A faster and more colorful version of the same imagery: http://www.youtube.com/watch?v=IBrEl8NW2n4
I think that the dark colors represent more radiation radiation from warm ocean surface and low clouds and the white colors represent less radiation from cold high clouds, so I would guess on the short term local effect of a hurricane would reduce longwave radiation to space by masking the warm surface with cold high cloud tops. How these short term local effects relate to the long-term global effects is beyond me ... except that it is clear that the dominant energy flux in hurricanes is upward (latent heating at the surface warming the troposphere) which would lead one to suspect that these systems tend to help energy escape to space. On Sat, Jun 6, 2009 at 2:38 AM, Ken Caldeira < [email protected]> wrote: > 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 -~----------~----~----~----~------~----~------~--~---
