Re: Ma scusate...
Inviato da NiHiLaNtH il 19/5/2014 19:55:59
Citazione:
lo studio postato da Cagliostro è il seguito di quello di Mitchell dove si parla dell'inseminazione con il tri-ioduro di bismuto ma non si tratta di creare dei cirri artificiali per schermare la radiazione infrarossa
"...As described under section 1, recent GCM studies suggest that cirrus clouds and upper tropospheric water vapor represent the component of the climate system that most strongly affects the prediction of climate sensitivity. Thus it seems logical to target this component in a geoengineering strategy. Moreover, greenhouse gases trap OLR, and cirrus affect OLR more than all other cloud types (Chen et al 2000, Hartmann et al 1992). In this way this strategy directly addresses the radiation imbalance due to greenhouse gases.
...The cirrus seeding option does not appear to suffer from these drawbacks, although slightly more solar radiation would reach the surface with less cirrus cloud coverage. Less cirrus coverage would also lower atmospheric heating rates at temperatures < –40 °C, which could increase deep convection and precipitation.
...Another geoengineering idea targeting cirrus clouds has been proposed by Cotton (2009). That idea suggests increasing the amount of soot in the upper troposphere to increase temperatures there to reduce cirrus coverage through sublimation. The solar radiation absorbed by soot would decrease temperatures at the surface, and the reduced cirrus coverage would allow more OLR to escape. However, the higher temperatures produced by soot may not change the RH (Held and Soden 2000), making the fate of cirrus less certain. Details describing the efficacy of this approach have not yet been released.
... If so, then the introduction of very efficient heterogeneous ice nuclei at these cold temperatures in the right concentration may result in larger ice crystals as the heterogeneous ice nuclei would out-compete the homogeneous freezing nuclei. This process has been coined as the negative Twomey effect in association with the traditional Twomey effect in liquid water clouds, where increases in cloud condensation nuclei produce higher cloud droplet concentrations and cloud albedo. The negative Twomey effect can lead to reductions in ice particle concentration by up to a factor of 10 under natural conditions and to decreased cirrus cloud albedo.
...Substances exist that nucleate ice crystals as effectively as silver iodide (AgI, the best ice nucleant known) at cirrus cloud temperatures, and some are relatively inexpensive and non-toxic . If significantly larger, these artificially seeded ice crystals would fall faster, and their higher fall velocities may lead to reduced cirrus cloud coverage as predicted in GCM simulations. The lower cirrus cloud coverage would result in greater OLR and cooler surface temperatures, thus reducing the impact of global warming.
... it may be possible to decrease cirrus cloud coverage by introducing efficient heterogeneous ice nuclei at these temperatures where the cirrus greenhouse effect is strongest. Due to vapor competition effects, this may result in larger ice crystals with higher fall velocities, which should decrease cirrus coverage and increase OLR, thus cooling surface temperatures. While there may be an initial increase in cirrus coverage due to ice supersaturation in clear skies, over time the increase in net downward transport of water substance (due to higher ice fall speeds) should reduce the relative humidity and cirrus coverage of the upper troposphere. Based on one GCM study, it appears that seeding cirrus clouds on a global scale could cool the planet by well more than 2.8 W m–2, perhaps enough to cancel the radiative forcing due to a doubling of CO2 (3.7 W m–2). The distribution of seeding material could be done relatively inexpensively through the airline industry. Seeding along conventional flight corridors should increase OLR preferentially over the northern high latitudes where global warming is most severe. "
abstract di una presentazione del paper originale di Mitchell
Seeding of Cirrus Clouds to Reduce Global Warming
David L. Mitchell, DRI, Reno, NV; and J. Mejia, M. Kuebbeler, U. Lohmann, and M. Xiao
"A new climate engineering (CE) method will be described where cirrus clouds are removed to cool the planet. Cirrus clouds have a warming effect on climate since they effectively “trap” outgoing longwave radiation (OLR)[/u] due to their cold temperatures. [b]They also reflect sunlight, but the OLR effect is stronger. If the cirrus cloud optical depth in the thermal infrared window region can be reduced and their cloud coverage reduced, then more OLR can escape to space, cooling the planet.
This is accomplished by seeding cold (T < -40°C) cirrus clouds with efficient ice nuclei such as silver iodide (AgI) or bismuth tri-iodide (BiI3), which is as effective as AgI for T < -20°C.
At these temperatures most ice crystals appear to result from homogeneous freezing nucleation, but seeding cold cirrus with AgI or BiI3 would replace homogeneous nucleation with heterogeneous nucleation processes, resulting in fewer but larger ice crystals. The larger ice crystals have higher fall speeds, which reduces cirrus optical depth and decreases cirrus cloud coverage. This kind of seeding operation would require seeding an air mass prior to cirrus formation, allowing an optimal background concentration of ice nuclei to become established.
This practice would initially produce more cirrus clouds in regions of clear sky supersaturated with respect to ice. But over time, with larger ice crystals forming with higher fall speeds, the flux of water substance to lower levels would increase, drying out the upper troposphere (UT). This reduces the UT relative humidity (RH). Thus, OLR increases for two reasons: less cirrus and lower RH in the UT.
qui la presentazione di Mitchell
https://ams.confex.com/ams/93Annual/flvgateway.cgi/id/24040?recordingid=24040
e qui un articolo del NewScientist che parla dello studio di Mitchell
http://www.newscientist.com/article/mg21729014.800-get-cirrus-in-the-fight-against-climate-change.html#.U3o4c20ZHPo
Proprio una delle ipotesi, la piu' gettonata, per giustificare l'enorme presenza di scie considerate "anomale" : esperimenti per tentare di ridurre/contenere il riscaldamento globale
lo studio postato da Cagliostro è il seguito di quello di Mitchell dove si parla dell'inseminazione con il tri-ioduro di bismuto ma non si tratta di creare dei cirri artificiali per schermare la radiazione infrarossa
"...As described under section 1, recent GCM studies suggest that cirrus clouds and upper tropospheric water vapor represent the component of the climate system that most strongly affects the prediction of climate sensitivity. Thus it seems logical to target this component in a geoengineering strategy. Moreover, greenhouse gases trap OLR, and cirrus affect OLR more than all other cloud types (Chen et al 2000, Hartmann et al 1992). In this way this strategy directly addresses the radiation imbalance due to greenhouse gases.
...The cirrus seeding option does not appear to suffer from these drawbacks, although slightly more solar radiation would reach the surface with less cirrus cloud coverage. Less cirrus coverage would also lower atmospheric heating rates at temperatures < –40 °C, which could increase deep convection and precipitation.
...Another geoengineering idea targeting cirrus clouds has been proposed by Cotton (2009). That idea suggests increasing the amount of soot in the upper troposphere to increase temperatures there to reduce cirrus coverage through sublimation. The solar radiation absorbed by soot would decrease temperatures at the surface, and the reduced cirrus coverage would allow more OLR to escape. However, the higher temperatures produced by soot may not change the RH (Held and Soden 2000), making the fate of cirrus less certain. Details describing the efficacy of this approach have not yet been released.
... If so, then the introduction of very efficient heterogeneous ice nuclei at these cold temperatures in the right concentration may result in larger ice crystals as the heterogeneous ice nuclei would out-compete the homogeneous freezing nuclei. This process has been coined as the negative Twomey effect in association with the traditional Twomey effect in liquid water clouds, where increases in cloud condensation nuclei produce higher cloud droplet concentrations and cloud albedo. The negative Twomey effect can lead to reductions in ice particle concentration by up to a factor of 10 under natural conditions and to decreased cirrus cloud albedo.
...Substances exist that nucleate ice crystals as effectively as silver iodide (AgI, the best ice nucleant known) at cirrus cloud temperatures, and some are relatively inexpensive and non-toxic . If significantly larger, these artificially seeded ice crystals would fall faster, and their higher fall velocities may lead to reduced cirrus cloud coverage as predicted in GCM simulations. The lower cirrus cloud coverage would result in greater OLR and cooler surface temperatures, thus reducing the impact of global warming.
... it may be possible to decrease cirrus cloud coverage by introducing efficient heterogeneous ice nuclei at these temperatures where the cirrus greenhouse effect is strongest. Due to vapor competition effects, this may result in larger ice crystals with higher fall velocities, which should decrease cirrus coverage and increase OLR, thus cooling surface temperatures. While there may be an initial increase in cirrus coverage due to ice supersaturation in clear skies, over time the increase in net downward transport of water substance (due to higher ice fall speeds) should reduce the relative humidity and cirrus coverage of the upper troposphere. Based on one GCM study, it appears that seeding cirrus clouds on a global scale could cool the planet by well more than 2.8 W m–2, perhaps enough to cancel the radiative forcing due to a doubling of CO2 (3.7 W m–2). The distribution of seeding material could be done relatively inexpensively through the airline industry. Seeding along conventional flight corridors should increase OLR preferentially over the northern high latitudes where global warming is most severe. "
abstract di una presentazione del paper originale di Mitchell
Seeding of Cirrus Clouds to Reduce Global Warming
David L. Mitchell, DRI, Reno, NV; and J. Mejia, M. Kuebbeler, U. Lohmann, and M. Xiao
"A new climate engineering (CE) method will be described where cirrus clouds are removed to cool the planet. Cirrus clouds have a warming effect on climate since they effectively “trap” outgoing longwave radiation (OLR)[/u] due to their cold temperatures. [b]They also reflect sunlight, but the OLR effect is stronger. If the cirrus cloud optical depth in the thermal infrared window region can be reduced and their cloud coverage reduced, then more OLR can escape to space, cooling the planet.
This is accomplished by seeding cold (T < -40°C) cirrus clouds with efficient ice nuclei such as silver iodide (AgI) or bismuth tri-iodide (BiI3), which is as effective as AgI for T < -20°C.
At these temperatures most ice crystals appear to result from homogeneous freezing nucleation, but seeding cold cirrus with AgI or BiI3 would replace homogeneous nucleation with heterogeneous nucleation processes, resulting in fewer but larger ice crystals. The larger ice crystals have higher fall speeds, which reduces cirrus optical depth and decreases cirrus cloud coverage. This kind of seeding operation would require seeding an air mass prior to cirrus formation, allowing an optimal background concentration of ice nuclei to become established.
This practice would initially produce more cirrus clouds in regions of clear sky supersaturated with respect to ice. But over time, with larger ice crystals forming with higher fall speeds, the flux of water substance to lower levels would increase, drying out the upper troposphere (UT). This reduces the UT relative humidity (RH). Thus, OLR increases for two reasons: less cirrus and lower RH in the UT.
qui la presentazione di Mitchell
https://ams.confex.com/ams/93Annual/flvgateway.cgi/id/24040?recordingid=24040
e qui un articolo del NewScientist che parla dello studio di Mitchell
http://www.newscientist.com/article/mg21729014.800-get-cirrus-in-the-fight-against-climate-change.html#.U3o4c20ZHPo
Messaggio orinale: https://old.luogocomune.net/site/newbb/viewtopic.php?forum=61&topic_id=2976&post_id=255697