Brad DeLong's Semi-Daily Journal: A Weblog

Why does it get so big? : Positive feedback?

See "Hurricane Structures and Energetics" at
http://www.newmediastudio.org/DataDiscovery/Hurr_ED_Center/Hurr_Structure_Energetics/Hurr_Struct.html

Snippets:

"During the initial development stages of a hurricane, as the radial and tangential wind speeds increase, so does the magnitude of the low-level moisture convergence and the rainfall. Water vapor condenses within the storm, releasing latent heat of vaporization, and the heated air rises. The latent heat released by these convective cloud clusters warms the upper troposphere (500 Ð 200 mb). Expansional cooling of the rising air triggers more condensation, release of even more latent heat, and a further increase in buoyancy. Deep convection produces a dense cirrus overcast at the tropopause.

"During this intensification process, clusters of intense thunderstorms, called convective bursts, occur. A single thunderstorm within a convective burst is known as a hot tower. Hot towers are cumulonimbus towers with cloud tops higher than 37,000 ft (~15 km)."

Sorry, the foregoing wasn't all that useful in making the case for "positive feedback." Try this from the same source,

"The warm core is vital to hurricane growth because it intensifies the upper anticyclone ..., leading to a "feedback' effect. When the surface pressure decreases, a larger pressure gradient is formed, and more air converges towards the center of the storm. This creates more surface convergence and causes more warm moist surface air to rise above the surface. This air, as it cools, condenses into clouds. While it does this, it releases even more latent heat and intensifies the upper level high pressure. This enhancement of a storm system by cumulus convection is termed Conditional Instability of the Second Kind, or CISK."

It's one thing to say "partial vaccuum", but that really doesn't explain anything. Ask yourself, why is there a partial vaccuum?

And it's what Dabbler Dave says, 'cause hot air rises. Followed by the release of heat as condensation occurs.

In short: the sun.

Latent heat of vaporization.

A small typo: the "cold air coming from the south" should be the "hot air coming from the south."

Unless they have glaciers in Jamaica.

What stops it from getting bigger? It other words what sets the equilibrum conditions?

Why does it get so big? Maybe because God doesn't like Florida?

A more "common language" description of this "intensification process" is found here:
http://www.mcdem.govt.nz/MEMWebsite.nsf/Files/tephra97/$file/tephra97.pdf
starting on p. 5, M.R. Sinclair "Anatomy of a Storm."

Tropical Cyclones

"Formation and maintenance of the tropical cyclone is by means of a positive feedback effect. The near-surface air spiraling in to the center of the low picks up heat and moisture from the sea to fuel new thunderstorms that release huge quantities of latent heat. Driven by this heating, the air accelerates upward and outward in the anticyclonic outflow region at the troposphere, giving rise to a net loss of air mass from the column above the cyclone. As a consequence, the surface pressure in the cyclone falls, leading to an even stronger cyclonic wind circulation. This results in even greater pick-up of heat and moisture from the sea to fuel heating in the eye wall cloud and increased upper-level outflow, leading to further pressure falls in the cyclone, and so on.

"If any of these processes are inhibited, the cyclone will weaken."

Sinclair includes this, as a follow-up to his description of the positive feedback buildup process:

"The latent heat released by a single hurricane in a single day is equivalent to the energy from several hundred atomic bombs."

another "techie" development re a potential falsification of the Copenhagen interpretation

http://en.wikipedia.org/wiki/Wave-particle_duality
http://www.kathryncramer.com/wblog/archives/000674.html

wikipedia blurb (near bottom of the page):

There is currently (August 2004) some doubt over the validity of Wave-particle duality due to Shahriar Afshar's 2004 contradictory result using a variation on the double-slit experiment, which also appears to invalidate the Copenhagen interpretation. So far this revised experiment has only been carried out with photons, not electrons, neutrons or protons, and the results have yet to be peer-reviewed.

A.Zarkov,

I'm no expert by any means, but it seems that Tropical storms weaken when they can't get the heat and moisture necessary for their growth.. That is, oversimplifying, when they go over warmer water they tend to intensify, when they go over cooler water they tend to settle down. When they hit land, they encounter conditions that tend to break them down rapidly, unless the land mass is too small..

A. Zarkov, I'm guessing that there is a square-cube limitation on hurricane size. The powering energy from water vapor evaporation would be proportional to the area of the hurricane, but the energy to move the winds would be proportional to the gas volume of the storm. At some point there would not be enough evaporation to enlarge the hurricane.

"The latent heat released by a single hurricane in a single day is equivalent to the energy from several hundred atomic bombs."

Oh no, another WMD! Blame Al Qaida again!

Gotta bear in mind that 'equilibrium' is the wrong term here-- A hurricane is a sort of steady-state 'metastable' instability with flows of moisture, pressure, temperature, and what-have-you. It moves at some velocity through different temperature and moisture zones, it gets bigger, it gets smaller.. Not a static situation.

"The latent heat released by a single hurricane in a single day is equivalent to the energy from several hundred atomic bombs."

I'm all for phun phacts, but atomic bombs range from 10 to 20,000+ kilotons. The above statement doesn't even give me an idea of how many digits we're talking about.

I think they get so big because somebody didn't drop a bomb on them.

"What stops it from getting bigger? It other words what sets the equilibrum conditions?"

I had a conversation many years ago with Kerry Emmanuel (of MIT) who analyzed this very problem. My (sadly, dim) recollection is that a hurricane is modeled very well as a Carnot engine, with the temperature driveer being the difference between the sea surface and upper atmosphere temperatures.

Kerry's paper is:
Emmanuel, Kerry A.,
"The theory of hurricanes,"
Ann. Rev. Fluid Mech., Vol. 23, 1991, pp. 179-197.

He discusses it on his web site at
http://www-paoc.mit.edu/~emanuel/home.html

I don't recall what factor stabilizes the hurricane & stops its growth.

I do recall him saying that if sea surface temperature were to increase to calue that is a bit more than we find on Earth (I think of order 10 to 20 degrees C) over a large enough basin, the theory says that the equilibrating process cannot keep up with the intensification process and you get a "hypercane" - a hurricane's worth of weather in something orders of magnitude smaller diameter (perhaps as small as a tornado?).

Social Systems too exhibit characteristics of complex systems.

It surprises me that I see so little talk of “complex systems framing” in most of the economics discussions I wander into. We can use both complex systems word models and mathematical models to talk about the weather, but seldom dare crosswalk to those aspects of social systems that seem to generally follow the non-linear dynamics of complexity (contagions, herding, rational exuberance (pessimism) giving way to irrational, etc.).

Kenneth Arrow did his best to protect Brian Arthur at Stanford from the many attacks leveled at him for telling complex systems stories and building complex systems models, but to no avail. Ultimately Arthur left (was forced to leave?)Stanford. There’s probably more to this story but it does make for interesting reading:
http://www.santafe.edu/arthur/Slate/Arrow.html
http://www.dialogonleadership.org/Arthur-1999.html

I suspect that Arthur was just getting his “due” as a pioneer, and that there is more complex systems chatter now than when he began his journey… But not in many forums and not enough, for my liking, in Brad’s very informative forums..

Permit me a few lines from Stuart Kauffmann’s book AT HOME IN THE UNIVERSE: The Search for Laws of Self-Organization and Complexity (1995), chapter titled “An Emerging Global Civilization”:

“… persistent innovation in an economy …. New goods and services create niches that call forth the innovations of further new goods and services. Each may unleash growth both because of increasing returns in the early phase of improvement on learning curves or new open markets. Some of these are truly triggers of Shumpeterian “gales of creative destruction,” ushering out many old technologies, ushering in many new ones in vast avalanches. Such avalanches create enormous arenas of increasing returns because of the massive early improvements climbing learning curves along the novel technological trajectories, as well as major new markets. Such large avalanches drive significant capital formation and growth. Other new technologies come and go with hardly a ripple. These differences presumably reflect, in part, how central or peripheral the new technology or product is in the current web and in its future evolution. The automobile and the computer were central. The hula hoop was peripheral. … Diversity begets diversity, driving the growth of complexity. (p. 296)..”

All the talk of growth, death, limits, and so on, in general and in specific circumstances seem to relate as well to economic contagions as they do to hurricanes. Yet too seldom do we discuss broader and narrower scale dynamics of complex social systems, methinks.

Agreed- an economist especially should have some awareness of some of the types of natural phenomena and systems.

Really cool- watch the satellite loops and worldsat photos for the weather for a while. You can't help but see some suggestive and informative patterns. Ths kind of learning that sticks with you. Can also see at NASA TV coverage of ISS- they frequently show the vieww from the ISS.

Also recommended, characteristics of turbulent flow. Fairly easy to find a book or site with illustrations to stimulate some basic learning processes.

Finally, Braudel's History of the World, in which he discusses the strong tendency of goods and money to flow from places of high concentration to places of low concentration. Fascinating window on the world of c. 1500.

I am working on an assignment for statistics which asks us for the absolute value of zero measurement. I've chosen to talk about Hurricane activity since I am in Orlando and in the smack middle of the event. Can anyone shed light on 1) how I can relate the hurricane to the absolute zero value measurement and 2) the best place to track interval temperature activity starting with the origination of the hurricane..temperature from sea level, temperature from the eye, and from the outside center of the hurricane? Help would be greatly appreciated as I have to turn this in shortly. Thanks so much!

Lisa