Pond Boss Forums INTRO Questions & Observations Ekman Effect and Sideways Aeration

The following may be wilder than anything Mudcat Joe has ever come up with, but I hope someone who knows will comment on it.

I came across an article today which explained the “Ekman effect,” where a strong wind across water produces a current at a right angle to the wind. Because of the Coriolis effect, according to the article, the water begins to flow cyclonically, spiraling clockwise and down in the Northern hemisphere. Outside the spiral, deep water flows upward.

The Ekman effect of prevailing westerlies (plus the California current) explains the rich fishery off the California coast, and some other coasts as well. However, I wonder if this effect explains an opposite result--the turnovers which occur when highly stratified water in the summertime is hit with a strong constant wind of several hours duration which does not change direction. Is it the Ekman effect which causes cold anaerobic water from deep to both mix and change places with warmer surface water which is rich in oxygen and phytoplankton? If so, I wonder if the sideways aeration that has been demonstrated here in previous posts could not only directly add oxygen but also disrupt nascent Ekman spirals and prevent turnovers, similar to the effect of “wind shear” when an upper level wind disrupts tropical cyclonic storms to weaken them?

Sorry for any headaches the above might have caused, but I got one, and I like to share. :p
Lou

Lou tell ole Mudcat my head hurts already. Where did this article come from and where can we find it.

I knew that toilets in the northern hemi spun opposite from the southern himi toilets and that old man river has some monster whirl pools that nothing comes up from -- but never heard of any guy named Ekman Coriolis . Where the heck is he from anyway. Sounds like one of those long haired pointy headed tin foil hat types. :p

Does this help explain those El Nimoy years when the weather is funny?

The Coriolis effect is of course quite real, but it is relatively weak wrt many other forces which can overwhelm it in small settings that we can easily observe - like the built-in swirling jets in a toilet bowl (much more dependent on manufacture than hemisphere) or slight imperfections in aiming or differences in pond bottoms (if, for example, Bruce were to try and observe the Ekman effect in a Horizontally aerated pond).

wow....I ummmm....ahh wow got to go flush the toilet and see what you guys are talking about!

i'm sorry mr. heronblu (ewest and theo LOL) but the first thing came to my mind was also the fluid dynamic of a toilet bowel...LIBWIC (laughing inside, but where it counts)

beyond toilets, perhaps we can apply it to ponds cause it sure sounds good to me in theory.

theo, dont forget fractal theory....(i.e. same or similar processes and phenomena occur on all levels of scale....couple examples

1)galactic spin, solar spin/orbit, terrestrial spin/orbit, electron spin/orbits

2) the geomorphology of continental delta/shoreline formation versus patterns observed in small puddles after a rainstorm (tiny rivers, deltas, and shorelines)

why not wind and current meterological patterns from ocean to pond?

The sweeper nozzles running in my pond act like a minor wind event at all times. The sago pond weed grows with a "swept-sideways" look throughout the pond. The angle of the sago is generally at a right angle to the force of the pressurized water.

Love and kisses,

Ekman Coriolis

Ewest, you asked, “Where did this article come from and where can we find it?”
Answer: Mudcat wanted to see how far south the California current went and looked on Wikipedia. The rest is mystery, er, history. However, it is not true that Ekman wears a tin hat, but like his mom and her brother, his dad, he does have a pointy head. :p And as to where he is from, he lives in a tarpaper shack on Eagle Lake over around Vicksburg–and sometimes, Mudcat Joe claims, runs Mudcat’s trotlines at night.

Theo, I also understand that the Coriolis effect is weak and easily overcome. But, I wonder if a strong enough wind, constant in direction over several hours might set up enough of an Ekman swirl to cause turnover in a pond in which conditions were just right. Maybe that would explain why some ponds have turnovers and some don’t. Are turnovers more frequent in ponds with only a little structure? I don’t know. Must go study the physics of swirlies. I wonder if Ekman would volunteer? That long hair would make a good directional marker. On the other hand, the tin hat could stop up the drain.

And for those of you with your minds in the toilet, thanks to Dave for thinking outside the bowl!
Lou

Lou, you haven't posted in a while. Glad to see you're back, and hope all is well with you.

I know just the source to ask - no not a pointy headed theoretical physics PhD - but the best source for first hand eyeball observation -- those Para-normal once boiled survivor killer YP in Bruce's pond. Someone stir up Deb and see if she can make contact.

Oh BTW Lou tell ole Mudcat Joe that that old wiskey-pedia book has a lot of good stuff in them pages.

It's really raather elementary. Very similar to the Heropian effect. The movement of a gyro(hero) known as precession, is at a 90 degree angle to the applied force.

Sweet Potato Existentialism

"I think, therefore I Yam!"

"I yam what I yam, and that's all I yam".

popeye the sweetpotato man

:rolleyes:

Heronblu,
The Ekman effect doesn't occur in small private ponds or small, shallow lakes. Therefore, it isn't the cause of 'turnover.' A turnover in a pond or lake is normally stimulated by temperature changes.
In some manmade public lakes, rivers and even the Great Lakes as well as some of the bigger private waters wind currents create what's called the Langmuir effect. Look next time you drive across a bridge over water. You will likely see long, parallel streaks of floating stuff or bubbles. Continual blowing of a wind across gentle waters causes formation of cells of rotating water that parallel the surface. Picture two empty paper towel cores suspended, rolling opposite ways, side by side. Those circular currents cause upwelling from deeper waters over a long distance. While it most likely won't destratify water, it can sure send suspended 'stuff' to the surface. Hence, the bubbles, foam and floating debris. That's where the term 'flotsam' comes from.
At the same time, those two bands of converging water create downwelling, pushing fresh aerated water down. Since this 'stuff' does not sink with downward bound water, it collects to form a streak, which is what you see on the surface.
The Languir currents rarely dip below 20 feet. Below, water remains fairly still. I have seen Langmuir currents form within minutes, but often they last several hours, then dissipate. Circulation can form quite quickly, and can last from several minutes to several hours.

Thanks, Bob. I knew my idea was somewhat wild when I put it in here, and I now consider it to be all wet, so to speak, but think how much more I know about circulation in toilets now!

I especially appreciate your mention of Langmuir circulation. Irving Langmuir was a very talented fellow, it seems, having invented the gas-filled incandescent light (and I always thought it was Edison-but I guess his wasn’t filled with an inert gas). He was a Nobel laureate and has a unit of something I don’t understand named after him. He became interested in the lines of debris and foam you mention when he observed them during an Atlantic crossing in 1938 and subsequently did experimental work in a lake to explain them.

In closing, I hope none of us gets any first hand experience with fish kills from turnovers or from any other cause, for that matter. The only turnovers I like are apple.
Lou

heronblu,

I'm glad you brought this phenomenon up. It's something we see on the Great Lakes and I was dicussing it with a friend a few weeks ago as we crossed the Mackinac bridge. Neither one of us knew the cause of the slicks which have everything but the kitchen sink in them including lots of terrestrial insects which the steelhead feed on. In fact these things are sometimes a magnet for steehead. Thanks Bob for explaining the dynamic behind this phenomoenon.

Lou thanks for you original post.

No doubt wind has a substantial effect in aerating one of our ponds via wind and current. Because of its shape , topography and orientation wrt the prevailing winds we see currents often in different directions at the same time. The winds move the water in a primary direction and then runs into the ridges and dam and changes to moving water in secondary directions as the wind moves down the ridge/dam thus causing (whatever the correct name) a mixing/whirl effect.

One of the things I have really enjoyed about being a pond-meister is the variety of things I have observed I would never have known about. Thanks to all of you for being as interested as I am in the “why” of what we see.

Eric, your post brings to mind the lack of mixing I sometimes see in my pond. In the winter, water flowing off the mountain (only in Alabama and England would the 1,200 foot high ridge which is the back edge of my property and which serves as my watershed be mapped as a mountain) has a peculiar milky appearance. It doesn't look muddy, but like water with a little milk of magnesia in it. (For those too young to have experienced the joys of milk of magnesia, think of water shaken with corn starch or even some flour.) The boundary between this water and the rest of the pond is often very sharp--not straight, but sharp, and the difference can last many hours. I can understand currents from river tributaries not mixing well for a while, but why should such a knife-edge boundary, several hundred feet in length, occur in a pond? Temperature difference doesn’t seem to be a reasonable explanation, and the wet-weather stream from which the water comes is relatively small in relation to the boundary zone which is produced.
Lou

Lou I know what you are describing and have seen that also. Sometimes you can fish the leading (clear) edge of one of the lines and catch a lot of LMB. They get in the milky water right at the edge and hide and snatch fish from the clear water that can't see them as well.

Today I took a couple of pics of what I described above. I sent them to the office (with my notes)where I can better edit them (different program) to show the effects. I will post them tomorrow.

Here are 2 pics from the dam with the currents and wind directions noted with the points located. This is with a 5-10 mph wind with gusts to 15. The currents are all over the place due to the points and dam. You can even see some calm places.

Very nice illustrations, Eric. I get much the same sort of variability because of a similar irregular shoreline. The combination of that and leaving the woods standing does mean that there is never a day without any calm water anywhere. I assume the pictures are taken from your dam. Is the nearest point the tip of a long peninsula or is it an island?
lou

Here's something interesting even though it occurs on land. I live near the peak of a hill. One of my neigbors used to fly a flag at his house which is at the peak of the hill. I've actually seen the wind blowing in the opposite direction on top of the hill (180 degrees) than down at my location as I could see the direction his flag was blowing. It happened more than once.

CB1 that is exactly what is happening in the pics above. The wind is coming uphill from behind the dam and hitting it and acting as a wind break at low level. Winds a little higher which are unimpeded hit the water and points. Mass confusion results with winds going in all different directions and causing cross currents in the air and water including whirling aeration effect where the currents cross or parallel the banks.

Lou the close one is a long peninsula. We wanted an island but there was to much rock that would have required way to much explosives to break.

You are describing my favorite striper pattern - long rocky main lake point - steep banks - wind coming from different directions - curents "eddy" - atttracts baitfish - FISH ON...

Ignorance is bliss. I will never be blissful again after visiting this site! :p :p :p

so this mass confusion effect explains the other day......went out on a reservoir on a day with sustained S-SW winds from 10-20 mph, thought i could find a secluded cove w/ quiet water......didnt matter which shoreline or which cove i tried, the wind was always blowing right at us, had great difficulty anchoring. if we tried to hide around any point of any orientation, the wind just seemed to "wrap around" and came right at us.....was a bit frustrating.....