Archive for September 18th, 2017

Physics Of Hurricanes: Force Six Hurricanes Someday Soon?

September 18, 2017

There is another powerful hurricane on the way in the Caribbean: Maria now already, category V and strengthening, will hit the large islands of Guadeloupe (population 500,000), Martinique (400,000), and Dominique (75,000) today. Steady winds up to 260 kilometers an hour (150 miles per hour) are already experienced, with gusts at 350 km/h. Meanwhile, long lasting hurricane Jose is still active, out there in the Atlantic ocean.

The physics of hurricane as usually depicted in the media shows what’s going on, but not fully, why it’s going on. Probably because those who write the articles have insufficient understanding. Let’s fill in the cognitive gap.

Overall, a hurricane works like a rotary thermal engine, with a warm source, the warm, moist ocean, and a cold sink (the icy stratosphere, up high). The warm moist air goes up, because it’s lower density than colder air.

The mechanism above depends only upon having a warm source and a cold source (known in thermodynamics as a “Carnot engine”). So one can have Polar Cyclones, or Cyclones on Jupiter (“Great Red Spot”)!

How does it start, why is it self-feeding? If the ocean is warm, many of these large clouds will rise, and dot the ocean. Now the overall rising of warm air creates a low pressure L in the center of a particularly active zone of storms (or “cells”). This is not, per se, exceptional: the entire tropical belt tends to be low pressure, just because the warm air rises more than colder air up north.

That phenomenon creates the trade winds, air from the upper tropical belt which rushes in towards the equator, the “inter-tropical convergence zone” (ITCZ). Because of the rotation of the Earth, the trade winds, which would just go straight south if the Earth didn’t turn, get deflected to the west.

Hurricanes have been piling up in September 2017, from lack of wind shear in the hurricane forming region… Six hurricanes in the Caribbean in 2 weeks… If this keeps up the question of evacuation of many islands arises…

Now let’s go back to hurricane formation. Three or four large cells in the ocean, if close by, will develop a particularly low Low L in the center of the formation. At that point, the cells will tend to gather towards that center. However, the cell closest to the equator will have a greater momentum to the east, thanks to the Earth’s rotation, and the one furthest to the equator, will deviate west. Thus a counterclockwise rotation (in the northern hemisphere) of the set of cells will appear. From conservation of angular momentum, the more the warm air rushes towards the center, the more it tends to rotate (the same effect which makes a skater rotate faster by closing her arms). Next, the cells will merge, a hurricane is formed.

Now the warmer the ocean, the more powerful the rise of air in the middle, the lower the Low L, the greater the rush of air towards the center, and thus the greater the rotating winds. And the greater the winds, the more warm, moist air can rush in from low above the surrounding seas, thus feeding the hurricane.

When part of the frontal edge of the hurricane touches land, or, worse, a mountain range, it loses power in that part (as the power comes from rushing warm, moist air), losing its low there. So naturally the hurricane steers towards areas which can feed it, avoiding large land masses and mountain ranges.

(Thus hurricane steering is reminiscent of how an elementary particle should be steered by the geometry in a future Sub Quantum Mechanics.)

In any case, the hurricane is a rotating engine, whose rotation brings in the warm moist air it uses as fuel. Thus, if the rotation can’t develop, the engine won’t start. And the rotation develops because of the unequal drag of the clouds depending upon how far the equator is (big word: Coriolis Force). In particular, if the clouds cells are astride the equator, they will be equally dragged, and no rotation will occur. Thus, there are no hurricanes around the equator itself.

(The energies involved are enormous: around a ten megaton H bomb every twenty minutes; nuking a grade 5 hurricane would have no effect whatsoever, but for augmenting a bit more the sucking action of the hurricane…)

What of the frequency of hurricanes? The scenario above supposes that the large storm cells can start to rotate. However, the greenhouse augments winds all over. Linear winds, not just rotating winds. It’s a question of equipartition of energy (spreading the energy around in all dimensions available).

https://patriceayme.wordpress.com/2008/03/08/the-equipartition-of-energy-theorem-should-be-applied-for-climate-change-and-predicts-wild-fluctuations-of-temperatures/

Those winds can, and will, shear thunderstorm cells… Just as Saharan sand can collapse them (so stronger trade winds also play against hurricane formation, at least in the Atlantic). Thus hurricanes will tend to form a more ferociously, but not more frequently. What will augment, though, will be the ferocity and frequency of linear storms, and many have ravaged Europe in the last decade.

So far, the Earth has warmed up one degree centigrade, from the anthropogenic greenhouse, since 1800 CE. Another two degrees seems baked in. In the Carboniferous (“Carbon-making”) era, 400 million years ago, the CO2 and the heat were greater. There is also evidence that pretty much all the continents had joined. Yet, there was moisture in the interior of said continents (because there were plants). Moisture, in the sort of climate we know now, should never have penetrated so deep. How come? Super giant hurricanes, obviously. So we can expect force six, or more, hurricanes in the future… It happened before.  

Patrice Ayme

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