Tag Archives: rainbow

#BergenWaveWatching: Rainbows!

Reposting from Elin’s blog here!

—

Kjersti, Steffi, Elin and myself (Mirjam) recently discussed ways to better integrate the GEOF105 student cruise into the course. My suggestion was to ask the students to observe things throughout the whole duration of the course, and then have them relate their time series with what they observe when “at sea”. In this mini series tagged #BergenWaveWatching, I write up a couple of suggestions I have for observations that are easy and fun to make. I am anticipating that my suggestions will be strongly biased towards #wavewatching, so if you have any other suggestions, I am all ears! :-)

Neither wave watching nor particularly Bergen-specific, but still super cool! And probably as close as I will ever come to suggesting any kind of meteorological observation. Clouds are pretty amazing, too, but I really don’t know enough about those…

Where to go

Nowhere specific, just keep an eye out for situations in which there are water droplets in the air and the sun is low enough in the sky for rainbows to appear. Be aware of where rainbows would appear if they were visible (the shadow of your head would be in the center of the rainbow) and check out if they are there.

It doesn’t actually have to rain for rainbows to appear…

When to go

Since the sun needs to be sufficiently low in the sky for rainbows to be above the ground, rainbows are more likely to appear in the morning and afternoon.

What to look out for

Duh. Rainbows?

What to do with the data

I think it could be fun to try and relate the appearance of rainbows to the kind of weather. Obviously, you need both sun and rain. But for double rainbows, you need several rain fronts behind each other. And for a secondary rainbow as in the picture on the very top (blog post on that here), you need strong sunshine.

The observations suggested here are also well suited for a description of the phenomenon and an explanation of the physics behind it.

How this is relevant for the student cruise

Not directly, but I think getting into the habit of observing something fairly specific and, over time, becoming an expert on spotting and explaining rainbows, is pretty awesome!

Do you have suggestions for us? What other spots or topics would you recommend in and around Bergen to be added to the #BergenWaveWatching list? Please leave a comment! We are always looking to expand this list!

Lille Lungegårdsvannet

1 Reply

The geometric shape of Lille Lungegårdsvannet makes for perfect wave watching conditions. Not only when wanting to look at waves from all sides, but also when you are just fascinated by reflections and geometric wave pattern.

And also by rainbows. Am I the only one who, when the sun is out and at a good angle, walks around Lille Lungegårdsvannet to see the rainbow that you know must be there?

April weather in September (Great for #WaveWatching and cloud watching!)

1 Reply

Minutes after drawing the illustration to the “you are not a drop in the ocean, you are the ocean in a drop” quote I shared yesterday in the most beautiful sunshine, the sky started looking like this.

Luckily I had a nice spot from which I could observe what happened next…

…lots of drops. In the ocean. Or oceans in the drops? Who knows. Anyway, after just having done that drop drawing, I couldn’t very well get upset, and I love watching rain on water anyway.

Just look at all the wave rings, and the way drops are catapulted up again only through surface tension!

Here is a (first normal speed, then slow motion) video so you can appreciate it properly, too:

As the rain passed, I found it super impressive to watch the rain showers as they went down elsewhere.

Like over the mouth of Kiel fjord, and I am showing the same spot repeatedly in the following (with more or less the same view, you can use the buoy as point of reference).

I don’t know enough about meteorology to understand what’s going on there, but I can still appreciate the beauty of the rain cloud and how differently things look where it is propagating to (to the right) and where it has already left (to the left).

See how much lower the clouds on the right are, and clearly a different kind of cloud compared to the ones on the left?

At times, it got really dark.

And I watched this one cloud move, continuously raining.

Then there was a dry period of a couple of hours, and when I walked home, it looked like this: Again distinct areas with rain showers.

What I found also really interesting is the swimmer’s wake you see below. There is so much to see in that one picture: The wake, the rain shower in the background, the changing surface roughness from rougher, darker areas, and smoother, lighter areas, and then the areas in the foreground where we can look into the water (see here for why we can do that in some places and not in others)

Same thing as above, only in a different picture…

And again, this time with a really impressive black cloud. And interference pattern in the waves in the foreground.

And now even ring waves that that seagull made…

And as if I hadn’t had enough wave watching in one day, here is a different spot in the afternoon. See the interference pattern as waves get refracted around the bollard?

And, of course, another strong shower came and made us retreat to the inside. But see the rainbow in the picture below? Those are the kind of things that make me really happy! :-)

Rainbows in regnbyen Bergen

Leave a reply

Yesterday when approaching Bergen airport, I saw something super cool: The lower half of a rainbow!

Even though I grabbed my phone and snapped a picture in record time, I didn’t manage to capture it. Bummer! But that doesn’t keep me from writing about it while showing you a “normal” rainbow I took a picture of a couple of minutes later.

Rainbow seen from a plane approaching Bergen airport

Have you ever seen the lower half of a rainbow?

But can you imagine it? A u-shaped rainbow?

Have you ever seen anything like that before? It’s not something that we are used to seeing, at least not if we are looking a) at rainbows that are occurring on natural rain “curtains” and b) while we are on the ground. Let me explain…

Under perfect conditions, a rainbow is a full circle

Imagine you are a floating in space, looking at a curtain of rain drops. The sun is shining from behind you onto that curtain. What you then see on that rain curtain is a full rainbow circle, purple towards the middle and red towards the outside.

The size of the rainbow depends on how far away from the rain curtain you are. Imagine looking at the shadow that your head is making on the rain curtain. The line from your eyes to the shadow of your head will be our reference. Now imagine looking at any point on the rainbow. The line from your eyes to any point on the rainbow will be at a 40 to 42 degree angle to the reference line (40 degrees if you are looking at a purple point, 42 if you are looking at a red point, anything in between for the other colors).

Tweaking the size of the rainbow

Now imagine moving the rain curtain farther away. The angle between the reference line and the line to the rainbow stays the same, but the further away the rain curtain, the larger the rainbow. And vice versa: The closer the rain curtain, the smaller the rainbow!

So now imagine a nice curtain of droplets that you can walk towards and away from (sprinklers! garden hoses!) — the further you walk away, the larger the rainbow gets. And the closer you come, the more it shrinks again.

Standing on the ground, you only see the upper half

If you walk close enough to the rain curtain, you can actually see a full rainbow. But typically when we think of rainbows, we think of those occurring naturally, and then the rain curtains aren’t as neat and tidy as those from a sprinkler, and rainbows that we see are usually far far away, and thus really big. And that is why we aren’t used to seeing the lower half of a rainbow: Where the lower half would be there isn’t any rain curtain for it to appear on, because there is ground there! And the only way not to have the rainbow hit the ground is either have it close enough in front of us so it’s too small to even reach the ground, or to look at it from a plane that is high enough above the ground that even a large rainbow has enough space above the ground to fully appear on the rain curtain.

Next steps

So where do we go from here? I need to a) play with sprinklers and take pictures of rainbows! b) draw illustrations of the stuff I tried to describe above, and c) hope that I’ll be faster next time to finally get my u-shaped rainbow picture from a plane!

Alexander’s band: the dark space in between a primary and secondary rainbow

3 Replies

Bergen is a fairly wet place with on average 240 rain days every year. But that actually provides us with the perfect opportunity to see plenty of rainbows. Here is the view from the window of my apartment in the university guest house yesterday (and I love the raindrops on the windowpane!):

Bergen, Norway: primary and secondary rainbow on August 17, 2018. Note the “Alexander’s band”, the dark space between the two rainbows!

Isn’t this beautiful?

I am always fascinated by the intensity of the colors in a rainbow, and in cases where you get a primary and a secondary rainbow, of the darkness between those two. That area is called “Alexander’s band”, and occurs because the inner, primary rainbow focusses light towards its inside, whereas the outer, secondary rainbow spreads it towards its outside. So we end up with this dramatic dark band in between the two. I love how dramatic it looks!

Bergen, Norway: primary and secondary rainbow on August 17, 2018. Note the “Alexander’s band”, the dark space between the two rainbows!

Fun fact on the side: A couple of years ago I did a couple of short movies on optics in rainbows, when I was playing around with different styles of teaching videos. Watching them back today is so painful, but at least this blog helps me to remember how far I have come… ;-)

But let’s get back to talking about the weather. As I learned during the “summer concert” of the Bergen Filharmoniske Orkester yesterday: According to conductor Edward Gardner, translating from Det finnes ikke dårlig vær, bare dårlige klær, “there is no such thing as bad weather, only bad cleather”. Hahaha.

Summer concert of the Bergen Filharmoniske Orkester under conductor Edward Gardner on August 17, 2018. On the big screen you get a glimpse of what the weather was like…

Above, on the big screen behind the orchestra, you see the kind of clothing that was appropriate for the occasion. That was one brilliant concert and totally worth sitting in the pouring rain with rain coat, rain pants, waterproof shoes! There really is no such thing as bad weather! :-)

A touristy post about my trip to Heligoland

1 Reply

I recently went on a trip to Heligoland, Germany’s only island that is far away from the mainland (70 km in this case). It was a great trip, and I know you’ll be reading about it for some weeks to come :-)

Today, we’ll just do the touristy parts, though, and get into the oceanography later.

The trip started out super awesome. I went on a ferry and got the chance to see ships being greeted by Wilkomm Höft, the Ship Welcome Station, by dipping the Hamburg flag and playing the national anthem. I’ve seen this before, but only from land (this is a place that I love going to for birthdays, mine and other people’s). Sitting on a ship and being bid farewell this way is really touching! I loved it and got a little teary-eyed.

Being bid farewell (by dipping the Hamburg flag and playing music) at Wilkomm Höft in Wedel on the Elbe river.

The ferry itself is a high speed catamaran, which, as you might have guessed, produces an amazing wake.

Wake of the Halunder Jet, the high-speed ferry going from Hamburg to Heligoland.

Unfortunately, the ship is set up such that the rescue boats obscure the view of the wake a little. How inconsiderate ;-) Please ignore the outboard engine…

On Heligoland itself, there are the famous red cliffs, and tons of birds. Let me just show you a few:

Heligoland

The best-known part of Heligoland is the Lange Anna — a red rock called “long Anna”. You see it on the picture below. What I liked most about it — besides the beauty of the rock and the birds, obviously — was the wave breaker build there to protect the coast, and what it did to the waves.

“Lange Anna”, the famous red rock on Heligoland in the German Bight

Zooming in on the wave breaker’s edge, there is clearly very strong winds coming around that corner:

To be fair, it was a super windy day.

They also have a very nice beach on Heligoland, where you can see the bending of waves due to changes in topography that we talked about before.

And if you look over to the second island, you can very nicely compare and contrast the upwind and downwind coasts of islands:

See how there are lots of breaking waves (well, you probably only see the foam) on the upwind coast of the island in the back of the image, and how there are absolutely no waves in the lee of the sea wall in the foreground of that picture?

Btw, the downwind side of that same second island looks also a lot calmer as it is sheltered by the island itself:

Unfortunately, I couldn’t take a picture of the whole island at once, I really need to upgrade my camera… But can you spot the rainbow above?

Also there is some more, pretty spectacular weather to be seen:

If you go over to the other island, there are TONS of seals. Like several hundred, right on the beach! Obviously, I only have pictures of seals when there are also nice waves happening at the same time :-)

Oh, and birds.

And more seals! This one is cute, I have to admit…

Oh, and I was lucky (lucky means bold enough to ask!) enough to hitch a ride on the local research vessel, Aade. Below, they just finish a plankton trawl. We weren’t allowed out on deck because the weather was so rough…

What looks like a calm and serene morning really wasn’t one. It was super windy and wavy! Good thing I don’t get sea sick.

It turns out it’s super difficult to take pictures of waves that look as impressive as the waves are in reality. I really need to learn how to do that! But even if you don’t see the size of the waves, at least you get a different look at “lange Anna” below.

And these are white caps on the “open” sea, not waves breaking on a shore.

And for a nice comparison: The Aade (the research vessel I was on) and the catamaran that took me home later that night.

Anyway, it was a great trip!

The difference between secondary rainbows and double rainbows

Leave a reply

More reflection or more rain?

Ha, aren’t you enjoying talking about optics again?

Sometimes you see two rainbows that both have red on the outside and blue on the inside. And according to my post on secondary rainbows, that should not be the case. Yet is has been observed. Why?

Rainbow and secondary rainbow, seen at Heathrow Airport. Picture by my friend F.

As you remember, secondary rainbows form outside the primary rainbows because the light is reflected twice inside the raindrop rather than only once as in the case of a primary rainbow. But that second rainbow with red on the outer rim and blue on the inner is formed differently.

Until now we’ve assumed that all the rainbows appear on the same rain front. This is not the case for the rainbow we are talking about here – it is formed on a second rain front behind the first one. So the path of light within rain drops of both rainbows on both fronts is similar, with light being only reflected once for each rainbow.

When you google double rainbows, you sometimes find pictures of two rainbows, both with red on the outer rim, nicely separated from each other. And when you see those pictures, you can be pretty sure that they’ve been photoshopped. Double rainbows of the kind we are talking about here overlap, and usually you see one full rainbow with all its colors, and then a slightly smaller rainbow with only green, blue and purple peeking out:

If you look closely, there is a green-and-purple band on the inside of the complete rainbow. Double rainbow!

Sun dogs

2 Replies

Recently spotted: sun dogs, a special form of halo! Or rather sun dog (singular), since there was only one to be seen and not a second one at equal distance from the sun but on its opposite side.

Sun dog spotted somewhere between Mölln and Hamburg

These pictures are exactly as my camera took them without any filters or color enhancement or anything. Isn’t it weird that we appeared to be the only car stopping every couple of minutes to watch while everybody just continued driving?

Sun dog spotted somewhere between Mölln and Hamburg

Rainbows and prisms

Leave a reply

Lets go back and talk about one of my favorite non-oceanographic topics: Rainbows!

When I had my rainbow phase about a year ago, my mom sent me the movie below, which shows what you see when you look directly into the prism that paints these kinds of rainbows all over my parents’ living room:

Rainbow from glass prism

When you look directly into the prism, you don’t see a rainbow like the one projected on the wall, but you see one color at a time. Only as the prism moves you experience all the different colors of the rainbow. And that is interesting because in a rainbow you see all colors at once, yet here you don’t. This is going to go into the next version of my rainbow movie, but for now check out my mom’s:

My renewed interest in rainbows was sparked one Saturday where I saw one on my way to the swimming pool in the morning.

And then a double rainbow on an evening walk with a friend.

And then another friend, F., sent me the picture below which he had taken at Heathrow and which he kindly allowed me to use for educational purposes on my blog.

Are you as exited as I am that we are finally getting back into rainbows? :-)

What are the ingredients of a rainbow?

Leave a reply

Still collecting materials for our instructional short movies.

A while back I talked about how my colleague and I were experimenting with short instructional screen casts, and I shared some first attempts at movies on how rainbows form. We are still working on a story board for an improved version, but I was lucky enough to see a very pretty rainbow in a fountain the other day.

The picture below is a good demonstration of how rainbows form where there are water droplets in the air (provided there is enough sunlight, too, and we are watching from the right position) – we still see a bit of the rainbow to the right of the fountain, even though the wind direction has changed and the fountain is now blown to the left, visible because of the mist and the lower part of rainbow.

Fascinated as I was I had to film clips of this, too, which are combined in the movie below. There you see the rainbow appearing and disappearing, depending on where the fountain is moved by the wind, i.e. whether it is moved to the part of the sky where all the angles are right for us to see a rainbow, or not.

It was a magical moment – enjoy! :-)

Adventures in Oceanography and Teaching

Dr. Mirjam S. Glessmer

Tag Archives: rainbow

#BergenWaveWatching: Rainbows!

Lille Lungegårdsvannet

Rainbows in regnbyen Bergen

Have you ever seen the lower half of a rainbow?

Under perfect conditions, a rainbow is a full circle

Tweaking the size of the rainbow

Standing on the ground, you only see the upper half

Next steps

Alexander’s band: the dark space in between a primary and secondary rainbow

A touristy post about my trip to Heligoland

The difference between secondary rainbows and double rainbows

Sun dogs

Rainbows and prisms

What are the ingredients of a rainbow?