PDA

View Full Version : Why do hurricanes always spin in one direction only?



DeDukshyn
3rd September 2015, 19:44
Ever wonder why a hurricane, which is a large storm in the northern hemisphere, only ever spins counter clockwise? And why does a Cyclone, a large storm in the southern hemisphere only ever spin clockwise? What could be the reasoning behind this?

It has everything to do with the shape and rotation of the Earth. In fact, if the earth were not spinning, these storms would not even spin at all.

The effect that causes this is the Coriolis effect, which is a pulling effect that constantly, but subtly, pulls east or west on an object that is traveling in the direction of either pole (north-ish or south-ish direction). This pulling on the air mass of a hurricane as the air tries to rush in to the low pressure area causes the spin.

This pulling is caused by the shape of the earth being a sphere. If the earth was any other shape than a sphere, these large storms would not spin in opposite directions 100% of the time. On a rotating sphere, the speed of spin at the equator is much faster than it is near the poles, therefore anything that moves from the area of the equator to either north or south carries with it the inertial forces of the speed of that spin, causing a pull either to the left or to the right, depending on which half of the sphere the object is. If the earth were, say, a spinning disk for example, the coriolis affect would cause all storms to spin the same direction. But because it is a sphere, we get the coriolis pull from two opposite directions dependant on hemisphere, as you would expect.

This is explained very well in this short little youtube clip, even a 10 yr old might be able to understand this:
i2mec3vgeaI

And here is some further explanation, again explained simply in a way that can be understood, and includes an experiment to try:
http://littleshop.physics.colostate.edu/tenthings/Hurricanes.pdf

ghostrider
4th September 2015, 00:46
gravity ...

DeDukshyn
4th September 2015, 02:43
gravity ...

Actually it is inertia ... :P

Citizen No2
4th September 2015, 05:49
I'm afraid it ain't so........... the Coriolis Effect is another myth.

CCUX6wIPSQ8


There is some 'fruity' language in this one if you are easily offended.

zBYzPyI6mQU


Taking account of the Coriolis Effect whilst shooting at distance is also a myth. The only things taken into consideration are windspeed, temperature, movement and distance.......... not the Coriolis Effect.

There is a vid that shows hurricanes on both hemispheres spinning in both directions but it is part of a flat Earth vid so I won't post it. It is easy to find on yootube if you want to look for it.


Regards.

Nick Matkin
4th September 2015, 12:16
The Coriolis Effect on something a few feet (or even tens of feet) across is indeed relevant. For example, which way your bath water swirls around the plug hole will depend on water movement as it first starts to escape, or even the arrangement of the plumbing! Trying to debunk the whole effect on a small scale only demonstrates the debunker's stupidity.

Vast hurricanes and cyclones on the other hand are strongly influenced by the rotation of the earth as clearly described in DD's posted video.

Someone could try to argue that HAARP does all this anyway, and has done for thousands of years, and could make these storms rotate any way they wish...

Nick

DeDukshyn
4th September 2015, 17:33
I'm afraid it ain't so........... the Coriolis Effect is another myth.

CCUX6wIPSQ8


There is some 'fruity' language in this one if you are easily offended.

zBYzPyI6mQU


Taking account of the Coriolis Effect whilst shooting at distance is also a myth. The only things taken into consideration are windspeed, temperature, movement and distance.......... not the Coriolis Effect.

There is a vid that shows hurricanes on both hemispheres spinning in both directions but it is part of a flat Earth vid so I won't post it. It is easy to find on yootube if you want to look for it.


Regards.

Errr ... I don't think you are understanding the Coriolis effect, and nor do the people who put up these "debunking" videos. Did you watch the OP video and read through the PDF to understand exactly what the Coriolis effect is and what it is not? The Coriolis affect only happens with large scale systems, not toilet's and drains. While it was explained in the media I presented I will break it down again.

The speed of rotation at the equator is far faster than it is say 500 miles to the north of the equator, because the sphere shape dictates this. It is the inertia generated by differential in speeds which creates the effect. A drain measuring 6 inches or one foot across does not have any speed differential between one side of the drain and the other because it isn't nearly large enough to have a speed differential anywhere. Therefore it is not debunked, you just don't understand what it is exactly.

If you would have read the PDF you would have came across this (below), which includes a link to a site of effects applied improperly to Coriolis. So again, not debunked at all. It is important to understand the claim that is being made, before one can debunk it.

This from the PDF I linked to in the OP:




"But the Coriolis force on earth only works on very large scales. It doesnít affect such small things as toilets and sinks. You may have heard of people claiming that toilets and sinks swirl counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere due to this force.

As cool as that would be, itís just not true. It turns out that the way the water swirls has to do with a number of conditions such as the shape of the bowl and the way the water enters the bowl. Alistair B. Fraser lists other goofy examples people attribute to the Coriolis force in the different hemispheres, including, the way dogs circle before lying down, and the way womenís ringlets curl. The website is called Bad Coriolis and can be found at www.ems.psu.edu. "



Find the website for "Bad Coriolis" here: http://www.ems.psu.edu/~fraser/Bad/BadCoriolis.html This is an excellent site that debunks all the myths surrounding the Coriolis effects with understandable scientific explanations.

Please do take the time to read through and try to understand this phenomenon rather than dismissing this wonderful explanation in favor of a video of a drain.

DeDukshyn
4th September 2015, 18:00
Here is a good Q&A from the "Bad Coriolis" site:

Questions arising out of Bad Coriolis:

You have it backwards

Question:
Recently I came across your "Bad Coriolis" Web page, which I read with great interest. It seems to me that it contains an important mistake, being that the Coriolis force causes clockwise spins in the northern hemisphere and counterclockwise in the southern (your Web page states the opposite). This is to be found in any university physics textbook.

Answer:
It is correct that the Coriolis force causes a moving object to experience a force to the right (left) of its path in the northern (southern) hemisphere. It is not correct that this necessarily produces a clockwise rotation. The direction of rotation (if any at all) depends upon the net force, not just a single force.

One must distinguish between the direction of deviation caused by the Coriolis force (operating on its own) and the direction of rotation (when other forces are present). Both directions of rotation are evident in both hemispheres depending upon the whether the flow is around a high pressure area (the pressure gradient force points radially outward) or around a low (the pressure gradient force points radially inward).In a geophysical flow, such as motion in the atmosphere or oceans, there is always some other force operating (such as the pressure gradient force) or how else would the material have started to move.

The illustration at the right shows a situation for a northern hemisphere low. The Coriolis force (Cf) does indeed point to the right of the flow. But it is slightly over balanced by the pressure gradient force (pgf) which points toward the center of the low (the imbalance is what causes the fluid to move along a curved path).

A good way to convince yourself of this behavior is to watch the direction of rotation seen in radar and satellite loops of storms. It is very easy to see the counterclockwise rotation around the low pressure areas in the (northern) hemisphere storms.


Why any spin at all

Question:
Excellent Site!!! Just one question re. the coriolis effect (or non-effect). I can understand that the direction of spin is dictated by local effects (shape of sink etc). But why does the water spin at all ?

Answer:
If there is any motion of the water at all (say from filling or washing), and the container has walls (which is inherent in the meaning of the word container), then there must be rotary motion. After all, as a fluid parcel moves toward a wall it will be deflected and turn. It is this rotary motion which is accentuated when the water converges toward the drain. The popular illustration of this is that of the skater who spins faster as outstretched arms are brought in close to the body; the scientific explanation involves a discussion of the conservation of angular momentum.


Its not the Coriolis force, but the Coriolis effect.

Question:
Coriolis force? Donít you mean coriolis effect? Pot/kettle/black?

Answer:
No, I donít mean the Coriolis effect. While one can use the word, effect, in almost any context for something which happens, I am referring to the Coriolis force. The modern convention (nearly a century old now) is that there are no preferred coordinate systems and that once you adopt a coordinate system, one gets a set of forces along with it. When you shift coordinate systems, some forces vanish, others appear. In an inertial coordinate system, there is no Coriolis force. In a rotating coordinate system there is.

No, in a rotating coordinate system, there is a Coriolis force which is as real as any other force in that it causes a mass to be accelerated. (When was the last time you saw Newtonís law say that an effect causes a mass to be accelerated?)


The Coriolis force is fictitious, because it cannot do work

Question:
I was taught that the Coriolis force was not a real force, but a fictitious one. The proof of this is found in the inability of the Coriolis force to do any work.

Answer:
It is true that the Coriolis force does no work. Yet, the ability to do work is not a prerequisite for a force. If the Coriolis force were to be disqualified owing to its inability to do work, it would take a number of other well established forces along with it into oblivion. For example, a charged particle, such as an electron, moving in a static magnetic field has no work done on it by that field even though it experiences the magnetic force. Alas, a claim for the fictitious nature of the Coriolis force based upon its inability to do work is an ex post facto argument (one concocted to support a position arrived at for different reasons).


The teacher was right

Question:
In class today, my teacher told us that the Coriolis force operates independently of the direction in which an object is traveling. Yet, I have seen demonstrations of the Coriolis force where someone draws a line radially across a slowly spinning turntable. That only works when the line is drawn towards or away from the center. This implies to me that the Coriolis force only works for objects traveling in a north-south direction (or, at least, for that component of the motion). How, can I convince my teacher that he is wrong about the Coriolis force being independent of the compass bearing of the moving object.

(Yes, I really did get this as a question from a student).

Answer:
I cannot help you convince your teacher, because he was right. But, maybe I can help you understand why he was right.

The conceptual difficulties arise from the demonstration you witnessed. It usually takes the form of a line (pen or chalk) drawn radially on a slowly spinning turntable. Even though the track of the pen is a straight line, the trace left on the turntable is curved. So, in the inertial frame of the classroom, the track was straight, while in the rotating frame of the turntable the track is curved. There is nothing wrong with the demonstration as it stands, however it is easy to draw the wrong conclusion from it when one tries to generalize the result, as you did. The difficulty arises from the fact that it is easy to draw the line radially, but very hard to match the velocities of the turntable and pen closely enough by hand to draw a similar line tangentially. The result of this purely logistical problem involving hand-eye coordination is that it is tempting to conclude that the Coriolis force only operates when something is traveling in a north-south direction (radially on the Earth). Incidentally, the conceptual difficulties here are similar to those experienced by the teacher in the discussion, below, about firing a missile in a northerly or southerly direction.

There are a number of ways to gain an understanding of why the magnitude of the Coriolis force is independent of the direction in which an object is traveling. I can think of (at least) three (not mutually exclusive) approaches.


1) If you reach the point where you can work through and understand the mathematics describing the force, it becomes clear that the direction of motion of the object is irrelevant; indeed, it does not even enter the equations.

2) The second approach relies upon the turntable demonstration, but applies a bit of abstract thinking to show that the result is actually far more general than it would appear to be at first blush. First one recognizes an equivalency between standing anywhere on a rotating platform (such as either the Earth or the turntable) and standing in the center of rotation. If you are standing some distance from the center, you may have thought of yourself as rotating about that distant center. But, your motion is equivalent to that of a translation and a rotation about the point at which you are standing. With this in mind, it is clear that no matter where you are, you are at the center of your own rotation. So, any movement you make over the surface is one in which you are traveling radially with respect to your own rotation center. But, traveling radially on a rotating platform was just what the turntable demonstration handled well. The trick then, is to realize that no matter in what direction you travel (say on the Earth) that you are traveling radially from the center of your own rotation (the concomitant translation component of the Earth or turntable is irrelevant) and as such your experience with what happens with the line drawn on the demonstration turntable is applicable.

3) The second approach (above) is better for students who can easily make and apply abstractions than it is is for those who cannot. So, I have built a Java visualization of the Coriolis force (and centrifugal force) which runs on the web (well, I coded up the original version, but my son rendered it into Java for me so that it would run on the web). It enables me to click anywhere and so start an object moving (green dots) over a rotating surface. Like the turntable with the line drawn by pen or chalk, this leaves a trail of footprints (red circles) which reveals the path on the turntable. But unlike the physical turntable usually used in classroom demonstrations, I can click anywhere and watch the behavior. Consequently, the student can watch as the trail moves tangentially (along a line of latitude). Further, as it is available on the web, the student can play with it him (her) -self to get an intuitive feeling for the behavior. Even better, there are controls which enable one to display the behavior in both hemispheres and even to turn various forces on and off. This maybe all well and good, but if you tried clicking on the (gif) illustration to the right and discovered that it goes nowhere, you can easily come to the conclusion that it is irrelevant if I can use a computer in class (and students can outside of class), if you do not also have access to it. Well, give me time; I will make it available to others soon, but I have run out of time this morning. Sigh...


In practice, I use all three approaches to help give my students an intuitive feeling for why the magnitude of the Coriolis force on an object is independent of the direction in which that object is traveling.



On firing missiles

Question:
As a secondary-school Earth Science teacher, I teach the concept [of Coriolis] using the missile fired north and landing east of itís target, and the return salvo fired south and landing west of itís target - explaining the miss as a result of different eastward components of motion (due to Earthís rotation) at different latitudes. Am I on solid ground here?

Answer:
Whether you are on solid ground here, or not, depends in part on how you handle the issue. Does the student believe that you are explaining why there is a Coriolis force, or merely giving an example of it. There is a difference.

As an example, your illustration is not bad, but it is sufficiently restrictive as to mislead the student into believing some things which are not true. For example, the student will probably be prompted to believe, as a result of this illustration, that:

1) the Coriolis force only operates on objects traveling in a north-south direction (indeed, I have seen web pages which offer this false claim); and

2) it really is the latitudinal differences in easterly component which causes the behavior (while, in fact it is not).


Alas, neither of these is true. (A cat may be an example of an animal, but that does not mean that to be an animal, one must be a cat).

In fact, the magnitude of the Coriolis force is independent of the direction in which something is moving. If you were to present your example as if it were an explanation of the Coriolis force, you are now stuck with its inability to handle the behavior of a missile as it goes similarly off track after being fired in an easterly or westerly direction.

But, there are pedagogical shoals to navigate here even if you are very careful to tell your students that you were not explaining the Coriolis force but merely giving an example of its behavior in a highly restricted situation: they are unlikely to believe you, or at least, not to understand the distinction you are making. They will take your description of the elephantís leg and assume that the whole beast is topographically equivalent to a tree trunk. Of course, students can be forgiven for failing to understand the difference between an example and an explanation, because so many teachers also fail to understand the distinction. Sigh....



Temporal scale versus spatial scale

Question:
I use the difference in the size of hurricanes and sinks to explain to students why the Coriolis force affects the one and not the other. Thus, I note that there is a much bigger difference in the underlying easterly component of the earthís velocity as one goes from the north side of a hurricane to its south side than there is if one goes from the north side of a sink to its south side. Yet, on your page, you stress that the differences in behavior result from differences in time, not space. Am I off base?

Answer:
Explanations are funny things. Indeed, what do you mean by suggesting that the difference in behavior is a result of the difference in the (underlying) velocity. Letís start by ignoring the fact that you thought (incorrectly) that the issue was just the easterly component of the velocity and just explore the difference between these two situations: the large scale with a big velocity difference and the small scale with a small velocity difference. The implication is that if one were to match the velocity differences on the two scales, then the Coriolis force, or maybe the displacement, would suddenly be the same in each case. Alas, it would not be so (unless other things were also fudged).

The traditional response to what you have suggested is that you have confused two things, a spatial scale and temporal scale. As usually presented, the Coriolis force (being a force) produces a result (such as displacement) over time. The spatial scale (how far it is across something, or how far an object travels) does not even appear in the equations. There is much to commend this approach. Within this context, it is not the spatial scale that produces the effect (for a given force), but how long the event lasts. A sink drains quickly (not much time for a small force to produce a significant displacement); a missile or the air in a hurricane takes much longer to traverse its territory (a much longer time for a force to produce a significant displacement).

Of course, any expression can be transformed into any related variable, so it is legitimate (although not conventional) to express the lateral displacement resulting from the Coriolis force as a function of the change in velocity of the (underlying) reference system (such as the latitudinal variation in the tangential velocity of the Earthís surface). But, when one puts the expression in terms of the velocity difference across the region, other variables pop up, and one discovers that such an approach moves one further away from a simple understanding what is going on, rather than closer to it.

So, I recommend that in your class, you not use the argument about the latitudinal variation of the Earthís tangential velocity. The first reason is that it cannot (intuitively) account for the Coriolis force when an object is traveling along a line of latitude (see, on firing missiles, above). The second reason is that it misleads the students into believing that it really is the velocity difference across the region that accounts for the difference in behavior between hurricanes and sinks.


Wacky things attributed to the Coriolis force

Bizarre ideas readers report that they have seen apparently being seriously attributed to the Earthís rotation. (The incredible is fodder for the credulous).


-The direction of rotation that arises out of the rocking motion of celts (known commercially as rattlebacks). The interesting motion of a celts is, in fact, determined by its shape.

-In the 1945 movie, Adventure, the Clark Gable character apparently points out that ringlets in a womenís hair curl in one direction in the Northern Hemisphere, the opposite direction in the Southern hemisphere!

-The spiraling hooks with which vines cling to their supports are asserted (incorrectly) to change from one hemisphere to the other.

-The direction dogs turn before lying down has been claimed to be be dependent upon the hemisphere in which they live.

ghostrider
4th September 2015, 18:34
The inertia created by gravity ... Lol

DeDukshyn
4th September 2015, 21:33
The inertia created by gravity ... Lol

It's actually inertia created from movement within a rotation (on a rotating sphere); gravity is a minor player in this effect specifically, but may contribute somewhat I imagine.

---------

When I first "understood" the Coriolis effect, I wondered why hurricanes didn't spin clockwise, if the force pulls the air to the right. But when you look to see where the speed differential is in relationship to the rotation itself, then you understand why it will turn counter clockwise. Here is a neat little image that explains it better than the OP video, in my opinion.

http://www.ems.psu.edu/~fraser/Bad/BadFAQ/cyclonic.gif

ghostrider
4th September 2015, 23:34
The inertia created by gravity ... Lol

It's actually inertia created from movement within a rotation (on a rotating sphere); gravity is a minor player in this effect specifically, but may contribute somewhat I imagine.

---------

When I first "understood" the Coriolis effect, I wondered why hurricanes didn't spin clockwise, if the force pulls the air to the right. But when you look to see where the speed differential is in relationship to the rotation itself, then you understand why it will turn counter clockwise. Here is a neat little image that explains it better than the OP video, in my opinion.

http://www.ems.psu.edu/~fraser/Bad/BadFAQ/cyclonic.gif
the ET's spoke about this but it's way over my head ... they say dark energy is a player , and black holes destroy galaxies but also create them, they create other room spaces a fraction of a second outside our room space ( other worlds on the other side of our time space, they say everything has a twin ) a whole other Earth Sun system a fraction of a second different than ours with everything we have ... the major player outside of gravity is dark energy which is not to be confused with dark matter ... they say the structure of creation is a double helix , enfolding on itself continually swirling , reminds me of the symbol for infinity ... their scientist were smart enough over 50,000 years ago to build a dimension gate to travel from their room space to ours ... We can't even leave our solar system ... we are kids , and know very little about the Universe ... the Et's say there are seven forces of Nature , we know of three or four ...

§=[Post Update]=§

hurricanes as tiny models of our sun system , everything spinning around a large energy source in the middle , just like an atom ... a cell ... keep going smaller and smaller it's still the same pattern/structure ... as above so below ...