from 3 September 2014 to 6 November 2014:

Animation of VIIRS Natural Color RGB composites from 3 September 2014 to 6 November 2014
Animation of VIIRS Natural Color RGB composites from 3 September 2014 to 6 November 2014.

Click on the image to view the animation. It’s 17 MB, so it may take a while to load. See if you can pick out when the first ice forms on either river.