Not sure what it means, but there is some interesting imagery at: http://www.youtube.com/watch?v=ApaiaShoUH0
On Sat, Jun 6, 2009 at 12:17 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. > > > 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? > > > 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. > > On Jun 5, 1:02 pm, "Alvia Gaskill" <[email protected]> wrote: > > 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. The reflection of sunlight is a separate issue and > I > > would argue that this is no more or less effective than any other white > > clouds or even the low level stratocumulus to be whitened using the cloud > > ships. Since one of the advantages of the cloud ships was to be reduced > > SST's and thus weaker or fewer tropical systems, the net impact of these > > would need to be further explored. > > > > ----- Original Message ----- > > From: "Mike MacCracken" <[email protected]> > > To: "Alvia Gaskill" <[email protected]>; < > [email protected]>; > > > > "Oliver Wingenter" <[email protected]>; "Geoengineering" > > <[email protected]> > > Sent: Friday, June 05, 2009 9:46 AM > > Subject: Re: [geo] Re: Just in Time for Hurricane Season > > > > A couple of notes: > > > > 1. 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. This heat wars the air and can then be > radiated > > to space, as happens in the subtropics. That the air column is dry makes > > radiation of energy to space easier, but it also makes radiation from the > > air harder. Together these help to explain the persistent inversions in > > broad areas where air is descending. > > > > 2. I would think it could be argued that hurricanes accelerate the > transfer > > of heat from the ocean to the atmosphere and thus to space. With the > strong > > dependence of evaporation rate on wind speed, having high winds > accelerates > > evaporation, cooling the ocean and transporting heat aloft. In addition, > > hurricanes have bright clouds and so reflect solar (which is why they are > so > > beautiful looking from space), so reduce warming of the ocean--though > they > > also likely restrict IR loss from the ocean. > > > > 3. On amounts of energy, the latent heat energy released (5.2 times > 10**19 > > joules/day) is equal to setting off a megaton nuclear weapon every 70 > > seconds (a megaton is 10**15 calories). Based on the friction energy > > dissipated being only about .2% of the energy released, the destructive > > power in energy is equal to about 2.5 Mt per day--assuming all the energy > in > > a megaton explosion goes into destruction--which is surely not the case > as > > the air is carried aloft, radiated away, etc., plus due to the very > > concentrated nature of a nuclear explosion. So, maybe the destructive > power > > of a hurricane is equivalent to the destruction created by a one megaton > > explosion every maybe 10-30 minutes or so. Seems roughly reasonable to > > me--if think about a hurricane spreading its destruction over a much > broader > > area. > > > > Mike MacCracken > > > > On 6/5/09 9:07 AM, "Alvia Gaskill" <[email protected]> wrote: > > > > > Some answers, perhaps to the question of what happens to all that > energy > > > in > > > a hurricane, provided by the aptly named Chris Landsea. Chris was also > on > > > TV last night on the National Geographic program, Hurricanes (2009). > In > > > addition to not knowing much about what happens above 35,000 ft in a > > > tropical cyclone, including the region of the boundary with the > > > (Overworld) > > > stratosphere and the upper troposphere, not much is known about what > > > happens > > > near the marine boundary layer at around 200 ft, where the hurricane > draws > > > the water vapor from the sea surface into its structure. To learn more > > > about it, pilots flew at around 200 ft above the sea surface of an > active > > > hurricane, Isabel. Brave or crazy. You decide. The danger at high > > > altitudes is icing. In their case, it was salt spray condensing on the > > > engines that caused them to end the mission. > > > > > As to where does the energy go, it appears that most of it stays in the > > > troposphere. Hurricanes are heat machines that draw their energy from > > > water > > > vapor. The water vapor condenses in the thunderstorms of the eyewall > and > > > feeder bands. The air flow is from the surface to the top of the > eyewall > > > and then it spills over and down back into the storm or over the edge > of > > > the > > > clouds at the top. In some ways, hurricanes resemble the tropics, with > > > rising moisture laden air that reaches a cold point where it is dried > out > > > and spreads out horizontally via the Brewer Dobson circulation. > > > > > The air that leaves the top of a hurricane is cold already, so it is > not > > > sending much energy back into space. The kinetic energy used to cause > the > > > winds to circulate is generated at the expense of heat energy from > > > condensed > > > water vapor, but is small by comparison with that released from > producing > > > clouds and rain. > > > > > Eventually all of the heat energy, in the form of infrared radiation, > > > leaves > > > the Earth's atmosphere and goes into space. Because this process is > > > continuous, individual photons only spend a fraction of a second in the > > > atmosphere, replaced by others instantaneously emitted. When a > hurricane > > > is > > > done for, the remnants are typically absorbed by another weather system > > > and > > > carried, in the case of Atlantic hurricanes, into the N. Atlantic, > > > sometimes > > > as far east as Ireland. Given the altitudes at which these weather > > > systems > > > operate, I don't think they send much IR back to space either. Thus, I > > > don't believe hurricanes are an effective means of reducing the amount > of > > > energy in the troposphere, what we typically mean when we say "the > > > atmosphere." > > > > > Stopping some tropical cyclones or all of them (we can't stop any of > them > > > now, so this is just speculation, no matter what technology is > considered) > > > might impact the regional heating of the planet, but I still doubt it > > > would > > > have much of any effect on GHG driven warming and overall global > warming. > > > Weakening the wind speeed of these storms would certainly be beneficial > in > > > terms of reduced property damage and loss of life, although storm > related > > > flooding is still the largest cause of death. Shifting their path away > > > from > > > populated areas would also be beneficial and wouldn't affect the heat > > > transport fluxes as much as preventing their formation. They do > provide > > > needed rainfall in some cases, but since their paths are unpredictable, > > > they > > > are not a reliable source of precipitation and thus that shouldn't be > used > > > as a reason to prevent landfall if it ever became possible to do so. > > > > >http://www.aoml.noaa.gov/hrd/tcfaq/D7.html > > > > > Subject: D7) How much energy does a hurricane release? > > > Contributed by Chris Landsea > > > > > Hurricanes can be thought of, to a first approximation, as a heat > engine; > > > obtaining its heat input from the warm, humid air over the tropical > ocean, > > > and releasing this heat through the condensation of water vapor into > water > > > droplets in deep thunderstorms of the eyewall and rainbands, then > giving > > > off > > > a cold exhaust in the upper levels of the troposphere (~12 km/8 mi up). > > > > > One can look at the energetics of a hurricane in two ways: > > > > > 1.. the total amount of energy released by the condensation of water > > > droplets or ... > > > 2.. the amount of kinetic energy generated to maintain the strong > > > swirling > > > winds of the hurricane (Emanuel 1999). > > > It turns out that the vast majority of the heat released in the > > > condensation > > > process is used to cause rising motions in the thunderstorms and only a > > > small portion drives the storm's horizontal winds. > > > > > a.. Method 1) - Total energy released through cloud/rain formation: > > > An average hurricane produces 1.5 cm/day (0.6 inches/day) of rain > inside > > > a > > > circle of radius 665 km (360 n.mi) (Gray 1981). (More rain falls in the > > > inner portion of hurricane around the eyewall, less in the outer > > > rainbands.) > > > Converting this to a volume of rain gives 2.1 x 1016 cm3/day. A cubic > cm > > > of > > > rain weighs 1 gm. Using the latent heat of condensation, this amount of > > > rain > > > produced gives > > > > > 5.2 x 1019 Joules/day or > > > 6.0 x 1014 Watts. > > > > > This is equivalent to 200 times the world-wide electrical generating > > > capacity - an incredible amount of energy produced! > > > > > b.. Method 2) - Total kinetic energy (wind energy) generated: > > > For a mature hurricane, the amount of kinetic energy generated is > equal > > > to > > > that being dissipated due to friction. The dissipation rate per unit > area > > > is > > > air density times the drag coefficient times the windspeed cubed (See > > > Emanuel 1999 for details). One could either integrate a typical wind > > > profile > > > over a range of radii from the hurricane's center to the outer radius > > > encompassing the storm, or assume an average windspeed for the inner > core > > > of > > > the hurricane. Doing the latter and using 40 m/s (90 mph) winds on a > scale > > > of radius 60 km (40 n.mi.), one gets a wind dissipation rate (wind > > > generation rate) of > > > > > 1.3 x 1017 Joules/day or > > > 1.5 x 1012Watts. > > > > > This is equivalent to about half the world-wide electrical generating > > > capacity - also an amazing amount of energy being produced! > > > Either method is an enormous amount energy being generated by > hurricanes. > > > However, one can see that the amount of energy released in a hurricane > (by > > > creating clouds/rain) that actually goes to maintaining the hurricane's > > > spiraling winds is a huge ratio of 400 to 1. > > > > > Back to Tropical Cyclones Winds Page | Back to Main FAQ Page > > > > > ----- Original Message ----- > > > From: "Margaret Leinen" <[email protected]> > > > To: <[email protected]>; "geoengineering" > > > <[email protected]> > > > Sent: Friday, June 05, 2009 7:21 AM > > > Subject: [geo] Re: Just in Time for Hurricane Season > > > > > Oliver and all, > > > > > Again, this is NOT my area of expertise, but I am aware of a little > work > > > that has been done based on hurricane measurements combined with > modeling. > > > Unfortunately, I haven't found anything that gives flux numbers, but > the > > > NOAA Aeronomy Laboratory group has been looking at this and those that > are > > > interested might contact them. Here's an example > > > > ... > > > > read more ยป > > > --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "geoengineering" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/geoengineering?hl=en -~----------~----~----~----~------~----~------~--~---
