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# Left @ 300 yds - Right @ 1000 yds? WTH?

#106
12-20-2008, 03:55 PM
 Silver Member Join Date: Jan 2008 Posts: 250
Re: Left @ 300 yds - Right @ 1000 yds? WTH?

If coriolis is making my bullet drift left down here in the Southern Hemisphere then I can forget about spin drift, neato.

I'm going to have to read up on it because I am having a hard time believing that my bullet will always drift left down here, no matter what compass bearing 'left' happens to be at the time.
#107
12-20-2008, 05:51 PM
 Platinum Member Join Date: Jan 2003 Location: The rifle range, or archery range or behind the computer in Alaska Posts: 3,740
Re: Left @ 300 yds - Right @ 1000 yds? WTH?

Quote:
 Originally Posted by Ballistic64 Im no scientist,but if the earth is spinning at a given speed,the equator has to move a greater distance in the same time span as a point say 500 miles south of the north pole and to my thinking the effect would be greater at the equator than at any distance closer to the poles.

I would agree with you in that this idea seems much more logical. I used to think the same way. I have been set straight.

Science isnt always "logic".

Here is one explanation. Taken from

Coriolus force - Hutchinson encyclopedia article about Coriolus force

Effect of the Earth's rotation on the atmosphere, oceans, and theoretically all objects moving over the Earth's surface. In the northern hemisphere it causes moving objects and currents to be deflected to the right; in the southern hemisphere it causes deflection to the left. The effect is named after its discoverer, French mathematician Gaspard de Coriolis (1792-1843).

Here is another explanation. Taken from Coriolus force definition of Coriolus force in the Free Online Encyclopedia.

Coriolis effect (kôr'ē-ō`lĭs) [for G.-G. de Coriolis, a French mathematician], tendency for any moving body on or above the earth's surface, e.g., an ocean current or an artillery round, to drift sideways from its course because of the earth's rotation. In the Northern Hemisphere the deflection is to the right of the motion; in the Southern Hemisphere it is to the left. The Coriolis deflection of a body moving toward the north or south results from the fact that the earth's surface is rotating eastward at greater speed near the equator than near the poles, since a point on the equator traces out a larger circle per day than a point on another latitude nearer either pole. A body traveling toward the equator with the slower rotational speed of higher latitudes tends to fall behind or veer to the west relative to the more rapidly rotating earth below it at lower latitudes. Similarly, a body traveling toward either pole veers eastward because it retains the greater eastward rotational speed of the lower latitudes as it passes over the more slowly rotating earth closer to the pole. It is extremely important to account for the Coriolis effect when considering projectile trajectories, terrestrial wind systems, and ocean currents.
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Long range shooting is a process that ends with a result. Once you start to focus on the result (how bad your last shot was, how big the group is going to be, what your buck will score, what your match score is, what place you are in...) then you loose the capacity to focus on the process.

Last edited by Michael Eichele; 12-20-2008 at 06:05 PM.
#108
12-20-2008, 06:07 PM
 Platinum Member Join Date: Jan 2003 Location: The rifle range, or archery range or behind the computer in Alaska Posts: 3,740
Re: Left @ 300 yds - Right @ 1000 yds? WTH?

Quote:
 Originally Posted by jmden Not to nit-pick here, but as I understand it, hurricanes are just a particularly intense warm core (tropical) low pressure system, and the term hurricane is more or less a regional name typically given to those intense low pressure systems generated over the Atlantic with an E to W stormtrack that is so typical to see in the SE US during the season. (In the Pacific NW, these storms with hurricane force winds (64kts. or more) are typically called a 'superstorm' and track W to E in that latitude. In SE Asia, they're called typhoons, etc. The generic term is cyclone for all these intense low pressure systems (anti-cyclone for high pressure systems) which is what they are called in the S. Pacific as my wife and I found out clinging to a tiny island as we got nailed by both sides of a Cat 3 cyclone eyewall... ) Low pressure systems rotate counterclockwise in the NH and and clockwise in the SH looking at them from space or from the weather satellite picture on the news. High pressure systems are just the opposite. Is that what you meant? Sorry...a little off topic... Tropical cyclone - Wikipedia, the free encyclopedia
I could be off base here. Perhaps I need to do a bit more research. However, below is one link to support what I was trying to explain.

Coriolus force - Hutchinson encyclopedia article about Coriolus force

And another referance.

Coriolis effect - Wikipedia, the free encyclopedia

Another good reference. USATODAY.com

In simple terms, as air begins flowing from high to low pressure, the Earth rotates under it, making the wind follow a curved path. In the Northern Hemisphere, the wind turns to the right of its direction of motion. In the Southern Hemisphere, it turns to the left. The Coriolis force is zero at the equator.

You might be wondering: If the Coriolis force turns winds to the right in the Northern Hemisphere, why do winds go counterclockwise around large systems, such as hurricanes, north of the equator?

This happens because Coriolis is only one of the forces acting on air to cause winds. In simple terms, in the Northern Hemisphere, while the Coriolis force is pushing the wind toward the right, the pressure-gradient force, caused by air pressure differences, is pushing the air toward the center of the area of low pressure, and for various reasons is stronger then the Coriolis force.
__________________
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Long range shooting is a process that ends with a result. Once you start to focus on the result (how bad your last shot was, how big the group is going to be, what your buck will score, what your match score is, what place you are in...) then you loose the capacity to focus on the process.

Last edited by Michael Eichele; 12-20-2008 at 06:26 PM.
#109
12-20-2008, 06:30 PM
 Platinum Member Join Date: Jan 2003 Location: The rifle range, or archery range or behind the computer in Alaska Posts: 3,740
Re: Left @ 300 yds - Right @ 1000 yds? WTH?

The best example so far is a video on youtube.

Check it out.

YouTube - The Coriolis Force

This one is even better.

YouTube - coriolis effect (2-11)

Another good clip showing the effects of even east verus west. Not just north and south.

YouTube - Coriolis Effect on the Surface of the Earth
__________________
__________________
Long range shooting is a process that ends with a result. Once you start to focus on the result (how bad your last shot was, how big the group is going to be, what your buck will score, what your match score is, what place you are in...) then you loose the capacity to focus on the process.

Last edited by Michael Eichele; 12-20-2008 at 06:56 PM.
#110
12-20-2008, 07:18 PM
 Platinum Member Join Date: Apr 2005 Location: Alaska Posts: 4,618
Re: Left @ 300 yds - Right @ 1000 yds? WTH?

Thanks meichele,

Those visuals clearly illustrate instructional intent that horizontal coriolis bullet drift is in-play regardless of the azimuth of fire - line of fire. Shoot any horizontal direction you want on the face of the earth and the bullet drifts right (from the shooter's perspective) in the northern hemisphere, and drifts left (from the shooter's perspective) in the southern hemisphere.

Saying it another way - your bullets will hit right of POA north of the equator, and left of POA south of the equator. The farther you're located from the equator, and the closer you are to the poles, the greater the drift over equivalent distances of fire.

I'll sleep better now...

Last edited by phorwath; 12-20-2008 at 10:35 PM.
#111
12-20-2008, 07:36 PM
 Platinum Member Join Date: Nov 2003 Location: Washington State Posts: 2,726
Re: Left @ 300 yds - Right @ 1000 yds? WTH?

Just making a comment about the direction (as viewed from space) of rotation of low/high pressure weather systems in the northern/southern hemispheres.

From 'Northwest Marine Weather' (Renner p.29-30):

"...Intense solar heating near the equator forces air to rise, creating a region of low pressure that rings the globe. Because air within this band rises, it also cools, which tends to condense water vapor into liquid droplets that form clouds, just as your breath condenses on a cold day. Satellite pictures show a series of thunderstorms marking this equatorial low-pressure zone, which is called the Intertropical Convergence Zone. It's a very wet area: more rain can fall in a single day within this zone than during and entire month in Washington, Oregon or British Columbia.
But the air sinking and moving south from the pole and that rising from the equator don't form a simple loop moving from the north to south and back again. The rotation of the earth is responsible for deflecting this air, creating a considerably more complicated circulation of air over our planet.
Some of the air rising from the equator descends over the subtropics. This sinking air creates a region of high pressure. As it sinks within this high, the earth's rotation produces a force know as the Coriolis force. The combination of the Coriolis force and the effect of friction from air moving moving over land and water causes the air sinking within the high-pressure system to rotate in a clockwise direction in the northern hemisphere and counterclockwise in the southern hemisphere." [opposite for low pressure systems]

That last video clip showing the Corilolis force on the surface of the earth is a particularly good visual. Thanks!
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#112
12-20-2008, 08:01 PM
 Gold Member Join Date: Dec 2004 Location: Black Hills,South Dakota Posts: 669
Re: Left @ 300 yds - Right @ 1000 yds? WTH?

Interesting videos meichele and I understand what your saying,but I guess Im not convinced its true over a much shorter course of fire.A 1000 yds for example.With the limited experience Ive had shooting 30 cal 185 and 210 VLDs out to 1000 yds,I guess Ive never had "conditions" perfect enough to notice spin drift or coriolis effects on my shots.Certainly not to the magnitude the original poster of the thread has experienced anyway.
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