talkFestool  

Go Back   talkFestool > Social Club (Off Topic) > Woodworkers Cafe

Woodworkers Cafe General Chat

Reply
 
LinkBack Thread Tools Display Modes
  #11 (permalink)  
Old 01-22-2009, 02:26 PM
BobSwenson's Avatar
Member
 
Join Date: Aug 2008
Location: The hub of Morris County, NJ
Posts: 580
Default Re: Me in real life: the job that pays for the tools...

For Cod's sake do some more.
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiFurl this Post!
Reply With Quote
  #12 (permalink)  
Old 01-22-2009, 08:22 PM
Member
 
Join Date: Jul 2008
Location: MI
Posts: 185
Default Re: Me in real life: the job that pays for the tools...

Great video! It's always amazed me at how distinct the different layers of water can be. Used to do a lot of fresh water scuba diving and have seen numerous times where moving your hand up or down a foot or so will put you in a total different temperature layer. One time I encountered an inversion layer in Lake Mich where the water on top was 15 or more degrees colder than the water a couple feet further down. Can't imagine that the condition would last long as it should be inherently unstable.

Fred

Last edited by bruegf; 01-22-2009 at 08:26 PM.
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiFurl this Post!
Reply With Quote
  #13 (permalink)  
Old 01-22-2009, 09:59 PM
Poto's Avatar
Super Moderator
 
Join Date: Jul 2008
Location: San Diego, CA
Posts: 8,999
Default Re: Me in real life: the job that pays for the tools...

Fred, you're right about the sharpness of the gradients. I've swum in lakes where my feet are freezing, and my waist is warm.

As for the temperature inversion it could have been because of salinity differences (doesn't take much to overcome temperature differences). Even the hardness of the water can make a difference. The other thing is what Steve mentioned above: freshwater is most dense at about 4 degrees C. So you could have 4 degree water deep down, and 1 degree water above. But my guess (my hope?) is that you wouldn't be swimming under those circumstances!
__________________
I don't have as many Festools as Fred. Or Marcou's, or Brese's, or Lie-Nielsen's, or Lee Valley's, or Blue Spruce's, or Harold and Saxon's, or...
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiFurl this Post!
Reply With Quote
  #14 (permalink)  
Old 01-22-2009, 10:32 PM
Member
 
Join Date: Jul 2008
Location: MI
Posts: 185
Default Re: Me in real life: the job that pays for the tools...

Salinity differences in Lake MI must be quite subtle - do you think it would be enough to cause that sharply defined of an effect?

The lake "turns over" frequently w/ strong east or west winds. All the warm surface water is blown over to the other side of the lake, which brings up the colder water from the bottom. I've seen over a foot of water depth increase w/ a strong west wind. I've always assumed (emphasis on assumed) that it might have been caused by one of these "turn overs", but truthfully I have no idea.

Fred
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiFurl this Post!
Reply With Quote
  #15 (permalink)  
Old 01-23-2009, 01:39 AM
Poto's Avatar
Super Moderator
 
Join Date: Jul 2008
Location: San Diego, CA
Posts: 8,999
Default Re: Me in real life: the job that pays for the tools...

The thing is, if there really is a density inversion that is driven by a temperature inversion, it would be extremely unstable, and would mix almost immediately (within hours). You would probably be able to feel the turbulence if you were swimming. So it's a very curious observation - I'd like to learn more!
__________________
I don't have as many Festools as Fred. Or Marcou's, or Brese's, or Lie-Nielsen's, or Lee Valley's, or Blue Spruce's, or Harold and Saxon's, or...
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiFurl this Post!
Reply With Quote
  #16 (permalink)  
Old 01-23-2009, 03:09 AM
RWeber's Avatar
Member
 
Join Date: Jul 2008
Location: Lincoln, NE
Posts: 1,212
Default Re: Me in real life: the job that pays for the tools...

Ok, that was really quite interesting for a topic I'd have otherwise known absolutely nothing about.
It did make me wonder. I had a buddy out of college go Navy, and subs. One of the things I recall about him talking sub life was that it's much harder for sonar to peg you if there's an inversion layer between the boat looking and the one you're in.
Is that a density thing also? Seemed kind of neat. Like sonar would bounce at the inversion layer and you'd be hidden under it.
Your little critters must love subs. Always coming up and dragging food with them in their wake.
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiFurl this Post!
Reply With Quote
  #17 (permalink)  
Old 01-23-2009, 04:28 AM
Poto's Avatar
Super Moderator
 
Join Date: Jul 2008
Location: San Diego, CA
Posts: 8,999
Default Re: Me in real life: the job that pays for the tools...

Randy, this is a way cool question that you've asked. You don't need a density inversion, but a vertical density gradient is key. Pycnoclines (and any density gradient) will refract the sound waves, just like a prism refracts light. The sound waves actually bend as they move vertically, because the speed of sounds depends on the density of the material. The sound waves from a surface source like a ship will move away from the ship, but bend as they go. Eventually (like at about 100 m depth or so), they bend so much that they start coming back up again. So the sound never penetrates too deep. It just keeps bouncing off the surface and the depth where it reverses direction.

And that's how you can hide a sub from sonar. The sub just needs to stay in a region where the density gradient of the water causes the sound waves to become trapped. In fact there are sound channels deep in the ocean, in which the sound waves just bounce up and down, traveling thousands of miles across the ocean. Whales often use this sound channel to communicate. If the sub is in a sound channel, it won't be audible from above or below the channel, because the sound never escapes.

Great questions everyone!
__________________
I don't have as many Festools as Fred. Or Marcou's, or Brese's, or Lie-Nielsen's, or Lee Valley's, or Blue Spruce's, or Harold and Saxon's, or...
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiFurl this Post!
Reply With Quote
  #18 (permalink)  
Old 01-23-2009, 01:24 PM
Member
 
Join Date: Jul 2008
Location: MI
Posts: 185
Default Re: Me in real life: the job that pays for the tools...

Quote:
Originally Posted by Poto View Post
The thing is, if there really is a density inversion that is driven by a temperature inversion, it would be extremely unstable, and would mix almost immediately (within hours). You would probably be able to feel the turbulence if you were swimming. So it's a very curious observation - I'd like to learn more!
From what little I remember I think it was probably around 8-12' down. Wish I could give you more details but this was at least 20 years ago and I'm lucky to even remember it happened. With my memory, all bets are off after the first time I've slept.

Fred
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiFurl this Post!
Reply With Quote
  #19 (permalink)  
Old 01-23-2009, 01:26 PM
NedYoung's Avatar
Founding Member
 
Join Date: Jul 2008
Location: Redlands, Southern California, USA
Posts: 317
Default Re: Me in real life: the job that pays for the tools...

Poto--

What do you call a guy who does what you do, only he specializes in, say, the Great Lakes?

I've never heard of a "lakeographer", but I imagine it would be a big enough field to have specialists.

Ned
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiFurl this Post!
Reply With Quote
  #20 (permalink)  
Old 01-23-2009, 03:25 PM
Poto's Avatar
Super Moderator
 
Join Date: Jul 2008
Location: San Diego, CA
Posts: 8,999
Default Re: Me in real life: the job that pays for the tools...

Ned, people who work in freshwater and do what I do are called "limnologists". Not a very obvious name. In fact, today, I'm leaving to attend the "American Society of Limnologists and Oceanographers" meeting.

Oceanographers look down on limnologists...
__________________
I don't have as many Festools as Fred. Or Marcou's, or Brese's, or Lie-Nielsen's, or Lee Valley's, or Blue Spruce's, or Harold and Saxon's, or...
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiFurl this Post!
Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

Forum Jump


All times are GMT +1. The time now is 09:15 PM.