Excuse me if I have not understood everything but it seems that all discussions about hurricane consider only horizontal wind. In that case, it seems important to consider vertical wind (rotational flow wirling system). Regards, François MAUGIS. ============================================================================ ===========
_____ De : [email protected] [mailto:[email protected]] De la part de Andrew Lockley Envoyé : lundi 8 juin 2009 10:18 À : [email protected] Cc : [email protected]; [email protected]; dsw_s; Geoengineering Objet : [geo] Re: Just in Time for Hurricane Season The energy in a nuclear bomb is quite small, but very concentrated, compared to that of a hurricane. The eye, as I understand, is primarily convective, so it's probably the wrong place. Dropping a nuclear bomb in advance of the hurricane, beyond the outer wall, would perhaps have more chance of disrupting its progress. The ability of a nuclear weapon to instantly create huge clouds of seawater mist and steam would probably have significant effects by changing albedo - probably more than that of the energy input from the weapon itself. However, the effect on marine life from the shockwave would be likely to be pretty devastating. 2009/6/8 Eugene I. Gordon <[email protected]> Has anyone considered droppong a miniature atomic bomb; such as used in artillery shells, down the middle of a hurricane before it makes landfall? -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Alvia Gaskill Sent: Saturday, June 06, 2009 8:38 PM To: [email protected]; dsw_s; Geoengineering Subject: [geo] Re: Just in Time for Hurricane Season Some more info about the effect of hurricanes or more generally, tropical cyclones on SST (sea surface temperature) from NOAA and the Wikipedia. Most of the temperature decrease is due to the mixing of water in the upper layer of the ocean by winds and most of the decrease occurs after the storm has passed. Limited data show that the decrease from evaporation of water is much less. NOAA also throws some cold water on artificial dissipation strategies including the one that got this discussion started, ocean pipes. They didn't address indirect approaches like the cloud ships and the desert cover. http://www.aoml.noaa.gov/hrd/tcfaq/H7.html Subject: H7) How does the ocean respond to a hurricane and how does this feedback to the storm itself? Contributed by Joe Cione The ocean's primary direct response to a hurricane is cooling of the sea surface temperature (SST). How does this occur? When the strong winds of a hurricane move over the ocean they churn-up much cooler water from below. The net result is that the SST of the ocean after storm passage can be lowered by several degrees Celsius (up to 10° Fahrenheit). Figure 1 shows SSTs ranging between 25-27°C (77-81°F) several days after the passage of Hurricane Georges in 1998. As Figure 1 illustrates, Georges' post storm 'cold wake' along and to the right of the superimposed track is 3-5°C (6-9°F) cooler than the undisturbed SST to the west and south (i.e. red/orange regions are ~30°'C [86°'F]). The magnitude and distribution of the cooling pattern shown in this illustration is fairly typical for a post-storm SST analysis. One important caveat to realize however is that most of the 3-5°C (6-9°F) ocean cooling shown in Figure 1 occurs well after the storm has moved away from the region (in this case several days after Georges made landfall). The amount of ocean cooling that occurs directly beneath the hurricane within the high wind region of the storm is a much more important question scientists would like to have answered. Why? Hurricanes get their energy from the warm ocean water beneath them. However, in order to get a more accurate estimate of just how much energy is being transferred from the sea to the storm, scientists need to know ocean temperature conditions directly beneath the hurricane. Unfortunately, with 150kph+ (100mph+) winds, 20m+ (60ft+) seas and heavy cloud cover being the norm in this region of the storm, direct (or even indirect) measurement of SST conditions within the storm's "inner core" environment are very rare. Thankfully in this case "very rare" does not mean "once in a lifetime". Recently, scientists at the Hurricane Research Division were able to get a better idea of how much SST cooling occurs directly under a hurricane by looking at many storms over a 28 year period. By combining these rare events, HRD scientists put together a "composite average" of ocean cooling directly under the storm. Figure 2 illustrates that, on average, cooling patterns are a lot less than the post storm 3-5°C (6-9°F) cold wake estimates shown in Figure 1. In most cases, the ocean temperature under a hurricane will range somewhere between 0.2 and 1.2°C (0.4 and 2.2°F) cooler that the surrounding ocean environment. Exactly how much depends on many factors including ocean structure beneath the storm (i.e. location), storm speed, time of year and to a lesser extent, storm intensity (Cione and Uhlhorn 2003). While the estimates in Figure 2 represent a dramatic improvement when it comes to more accurately representing actual SST cooling patterns experienced under a hurricane, even small errors in inner core SST can result in significant miscalculations when it comes to accurately assessing how much energy is transferred from the warm ocean environment directly to the hurricane. With all other factors being equal, being "off" by a mere 0.5°C (1°F) can be the difference between a storm that rapidly intensifies to one that falls apart! With that much at stake, scientists at HRD and other government and academic institutions are working to improve our ability to accurately estimate, observe and predict "under-the-storm" upper ocean conditions. These efforts include statistical studies, modeling efforts and enhanced observational capabilities designed to help scientists better assess upper ocean thermal conditions under the storm. With such improvements, it is believed that future forecasts of tropical cyclone intensity change will be significantly improved. Reference Cione, J. J., and E. W. Uhlhorn, 2003: Sea Surface Temperature Variability in Hurricanes: Implications with Respect to Intensity Change. Monthly Weather Review, 131, 1783-1796. Last updated August 13, 2004 http://en.wikipedia.org/wiki/Typhoons Tropical cyclones are characterized and driven by the release of large amounts of latent heat of condensation, which occurs when moist air is carried upwards and its water vapour condenses. This heat is distributed vertically around the center of the storm. Thus, at any given altitude (except close to the surface, where water temperature dictates air temperature) the environment inside the cyclone is warmer than its outer surroundings.[2] Mechanics Tropical cyclones form when the energy released by the condensation of moisture in rising air causes a positive feedback loop over warm ocean waters.[14] A tropical cyclone's primary energy source is the release of the heat of condensation from water vapor condensing at high altitudes, with solar heating being the initial source for evaporation. Therefore, a tropical cyclone can be visualized as a giant vertical heat engine supported by mechanics driven by physical forces such as the rotation and gravity of the Earth.[15] In another way, tropical cyclones could be viewed as a special type of mesoscale convective complex, which continues to develop over a vast source of relative warmth and moisture. Condensation leads to higher wind speeds, as a tiny fraction of the released energy is converted into mechanical energy;[16] the faster winds and lower pressure associated with them in turn cause increased surface evaporation and thus even more condensation. Much of the released energy drives updrafts that increase the height of the storm clouds, speeding up condensation.[17] This positive feedback loop continues for as long as conditions are favorable for tropical cyclone development. Factors such as a continued lack of equilibrium in air mass distribution would also give supporting energy to the cyclone. The rotation of the Earth causes the system to spin, an effect known as the Coriolis effect, giving it a cyclonic characteristic and affecting the trajectory of the storm.[18][19] What primarily distinguishes tropical cyclones from other meteorological phenomena is deep convection as a driving force.[20] Because convection is strongest in a tropical climate, it defines the initial domain of the tropical cyclone. By contrast, mid-latitude cyclones draw their energy mostly from pre-existing horizontal temperature gradients in the atmosphere.[20] To continue to drive its heat engine, a tropical cyclone must remain over warm water, which provides the needed atmospheric moisture to keep the positive feedback loop running. When a tropical cyclone passes over land, it is cut off from its heat source and its strength diminishes rapidly.[21] Chart displaying the drop in surface temperature in the Gulf of Mexico as Hurricanes Katrina and Rita passed over The passage of a tropical cyclone over the ocean can cause the upper layers of the ocean to cool substantially, which can influence subsequent cyclone development. Cooling is primarily caused by upwelling of cold water from deeper in the ocean because of the wind. The cooler water causes the storm to weaken. This is a negative feedback process that causes the storms to weaken over sea because of their own effects. Additional cooling may come in the form of cold water from falling raindrops (this is because the atmosphere is cooler at higher altitudes). Cloud cover may also play a role in cooling the ocean, by shielding the ocean surface from direct sunlight before and slightly after the storm passage. All these effects can combine to produce a dramatic drop in sea surface temperature over a large area in just a few days.[22] Scientists at the US National Center for Atmospheric Research estimate that a tropical cyclone releases heat energy at the rate of 50 to 200 exajoules (1018 J) per day,[17] equivalent to about 1 PW (1015 watt). This rate of energy release is equivalent to 70 times the world energy consumption of humans and 200 times the worldwide electrical generating capacity, or to exploding a 10-megaton nuclear bomb every 20 minutes.[17][23] While the most obvious motion of clouds is toward the center, tropical cyclones also develop an upper-level (high-altitude) outward flow of clouds. These originate from air that has released its moisture and is expelled at high altitude through the "chimney" of the storm engine.[15] This outflow produces high, thin cirrus clouds that spiral away from the center. The clouds are thin enough for the sun to be visible through them. These high cirrus clouds may be the first signs of an approaching tropical cyclone.[24] http://www.aoml.noaa.gov/hrd/tcfaq/C5e.html Subject: C5e) Why don't we try to destroy tropical cyclones by cooling the surface waters with icebergs or deep ocean water ? Contributed by Neal Dorst Since hurricanes draw their energy from warm ocean water, some proposals have been put forward to tow icebergs from the arctic zones to the tropics to cool the sea surface temperatures. Others have suggested pumping cold bottom water in pipes to the surface, or releasing bags of cold freshwater from near the bottom to do this. Consider the scale of what we are talking about. The critical region in the hurricane for energy transfer would be under or near the eyewall region. If the eyewall was thirty miles (48 kilometer) in diameter, that means an area of nearly 2000 square miles (4550 square kilometers). Now if the hurricane is moving at 10 miles an hour (16 km/hr) it will sweep over 7200 square miles (18,650 square kilometers) of ocean. That's a lot of icebergs for just 24 hours of the cyclone's life. Now add in the uncertainty in the track, which is currently 100 miles (160 km) at 24 hours and you have to increase your cool patch by 24,000 sq mi (38,000 sq km). For the iceberg towing method you would have to increase your lead time even more (and hence the uncertainty and area cooled) or risk your fleet of tugboats getting caught by the storm. For the bag/pipe method you would have to preposition your system across all possible approaches for hurricanes. Just for the US mainland from Cape Hatteras to Brownsville would mean covering 528,000 sq mi (850,000 sq km) of ocean floor with devices. Lastly, consider the creatures of the sea. If you suddenly cool the surface layer of the ocean (and even turn it temporarily fresh), you would alter the ecology of that area and probably kill most of the sea life contained therein. A hurricane would be devastating enough on them without our adding to the mayhem. Last updated August 13, 2004 ----- Original Message ----- From: "Mike MacCracken" <[email protected]> To: "dsw_s" <[email protected]>; "Geoengineering" <[email protected]> Sent: Saturday, June 06, 2009 1:41 PM Subject: [geo] Re: Just in Time for Hurricane Season Some further comments are included (labeled "MCM"): On 6/6/09 3:17 AM, "dsw_s" <[email protected]> wrote: > >> The air that leaves the top of a hurricane is cold already, so it is not >> sending much energy back into space. > > What about radiation from cloud tops? I would expect cloud tops to > radiate much more readily than air at that altitude, both because of > being a condensed phase that can emit blackbody radiation effectively > and because of being warmer than air at that altitude normally is. > MCM: There is some going out from cloud tops, and indeed more than from dry air, but it is far less than would go out in absence of the clouds reaching that high. >> Most of the energy to carry the air up is used to push air elsewhere back >> down--as air comes down elsewhere, it is compressed and this takes >> energy--adiabatic heating. > > That doesn't sound right. At adiabatic lapse rate, a convection cell > should be energy-neutral before friction is taken into account. > Energy needed to compress air is balanced by work done by expanding > air, just as energy needed to lift air against gravity is balanced by > the work done by gravity on sinking air. So energy applied to drive > convection would all be available to be dissipated in other ways. > > Or are you saying that cyclones occur within a situation where the > background lapse rate is well below adiabatic, and the energy mostly > goes to overcome that stability? > MCM: Air goes up at moist adiabatic rate, but has to be forced down at the dry adiabatic rate (e.g., over deserts). This tends to go on remotely--like monsoons rising in one place, and dry subtropics being in another. If getting this cycle going were easy (as you suggest--self-compensating), we'd be having convection all the time--and we don't. It takes moisture release to drive the system (cold air aloft does not come cascading down--the air up there has to be forced down over a very broad area). >> One way to test the theory that the tropical cyclones increase radiation >> of >> IR to space would be to observe the upwelling IR in the path and area >> surrounding these storms using satellites and compare to the IR prior to >> the >> arrival of the storm. > > If you look at the path after the hurricane has gone by, the IR > emission from the surface will be affected by the fact that the storm > mixed warm surface water with cooler water below. So if you want to > include the surroundings where the air sinks, you would have to > account for that. > MCM: Yes, but the oceans are also cooled a lot by all the evaporation that took place to power the hurricanes. --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "geoengineering" group. 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