I tried to post this on the 15th and it never appeared, so to keep it within the same thread, here it is.
One of the other articles I previously posted in this thread also mentions the effect on observing lunar eclipses. I think the term "vog" also has some future. Will the apocalyptic obsessed critics of aerosol geoengineering now refer to the "Vognerian" strategy? Makian is yet another one of those bad boy stratovolcanoes in Indonesia, located right on the equator. In all of the articles I've seen to date, including the mention in the first one of Pinatubo also having affected observation of a lunar eclipse, no one has noted that the eruptions had a negative impact on visible or other types of astronomy other than on lunar eclipses. I couldn't find any numbers on the SO2 emitted from Makian in 1760-1761, so it's hard to gauge its impact relative to that of Pinatubo. Remember also that large pre-industrial eruptions lowered temperatures below the "normal" level, while those today would first have to offset the AGW greenhouse forcing. So Makian may have been a much smaller eruption than Pinatubo, yet had a greater impact on climate. Regardless, it doesn't seem like aerosols represent a problem for astronomers. What say you about this, Roger Angel? http://www.volcano.si.edu/world/volcano.cfm?vnum=0608-07= http://news.nationalgeographic.com/news/2009/01/090116-eclipse-volcano.html "Missing" Moon Linked to Major 1761 Eruption? Ker Than for National Geographic News January 16, 2009 A "disappearing" moon that preceded an unusually bitter winter in China was most likely the result of a mysterious volcanic eruption in the 1700s, a retired NASA scientist says. Astronomer Kevin D. Pang collected evidence from the fields of geology, biology, and Chinese history that suggests a major eruption belched out enough dust and gas to completely blot out the moon during a 1761 total lunar eclipse. A total eclipse occurs when the moon enters completely into Earth's shadow. (Watch video of the February 2008 lunar eclipse-the last total eclipse of the moon until December 2010.) Lunar eclipses can vary in brightness and color based on the angle of the moon's path and the composition of Earth's atmosphere. While no sunlight hits the moon directly, some gets filtered by Earth's atmosphere and is bent toward the moon, causing it to shine in hues ranging from bright orange to blood red. "But when there's a large volcanic eruption," Pang said, "the moon can drop in brightness by a million times, or in some cases disappear altogether." Pang presented his results last week during the 213th meeting of the American Astronomical Society in Long Beach, California. Volcanic Winter Heavy amounts of particles in the air could explain why, in May of 1761, astronomers reported that the moon appeared very dark or disappeared altogether, even with the aid of telescopes. An atmosphere clogged by a powerful volcanic eruption would also lead to global cooling and trigger extended bouts of strange weather, experts say. (Related: "Ancient Global Dimming Linked to Volcanic Eruption" [March 19, 2008].) To test his theory, Pang searched the scientific literature about tree rings and ice cores from Antarctica and Greenland. He found evidence of a "volcanic winter" around the same time as the dark eclipse. For example, sulfur dioxide gas ejected during a volcanic eruption can react with water vapor in the air to form acid rain, which then leaves chemical fingerprints in polar ice. Furthermore, bristlecone pine trees high in the Sierra Nevada mountains experienced stunted growth and frost damage in 1761, Pang said. The researcher also looked through old Chinese weather chronicles from the early 1760s. Those records revealed that large parts of China experienced an unusually bitter winter and heavy snowfall in 1761 and 1762. Rivers and wells across central China froze, ships could not sail, and innumerable trees, birds, and livestock died due to the cold, the chronicles state. Finding a Culprit A good candidate for the cause of the 1761 events is the Makian volcano on the Indonesian island of Halmahera, Pang thinks. Records show that this volcano experienced a series of eruptions beginning in September of 1760 and lasting until spring of the following year. Makian's equatorial position could explain why evidence of its eruption was found at both poles. But it's also possible the culprit volcano went unrecorded, Pang added. Richard Keen is a climatologist at the University of Colorado in Boulder who was not involved in the study. "[Pang] is absolutely correct in saying that volcanoes can darken a lunar eclipse," Keen said. But for the 1761 event, he noted, historical accounts about the dimness of the moon varied by geographical location. Most of the reports of the moon disappearing were from astronomers in Sweden, Finland, and northwestern Russia. At more southern latitudes, the moon only appeared dimmer than usual. The differing accounts could be due to the patchy distribution of dust and sulfur particles that occurs shortly after a volcanic eruption, said Fred Espenak, an eclipse expert at NASA's Goddard Space Flight Center in Maryland. "But if this dust is up there long enough, it tends to uniformly distribute itself over weeks or months," said Espenak, who also did not participate in the research. Espenak witnessed a modern dimming of the moon during a total lunar eclipse in 1992. That event was also probably due to a volcano, he said. "It was here in Maryland, but the volcano was Mount Pinatubo in the Philippines the year before." Michael Baillie, a paleoecologist at Queen's University Belfast in the U.K., said Pang's claim is "very interesting and indeed plausible," but he questioned the scientific usefulness of using lunar eclipses to pinpoint historic volcanic eruptions. Pang is "almost intimating that we should be able to look at very black eclipses and assess that volcanoes have gone off," Baillie said. "But it's always going to be a patchy thing. If someone didn't see an eclipse, is that because it was obscured [by volcanic smog] or because it was cloudy that night?" http://news.yahoo.com/s/livescience/20090415/sc_livescience/strange1761atmosphericphenomenonexplained Strange 1761 Atmospheric Phenomenon Explained Harvey Leifert Natural History Magazine LiveScience.com harvey Leifert natural History Magazine livescience.com 2 hrs 47 mins ago Unusual atmospheric phenomena were recorded worldwide in 1761, unexplained at the time. Now independent astronomer Kevin D. Pang of La Cañada Flintridge, California, says he's figured out the cause - and he credits Benjamin Franklin with a conceptual assist. While serving as American ambassador in Paris, Franklin first made the connection between a "dry fog" that had obscured the Sun for months in 1784, the extremely cold weather in Europe and North America that same year, and the 1783 eruption of Iceland's Laki volcano. The fog was, we now know, droplets of sulfuric acid, called vog (volcanic fog). Pang learned that on May 18, 1761, astronomers could not see the fully eclipsed Moon, which usually glows faintly with refracted Earthlight. Suspecting vog, he checked other sources, which corroborated his hunch. Chinese history books and weather logs documented bitter cold over subtropical parts of the country the following winter. In the Sierra Nevada of the United States, tree-ring studies of bristlecone pines revealed frost damage and stunted growth in 1761. Ice cores from Greenland and Antarctica showed abnormally high concentrations of sulfuric acid that year and the next. A massive volcanic eruption at low latitude in late 1760 or early 1761 must have caused the worldwide cooling, Pang asserts. A likely culprit is Indonesia's Makian volcano, which blew its top in 1761, he says, but some other, unidentified eruption could be to blame. The research was presented at the American Astronomical Society meeting in January. On Apr 10, 2:46 pm, dsw_s <[email protected]> wrote: > The atmosphere is mostly troposphere, by mass. The troposphere is > also the grimiest part of the atmosphere, even relative to mass. The > contribution of stratospheric aerosols to interfering with > astronomical observation seems likely to be negligible -- as it > apparently was in the case of Pinatubo. > > But if not, tough luck, obviously. It's not going to be done unless > the trillion-dollar considerations dictate so, and all earth-based > astronomy could be replaced with space-based observations for a tithe > of the amounts at stake in climate change. > > On Apr 9, 7:40 pm, Alan Robock <[email protected]> wrote: > > > > > Dear Dan, > > > Yes, again this shows how astronomical observations can characterize > > aerosols, but it does not say that observations of faint objects will > > not be severely impacted by a permanent aerosol cloud. > > > You will note that this article also mentions the issue of the growth of > > the size of the Pinatubo aerosols over time. With a permanent cloud, > > additional SO2 injections may make existing particles larger rather than > > produce more particles of a size more effective at scattering solar > > radiation. This means that while we might have a handle on putting SO2 > > into the stratosphere, we still do not know how to make aerosols of the > > most effective size. This is an area of ongoing research by our group, > > led by Rich Turco. > > > Alan > > > Alan Robock, Professor II > > Director, Meteorology Undergraduate Program > > Associate Director, Center for Environmental Prediction > > Department of Environmental Sciences Phone: +1-732-932-9800 x6222 > > Rutgers University Fax: +1-732-932-8644 > > 14 College Farm Road E-mail: [email protected] > > New Brunswick, NJ 08901-8551 USA http://envsci.rutgers.edu/~robock > > > On Thu, 9 Apr 2009, DW wrote: > > > > This is apparently (as one might imagine) a fairly well explored > > > topic. One good reference which talks about Pinatubo as well as > > > Saharan dust events which affect observatories in the Canaries, and > > > even marine aerosols which result from sea spray is at (graphs did not > > > copy): > > > >http://www.saao.ac.za/~wgssa/as5/winkler.html > > > > An excerpt > > > > Aerosols and their effect on optical radiation > > > Aerosols may be defined as particles suspended in the atmosphere, and > > > the term is generally used to denote units larger than molecules. > > > Aerosol diameters typically range from about 10-4 to 100 m. > > > > Apart from their use as tracers in atmospheric circulation studies, > > > aerosols have more recently been recognised as important contributors > > > to weather phenomena and climate change. This is partly due to their > > > role as nuclei on which water droplets can grow, and also partly > > > because of their effect on the global radiation balance. > > > > Three processes determine the concentration and particle size > > > distribution of an aerosol ensemble: > > > > * The injection of aerosol into the atmosphere from ground level > > > through a variety of mechanisms described below; > > > * The growth of particles through the coalescing of smaller > > > particles; > > > * The deposition of airborne particles on the ground through > > > precipitation. > > > > The composition, shape, size and refractive properties of aerosol > > > particles are often determined by their mode of generation. It is > > > convenient to categorise aerosols accordingly: > > > > (a) Volcanic ash: Propelled skywards in the course of volcanic > > > eruptions, these sulphur-rich aerosols are occasionally lifted as high > > > as the stratosphere, where they have typical lifetimes of several > > > years, much longer than their tropospheric counterparts. Recent such > > > events include the eruptions of Agung (1963), El Chichon (1982) and > > > Pinatubo (1991). Characteristically, the aerosols get dissipated > > > throughout the stratosphere within a few months. The particles then > > > coalesce until they become too large to be supported and fall to the > > > ground. > > > (b) Pyrogenic aerosols: These are in essence the smoke from > > > forest and savannah fires. High concentrations of these aerosols are > > > usually recorded over sub-Saharan Africa during and just after the dry > > > season. > > > (c) Windborn sand and dust: Such aerosols are usually generated > > > in arid regions and tend to be rich in silicates. Significant > > > generation of dust also occurs in wetter areas following the ploughing > > > season or even through traffic on dirt roads. > > > (d) Maritime aerosols: These result from the uplifting of sea > > > spray through wind. These particles characteristically have high > > > abundances of sodium chloride. Though prevalent over the oceans, these > > > aerosols can be transported far inland. > > > (e) Biogenic emissions: Biogenic processes are more commonly > > > responsible for trace gas generation, which may contribute to the > > > formation of aerosols. They also produce airborne microscopic > > > organisms such as pollen. > > > (f) Industrial and other anthropogenic emissions: Aerosols > > > originating in this fashion include the emissions from coal burning > > > power stations, dust generated by opencast mining operations and > > > domestic wood and coal burning. > > > > Aerosols contribute to the attenuation of incoming starlight, which in > > > turn implies that their concentration may be estimated by measuring > > > the degree of extinction in the atmosphere. Extinction in the > > > wavelength range 350-800 nm may be due to Rayleigh scattering, > > > stratospheric ozone or aerosols, > > > k = k ,Rayleigh + k ,ozone + k ,aer > > > > where k is the standard astronomical extinction coefficient, defined > > > as > > > > k = 2.5 (log Intensity above atmosphere > > > -log Intensityon ground) > > > for a star at the zenith. > > > > The Rayleigh extinction is almost constant at any particular location > > > and altitude, while ozone only affects specific parts of the spectrum. > > > Outside these spectral regions any variations in the extinction are > > > thus due to changes in the aerosol concentration or characteristics. > > > > Extinction by aerosols is largely the result of Mie scattering, and > > > its dependence on wavelength may be described by the following > > > relation [4]: > > > log k ,aer - log . > > > > The coefficient ranges from 0 for very large particles to 4 for very > > > small particles. > > > Examples of cases where astronomical extinction > > > measurements facilitated atmospheric research in Africa > > > Properties of Saharan dust and its transportation to the Canary > > > Islands > > > > Saharan dust is occasionally transported as far as the Canary Islands > > > in the northern hemisphere summer months. It manifests itself as an > > > almost fog-like haze at the various astronomical sites on the > > > archipelago, such as the Roque de los Muchachos observatory on La > > > Palma. Through the measurement of the extinction during such events it > > > has been possible to not only monitor the passage and density of the > > > dust clouds, but also to determine the colour dependence of the > > > aerosol opacity (and hence particle size distribution) of Saharan > > > dust. Stickland et al (1987) found that the aerosol opacity at La > > > Palma is independent of wavelength to a good approximation[9]. This > > > confirmed the theoretical work of several authors[10], who showed that > > > the refractive properties of typical Saharan dust grains are expected > > > to be colour-neutral. Kidger[5] and Andrews & Williams[1] found a > > > small wavelength dependence on the extinction coefficients in the > > > infrared and optical regimes respectively, which is likely to be the > > > result of mixing of the type of grains modelled by Whittet, Bode & > > > Murdin with smaller particles[10]. > > > > The Pinatubo ash-cloud and its evolution > > > > The volcanic eruption of Mount Pinatubo in the Philippines in 1991 > > > injected huge quantities of volcanic ash into the stratosphere. Within > > > a couple of months these volcanic aerosols became distributed around > > > the globe. The development of the volcanic ash clouds over the South > > > African Astronomical Observatory in Sutherland can be traced by > > > plotting the measured extinction coefficients[6]. The study showed > > > that enhanced aerosol concentrations persisted for several years. It > > > also illustrated the patchy nature of the stratospheric ash clouds. > > > > Figure 1 shows the volcanic ash extinction coefficients calculated by > > > Kilkenny as a function of wavelength for two high-extinction events > > > following the eruption. These were obtained by subtracting the > > > Sutherland "normal" (i.e. pre-Pinatubo clear day) values from the > > > measured extinction coefficients. Note that the value of a i.e. the > > > slope of the graph) is much smaller on 26 September 1992 than on 10 > > > September 1991. This illustrates the change in the particle size > > > distribution in the intervening period - the smaller particles that > > > had dominated the distribution soon after the eruption had coalesced > > > into bigger units a year later. > > > > The brown haze in Cape Town > > > > Where telescopes equipped with photometers exist in urban areas, the > > > extinction measurements may be utilised to study pollutants. The city > > > with the largest available extinction value database in Africa is > > > probably Cape Town, as a result of the extensive standard star work by > > > Cousins at the South African Astronomical Observatory headquarters. > > > Cousins has described extinction coefficient behaviour as a function > > > of meteorological conditions[2]. He has been able to detect maritime > > > aerosols and the "brown haze", which is caused by domestic fires in > > > the Cape Flats. Future measurements of the extinction at the site will- > > > Hide quoted text - > > - Show quoted text -... > > read more » --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "geoengineering" group. 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