The Gear Model Of Hurricanes

This posting will later be moved to the meteorology and biology blog, www.markmeeklife.blogspot.com .

I explained in the posting on the meteorology and biology blog, "The Weather Cycle", my concept of how weather must follow a cycle which eventually starts back at the beginning and repeats itself. Everything to do with the weather is actually a cycle. This includes the seasons, the heating and cooling of day and night, the water cycle of evaporation to falling as precipitation, the rising of air over warm areas and the descending of air over cool areas and, the driving of the wind by rotation of the earth.

This means that the weather can be compared with a complex system of mechanical gears. When gears are coupled together, smaller ones will turn faster and larger ones slower. If we were to assemble a system of gears of all different sizes, and put a piece of tape across all couplings of gears at the starting point, and then began to turn the gears, eventually all of the pieces of tape would line up as at the beginning.

If every factor in the weather is cyclical, and all of those cycles are finite, then the weather absolutely must repeat itself. We do not notice this because the cycle may be longer than a human lifetime, but graphing this cycle and taking global warming and human activities such as city building and deforestation would be the ultimate breakthrough in weather forecasting.

Today, I would like to explain my concept of how weather relates to mechanical gears in another way. A hurricane and the rotating earth operate exactly like a set of gears.

Have you ever wondered about why the winds are as powerful as they are? Why aren't they more powerful, or less powerful? Notice that ordinary linear winds cannot move a solid equi-dimensional object on the earth's surface. By linear wind, I mean ordinary non-circular winds such as hurricanes or tornadoes. By equi-dimensional, I mean all dimensions equal such as a cubic block of wood. The wind can move leaves, but leaves are far from equi-dimensional in that they have much less thickness than width.

The reason for this is gravity. The block of wood is held to the earth by the same gravity that holds the air to the earth. The wood must have more density than the air or else it would not be on the surface. This means that it would not make sense for the wind to be able to move the wood, at least for ordinary winds formed by uneven heating of the earth as air rises over warm areas and sinks over cool areas. Such linear winds are not exactly linear because the effect of the earth's rotation causes the wind to spiral around a high pressure center to and then around a low pressure center.

But there are storms which can move such a block of wood. These are the circular storms referred to as hurricanes, cyclones or, typhoons. These are different in nature and much more powerful than linear winds.

In the posting on the meteorology and biology blog, "The Atlas Barrier", I explained my observations involving hurricanes and the barrier islands that they tend to produce along coastlines. A hurricane forms as dust is swept out over the sea by winds, typically from north Africa or Australia. This airborne dust allows the air to hold much more condensed water vapor (vapour) than usual by acting as condensation nuclei.

The updraft of air over the warm sea is affected by the rotation of the earth, which adds a circular motion to the zone of exceptional water condensation. The spin makes the budding hurricane semi-independent of the earth's gravity so that it moves west, although it is not actually the hurricane moving west but the earth rotating eastward beneath it.

Another fact about such circular storms is that they cannot form at the equator, and always move away from the equator. This is what brings us to how a hurricane operates in the same way as a gear system.

The earth exerts centrifugal (outward) force as it spins. This force, however, is much weaker than the gravity which it opposes. If this were not the case, the earth itself would fly apart because gravity is what is holding the earth together. The textbook explanation of why hurricanes cannot form at the equator is that this is where there is no "spin". My explanation here is that there is centrifugal force of the earth's rotation at all latitudes, but that this centrifugal force is at it's maximum at the equator. This is simply due to the nature of a sphere, if the earth were a cylinder instead then centrifugal force would be equal at all latitudes.

The centrifugal force is actually a function of the cosine of the latitude. Cosine is the trigonometric function which starts at 1 at 0 degrees, and drops to 0 at 90 degrees. On the earth, 0 degrees latitude represents the equator and 90 degrees represents either pole.

I found it significant that, on a sphere, the cosine does not decrease at an even rate from equator to pole, that would be represented as an equilateral cone, but decreases progressively faster. The midway point between the equator and pole, 45 degrees latitude for example, has a cosine not of 0.5 but of 0.707. This means that the cosine of the latitude will drop much more from 45 to 90 degrees than it did from 0 to 45 degrees. Thus, the difference in centrifugal force from one latitude to another is greater the further we go from the equator.

This is actually the basis for hurricanes. It is not the centrifugal force of the spin of the earth which drives the circular motion of a hurricane. Rather, it is the difference in the centrifugal force of the spin of the earth which drives the circular motion of a hurricane. The hurricane has a certain width and there is a difference in the centrifugal force from one side to the other. Just as a gear will turn if there is a difference in force from one side to the other, so does a hurricane.

The reason that hurricanes do not form at the equator now becomes clear. The equator is the lowest of latitudes and this means that there is the least difference in centrifugal force from one latitude to another there. The reason that hurricanes move away from the equator is to seek more difference in centrifugal force from one side of the hurricane to the other.

(Note-If this sounds familiar, it is similar to the principle behind tides. The moon is close enough for there to be a significant difference in it's gravitational pull between the surface of the ocean and the bottom. The water near the surface is pulled upward more strongly than the water at the bottom, and the result is the tidal bulge. The sun has far more mass than the moon, but it is also much further away so that it's tidal force on the oceans is only about 40% that of the moon).

So, a hurricane is essentially a smaller gear coupled to a larger one, which is the earth. It is more complex than this in that there is force applied to both sides of a hurricane but the force on one side, the low latitude side, is greater. This is what drives the spin of the hurricane. As the hurricane moves away from the equator, there is less centrifugal force to drive it but there is more difference in centrifugal force from one side of the hurricane to the other.

The hurricane acts as a gear which brings centrifugal force from lower to higher latitudes, moving away from the equator. The momentum imparted to the hurricane by the difference in the centrifugal force of rotation from one side to the other accumulates so that the winds within the hurricane become faster and faster. The velocity being imparted to the system at any one time must be the eastward velocity of the earth's rotation on the low latitude side of the storm minus the velocity of the earth's rotation on the high latitude side which would depend on the width of the storm.

Hurricanes.spin counterclockwise in the northern hemisphere and clockwise in the southern hemisphere because of the rotation of the earth. The earth rotates eastward and it is this rotation which drives the hurricane so that the side closest to the equator must be moving eastward. Where I live, the prevailing wind is from the west and east winds are rare. When there is an east wind it is usually the remnants of a hurricane and is very powerful. During Hurricane Sandy, in the autumn of 2012, I periodically looked out to see how my trees were holding up and the wind was definitely from the east.

There is another way in which the operation of a hurricane is like that of a gear system. The centrifugal force of the earth's rotation is exerted perpendicular to the planet's axis of rotation. Due to the nature of a sphere, this means that this force is exactly perpendicular to the ground only at the equator. In fact, the angle between a flat surface of the earth and the thrust line of the centrifugal force of rotation is the same as the latitude.

Imagine that one gear cannot turn another if the two are perpendicular in alignment because it will be exerting an equal force on both sides of the other gear. But if there is some angle between the two gears, the exerted force will be unequal and the passive gear will begin to turn. The greater the angle between the two from the perpendicular, the faster the passive gear will turn.

The centrifugal force of earth's rotation is perpendicular to the surface only at the equator, due to the nature of a sphere. But the earth's atmosphere is parallel to the surface at all latitudes. This means that the higher the latitude, the more spin the centrifugal of rotation can exert on a system in the atmosphere such as a hurricane, and this is why hurricanes tend to move away from the equator until it crosses land so that there is no more evaporation of water to feed it or it becomes too cold to drive enough evaporation to sustain it.

The so-called "Great Red Spot" on Jupiter, which is larger than the entire earth, is actually such a storm system that has been underway for centuries.

The reason that South America does not get hurricanes, like North America does, is that hurricanes require a lot of dust to be swept up into the air by the wind. This dust acts as condensation nuclei for water vapor. When water vapor in the air condenses on particles of so much dust, it lowers the relative humidity of the air so that more water can evaporate, which then condenses on the particles of dust, and so on.

The dust that makes Atlantic hurricanes in the northern hemisphere comes from north Africa. But Africa south of the equator, which could supply the dust to bring comparable hurricanes to South America, is mostly green. There is not enough dust to send hurricanes toward South America, like there is in the northern hemisphere.

Due to the nature of a rotating sphere, like the earth, the nearer a point is to the equator, the faster it is moving with the rotation. This means that the earth underneath the mass of rising water vapor that is closer to the equator is moving eastward, with the earth's rotation, faster than the side that is further away from the equator.

This difference in relative speed, from one side to the other, it what gives the hurricane it's spin. In the northern hemisphere, a hurricane spins counter-clockwise because the side furthest south, and thus closer to the equator, is moving faster than the side that is further from the equator, northward. If you look down on the north or south pole, the direction that the earth appears to be spinning, clockwise or counter-clockwise, is the direction that a hurricane will also spin in that hemisphere.

The hurricane does not actually move westward, as it appears. The earth is rotating eastward and the increasing spin of the hurricane gives it some independence from the earth's gravity, so that it does not move eastward as fast as the earth is rotating eastward. This makes the hurricane seem to move westward.

A hurricane in the northern hemisphere, in addition to moving westward, will also move northward because the earth beneath it is moving eastward faster on the southern side, closer to the equator, and this directs the hurricane to the northwest, instead of due west.

But when a hurricane in the northern hemisphere gets far enough north, it starts to move eastward with the earth's rotation. This can be explained simply. When the hurricane was further south, in the tropics, it actually was moving eastward but it's spin gave it some independence from the earth's gravity. This caused it to still move eastward, but not as fast as the earth was rotating eastward. This caused it's apparent movement to be westward.

But due to the nature of a rotating sphere, the spin is less as we move further from the equator. As the hurricane moves to the northwest, it still has the eastward momentum that it had when it was in the tropics, where the spin of the earth was much faster. Going northward, a point is reached where that eastward momentum of the hurricane is greater than the eastward rotational velocity of the earth beneath it. At that point, the hurricane's apparent movement is eastward.

Remember that the motion of a hurricane is easy to understand if we consider it and the earth as a system of gears.