Recently, more and more of my friends send me pictures of waves they spotted when walking along a lake side or taking a ferry ride. I love how contagious wave watching is, and I love sharing my fascination with you! :-)
Here are some pictures that Fred sent me of his lovely Sunday walk today. There are at least five interesting things that I notice in the picture below. How about you?
Look at the beautiful interference pattern where two wave fields are almost perpendicular to each other, creating the checkerboard pattern! As you see in the picture below, there is one wave field coming in at a 45ish° angle to the sea wall, so its reflection is at 90ish° to the original wave field.
In the background you see the surface roughness changing and the water seeming darker where there is a breeze going over the water, creating small ripples that reflect the sky in a different way than the smooth surface closer to us.
See the waves the seagull made where it landed on the water?
Looking at the foreground, do you see the tiny ripples that show up not so much on the surface of the water, but rather at the sandy ground, because they focus the light?
And notice how you can look into the water in the foreground but not in the background? That’s the awesome phenomenon of total internal reflection where, if you look at water at an angle that is smaller than a critical angle, you cannot look into the water any more but just see light reflected at the surface! One of the things I never understood we had to learn about in school, but that I find super cool now.
And in the picture below, what do you see?
What I find most interesting in the picture above is how the reflection of that storehouse tower looks different in areas with different surface roughnesses. Where there is a breeze on the water in the background and in the foreground, it’s a lot more spotty than in the calm and smooth surface in between. And the checkerboard waves pattern (now you see the seawall that created the reflection, btw) carries through to the reflections, too, with the blue crisscross going into the white area where a cloud is reflected.
And then the phenomenon of total internal reflection is really clearly visible here with a lot of reflections on the water (or just more interesting things to reflect than just a blue sky in the previous picture) and a view down to the ground only in the very foreground of the picture.
Today we are focussing on tiny waves right near the shore inside the sheltered harbor. See how below there are two wave fields, one with longer waves with crests that are parallel to the water’s edge, and then shorter ones propagating at a right angle relative to the first field?
Where the rope swims on the water you see how the short wind waves are stopped and only start forming again at a distance downwind of the rope.
The same here: Where there are ropes floating on the water, the water’s surface looks a lot smoother because the wind waves that propagate perpendicularly to the ropes are erased. But there are some wave crests parallel to the rope, formed by the rope hitting the surface and being pulled out again!
Below, the ropes don’t actually touch the water’s surface, but we have cool reflections of waves with crests parallel to the two walls that form the corner. The water level is right at the height where there is a little ledge on the wall that gets flooded with wave crests arriving and then falls dry during wave troughs. This causes this cool pattern of wave crests that seem to be interweaved right at the corner.
Sometimes looking really closely at small scale pattern is even more fun than looking at the sea and all the big and flashy (or splashy?) stuff going on there!
Do you know the phenomenon that once you start noticing something, you see it everywhere? That’s been the case with me and total internal reflection. Not quite as impressive as last time, but still there:
And what I found really interesting this time: a swarm of tiny fishies making wave rings! I only noticed them because of those tiny waves. And if you look closely you can see so many of them just below the surface right where the wave rings are!
So funny to see the water almost boiling with fish on such a calm morning.
And another thing that fascinated me: how it’s so much easier to see into the water in places that are shaded (or dark) from the reflection of that pier. Not quite sure yet why it’s so much easier to see here, maybe just because there isn’t any glare? Any ideas?
Have you ever wondered why at some angles the sea looks blue (or whatever the color of the sky that day) and at others you can actually look into the water? That’s the phenomenon of total internal reflection. There is a critical angle at which you switch from “being able to look into water” to “total internal reflection”, i.e. the sky being reflected off the water’s surface and reaching your eye. Below you see a nice example of this: The more perpendicular you look at the water surface (i.e. those sides of the wave facing you), the better you can look into the water. Whereas all those parts of the sea surface that face away from you look blue and you can’t look into the water there.
I think this is totally fascinating! Don’t those pictures look almost fake?
And, btw, this doesn’t only happen if you look in parallel to the direction of wave propagation. Although it looks even weirder at an angle:
Can you see how all those tiny ripples on the wave each show the same phenomenon of either reflecting the sky or being transparent and showing the sea floor underneath? How cool is that? :-)
When I said that wake watching made me happy last week, did you really think those were all the wakes I was going to show you? Ha! No, I have plenty more! :-)
Today, I want to show you a couple that have one thing in common: the way that they show up against the sun’s reflection and thus become a lot more visible than they would be if they were just reflecting a uniformly blue or grey sky.
This is an old picture from early spring, but I just love how the reflection of that pier shows up the different wave lengths so clearly. The longer swell wouldn’t have been visible just from reflections of the sky…