Tag Archives: aerosols

AGU2011: Dust Storm Triggered Phytoplankton Blooms in the South China Sea

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Between March 19th and 21st, an unusually strong storm in the Gobi Desert sent a large cloud of dust and pollution toward the Pacific Ocean.  Most of it went east toward Japan, but plumes of particles also made their way south toward Taiwan and the South China Sea. NASA satellites orbiting overhead observed the dust moving south, and for a period of eight hours on March 21 a mobile laboratory managed by scientists from NASA’s Goddard Space Flight Center on the Dongsha Islands observed the dust storm and recorded a dramatic spike (top graph below) in particle mass, as well as counts.

Months later, an analysis conducted by scientists atNASA’s Goddard Space Flight Center including Si-Chee Tsay andSheng-Hsiang Wang showed that over the next ten days following thearrival of the dust, satellite instruments on Aqua and SeaWiFS detecteda marked jumped in phytoplankton abundance (shown by the green circle in the chart above). That’s notable because the nutrient-limited ocean water in the area isn’t known to support much life.


The key ingredient that triggered the bloom, the scientists believe, was iron and phosphorus within the dust particles. Many types of phytoplankton require trace amounts of key nutrients to thrive and blooms can’t easily occur when levels are low, as they are in the northern South China Sea. Satellites have observed dust plumes triggering phytoplankton blooms in the past, but this is the first time the phenomenon has been observed in the South China Sea, an area where heavy dust deposition is relatively infrequent.

Text by Adam Voiland. Top and middles figures courtesy of Sheng-Hsiang Wang. Phytoplankton illustration and Gulf of Tonkin phytoplankton bloom originally published by NASA’s Earth Observatory. The phytoplankton bloom shown is from 2008 and not the bloom discussed in this blog post. Si-Chee Tsay presented a poster on this topic at the American Geophysical fall meeting on Dec. 6, 2011.

AGU2011: What Would Pristine Air Mean for the Climate?

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Imagine that all the aerosols (the miniscule particles of pollution, dust, sea salt, and many other things) floating around in the air over the United States suddenly disappeared. What would their absence mean for the climate? Loretta Mickley, a climatologist and aerosol expert from Harvard University, has tackled just that question by running a series of simulations with a high-resolution computer model developed at NASA’s Goddard Institute for Space Studies.

Her conclusion: the elimination of the particles would increase ground temperatures across the eastern United States, cause more springtime rain to fall, and drive an uptick in heat waves. All of this would be driven by something scientists call the “direct effect” of aerosols – the particles’ ability to warm or cool the atmosphere by either absorbing or scattering incoming energy from the sun. (In this case, the model didn’t account for the “indirect effects” of aerosols – how the particles affect clouds, a detail that can have an impact on how they affect the climate as well).

Atmospheric Environment published a study that details the experiments in July of 2011. Here’s how Mickley summarized the findings:

We find that removing U.S. aerosol significantly enhances the warming from greenhouse gases in a spatial pattern that strongly correlates with that of the aerosol. Warming is nearly negligible outside the United States, but annual mean surface temperatures increase by 0.4-0.6 K in the eastern United States. Temperatures during summer heat waves in the Northeast rise by as much as 1-2 K due to aerosol removal, driven in part by positive feedbacks involving soil moisture and low cloud cover. Reducing U.S. aerosol sources to achieve air quality objectives could thus have significant unintended regional warming consequences.

There’s good reason to consider how falling levels of aerosols will affect the climate. In the United States, several kinds of aerosol particles have actually seen their numbers fall steadily as regulations have gone into place to clean up the air for the sake of public health. Emissions of sulfur dioxide, for example, a gas produced by coal power plants that generates reflective sulfate particles has fallen by 83 percent since 1980.

Mickley presented her poster on Monday, Dec. 5, 2011. Text by Adam Voiland. Aerosols panel (from left to right:ash, pollen, sea salt, soot) published originally by NASA’s Earth Observatory. Lowerfigure courtesy of Loretta Mickley. 

What on Earth is That? #1

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(Please post your guesses and your name in the comments, and we’ll give the answer next week…)

Here at What on Earth, we’re constantly stumbling across interesting photos, videos, and audio clips from NASA’s exploration of our planet (be it from space, the field, or the lab.) Whether it’s a satellite montage captured from thousands of miles up, the roar of our B-200 research aircraft, or a microscopic view of a cloud droplet, there’s literally always something strange and wonderful passing across our desks.

To have a little fun (and spare all that fascinating stuff from the circular file), we’re going to post snippets of it every now and then, usually on Fridays. What we post will change, but the question to you all will always be the same: “What on Earth is that?

Our only hints:

  • Our picks will always be related to Earth science in one way or another, and…
  •  It will have some relation to what we do at NASA.

We’ll give you a week to post your guesses, and we’ll post the answer the following Friday.

***********************

Updated 7/16/2010

So, what on Earth was that? We received a barrage of thoughtful—and creative—responses that ranged from pollen, to DNA, to carbon nanodiamonds embedded in Antarctica ice. Ant-related answers were surprisingly common. (Nope, it isn’t an ant eating salt, spitting up acid, or laying eggs.) It is, drum roll please, a microscopic view of soot from wildfire smoke in Africa. Congratulations to posters MicroMacro (comment 121), Arbeiterkind (comment 124), Mike (comment 125), Michael & Marion Dreyer (comment 130), and Rosemary Millham (comment 141), who were correct or on the right track. A more complete description of the aerosols from this particular fire, including the image above, was published in the Journal of Geophysical Research (account required).

Here are a few more details to impress your pals: Bits of soot (a type of aerosol particle) tend to clump together into the chain-like structures visible above. Wildfires, diesel trucks, factories—anything that partially burns the carbon locked away in fossil fuels and organic materials can produce soot and release it into the air. Soot makes doctors nervous as it can cause health problems when it lodges in our lungs and works its way into our bloodstream. And climatologists are wary of the particles as well because they absorb the sun’s energy and hasten global warming and climate change by heating the atmosphere directly or coating the surface of glaciers. In recent years, black carbon is an active area of research in climate science, and it’s a target of study for a number of NASA’s Earth science projects, including the forthcoming Glory satellite


Image(left) from Peter Buseck, Arizona State University. Image(right) from Jim Ross, NASADryden Flight Research Center.

–Adam Voiland, NASA’s Earth Science News Team

Black Carbon's Day on the Hill

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Drew Shindell (left), Veerabhadran Ramanathan, and Tami Bond speak with Representative Edward Markey after the three scientists testified. Credit: NASA/Voiland

Leading aerosol scientists, including NASA’s Drew Shindell, explained the intricacies of a sooty component of smoke called black carbon to members of the Select Committee on Energy Independence and Global Warming during a hearing on Capitol Hill last month.

Their message: controlling black carbon emissions could be a win-win for both human health and the environment.

Not only can partially combusted particles of carbon lodge in the human respiratory system and cause disease, the panelists explained, they also contribute to climate change by warming the atmosphere and changing the way Earth reflects sunlight back into space.

Three lawmakers—Representative Edward Markey (D-Mass.), Representative Jay Inslee (D-Wash.), and Representative Emanuel Cleaver (D-Mo.)—questioned the scientists.

Tami Bond, a black carbon specialist from the University of Illinois, began the hearing by offering a summary of black carbon’s potent short-term climate impacts. She noted, for example, that:

•     One ounce of black carbon absorbs as much sunlight as would fall on an entire tennis court.

•     A pound of black carbon absorbs 650 times as much energy during its one-to-two week lifetime as one pound of carbon dioxide gas would absorb during 100 years.

•     An old diesel truck driving 20 miles would emit about one-third of an ounce of black carbon and 70 pounds of carbon dioxide. The carbon dioxide from that truck would have five times the warming power of the black carbon, but it would spread out over 100 years. The truck’s more potent black carbon impact would have an effect in the span of a few weeks.

Drew Shindell, a climate modeler from NASA’s Goddard Institute for Space Studies (GISS) in New York City, provided more details about where black carbon comes from and how much impact it has on Earth’s climate.

As seen in this scanning electron microscope still image, small chain-like aggregates of soot cling to larger sulfate aerosol particles.  Credit: Arizona State University/Peter Buseck

Diesel vehicles, agricultural burning and wildfires, and residential cooking stoves are key sources of black carbon. However, combustion that occurs at higher temperatures — such as the type that takes place in power plants — does not produce much of the substance.

Shindell said climate models from NASA GISS and elsewhere show that 15 to 55 percent of global warming is due to black carbon. The wide range is primarily because of incomplete knowledge about how black carbon and clouds interact.

One of the more interesting questions came from Rep. Inslee, who asked the scientists whether black carbon’s impact is due to the fact that it absorbs sunlight and warms the atmosphere, or because it covers snow and ice with dark soot, which reduces Earth’s albedo and makes the planet less reflective.

Veerabhadran Ramanathan , a professor at the Scripps Institution of Oceanography, responded: “The albedo effect contributes about 10 percent of the total black carbon effect. But if you look in the Arctic or in the alpine glaciers, then the darkening effect may be the dominant effect.”

Shindell added that the scientific understanding of black carbon’s impact varies by region. “In places like the Himalayas, the results are somewhat ambiguous,” said Shindell. Over Himalayan glaciers, large amounts of dust — which also absorb radiation — and other pollutants in the air may dampen the effect. “In the Arctic, which tends to be very far from dust sources, the snow is very clean, so the effect is extremely large.” Increasing levels of black carbon combined with decreasing levels of sulfates may account for more than half of the accelerated warming in the last few decades, Shindell’s research suggests. 

Inslee also expressed frustration about the lack of understanding of science and climate change among his fellow lawmakers.”If I was scientist and I knew what was going on out there, I’d be in somebody’s grill, telling them we need action,” he said. “And yet you just don’t see that from the scientific community….Why doesn’t that happen? Should it happen?”

 Drew Shindell testifies as Veerabhadran Ramanathan looks on.
Credit: Committee on Energy Independence and Global Warming

The scientific method and the culture of scientists, Bond replied, makes it very difficult for scientists to lobby lawmakers or advocate a policy position and remain credible. “This is a difficult question and has to do with the nature of scientists and how they approach science,” she said. “If you have an action outcome, one is almost afraid that you’ll affect the science because you’re supposed to look at it dispassionately. How we conduct our business, 99.9 percent of the time, we must step back from what we want the outcome to be. We’re not allowed to want an outcome.”

Adam Voiland, NASA’s Earth Science News Team

Has Sulfate Pollution from Asia Masked a Decade of Warming?

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Warming overwhelms the cooling effect of sulfates by about 2045 even if China and India continue to grow rapidly and delay pollution controls. Radiative forcing is a measure of influence that a climate factor has in altering the balance of Earth’s incoming and outgoing energy. Positive forcing tends to warm the surface, whereas negative forcing tends to cool it. A more detailed definition of radiative forcing is available here.


Science News
, the Washington Post, and Climate Central have all written about a new study, published this week by the Proceedings of the National Academy of Sciences, that suggests a decade-long lull in global warming, which has caused some commentators to question the scientific underpinnings of climate change, stems from large increases in sulfur dioxide emissions in Asia.
Between 2003 and 2007, global sulfur emissions have gone up by 26 percent. In the same period, Chinese sulfur dioxide emissions have doubled.

While burning coal is best known for emitting carbondioxide, a greenhouse gas, the sulfur dioxide the same process generates leads to the formation ofreflective sulfate particles that have the opposite effect on the climate. Releasing sulfates might seem, then, like a reasonable way to counteract global warming, but there’s a catch. Sulfates also cause acid rain and health problems. The World Health Organization estimates that air pollution, including sulfates, causes as many as 2 million premature deaths each year.

The combination of the contradictory coal burning impacts leaves policy makers in a bind: clean up the sulfates and accelerate the pace of global warming or allow sulfates to build up and people will die directly of air pollution. Reducing sulfate is relatively cheap and the health benefits don’t take long to realize, so most industrialized countries end up adopting pollution controls that reduce sulfate emissions. The United States, as well as industrialized European countries and Japan, cut sulfate emissions significantly in the 1970s and 1980s, and there’s little reason to believe that China will follow a different path.

In fact, the Chinese government is already in the midst of an effort to reduce sulfate pollution. A team of researchers, including NASA Goddard’s Mian Chin, used satellite imagery and other data about emissions to estimate sulfate emission trends in China in a 2010 paper published in Atmospheric Chemistry and Physics They found that sulfur dioxide emissions increased dramatically between 2000 and 2005, particularly in Northern China. But they also found that sulfur dioxide emissions in China, which I wrote about in an earlier post, began to decline in 2006 after the government began installing large numbers of flue-gas desulfurization (FGD) devices in coal power plants.


Since 2006, flue-gas desulfurization (FGD) devices in coal power plants have caused sulfur dioxide emissions from power plants in China to begin declining.


What does it all mean for the climate? In 2010, Drew Shindell and Greg Faluvegi of NASA’s Goddard Institute for Space Studies simulated a number of emission scenarios for China and India to find out. They looked, for example, at how the climate would respond if the Chinese and Indian economies continue to expand rapidly or only grow at a moderate pace. Likewise, they modeled what would happen if China and India instituted sulfate pollution controls immediately or waited a number of decades before doing so.

In their paper, Shindell and Faluvegi present their results, shown in the line graph at the beginning of this post, as a suite of projections. The strength of warming predicted depends on whether the economies continue to grow quickly and whether sulfate pollution slows, but there is one common – and concerning – similarity between all of the projections: regardless of how fast China or India grow or put off sulfate pollution controls, it’s not enough to mask warming from carbon dioxide in the long term, particularly in the mid-latitudes of the Northern Hemisphere where the climate impacts of sulfates from Asia are the most noticeable.

Here’s how the GISS authors explained the situation:

We find that while the near-term effect of air quality pollutants is to mask warming by CO2, leading to a net overall near-term cooling effect, this does not imply that warming will not eventually take place. Worldwide application of pollution control technology in use in Western developed countries and Japan along with continued CO2 emissions would lead to strong positive forcing in the long term irrespective of whether the pollution controls are applied immediately or several decades from now. Continued emissions at current (year 2000) pollutant and CO2 levels may have little near-term effect on climate, but the climate ‘debt’ from CO2 forcing will continue to mount. Once pollution controls are put into place as society demands cleaner air it will rapidly come due, leading to a “double warming” effect as simultaneous reductions in sulfate and increases in CO2 combine to accelerate global warming. The only way to avoid this would be not to impose pollution controls and to perpetually increase sulfur-dioxide emissions, which would lead to a staggering cost in human health and is clearly unsustainable.

Text by Adam Voiland. Imagery first published in Atmospheric Chemistry and Physics.  

Smog Blog Outtakes

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On Earth Day, we published an interview about the “smog blog” created by Ray Hoff of the University of Maryland – Baltimore County. Today, we follow up by sharing this video, which has some striking shots of laser pulses from the instrument that Hoff’s atmospheric LIDAR group uses to take air quality measurements near Baltimore.

 

Plus, here are some outtakes from Hoff that did not fit into the original interview:

On the importance of satellites…
“We spend quite a bit of time trying to use satellite measurements as a surrogate for what we see on the ground because the Environmental Protection Agency can’t be everywhere. EPA has a thousand monitors in the United States, but those monitors are largely in urban areas, and they can be spaced quite far apart. There are, for example, no EPA samplers in Wyoming. NASA satellites can look everywhere.”

On why satellite measurements of aerosols are less accurate in the western U.S…
“In the West, the correlation between what happens on the ground is worse for two reasons. The land surface out in the western United States does not have as much vegetation, so it’s brighter and more difficult for NASA satellites to see the aerosols from space. The other thing is that there are a lot of fires in the West, which make it challenging to distinguish between aerosol types.”

On the challenges facing air quality researchers…
“One of the things they’d really like to have is better measurements of ozone at the ground level. Much of the ozone we have on the planet is in the stratosphere, about 20 kilometers or 15 miles up, and it’s hard to see through the ozone layer, since it’s so thick. We have to combine models with measurements from the ground and NASA airborne platforms, but the difficulty of seeing through this layer to surface ozone is kind of the holy grail of tropospheric air quality research right now.”

On geoengineering the climate with sulfate aerosols…
“A Nobel Prize winner has suggested putting more pollutants in the atmosphere in order to keep the planet cool. I actually think that’s a rather poor experiment for us to be trying with so little knowledge of how the atmosphere works. Humans have a pretty bad record of trying to “fix the planet.”

–Adam Voiland, NASA’s Earth Science News Team

Has the Arctic Gotten Sootier Over the Last Century?

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Black carbon, the sooty particle that gives smoke from diesel engines and cooking fires a dark appearance, took center stage this week when Secretary of State Hillary Clinton attended a high-profile meeting of the Arctic Council in Nuuk, the capital of Greenland.

Black carbon has attracted the attention of climatologists and policy makers alike because its complex structure makes it so good at absorbing sunlight. To make this point, University of Illinois-based Tami Bond, one of the nation’s leading black carbon specialists, noted during a Congressional hearing last year that one ounce of black carbon dispersed in the atmosphere would block the amount of sunlight that would fall on a tennis court. The absorbed energy then gets transferred to the atmosphere as heat and contributes to global warming.

The Arctic Council meeting coincided with the release of two scientific reports focused on the cryosphere. The first, authored by the scientific arm of the Arctic Council, argued that the United Nations underestimated the rate at which the Arctic is losing sea ice and concluded the Arctic Ocean could be ice-free within the next thirty to forty years. The second makes the case that it’s possible to cut Arctic ice loss significantly by curbing black carbon emissions.

I’ve written before about the possibility that reducing black carbon emissions could save Arctic Sea ice. Recent modeling, conducted by Stanford’s Mark Jacobson and funded in-part by NASA, suggests that eliminating soot emissions from fossil fuel and biofuel burning over the next fifteen years could reduce Arctic warming by up to 1.7 °C (3 °F). (Net warming in the Arctic, in comparison, has been about 2.5 °C (4.5 °F) over the last century.

Future emissions aside, what has actually been happening with black carbon deposition trends in the Arctic? Have black carbon emissions, like carbon dioxide emissions, been going steadily up in recent decades?

A recent report, authored by climatologists at NASA’s Goddard Institute for Space Studies, offers a nice overview that I’ve excerpted below. It may come as a surprise that the amount of black carbon winds are dumping on Arctic ice has actually fallen over the last few decades. From the GISS study:

Recently there has been concern about impacts of black carbon on snow albedo in the Arctic and whether that has contributed to melting of Arctic sea-ice and snow. Some studies have focused on changes in Arctic BC since the 1980s when measurements were first made. Sharma et al. (2004) found a 60% decrease in atmospheric black carbon at Alert between 1989 and 2002. Recent Arctic snow measurements (e.g. Grenfell et al., 2009; Hegg et al., 2009) found BC concentrations to be about 5-15 ng g−1 in Canada, Alaska and the Arctic Ocean, about a factor of two lower than measured in the 1980s (e.g. Clarke and Noone, 1985). Contemporary Russian measurements are larger than the western Arctic, ranging from about 15-80 ng g−1, while BC concentrations in the Barants and Kara seas were measured at about 15-25 ng g−1 (Grenfell et al., 2009; Hegg et al., 2009). The Greenland ice sheet has relatively very low BC levels, about 2-3 ng g−1, similar to the measurements in the 1980s (Grenfell et al., 2009).

Bond showed some particularly helpful graphs during her testimony last year that give long-term emission trends. According to Bond’s estimates, black carbon emissions peaked around the turn of the century when dirty cooking stoves were common.

She also has showed a good graph that shows the sectors that produce the most black carbon.

Text by Adam Voiland. Image of Pitufkin Glacier in Greenland from NASA’s IceBridge Mission. Graphs from Tami Bond. 

A Moment for Glory

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NASA held a press conference about its soon-to-launch Glory satellite on January 20 in Washington, DC. The  mission will advance understanding of the energy budget and climate change by taking critical measurements of aerosols and total solar irradiance.

Want to learn more about Glory? Read an overview of the mission, view one of these two image galleries, brush up on aerosol science, take a look at this Q & A (pdf), follow along on Twitter, or browse the mission websites. Also, see what Nature, Discovery, and SpaceFlight Now have to say about Glory.

–Adam Voiland, NASA’s Earth Science News Team

Is Coagulation Geoengineering's Achilles' Heel?

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Jason English, a graduate student at the University of Colorado at Boulder and a participant in NASA’s Graduate School Researchers Program, chats with us about some of his recent research into geoengineering.

WoE: Do you find there is a taboo of sorts against studying geoengineering among Earth scientists? It’s fairly unusual to see the topic come up at conferences, so your poster caught our eye.

English: There is more acceptance of studying it in just the last couple of years. I think scientists are facing the reality that countries aren’t doing much to slow the emissions of greenhouse gases. Eventually, we may have to choose between the risks and consequences of climate change and the risks and consequences of climate engineering. The only way to make an educated decision about that is to study it.

WoE: What type of geoengineering are you focusing on?

English: For my PhD, I have been looking at stratospheric aerosols.

WoE: Hold up. What are stratospheric aerosols?

English: They’re the tiny particles that are aloft in the atmosphere about 20 kilometers above the surface of the Earth. One of the leading geoengineering ideas is to inject aerosols into the stratosphere. I decided, after getting help and input from colleagues such as Michael Mills and Brian Toon, to set up a computer model that would analyze exactly how something like that would work.

WoE: And what do stratospheric aerosols have to do with climate?

English: People have suggested we could use a type of a particle for geoengineering that is actually composed of tiny droplets of sulfuric acid. Those are called sulfates. Sulfates reflect sunlight. If you have a layer of these particles up in the stratosphere they reflect part of the incoming solar radiation from the sun back to space. Overall, they have a cooling effect.


WoE: And sulfates can make it all the way up to the stratosphere?

English: Yes, some of the stronger volcanic eruptions can send particles into the stratosphere. They take a couple of years to settle back down to the surface. Very tiny amounts from power plants and other sources can also make it up that far.

WoE: I get that you modeled what might happen if humans decided to inject sulfates into the stratosphere, but what was the precise question you set out to answer?

English: There have been a few other scientists who have looked at geoengineering using stratospheric aerosols, but they didn’t simulate all the processes that can affect the particles. Recently, a team led by Patricia Heckendorn, a researcher based in Zurich, simulated all of these processes in a 2D model and found that the effectiveness of sulfate geoengineering diminished as more sulfate was added. I wanted to use a 3D model that looked at all of the processes, and I wanted to compare our results to Heckendorn’s.

WoE: What processes did you include that others didn’t?


English: For example, our model simulates coagulation, the process by which multiple particles can combine to become one. We also included nucleation – that’s when tiny gas molecules condense on each other to form liquid droplets. Also condensational growth. If you watch, say, water drops grow bigger and bigger on a piece of grass on a foggy morning you’re looking at condensational growth.

WoE: What did you find when you included all of that in your model?

English: What we found was that effective geoengineering required injecting larger masses of sulfuric acid than some have hoped because the particles coagulate and get much bigger than thought. Larger particles fall out of the stratosphere faster to the surface, so they’re not as effective at reflecting light. This matched Heckendorn’s results.

WoE: How much less effective?

English: It depends on how much sulfate we add. The more we add the less effective they become.

WoE: That’s the opposite of what people probably think…

English: It still gets more effective as you add more, but it has a diminishing return. We haven’t done a detailed assessment yet, but the group led by Heckendorn did, and they had a similar result. They found that you would need to inject more than 10 million metric tons of sulfur into the stratosphere per year if you wanted to offset the current forcing from greenhouse gases. People used to think it could be done with about 3 million metric tons.

WoE: Ten million metric tons sure sounds like a lot.

English: It is. Mount Pinatubo released about 10 million metric tons, but that was a one-time shot. Basically, we would need one or two Mount Pinatubo’s every single year.

WoE: Where do we go from here?

English: These results were surprising. If geoengineering is going to work, I think we’re realizing that scientists will need to look at new and creative ways to add particles to the stratosphere in such a way that they don’t grow too big and fall out too quickly.

Image Information: Astronauts took this image of Mount Etna erupting in 2002. Credit: NASA/JSC/Gateway to Astronaut Photography. The lower image is courtesy of Jason English.

–Adam Voiland, NASA’s Earth Science News Team

Searching for Rainbows

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Image courtesy of Earth Science Picture of the Day. Credit: David Lien, Planetary Science Institute

Ubiquitous airborne particles called aerosols, which can have a big impact on the energy budget, are one the most poorly understood factors that influence our climate. Could searching for rainbows help scientists pinpoint the impact of the perplexing particles? Brain Cairns, the instrument scientist for the Aerosol Polarimetery Sensor (APS) on NASA’s Glory Mission, explains:

“The way that we diagnose whether we have small aerosol particles, big aerosols particles, non-spherical particles, ice particles, cloud droplets is primarily using polarization.

This is the most obvious and visually enticing example of polarization. On the left, is a picture that shows a rainbow. A polarizer was used, so you can actually see that rainbow. On the right, there’s no rainbow because there was no polarizer. The reflected light is so bright you simply can’t see the rainbow without a polarizer.

Why do we want to measure things like rainbows? It’s because the angular distribution and color of that light tells you exactly how big those close droplets are, and it tells you what the width of the size distribution is. This kind of information is what we use when we’re trying to diagnose how clouds form.”

–Adam Voiland, NASA’s Earth Science News Team

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