Category Archives: observation

Help! Weird ice crystals

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Geli, Torge, and all you other ice people – do you know what this is?

Browsing pictures on my phone, I came across the pictures below that I took a while back in Bergen. What you see in the picture below is a photo taken down at the flat surface of a picnic bench. Each individual ice needle is about 1 cm high measured from the wooden surface of the bench. I only saw the crystals on that one bench that one day, but not on any other surface.

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Ice crystals growing on a picnic bench

I’ve googled a little to figure out how these crystals formed, since they don’t look like either ice flowers or ice needles or any other ice crystal that I am used to seeing. However, I haven’t found anything yet.

The picture below is a close-up of some of the crystals and even though it looks like the picture has a very bad resolution and like you can see individual pixels, that is not the case. That impression is caused by the weird shapes of the ice crystals.

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Close-up of some of the ice crystals

Geli, Torge, anyone – do you know what these crystals are and how they form? Or do you have any idea where I could find out more?

P.S.: People who don’t understand why it’s awesome to have a camera on your phone either never had one or don’t have a blog.

Guest post: Arctic sea ice thinning.

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Exciting guest post on a newly published paper by Angelika H. H. Renner.

I’ve met Angelika on a cruise in the Antarctic Circumpolar Current a long time ago where we worked on an instrument together and created an advent calendar to keep up everybody’s morale during the second month of the cruise before flying home on christmas eve, and we’ve since gone white(ish) water kayaking, hiking in the norwegian mountains, visited each other’s institutes, helped each other out in research and teaching crises (mainly Geli helping me out, to be honest ;-), and we are planning an exciting project together. Angelika and coauthors recently published the paper “Evidence of Arctic sea ice thinning from direct observations“. In today’s post, Angelika writes about how the observations that went into the paper were obtained, and I am excited to share her story – and her amazing photos – with all of you.

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There’s been so much liquid water on Mirjam’s blog lately, I was happy to take her invitation for a guest blog to bring back some of the most amazing, interesting, and beautiful variation of sea water: sea ice!

Sea ice comes in various shapes, from very flat, smooth, and thin sheets of newly formed ice to huge ridges several tens of meters thick. Assessing the thickness of the sea ice cover in the Arctic remains one of the biggest challenges in sea ice research. Luckily, methods become more refined, and numbers derived from satellite measurements become more accurate and reliable, but they don’t cover a long enough period yet to say much about long-term changes.

My first proper science cruise in 2005 went to Fram Strait, the region between Greenland and Svalbard. I learned how to measure sea ice thickness the hard way: drilling holes. And more holes. And even more holes. Or the slightly-less-hard way: carry an instrument around that uses electromagnetic induction to measure ice thickness (since sea ice is much less salty than sea water and therefore much less conductive). This instrument is called ”EM31” and we kept joking that the number comes from its weight in kilograms…. So, using drills and the EM31 we measured on as many ice floes as we could and given that the cruise went all the way across Fram Strait, that gave as quite a few datapoints covering quite a large area.

These measurements have been done by the sea ice group at the Norwegian Polar Institute every summer since 2003, and in some years also in spring. It takes dedication to build such a time series! When we could, we also used an airborne version of the EM31, the EM-bird, to do surveys over larger areas. Now, finally, the results of all these measurement have been processed, and analysed – and what do we see? The sea ice in Fram Strait is thinning a lot. Depending which measure you use (nothing about sea ice thickness is straight forward…), the ice has thinned by more than 50% over the 10 years from 2003 to 2012!

It’s one thing to know that it has thinned, but it’s a lot more interesting to find out why. Fram Strait is a special place: Most of the sea ice that is formed somewhere in the Arctic Ocean (and doesn’t melt there again) leaves the Arctic through Fram Strait. It is a very dynamic region with strong currents and winds, which results in a lot of deformed ice regardless of its age. The extent of the ice cover here is not necessarily linked to the development of the ice in the Arctic Basin – most prominent example was the heavy ice year in Fram Strait 2007 whereas this was up to then the year with the lowest Arctic-wide ice extent in the satellite era.

We looked in more detail at where the ice came from and found that this, too, does not correlate with our thickness time series. While the source region of the ice varied from year to year, it was continuously thinning – in our opinion a sign that the thinning occurs Arctic-wide.

A lot of effort went into this paper and the dataset behind it, and I was very very lucky that I got the opportunity to participate in several of the cruises, do the data analysis and write the paper. It’s even more satisfying to see your work published when you know how much work drilling all those holes was……

Tidal currents at Saltstraumen.

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Watching the strongest tidal current in the world.

Together with my friend P, I went to see the strongest tidal current in the world more than two years ago. And it only occurred to me last night that I had not shown you the movies! If you ever find yourself close to Bodø, Norway, you should definitely go. And either stay for 6 hours or – as we did – go there, leave to do something else, and come back 6 hours later. Because the currents at Saltstraumen are not only the world’s strongest currents, but they are also reversing with the tide. How amazing is that?

So this is what the current looked like when we first were there at around lunch time:

And this when we came back at 6 pm-ish (and this is filmed from pretty much the exact same spot as the movie above)

And just to confuse you, the same current but the camera moving in the opposite direction:

Look at all those huge whirlpools!

 

Guest post: The 5-minute warning of a summer’s day sudden end.

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More bad weather in Hamburg.

Today I have the pleasure to announce a guest post by Torge Martin. Torge, together with J&J, came to visit Hamburg recently, and we got stuck in some pretty bad weather. Which, being the oceanographers and meteorologists we are, meant that we got very excited, took about 100 pictures each, and me talking Torge into writing about what actually happened there. Which he did! So without further ado – enter Torge!

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The 5-minute warning of a summer’s day sudden end.

Guest post by Torge Martin

A week ago we spent a wonderful day with Mirjam in Hamburg touring the harbor and downtown – very touristy. It was sunny and pretty hot for the average northern German. In the early afternoon the thermometer hit 28˚C. Perfect conditions for eating a big cup of ice cream at the Binnenalster, jumping on a Barkasse (little boats that ship tourists around the harbor) to catch at least a slight breeze, and for … a gorgeous thunderstorm.

When we climbed the 429 steps of the Michel (St. Michael’s tower) later in the afternoon we didn’t know that this was perfect timing to witness an impressive natural spectacle: The sky darkened quickly in the West and Southwest and within minutes a dramatic cloud formation took over the scene.

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Photo by Torge Martin.

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Photo by Torge Martin.

The horizontal “roll” across the picture (below the bright stripes) is a so-called shelf cloud that marks the leading edge of the approaching thunderstorm. In German such a cloud is often called Böenkragen (“gust collar”) or Böenwalze (“gust roll”), which hints at its shape and the strong winds that it is accompanied by.

How does such a shelf cloud form? I won’t go into all details of thunderstorm formation. The high cumulonimbus clouds of typical summertime thunderstorms are formed by strong, thermally driven updraft. Updrafts can reach vertical velocities of 50 km/h. When the moist air is cooled at higher levels, say at 6-9 km, condensation starts, and water droplets or ice crystals form. The droplets begin to fall within the cumulus cloud simply due to their weight and pull the ambient air with them along their way. This forms a downdraft, which is typically found in the rear part of the cloud while updraft still dominates the front side of the cloud. The downdraft flow spreads out horizontally near the ground and often comes with strong gusts at surface level. Since downdraft air is much cooler than the surrounding warm summer air, its spreading is associated with a cold front. The latter rapidly pushes upward the warm, moist surrounding air. As the warm air is lifted condensation may occur, which we then observe as a shelf cloud marking the leading edge of the gust front. On the ground we typically feel the downdraft from a thunderstorm as a drop in temperature and strong winds—in our case the 10-minute averaged wind speed peaked at 44 km/h and temperature dropped by 5˚C—while a change in wind direction and increase in air pressure can also be observed.

The shelf cloud, however, is not only beautiful and fascinating to observe, it also is nature’s “5-minute” warning to stop playing and go home (or find another safe place) before strong gusts and downpour hit.

In our case rainfall was heavy enough to reduce visibility from about 15 km to a mere 2 km. The rain was pushed horizontally through the tower top hurting on the skin. The crowd remaining at the top huddled together on the lee side of the hut, which shields the staircase from the elements. The gusts picked up dust from a nearby construction site in the harbor

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Photo by Torge Martin.

which probably helped the dramatic coloring of the lee side scenery. But that’s a different story …

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Photo by Torge Martin.

Data kindly provided by http://www.wetter22459.de

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Photo by Torge Martin.

 

Surface tension and office supplies.

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Lots of stuff an be made to float on water just because of surface tension.

This morning, I was taking pictures of heaps of waters on coins. I was planning to follow up on that post with pictures of a dome of water on a full mug. So far so good.

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Surface tension preventing this over-full mug from overflowing.

Then, I was planning on putting paper clips on top to show how surface tension would keep them afloat.

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More surface tension.

Except it DID NOT WORK. Maybe there was dish soap residue in the glass? Maybe I was too clumsy? I have no idea what was wrong. Anyway, I was on the phone with my mom later that day, and within half an hour I had the picture below in my inbox.

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Paper clips and other stuff floating on the surface of a mug filled with water. All because of surface tension.

I guess you can make almost anything float on the surface if you put your mind to it… ;-)

Surface tension – heaps of water.

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The classical way of demonstrating surface tension.

When talking about surface tension, the classical thing to do is to talk about the shape of drops of water.

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Water drop on a coin.

As seen before in this post, the drops of water act as lenses.

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It is pretty amazing how much water you can pile on a single coin!IMG_6533

If you can’t see it from the photos, here’s a video. But rather than watching the video, you should try it yourself. It’s fun!

Surface tension and water striders

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 How water striders can walk on water.

More pictures from the same spot at the banks of the Pinnau.

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Water strider making waves.

Looking more closely, you can see the water strider:

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Water strider

And now a real close-up from the pond in my parents’ garden (because those pesky little bugs are too fast to take pictures off when you are ashore and they are on the water, and the water is wider than a meter in each direction).

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Picture taken by my dad

See how you can see the impression its feet make on the water surface?

Refraction of light in water – sticks and lenses.

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Deformation in the water surface focussing light.

Talking about how a deformation in the surface leads to light being focussed in different ways here and here, another example came to my mind. Remember how my mom and I were watching the standing waves at the Pinnau a while back? That was the same place where we also observed the “shadows” of the eddies, so as we were playing with water and light anyway, this happened:

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A stick poking through the water surface. See the deformation of the surface and the effect that has on focussing the light at the ground (when you follow the stick down to the ground and then follow its shadow)?

See how the stick is deforming the water surface? This again leads to a focussing of light at the ground which you can observe if you follow the stick until you reach the ground and then follow its shadow.

Eddies – surface imprint and optical properties

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You can see “shadows” of eddies on the ground!

As everybody who has ever watched a bath tub drain knows – eddies do lead to a deformation of the water’s surface. Here is an example of what that looks like in the real world:

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Eddies coming off the edge of a rock in a current.

In case you don’t see the eddies like pearls on a string coming off the edge of that rock in the picture above, watch the movie below – it’s much clearer when it is moving! Do you see the surface dipping where those little eddies are?

And in the movie below you can see how there is a shadow at the bottom underneath each of those eddies.

Why, you ask? Well, remember this from last weeks post?

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Two 1 NOK coins, the one in the back with a water droplet in the hole in the middle.

The water droplet with the convex surface focusses the light. The eddies with a concave surface, on the other hand, does have the opposite effect: As the light enters the water, it is refracted away from its previous axis, leading to a “shadow” at the bottom underneath the eddy. How cool is that?

Refraction of light in water – coins and lenses.

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More on what water can do to light.

Remember my fascination with dandelions? Just to remind you:

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Dandelions.

Especially in combination with coins and water droplets, dandelions are a source of nearly endless entertainment:

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1 NOK with water droplet in the hole in the middle.

See how much cooler 1 NOK coins become only by adding a little water?

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The upper coin does not have water in the hole, the lower one does. See the difference?

Here the same two coins in the sun – see how the water droplet in the coin in the back focusses the light whereas the empty hole in the coin in the front is just a hole?

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The coin in the foreground doesn’t have water in the hole, the one in the back does. See how they affect light differently?

Pretty cool stuff. And in the next post I’ll show you what this very effect does out in the real world!

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Left coin without water, right coin with water in the hole in the middle.