The Cayuga Fisher

Random Photo Spotlight:

Conesus Pike!

Fish and Tips

2008 Goal: postponed...

Currently:  ? species

More info

Hot Knots

Never tie an improved clinch again.

The uni knot is versatile, easy to tie, and strong. Use it to tie on hooks or join two lines together with the double uni knot. Works great for tying dissimilar lines together or a leader to braid. For tying a braid backing to heavier mono or even a leader to braid the Red Phillips knot is faster and smaller.

The Water:  Wind Driven Water:  Coriolis and Currents

Coriolis: what?  <=  Water Index  =>  next

Wind Driven Water:  Currents and Seiches Formed by the Coriolis Effect

When the wind blows, the current moves downwind and to the right.   But if it the lake basin restrains the movement, what happens?  As a practical matter this is very important to Finger Lakes fishermen!  The long and narrow basins of the Finger Lakes make for relatively unusual water movement patterns;  the internal seiches in particular are much stronger than other lakes and understanding their movement is a key to success. The Coriolis Effect influences these seiches and surface currents markedly.

While turning to the right, the current piles up and moves along the righthand shoreline.  Upon reaching the far end of the lake, it turns, usually drops subsurface, and returns.  The result is a counterclockwise circulation pattern.  The diagram illustrates a South wind causing counterclockwise water movement at the North end.  This effect is achieved no matter the wind direction!  Blowing from the North, the surface current collects and follows the West shore, finally reaching the Southern end, where it has to turn and head North on the far side of the lake.  

Depending on conditions, this 'far side' water movement can occur at varying depths, sometimes deep in the water column, sometimes at the surface.  Recently I was out with a light South wind, in a sheltered place on the West shore.  I could feel the breeze, but it wasn't enough to prevent me from drifting South, into the wind!  The wind had been blowing steadily from the South for a few days, a fairly strong counterclockwise current had developed lakewide, and I was being pushed South down the West shore, into the breeze.

During unstratified conditions this return flow can be at any depth, while during stratified periods, the return flow is strongest at the thermocline.  Sound familiar?  It should, we are working on applying the Coriolis Effect to both surface currents and internal seiches, going from the simple nonrotating model already covered to a more complex rotating model of internal currents.  The lake not only sloshes back and forth, it rotates while it does so!

This happens on the surface and below, whenever currents move the length of the lake.  Since the internal seiches move the most water, it stands to reason that internal seiches are also most affected by the Coriolis Effect.  The above tale of drifting into the wind is a good example of a surface current, imagine the amount of water moving below the surface! 

When stratified and subject to a seiche, the thermocline moves in response.  As the wind drives warm water into one end, the thermocline there deepens in response, with the colder water moving away.  The key is the opposing directions of the current- the surface water (epilimnion) moves downwind and to the right, the hypolimnion moves upwind and to its right.  When the wind stops, the currents reverse and flow in the other direction, again moving to the right.  The result is a twisting of the thermocline, rather than a straight rocking back and forth, as the seiche oscillates.  This twisting of the thermocline will rotate in a counterclockwise direction, just like the surface current.

For example, a strong North wind pushes warm water South.  As it does, it drifts to the right.  Importantly, the warmer water collects on the right side of this current, and the cooler water on the left.  (The details are too complex to get into, but it does... ever wonder why one side of the lake is warmer than the other during summer?)  This current heads down the West shore, and will eventually concentrate the warmest, biggest pile of water in the SW corner of the lake, depressing the thermocline the most in that area.  Correspondingly, the thermocline rises the most in the Northeast as cool water moves in below. 

When the wind stops, the warm water in the SW corner heads Northeast.  This water, flowing in a current, is again subject to the CE, and piles along the East shore.  The cold return current flows from the NE to the SW, reversing the earlier scenario.   The cold water returning below the thermocline also moves to the right, hugging the Western shore.  All this cool water rushing South pushes the thermocline towards the surface.  Meanwhile, the surface water moving to the NE pushes the thermocline down on the East shore. 

This is very important!  The currents generated from wind do not move uniformly up and down the lake!

The movements of the epilimnion and hypolimnion (warm and cold layers) follow the same path, a counterclockwise rotation around the lake, but since their movements are opposite, the waves are 180 degrees out of phase.  When the surface seiche is highest at one end and temporarily at rest, the internal thermocline seiche is 'flat' but experiencing its highest currents and greatest thermocline displacement.  Imagine a giant 'bump' of warm water, half the width and length of the lake, moving counterclockwise around the interior of the lake.  At the same time, and in the other corner of the lake, a giant 'bump' of cold water follows its own counterclockwise path, like two boxers facing off in the ring.  These bumps move slowly when at the far ends of the lake, but speed up and squeeze in as they pass each other across the width.

the shape of the lake basin itself, the fact that it's not oriented directly N-S, the higher hills at the South end vs. the Northern Plains, the several large points in the lake, etc...

Coriolis: what?  <=  Water Index   |  Top  =>  next

Contact | About | © 2005-2012