What do you do when you want to study clouds and all you have is balloons because airplanes are not very reliable and they are expensive? Like any good scientist you try to make clouds in your lab. Which is exactly what C. T. R. Wilson did in 1912.
The study of high energy particles was greatly aided in 1912 when C. T. R. Wilson, a Scottish physicist, devised the cloud chamber. The general procedure was to allow water to evaporate in an enclosed container to the point of saturation and then lower the pressure, producing a super-saturated volume of air. Then the passage of a charged particle would condense the vapor into tiny droplets, producing a visible trail marking the particle's path.Why did Wilson invent the cloud chamber? It certainly wasn't to study nuclear physics which was in its infancy at the time. It really was the case that he wanted to study clouds.
The device came to be called the Wilson cloud chamber and was used widely in the study of radioactivity. An alpha particle left a broad, straight path of definite length while an electron produced a light path with bends due to collisions. Gamma rays did not produce a visible track since they produce very few ions in air. The Wilson cloud chamber led to the discovery of recoil electrons from x-ray and gamma ray collisions, the Compton-scattered electrons, and was used to discover the first intermediate mass particle, the muon. Wilson was awarded the Nobel Prize in physics in 1927 for the development of the cloud chamber.
Inspired by sightings of the Brocken spectre while working on the summit of Ben Nevis in 1894, he began to develop expansion chambers for studying cloud formation and optical phenomena in moist air.So how did all this interest by people studying nuclear physics come about?
Very rapidly he discovered that ions could act as centres for water droplet formation in such chambers. He pursued the application of this discovery and perfected the first cloud chamber in 1911. In Wilson's original chamber the air inside the sealed device was saturated with water vapor, then a diaphragm is used to expand the air inside the chamber (adiabatic expansion). This cools the air and water vapor starts to condense. When an ionizing particle passes through the chamber, water vapor condenses on the resulting ions and the trail of the particle is visible in the vapor cloud.Fun stuff. In fact it is so much fun that improved chambers have been developed that can make the required clouds continuously so that you do not have to keep re-pumping the chamber to get the required conditions for cloud formation. Mad Physics has a nice diagram of Wilson's original design and instructions on how to build a more modern version using methanol (wood alcohol), pure ethanol (the drinking kind), or pure isopropyl alcohol (used in diluted form in rubbing alcohol)and dry ice. Cornell University also has similar instructions along with a trouble shooting guide.
OK, so men have been making clouds in chambers since 1912. Since not long after that time we have understood that high energy nuclear particles can help clouds to form.
Which leads us to the question of climate and how our sun's magnetic field can affect climate. I wrote some about that in Clouds and More Clouds. As usual with any "new" science there are sceptics and deniers (you know who you are). So let us follow this along, look at some really big cloud chambers, and see if we can shed some light instead of just generating heat.
Let us start with the experiment that triggered off the whole brouha. An experiment done under the auspices of the Danish Space Agency first reported in the summer of 2006.
An essential role for remote stars in everyday weather on Earth has been revealed by an experiment at the Danish National Space Center in Copenhagen.Well that is just one experiment you say. I suppose that is true if you don't count all the millions of cloud chamber experiments done since 1912. However, there are sceptics and deniers among us and we need evidence beyond a reasonable doubt. I'm all for that! Now there will always be a few flat earthers, however we want to satisfy the reasonable sceptics. The way to do that? Why get another team to to perform the same experiment to see if they get the same results. So will this be done? Yep. And by whom? Well atomic scietists to the rescue.
It is already well-established that when cosmic rays, which are high-speed atomic particles originating in exploded stars far away in the Milky Way, penetrate Earth's atmosphere they produce substantial amounts of ions and release free electrons.
Now, results from the Danish experiment show that the released electrons significantly promote the formation of building blocks for cloud condensation nuclei on which water vapour condenses to make clouds.
Hence, a causal mechanism by which cosmic rays can facilitate the production of clouds in Earth's atmosphere has been experimentally identified for the first time.
Geneva, 19 October 2006. A novel experiment, known as CLOUD (Cosmics Leaving OUtdoor Droplets), begins taking its first data today with a prototype detector in a particle beam at CERN, the world�s largest laboratory for particle physics. The goal of the experiment is to investigate the possible influence of galactic cosmic rays on Earth's clouds and climate. This represents the first time a high energy physics accelerator has been used for atmospheric and climate science.Data from this experiment will be out around 2010. So we have to wait a while.
The CLOUD experiment is designed to explore the microphysical interactions between cosmic rays and clouds. Cosmic rays are charged particles that bombard the Earth's atmosphere from outer space. Studies suggest that cosmic rays may influence the amount of cloud cover through the formation of new aerosols (tiny particles suspended in the air that seed cloud droplets). Clouds exert a strong influence on the Earth's energy balance, and changes of only a few per cent have an important effect on the climate. The CLOUD prototype experiment aims to investigate the effect of cosmic rays on the formation of new aerosols.
Understanding the microphysics in controlled laboratory conditions is a key to unravelling the connection between cosmic rays and clouds. CLOUD will reproduce these interactions for the first time by sending a beam of particles � the �cosmic rays� - from CERN�s Proton Synchrotron into a reaction chamber. The effect of the beam on aerosol production will be recorded and analysed.
The collaboration comprises an interdisciplinary team from 18 institutes and 9 countries in Europe, the United States and Russia. It brings together atmospheric physicists, solar physicists, and cosmic ray and particle physicists to address a key question in the understanding of clouds and climate change. "The experiment has attracted the leading aerosol, cloud and solar-terrestrial physicists from Europe; Austria, Denmark, Finland, Germany, Switzerland and the United Kingdom are especially strong in this area" says the CLOUD spokesperson, Jasper Kirkby of CERN.
In the mean time the BBC reports on some other experiments going on.
A three-week experiment to resolve the biggest riddle in climate science begins in Australia on Thursday.Just how bad is the cloud problem? I cover some of that in More Uncertainty. However, let us see what the above linked BBC report has to say:
Scientists will use radar, aeroplanes, weather balloons and a ship to study the life cycle of tropical clouds.
They are searching for details of how clouds form and carry heat high up into the atmosphere.
A better understanding of these crucial processes should lead to computer models that can predict the extent of global climate warming more accurately.
Tropical clouds carry heat and moisture from the Earth's surface high up in the atmosphere, a key process in driving heat around the globe.So even without the nuclear particle (cosmic ray) connection to cloud production there is a lot of uncertainty.
"You have these 'hot towers', tropical storm clouds acting like chimneys to carry heat to the upper atmosphere," said Peter May from the Australian Bureau of Meteorology Research Centre, co-chair of the project's organising committee.
"Also, you've got large areas of cirrus clouds which are reflecting a lot of incoming sunlight back away from the Earth; but they're also absorbing infra-red radiation coming back from below," he told the BBC News website.
"So you've got competing processes going on; and that balance depends on how big the ice crystals are and what the density is, how high they are and so on."
Existing computer models did not reflect these processes accurately, said Tom Ackerman of the University of Washington in Seattle, US, because they typically treated convection and cloud formation as separate processes.
Obviously more information is needed. One of the things we need is an understanding of how the sun affects the cosmic ray intensity on earth.
So let us look into it. First off let us look into Dr. Nir Shaviv's review of the Danish experiment.
After a long embargo, results from the Danish National Space Center (DNSC) Sky experiment were finally published in the Proceedings of the Royal Society. These results will probably we overshadowed with today's announcement of this years' physics nobel prize winner (for the COBE microwave background experiment), but they are very important nonetheless.Nir is kind enough to provide the pertinent graph, pictures of the experiment and the scientists involved, and some more discussion at the previous link.
This is the Royal Society's press release on the publication of Svensmark et al.:�Using a box of air in a Copenhagen lab, physicists trace the growth of clusters of molecules of the kind that build cloud condensation nuclei. These are specks of sulphuric acid on which cloud droplets form. High-energy particles driven through the laboratory ceiling by exploded stars far away in the Galaxy - the cosmic rays - liberate electrons in the air, which help the molecular clusters to form much faster than atmospheric scientists have predicted. That may explain the link proposed by members of the Danish team, between cosmic rays, cloudiness and climate change.�
Now what does all this have to do with the sun?
Nir again provides us with a connection
The activity of the sun manifests its self in many ways. One of them is through a variable solar wind. This flux of energetic particles and entangled magnetic field flows outwards from the sun, and impedes on a flux of more energetic particles, the cosmic rays, which come from outside the solar system. Namely, a more active sun with a stronger solar wind will attenuate the flux of cosmic rays reaching Earth. The key point in this picture is that the cosmic rays are the main physical mechanism controlling the amount of ionization in the troposphere (the bottom 10 kms or so). Thus, a more active sun will reduce the flux of cosmic rays, and with it, the amount of tropospheric ionization. As it turns out, this amount of ionization affects the formation of condensation nuclei required for the formation of clouds in clean marine environment. A more active sun will therefore inhibit the formation of cloud condensation nuclei, and the resulting low altitude marine clouds will have larger drops, which are less white and live shorter, thereby warming Earth.Ah, but Dr. Shaviv has more:
Today, there is ample evidence to support this picture (a succinct introduction can be found here). For example, it was found that independent galactic induced variations in the cosmic ray flux, which have nothing to do with solar activity do too affect climate as one should expect from such a link. There are many more examples.
So why is this link important for global warming? As previously mentioned, solar activity has been increasing over the 20th century. This can be seen in fig. 5. Thus, we expect warming from the reduced flux of cosmic rays. Moreover, since the cosmic ray flux actually had a small increase between the 1940's and 1970's (as can be seen in the ion chamber data in fig. 6), this mechanism also naturally explains the global temperature decrease which took place during the same period.Naturally you will have to visit Dr. Shaviv's site to see the figures. However, if what he says is correct then CO2 is an amplifying mechanism and not the driver. In fact if his numbers are correct solar variation amplified by the cosmic ray effect accounts for 80% of the global warming we have seen.
Using historic variations in climate and the cosmic ray flux, one can actually quantify empirically the relation between cosmic ray flux variations and global temperature change, and estimate the solar contribution to the 20th century warming. This contribution comes out to be 0.5�0.2�C out of the observed 0.6�0.2�C global warming (Shaviv, 2005).
Dr. Shaviv has a paper that originally appeared in PhysicaPlus that has more on the cosmic ray/climate connection over geological time. You can read it here along with some interesting pictures.
But wait. That is not all. Let us take another look at Dr. Svensmark's research.
For more than a decade, Henrik Svensmark of the Danish National Space Center has been pursuing an explanation for why Earth cools and warms. His findings -- published in October in the Proceedings of the Royal Society -- the mathematical, physical sciences and engineering journal of the Royal Society of London -- are now in, and they don't point to us. The sun and the stars could explain most if not all of the warming this century, and he has laboratory results to demonstrate it. Dr. Svensmark's study had its origins in 1996, when he and a colleague presented findings at a scientific conference indicating that changes in the sun's magnetic field -- quite apart from greenhouse gases -- could be related to the recent rise in global temperatures. The chairman of the United Nations Intergovernmental panel on Climate Change, the chief agency investigating global warming, then castigated them in the press, saying, "I find the move from this pair scientifically extremely naive and irresponsible." Others accused them of denouncing the greenhouse theory, something they had not done.Well that should be more than enough to keep the deniers and sceptics busy for a while.
Svensmark and his colleague had arrived at their theory after examining data that showed a surprisingly strong correlation between cosmic rays --highspeed atomic particles originating in exploded stars in the Milky Way -- and low-altitude clouds. Earth's cloud cover increased when the intensity of cosmic rays grew and decreased when the intensity declined.
Low-altitude clouds are significant because they especially shield the Earth from the sun to keep us cool. Low cloud cover can vary by 2% in five years, affecting the Earth's surface by as much as 1.2 watts per square metre during that same period. "That figure can be compared with about 1.4 watts per square metre estimated by the Intergovernmental Panel on Climate Change for the greenhouse effect of all the increase in carbon dioxide in the air since the Industrial Revolution," Dr. Svensmark explained.
The Danish scientists put together several well-established scientific phenomena to arrive at their novel 1996 theory. The sun's magnetic field deflects some of the cosmic rays that penetrate the Earth's atmosphere, and in so doing it also limits the immense amounts of ions and free electrons that the cosmic rays produce. But something had changed in the 20th century: The sun's magnetic field more than doubled in strength, deflecting an extraordinary number of rays.
A paper by Dr. Svensmark. This appears to be one of his earlier papers on the subject (no date given) and not the results published in 2006.
Another Svensmark paper [pdf] Dec. 2006
A paper by Jan Veizer [pdf] on climate over geological time.
Empirical evidence for a nonlinear effect of galactic cosmic rays on clouds [pdf]
The possible connection between ionization in the atmosphere by cosmic rays and low level clouds [pdf]
Cosmic Rays and the Evolution of Earths Climate During the Last 4.6 Billion Years
Low cloud properties influenced by cosmic rays
The Sun is More Active Now than Over the Last 8000 Years
Solar Resonant Diffusion Waves as a Driver of Terrestrial Climate Change
Galactic Cosmic Rays and Insolation are the Main Drivers of Global Climate of the Earth
Reader linearthinker has a post up on his blog about the politics behind the science with reference to the IPCC and Dr. Svensmark.
Cross Posted at Classical Values