Tag Archives: rain

Wildfires could ‘seed’ new clouds with the particles they release

‘Ice’ is not the first thing that pops into your mind when thinking of wildfires, is it? And yet, new research is pointing to a link between such fires and the teeny tiny bits of ice that form clouds.

Image credits Sippakorn Yamkasikorn.

A new study is looking at the link between wildfires and ice-containing clouds like cumulonimbus or cirrus, the main drivers of continental precipitation. According to the findings, these clouds require microparticles to start forming — which a wildfire can supply in great quantities.

Ashes to rain

Cloud formation is a complex phenomenon, one that can shift quite significantly depending on conditions such as temperature or atmospheric dynamics. The clouds you’re used to seeing, for example, start their lives around very tiny particles, known as ice-nucleating particles (INPs). These can be anything from bacteria to minerals, just as long as they’re very tiny.

And that’s why the team was interested in studying how wildfires could influence the genesis of such clouds: wildfires can generate tons and tons of small particles. Because of this, they argue that wildfires could have a very important role to play in the dynamics of clouds, at least on a local level.

In order to find out, one study analyzed the plumes of the 2018 wildfires in California (western US) from samples taken at high altitudes, where the particles it contains might directly affect cloud formation. In very broad lines, this study found that INP quantities can become up to 2 orders of magnitude higher in a wildfire smoke plume compared to normal air. However, this didn’t account for the types of particles involved. Fires can produce a wide range of particles depending on the fuel they’re burning, their location, the specific conditions this burn is taking place in, and its temperature. One useful bit of information we can glean from this study is that the INPs were dominated by organic materials.

Spherical tar balls accounted for almost 25% of INPs in certain conditions, although this seems to vary widely with the type of fuel and the type of fire involved — understanding how they factor in is still “an open question,” according to the researchers.

Wildfires are predicted to become much more common in the future due to climate change, the team explains, so understanding how they can influence clouds (and thus, precipitation patterns) will do us a lot of good in the future. So far, the papers showcase that they can lead to very high levels of INPs accumulating in the troposphere, which could in turn influence how clouds and rain behave.

At this time, however, we need more modeling and sampling studies to understand these mechanisms in detail, and how they influence the world around us.

The paper “Observations of Ice Nucleating Particles in the Free Troposphere From Western US Wildfires” has been published in the journal Journal of Geophysical Research: Atmospheres.

The 2018 eruption of Mount Kīlauea in Hawaii likely caused by rain

The 2018 eruption of Mount Kīlauea in Hawaii was likely triggered by excessive and sustained rainfall in the region, according to a new paper from the University of Miami (UM) Rosenstiel School of Marine and Atmospheric Science.

Kīlauea Erupting with lava at Hawaii Volcanoes National Park.
Image credits USGS.

Such findings have implications for volcanoes around the world, not just those in Hawaii, as they suggest local precipitation patterns could have an important role to play in the timing and frequency of eruptions.

Just add water

“We knew that changes in the water content in the Earth’s subsurface can trigger earthquakes and landslides. Now we know that it can also trigger volcanic eruptions,” said Falk Amelung, professor of geophysics at the UM Rosenstiel School and coauthor of the study.

“Under pressure from magma, wet rock breaks easier than dry rock. It is as simple as that.”

The team shows that the eruption was preceded by prolonged and at times extreme, rainfall in the months leading up to the event.

Kīlauea is an active shield volcano, one of the liveliest volcanoes in all of Hawaii. On May 3, 2018, it started spewing lava nearly two hundred feet in the air, eventually covering over 13 square miles of the well-populated east coast of Hawaii’s Big Island. The unprecedented event destroyed hundreds of homes and only ended four months later, in September, when the summit of the caldera (the volcano’s top) collapsed in on itself.

The researchers used data from ground- and satellite-based stations from NASA, the European Space Agency (ESA), and the Japanese Space Exploration Agency (JAXA), to model rainfall patterns in the area before the event and, from that, estimate the fluid pressure within the volcano over time.

This pressure is, essentially, what drives volcanoes to explode. Magma itself may be molten-hot, but it is generally quite harmless if left to its own devices. What actually pushes it out of the volcano is the buildup of fluids — gas and liquids — in the enclosed space. These fluids typically seep out of the magma as they escape the depths of the Earth, and thus encounter lower pressures. It’s the same mechanism that makes a can of soda pop if you shake it before opening.

All in all, the team explains that fluid pressure was highest just before the eruption — this wasn’t surprising. But they also calculated that it was the highest recorded pressure value in half a century at this point, which they argue helped move the magma and caused the eruption. Their hypothesis would also explain why there was no widespread uplift (from gas building up beneath the surface) at the volcano in the months prior.

“An eruption happens when the pressure in the magma chamber is high enough to break the surrounding rock and the magma travels to the surface,” said Amelung. “This pressurization causes inflation of the ground by tens of centimeters. As we did not see any significant inflation in the year prior to the eruption we started to think about alternative explanations.”

This is the first time that this mechanism has been invoked to explain deeper magmatic processes. In support of their theory, the team notes that Kīlauea’s historical eruption record shows it was almost twice as likely to erupt during the wettest parts of the year.

And, if this process is at work here, it’s likely to also take place at other volcanoes, the authors add. If such a link between rainfall and volcanism can be reliably determined, it “could go a long way towards advanced warning of associated volcanic hazards,” according to Jamie Farquharson, a postdoctoral researcher at the UM Rosenstiel School and lead author of the study.

“It has been shown that the melting of ice caps in Iceland led to changes of volcanic productivity,” said Farquharson. “As ongoing climate change is predicted to bring about changes in rainfall patterns, we expect that this may similarly influence patterns of volcanic activity.”

The paper “Extreme rainfall triggered the 2018 rift eruption at Kīlauea Volcano” has been published in the journal Nature.

Scientists find extreme exoplanet raining with iron

Rain is not necessarily synonymous with water on other planets. Astronomers working with the European Southern Observatory’s Very Large Telescope (VLT) have come across a bizarre exoplanet where it rains iron in the evening.

Artist illustration showing the night-side of WASP-76b, where it rains iron. Credit: ESO/M. Kornmesser.

The exoplanet, known as WASP-76b, is located about 6400 light-years away from Earth in the constellation Pisces. The ultra-hot gas giant orbits so close to its parent star that temperatures regularly climb above 2,400°C — but only on the planet’s day-side.

Just like the moon, WASP-76b is tidally locked, meaning it only shows one face to its parent star, since the planet takes just as long to rotate around its own axis as it does to orbit around the star. As a result, the night side is shrouded in perpetual darkness and is much cooler.

The exoplanet receives thousands of times more radiation than Earth does from the Sun, making the surface of Wasp-76b’s day side so hot it vaporizes metals like iron. Vigorous winds generated by the extreme temperature difference between the planet’s two sides carry a fraction of this iron vapor to the cooler side, where temperature decreases to 1,500°C. That’s still very hot, yet cool enough for iron vapor to condense and rain down.

“One could say that this planet gets rainy in the evening, except it rains iron,” says David Ehrenreich, a professor at the University of Geneva in Switzerland, who led the new research published in the journal Nature.

“Surprisingly, however, we do not see the iron vapor in the morning,” says Ehrenreich, adding that “it is raining iron on the night side of this extreme exoplanet.”

The discovery was made possible thanks to a new instrument equipped on ESO’s VLT in the Chilean Atacama Desert. Known as the Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations — or ESPRESSO — the instrument was originally designed to hunt for Earth-like planets around Sun-like stars. However, ESPRESSO has proven itself much more versatile than originally thought, allowing astronomers to detect a strong signature of iron vapor at the evening border that separates Wasp-76b’s two sides.

“We soon realised that the remarkable collecting power of the VLT and the extreme stability of ESPRESSO made it a prime machine to study exoplanet atmospheres,” says Pedro Figueira, ESPRESSO instrument scientist at ESO in Chile.

This crazy planet is not just some curious oddity. The insight gained by studying its atmosphere will help scientists better fine-tune and test climate and global circulation models. Ultimately, outlier planets like WASP-76 b will better our understanding of exoplanet atmospheres in general.

“What we have now is a whole new way to trace the climate of the most extreme exoplanets,” concludes Ehrenreich.

If you found an iron-raining planet weird, this exoplanet is actually not that peculiar. On Venus, it rains sulfuric acid, while on Neptune rainfall is in the form of diamonds.

Rain.

Water from thin air: a look at how rain and precipitation forms

When it rains, it pours — but why does it rain in the first place?

Rain.

Image via Pixabay.

Water is a vital part of life on Earth and, luckily for us, it always keeps moving around. There’s always a bit of it floating around in the air as vapor, for example. If enough of it builds up in the atmosphere, it falls as precipitation — most commonly as ‘rain’. It sounds simple enough, but the mechanisms that generate precipitation are actually very complex and finely-tuned. So let’s break them down and see how each part works, and how they fit together.

Water vapor and clouds

Water in puddles, rivers, lakes, or oceans evaporates constantly and builds-up in the atmosphere as vapor. However, there’s only so much water that air can hold, which we call its ‘saturation value’. This value fluctuates with changes in temperature; the warmer the air, the more water it can hold.

Air tends to be warmest near the surface of the Earth and cools down when it rises. As it cools down, its water saturation value drops progressively. At a certain point, it drops enough that the air has to shed water, at which point the vapor starts to condense. This temperature is known as the ‘dew point’. Further cooling will cause excess vapor to condense onto solid surfaces (i.e. dew), or onto condensation nuclei (this forms droplets). These condensation nuclei, or ‘aerosols‘ are tiny particles of various origins (such as dust, fog, pollen, or pollution).

The water droplets formed as air reaches its dew point clump together and scatter incoming sunlight. Our eyes perceive this as white, diffuse clouds. Air masses with little buoyancy relative to the surrounding atmosphere don’t rise very fast, and generate ‘fair wind’ clouds. Air that’s very buoyant compared to its surrounding atmosphere rises rapidly and much higher, forming thick clouds that produce heavy rains. Clouds can also form from the cooling and condensation that occurs as air flows over physical obstructions like mountain ranges.

So around this point, we have our clouds all ready to go. Let’s see how it all comes down.

Precipitation

The droplets that create clouds are really, really tiny — about one-hundredth of a millimeter in diameter. They’re so small that they can just remain suspended in the air, essentially floating around freely. However, they’re not motionless: they do move when pushed by air currents. As they do, some collide, growing larger and heavier and start a slow descent through the cloud. They collide with even more droplets on the way, which makes them grow even heavier.

Meteorologists define rain as liquid water drops that have a diameter of at least 0.5 millimeters when they reach ground level. Drops smaller than this are considered drizzle. Drizzle is generally produced by low-level clouds (Stratus clouds) in temperate areas. It’s very thin — drizzle feels like a mist — and forms when there aren’t enough rising air currents to keep small droplets within the cloud.

If the cloud is dense enough that droplets grow to over one-tenth of a millimeter in diameter, they will survive all the way to the ground despite evaporation. This forms ‘warm rain’, which in temperate zones are thin rains. In the tropics, this process leads to heavy rainfall from clouds lower than 5km above ground level.

Clouds.

Image credits Engin Akyurt.

In temperate areas, heavy rains tend to be generated by a process that involves frozen particles. Temperatures at cloud level tend to be below 0ºC, but the droplets remain liquid. However, they do feel the temperature and spend their time in a state known as ‘supercooling‘. In such a state, even a slight disturbance, such as a collision or contact with an aerosol particle causes them to freeze solid almost instantly.

Water vapor condenses faster onto solid ice particles than it does on liquid droplets, so these little bits of ice grow much faster than surrounding drops and fall sooner. They also grow more as they fall. Warmer masses of air closer to the surface melts the ice as it’s falling, and they reach the ground as rain.

Very thick clouds, however, can create hail. The process is largely similar to the one above, with the exception that the ice particles they form are so large that they can’t melt before reaching the ground. Powerful storms can also generate upward winds that yank these falling bits of ice back into the cloud and re-freeze them. The process is repeated several times as the particles fall, grow larger, and are pulled back up. Eventually, they grow too heavy for the wind to affect them any more and fall to the ground as large, layered hailstones.

How air temperature influences things

Hailstones.

Image credits Etienne Marais.

Drizzle can also be produced by thick clouds if the drops that fall out of them go through a very dry and warm layer of air and evaporate until they are less than 0.5mm in diameter. If drops pass through a layer of cold air, you get snow. If the layers of air within the cloud and those between the cloud and the ground alternate between below and above freezing, you get all kinds of precipitation.

Hail, as we’ve seen, can form when drops go through a succession of warm-cold layers. Freezing rain forms in a similar fashion. If a droplet or ice particle falls through a moderate or warm layer of air (enough to make it fully liquid) but hits a very cold layer right above the ground, it becomes supercooled — and freezes right as it hits the cold ground. This coats everything in a thin layer of ice that becomes progressively ticker as more drops fall down. Frozen rains have been known to snap tree limbs and down power lines with the weight of the ice coat.

Fun facts about rain

  • Although raindrops are depicted in the classic teardrop shape, they’re actually dome-shaped as they fall; the bottom is flat due to air resistance.
  • The USGS estimates that one inch of rain per acre is equal to roughly 27,000 gallons (102,206 liters) of water.
  • Mawsynram, a village in Meghalaya, India, receives the most annual rainfall — about 10,000 millimeters of rain per year on average; most of it falls during the monsoon season.
  • Yungay, Chile, is the driest village on Earth, by comparison — around 0.1 mm each year on average.
  • Acid rain forms when pollutants such as sulfur dioxide and nitrogen oxide (some are natural but mostly man-made) bind with water vapor in the atmosphere. The mix is acidic enough to damage organic material, but can also corrode steel and weather stone.
  • While Earth’s rains are made of water drops, other planets have much more exotic rains — boiling sulfuric acid, sideways glass rains, and diamond hailstones are just a few.

Saturn’s moon Titan has rainfall and seasons

Titan has seas, lakes, and rivers — and now, researchers have found, it also has rainfall and seasonal variation.

A false-color radar mosaic of Titan’s north polar region. Blue coloring depicts hydrocarbon seas, lakes and tributary networks filled with liquid ethane, methane and dissolved nitrogen. Image credits: NASA / JPL-Caltech / USGS.

If you’d picture a place that has an atmosphere and liquids on its surface, it probably wouldn’t be Titan. This frigid moon is only 50% larger than Earth’s moon and mostly consists of ice and rocky material. It features a young and smooth geological surface, with few volcanic or impact craters, and remarkably, it has not only an atmosphere, but also geological features dunes, rivers, lakes, seas, and even deltas. But there’s a key difference.

Unlike Earth’s seas, which consist of water, Titan’s seas consist of hydrocarbons such as methane and ethane.

Conversely, Titan features a nitrogen atmosphere and has a nitrogen cycle analogous to Earth’s carbon cycle, something which stunned astronomers when it was first discovered. The Cassini mission, which landed a probe on Titan in 2005, first revealed a surface which seemed to be shaped by fluids.

But Titan has far from shared all its secrets. Recently, astronomers have analyzed images suggesting that intense rainfall occurs on Titan, indicating the start of “summer” in the northern hemisphere. It’s something researchers were expecting for a long time, especially as rain had been previously observed in the southern hemisphere.

“The whole Titan community has been looking forward to seeing clouds and rains on Titan’s north pole, indicating the start of the northern summer, but despite what the climate models had predicted, we weren’t even seeing any clouds,” said Rajani Dhingra, a doctoral student in physics at the University of Idaho in Moscow, and lead author of the new. “People called it the curious case of missing clouds.”

New research provides evidence of rainfall on the north pole of Titan, the largest of Saturn’s moons, shown here. The rainfall would be the first indication of the start of a summer season in the moon’s northern hemisphere, according to the researchers. Credit: NASA/JPL/University of Arizona.

The image was taken in 2016, by the near-infrared instrument on the Cassini probe, which offered the bulk of what we know about Titan. The instrument spotted a reflective feature covering approximately 46,332 square miles, which did not seem to appear on any other images of Cassini. The analyses suggest that this reflective feature represents a wet surface.

“It’s like looking at a sunlit wet sidewalk,” Dhingra said.

So we have a strong confirmation that seasons are happening on Titan, which confirms the predictions astronomers made. However, this poses a new question that researchers will have to answer.

“We want our model predictions to match our observations.” Dhingra said. “Summer is happening. It was delayed, but it’s happening. We will have to figure out what caused the delay, though.”

The study was published in Geophysical Research Letters.

It Is Possible Jupiter Could Support Life, Scientists Say

Jupiter and its shrunken Great Red Spot. Credit: Wikimedia Commons.

Jupiter and its shrunken Great Red Spot. Credit: Wikimedia Commons.

A new factor has been added to the debate on whether or not living organisms could exist on Jupiter. You probably know Jupiter is a Jovian planet, a giant formed primarily out of gases. So how could alien life be able to exist in an environment where most of the phases of matter are absent? The answer is simply found in the element of water.

Within the rotating, turbulent Great Red Spot, perhaps Jupiter’s most distinguishable characteristic, are water clouds. Many of the other clouds in this enormous perpetual storm are comprised of ammonia and/or sulfur. Life theoretically cannot be sustained in water vapor alone; it thrives in liquid water. But according to some researchers, the fact alone that water exists in any form on the planet is a good first step.

The Great Red Spot is still a planetary feature which stumps much of the scientific community today. As it has been observed for the past century and a half, the Great Red Spot has been noticeably shrinking. The discovery of water clouds may lead to a deeper understanding of the planet’s past, including whether or not it might have sustained life, as well as weather-related information.

Some scientists have pondered the possibility that, due to the hydrogen and helium content in its atmosphere, Jupiter could be a diamond-producing “factory.” They have further speculated that these diamonds could enter into a liquid state and a rainfall of liquid diamonds would be in the Jovian’s weather forecast.

Likewise, the presence of water clouds means that water rain (a liquid) is not entirely impossible. Máté Ádámkovics, an astrophysicist at Clemson University in South Carolina, had this to say on the matter:

“…where there’s the potential for liquid water, the possibility of life cannot be completely ruled out. So, though it appears very unlikely, life on Jupiter is not beyond the range of our imaginations.”

Scientists are acting accordingly, researching the part which water plays in the atmosphere and other natural systems on Jupiter. They remain skeptical but eager to follow up on the new discovery. They shall also strive to find out just how much water the planet really holds.

Contrary to popular belief, drought actually leads to fewer snakebites

There are many myths and popular beliefs regarding snakes — but this one certainly isn’t true.

Image credits: Noah Loverbear.

A few years ago, Grant Lipman, an emergency medicine physician at Stanford Medicine, was jogging on the hills around campus. It was a terrible drought, but that wasn’t the highlight of his day — the highlight would be a 3-foot-long rattlesnake lying on the trail. He discussed this with his colleagues, and one of them reported a similar sighting. This got Lipman thinking. Could the drought be in any way connected to the rattlesnakes they were seeing or was it simple coincidence?

“I wondered if there are more snakebites during droughts,” said Lipman, clinical associate professor of emergency medicine at the Stanford School of Medicine, who routinely treats patients with venomous snakebites.

So he started work and worked with a team of researchers to answer the question.

Everyone sure seemed to believe that droughts exacerbate snakebites. “Deadly Snakebites Set to Skyrocket During Record-breaking Drought,” read one article in 2018 in the Daily Mail. Another, “Snakes Cross Paths with Humans in Bay Area Due to Drought,” was reported on ABCNews.com in 2015.

It seemed to make some sense. The idea was that snakes are more active during warm weather, and they also need to wander more during droughts. But the scientific information was pretty scant on the subject.

The results, funnily enough, showed that the opposite is true: during dry spells, snakebites actually go down.

Lipman and colleagues analyzed 20 years of snakebite data from every phone call made to the California Poison Control System from 1997 to 2017. In total, 5,365 snakebites were reported, from rattlesnakes. Five of them were fatal. The number of bites varied significantly from county to county, ranging from 4 to 96 per one million people.

It was actually rain that seemed to get the snakes out.

Snakebites went down by 10% following a drought but increased by 10 percent following high levels of precipitation. Researchers believe that this happens because, during the rainy season, shrubs grow more, which also favors rat populations — snakes’ favorite prey.

The study isn’t frivolous — this isn’t only about satisfying a curiosity. It can be quite important, and potentially even save lives. By knowing when snakebites are more and less likely to happen, authorities and hospitals can stockpile and transfer antivenom — which is often a scarce commodity, accordingly.

But Lipman, who has vast experience on treating this type of bite, says that the best way to reduce the frequency of bites is to simply be more careful. Snakes never go out of their way to attack anyone, quite the opposite — they go out of their way to avoid people as much as they can.

“The most common comment I usually hear from snakebite victims in the emergency room is: ‘I was just minding my own business,'” Lipman said. “Usually, though, it’s the snakes that were minding their own business, having a nice nap. It’s people who tend to disturb them.”

Artist impression of Mars covered in a primitive ocean. Credit: NASA/GSFC.

It used to rain so hard on Mars it shaped the planet’s geology

Mars, the fourth planet from the sun, is a desolated wasteland. But billions of years ago, it held more water than Earth’s Arctic Ocean. In other words, it was very similar to Earth in many respects, as evidenced by geological features like canyons, channels, craters, and valleys. Although it doesn’t rain at all today on Mars most of these features were carved by rainfall, according to an amazing study recently published by researchers at the Smithsonian Institution and the Johns Hopkins University Applied Physics Laboratory.

Valley networks on Mars that show evidence for surface runoff driven by rainfall. Credit: Elsevier.

Valley networks on Mars that show evidence for surface runoff driven by rainfall. Credit: Elsevier.

The team led by geologists Dr. Robert Craddock and Dr. Ralph Lorenz turned to the same vetted methods used here on Earth to determine the erosive effect of rain on the planet’s surface. By reverse engineering from the kind of geological features present today, the team was able to assess how powerful rainfall must have been across Mars’ geological history.

“By using basic physical principles to understand the relationship between the atmosphere, raindrop size and rainfall intensity, we have shown that Mars would have seen some pretty big raindrops that would have been able to make more drastic changes to the surface than the earlier fog-like droplets,” commented Dr. Lorenz of John Hopkins University, who has also studied liquid methane rainfall on Saturn’s moon Titan, the only other world in the solar system apart from Earth where rain falls onto the surface at the present day.

When the researchers applied the same Earth physics to valley networks on Mars, they not only found that it used to rain on Mars — but that it was so considerable it permanently altered the planet’s surface.

“In addition to modified impact craters, valley networks, alluvial fans, and analyses of fluvial sediments at a variety of landing sites, large outflow channels, evidence for crater lakes, intracrater lakes, and a northern ocean attest to large bodies of liquid water on the surface, which is predicated by rainfall,” the authors wrote in the journal Icarus. 

Artist impression of Mars covered in a primitive ocean. Credit: NASA/GSFC.

Artist impression of Mars covered in a primitive ocean. Credit: NASA/GSFC.

The whole analysis first starts with assessing the planet’s atmosphere since it’s the main primer for rainfall. Some 4.5 billion years ago when both Mars and Earth formed, the Red Planet had a very thick atmosphere, unlike the thin veil that passes for an atmosphere today. This meant that the atmospheric pressure was very high, which in turn altered rainfall patterns. The more pressure there is, the smaller the raindrops and early on in Mars’ existence, the droplets must have been very small producing something more akin to fog than what we’d familiarly call rain.

[ALSO SEE] How it rains on different planets 

For instance, Dr. Lorenz claims early Mars had an atmospheric pressure of 4 bars or four times higher than the atmospheric pressure on Earth’s surface today. At this kind of pressure, raindrops could not have been bigger than 3mm across. For this diameter, the raindrops couldn’t penetrate the soil but once the pressure fell to 1.5 bars, the droplets could grow bigger and fall harder. Literally drop by drop, the Martian geology became altered as the raindrops cut through soil. Considering conditions at the time, had the pressure been the same as that on Earth, Martian raindrops would have been 7.3 mm across or a millimeter bigger than here on Earth.

“There will always be some unknowns, of course, such as how high a storm cloud may have risen into the Martian atmosphere, but we made efforts to apply the range of published variables for rainfall on Earth,”said Dr. Craddock in a statement. “It’s unlikely that rainfall on early Mars would have been dramatically different than what’s described in our paper. Our findings provide new, more definitive, constraints about the history of water and the climate on Mars.”

Journal reference: Robert A. Craddock, Ralph D. Lorenz. The changing nature of rainfall during the early history of Mars. Icarus, 2017; 293: 172 DOI: 10.1016/j.icarus.2017.04.013

Red Skies.

Silica rains helped form Earth’s crust four and a half billion years ago

Earth’s crust may have been formed in part by atmospheric chemicals which settled on the surface as the planet cooled, McGill University researchers report.

Red Skies.

Image credits David Mark.

We know that about 4.5 billion years ago, a planetoid roughly the same size as today’s Mars slammed into early Earth with enough force to melt the whole thing into a ball of magma. The event was so violent that we believe it led to the formation of the Moon and altered the chemical composition of our planet into the iron-rich Earth we know and love today.

Conventional wisdom holds that following this impact, the Earth gradually cooled down and the outer surface of this ball of lava hardened into a crust — in other words, the rocks on the planet’s surface are igneous in origin. But Don Baker and Kassandra Sofonio, a team of earth scientists from McGill University, say that the event played a direct hand in forming the planet’s modern crust. According to their theory, some of the chemical components we see in the crust today were deposited from the super-heated atmosphere left in the wake of the impact.

Igngaseous

Largely speaking, Earth’s crust comes in two flavors: oceanic and continental. Oceanic crust is the stuff plates are formed of, the rocks that cool from magma at mid-ocean rifts (they are igneous) then get subducted and recycled on the other side of the plate. It’s usually pretty thin and it’s what the ocean floor rests on.

Continental crust is the stuff that we actually live on. These thicker slabs of rock form on top of oceanic crust and reach high enough altitudes (usually) to form continents above water — hence their name. The rocks that go into continental crust can come from many different places, but what’s important now is that more than 90% of these rocks are estimated to be formed from silica-rich minerals, such as feldspar and quartz. Which, as you may have guessed, adds up to a lot of silica.

So where did all this silica-rich crustal material come from? The duo says that the collision 4.5 billion years ago turned the atmosphere into high-temperature steam which dissolved the rocks in the surface into a gaseous solution.

“These dissolved minerals rose to the upper atmosphere and cooled off, and then these silicate materials that were dissolved at the surface would start to separate out and fall back to Earth in what we call a silicate rain,” Baker says.

To test their theory, the team recreated the conditions of early Earth in the lab. They used a mix of bulk silicate materials and water which was enclosed in gold palladium capsules, then heated to 727 degrees Celsius (1340 Fahrenheit) at 100 atm to simulate conditions in the atmosphere about 1 million years after the moon-forming impact.

Using previous work on rock-water interactions at high pressure as a starting point, the team successfully recreated a “surprisingly similar” material to the Earth’s modern crust. The authors believe that following the impact, surface silicate rocks would dissolve and separate, rising to the upper layers of the atmosphere. Here, they cooled off enough to crystallize and fall back to Earth in a “silicate rain.” Sofonio christened the process “aerial metasomatism.”

One surprising implication of the paper is that it could provide researchers with a better understanding of how to spot planets fit for human habitation, or even those that harbor alien life.

“This time in early Earth’s history is still really exciting,” he adds. “A lot of people think that life started very soon after these events that we’re talking about. This is setting up the stages for the Earth being ready to support life.”

The paper “A metasomatic mechanism for the formation of Earth’s earliest evolved crust” has been published in the journal Earth and Planetary Science Letters.

Emei shan china

The top 10 wettest places on Earth

Technically speaking, the wettest place on Earth must be the Mariana Trench which has 10,000 meters of water above it. Smug responses aside, when meteorologists class regions by ‘wetness’ what they’re mainly looking at is the annual amount of precipitation. This is measured in millimeters or inches and includes rainfall, snow, drizzle, fog — anything wet. Bearing this classification in mind, the wettest places on Earth can be ranked as follows.

#10 Emei Shan, Sichuan Province, China — 8,169mm

Emei shan china

Credit: Wikipedia

Éméi Shān (峨眉山; 3099m) is one of China‘s four sacred Buddhist Mountains. It’s the highest among all the famous sight-seeing mountains in China, but also the wettest place in the nation. All that rainfall doesn’t seem to disrupt the scenery one bit, though. Here trees are verdant almost all the year around and locals call it the most peaceful place on Earth.

#9 Kukui, Maui, Hawaii — 9,293 mm

Credit: Wikipedia

In March of 1942, Puu Kukui recorded nearly 2565.4 mm of rainfall, which stands as the greatest precipitation total ever recorded in one month in the United States. Puu Kukui also holds the annual rainfall record for the United States with more than 17902 mm of rain in 1982.

#8 Mt Waialeale, Kuai, Hawaii — 9,763 mm

Mount-Waialeale

Credit: Wikimedia Commons

Kuai is home to many dormant volcanoes, but Mount Waialeale plenty of flowing each year — and I don’t mean lava. The name Waialeale means “rippling water” or “overflowing water” in Hawaiian and it couldn’t be more fitting. This mountain gets more than five times the amount of rainfall of other mountain peaks on Kaua’i.

#7 Big Bog, Maui, Hawaii – 10,272mm

Big-Bog-Maui-Hawaii

Credit: Wikimedia Commons

Big Bog is a rain gauge on the edge of Haleakala National Park on Maui Island. It’s a major tourist attraction attracting thousands each year who come to see its beautiful scenery, and the wettest out of all three mountains in Hawaii included in this list.

#6 Debundscha, Cameroon, Africa — 10,299mm

debundscha, cameroon

Credit: Wikipedia

Debundscha has a very long rainy season and a very short dry season, thanks to its proximity to the equator. Behind Debundscha we can find the giant Mount Cameroon towering above. This mountain rises from the coast of the South Atlantic ocean and blocks rain forming clouds from passing. Instead, all that rain is being dumped in Debundscha.

#5 San Antonio de Ureca, Bioko Island, Equatorial Guinea — 10,450 mm

San-Antonio-de-Ureca

Credit: Wikimedia Commons

San Antonio de Ureca is located some 37 mi (or 60 km) South of Malabo, the capital of Equatorial Guinea. It is the wettest place in the Africa.

#4 Cropp River, New Zealand — 11,516 mm

Cropp_River_Westland_New_Zealand

Credit: Wikimedia Commons

Most of New Zealand’s rain falls in its mountains, but the wettest place in the country is the Cropp River in the Hokitika River catchment. It’s only 9 km long but it sure does get a lot of rainfall.

#3 Tutunendo, Colombia, South, America — 11,770 mm

MountWaialeale

Credit: Discover Something New

Tutunendo is a small town in Choco department, with a population of fewer than 1,000. Here the climate is like a tropical rainforest stereotype — extreme warmth, high humidity, lack of wind, and significant precipitation. If that wasn’t enough, there are two rainy seasons which bucket ample rain. The neighboring city of Quibdo is considered the wettest city in the world.

#2 Cherrapunji, India — 11,777 mm

Rope bridge in Cherrapunji. Credit: Buena Vibra

Rope bridge in Cherrapunji. Credit: Buena Vibra

Because of the elevation of Cherrapunji, air that blows over the plains below is cooled as it rises to the higher elevation. This cooling of the air causes the moisture trapped in the air to condense, forming clouds, which then release rain.

#1 Mawsynram, India — 11,871 mm

Credit: Veg Momos

Topping the list as the wettest place in the world is Mawsynram, a village in the East Khasi Hills district of Meghalaya state in north-eastern India. A few times a year, torrents of water turn the streets of the village into waterfalls. Every year this village is battered by nearly 12 meters of rain but the villagers are used to it — they only mind when they have to plug the leaking holes in their homes.

 

The moon’s phases affect rainfall, says first-of-its-kind study

The moon does more than cause tides and delight lovers – according to a new study, it can also affect how much rainfall falls down on the ground.

Image via Wikipedia.

Since ancient times, the moon has been an object of fascination for people, both romantics and scientists. Now, researchers from the University of Washington found that when the moon is high in the sky, it creates “bulges” in the planet’s atmosphere, slightly affecting falling rain. This is the first study to document the effect of the moon on rainfall.

“As far as I know, this is the first study to convincingly connect the tidal force of the moon with rainfall,” said corresponding author Tsubasa Kohyama, a UW doctoral student in atmospheric sciences.

 

Satellite data over the tropics, between 10 degrees S and 10 degrees N, shows a slight dip in rainfall when the moon is directly overhead or underfoot. University of Washington

He started noticing something was up while studying atmospheric waves, periodic disturbances of pressure, temperature or wind velocity. He noticed slight, but consistent oscillations in the air pressure. He and co-author John (Michael) Wallace, a UW professor of atmospheric sciences, spent the next two years tracking these oscillations and attempting to explain them.

It’s not the first time atmospheric variations have been tied with the moon. Air pressure changes were connected to the phases of the moon back in 1847 and temperature in 1932. Furthermore, a 2014 paper from the same University showed how air pressure varies with the phases of the moon.

“When the moon is overhead or underfoot, the air pressure is higher,” Kohyama said.

After that, it seemed highly likely that rainfall is also affected by the moon, and this did turn out to be the case. When the satellite is overhead, its gravitational attraction tugs and pulls a slight damper on the rain. Higher pressure also creates warmer temperatures in the air parcels below. Warmer air holds more moisture, and having a higher moisture capacity means they don’t shed as much water.

“It’s like the container becomes larger at higher pressure,” Kohyama said. The relative humidity affects rain, he said, because “lower humidity is less favorable for precipitation.”

They used data collected from 1998 to 2012 to show that the rain is indeed slightly lighter when the moon is high. It’s a very slight and subtle change, of only about 1% total rainfall. It is consistent, but you shouldn’t really worry about it.

“No one should carry an umbrella just because the moon is rising,” Kohyama said.

However, this could have an effect on weather and climate models. It’s another valuable piece of information to piece into extremely complicated prediction models. Wallace plans to continue exploring the topic to see whether specific types of rain are more affected by lunar phases.

Journal Reference [open access] – Rainfall variations induced by the lunar gravitational atmospheric tide and their implications for the relationship between tropical rainfall and humidity.

Why raindrops are basically sky pearls

At the center of every raindrop there is an impurity (dust, clay, etc) – basically all raindrops have something like that at its core, just like pearls do. So in a way, raindrops form just like pearls. Let’s look at this phenomenon in more detail.

Image via UCSD.

In one form or another, water is always present in the atmosphere. However, water particles are simply too small to bond together for the formation of cloud droplets. They need another substance, a ‘seed’ with a radius of at least one micrometer (one millionth of a meter) on which they can form a bond. Those objects are called nuclei, or to be more exact, cloud condensation nuclei.

Cloud condensation nuclei or CCNs (also known as cloud seeds) are small particles typically 0.2 µm, or 1/100th the size of a cloud droplet on which water can condens. There are different types of seeds; it’s usually thin particles of dust or clay, but soot or black carbon from fires can also play this role. The ability of these different types of particles to form cloud droplets varies according to their size and also their exact composition, as the hygroscopic properties of these different constituents are very different. Some particles are better than others at seeding rain, while others can be better at seeding snow or ice. Temperature actually plays a key role.

Image via NOAA.

A cloud results when a block of air (called a parcel) containing water vapor has cooled below the point of saturation. As it moves higher and higher, it moves into areas of lower pressure and it expands. This requires heat energy to be removed from the parcel. As the parcel reaches saturation temperature (100% relative humidity), water vapor will condense onto the cloud condensation nuclei resulting in the formation of a cloud droplet – if there is a seed, of course.

Phytoplankton can also play a special role in seeding rain – some have supposed that it can actually act as a regulator mechanism for rain. It goes like this: Sulfate aerosol (SO42− and methanesulfonic acid droplets) act as CCNs. Large algal blooms in ocean surface waters occur in a wide range of latitudes and contribute considerable DMS into the atmosphere to act as nuclei. According to James Lovelock, author of The Revenge of Gaia, this happens because arming oceans are likely to become stratified, with most ocean nutrients trapped in the cold bottom layers while most of the light needed for photosynthesis in the warm top layer. Under this scenario, deprived of nutrients, marine phytoplankton would decline, as would sulfate cloud condensation nuclei, and the high albedo associated with low clouds. This is known as the CLAW hypothesis, but until now, it has not yet been thoroughly confirmed.

Phytoplankton bloom in the North Sea and the Skagerrak – NASA

The take-away message is that you don’t only need water for rain – you also need a seed.

Credit: Flickr

Why does it rain so much in London? Well, it’s not that much really

Credit: Flickr

Credit: Flickr Creative Commons

Before I first set foot in London, I – like most people – was under the impression that hellish gusts of wind and rain would be the most memorable parts of my trip. In reality, even though I visited in January, there were only a couple of days of rain, and even these quite mild. So I decided to investigate a bit.

What I found was that London isn’t by far the rainiest city out there, and moreover, because it rains time and time again this makes England considerably warmer than it should have been. Where does it all come from? If you ask me, it has something to do with the British love-hate relationship with rain: they say the weather’s dreadful, but they never seem to talk about anything else. In fact, I think it’s their best ice breaker during conversations. Secretly inside, every Brit adores the rain and I’m certain they couldn’t live without it – not without a short burst from time to time, at least.

The myth of a rainy London

Yet, even so, it doesn’t rain that much in London. Granted, the rest of Britain is one different matter altogether, especially the Highlands, but we’ll get to that soon enough. According to the Met Office Climate data, over the 30 year period, there were 106.5 days of rainfall per year on average (which counts as a day in which 1mm of rainfall or over fell). This means that there was rainfall on 29 per cent of days per year and on average it didn’t rain 71 per cent of days per year. Average rainfall is 557.4mm with 1410 “sunshine hours.”

There are more rainy days in Miami (at 135) and Orlando, Florida (117) than there are in London. New York City clocks in at 122 days and 1,268mm of rain. Washington DC, Rio de Janeiro, Sydney, and Mexico City all have more rainy days on average in any given year than London.

In the rest of the country, according to the UK Met Office, the average rainfall in Britain is 1,154mm per year. On average it rains for 156.2 days per year (data from 1981 to 2010). However, some parts of England are much wetter than others, and the farther west you go the likelier it is you’ll need to pack the iconic umbrella. The Scottish western Highlands get doused annually with over three meters of rain, the Lake District and the Pennines in the northwest of England top the rainy charts too, as well as the mountainous Snowdonia area in Wales and the higher ground of the Cornish and Devonshire moors. The map below released by the Met Office is quite revealing.

Rainfall average (1981 - 2010)

Rainfall average (1981 – 2010)

Why it rains so much in Britain

Granted, it does rain rather frequently in Britain, despite the exaggerated rumors. This mostly due to the island-state’s unfortunate location, being right in the path of the atmospheric jet stream. The jet stream, a massive but mysterious driver for British weather, usually passes along a steady path from West to East across the Atlantic – sometimes a bit to the North of us, sometimes a bit to the South. The flow of these streams is not a neat curve but a series of massive meanders. Britain is right on the northern side of those meanders where conditions are cooler and wetter which means which means the country keeps getting hit by rain.

Normally, we would expect the pattern of the jet stream to keep shifting, for its shape to switch every few days and for our weather to change as a result. Instead for week after week – and possibly for weeks ahead too – the meanders of the stream are sticking to the same shape so repeated rainstorms have become the norm. Nobody knows why this pattern is so static.

jet stream

Credit: Metro Office

On top of this, there is the related question of climate change. Most researchers are extremely reluctant to attribute any single weather event to global warming. But Dr Peter Stott, a leading climate scientist at the UK Met Office, says that since the 1970s the amount of moisture in the atmosphere over the oceans has risen by 4%, a potentially important factor.

It’s worth mentioning that 2012 was an unusually rainy year having seen the”most exceptional period of rainfall in 248 years”. The report released by the Met Office reveals that while downpours and storms have not been out of the ordinary, their frequency has been.

“Each one of these individual events has not been particular outstanding, they’ve been broadly along the lines of what we would expect for a typical winter storm in the UK,” said Simon Parry from the CEH and co-author of the report. “What’s been notable about it, and different from what we’ve seen in the past, is the persistence.”

Two key factors the authors believe have contributed to the effect:  a persistent high-pressure system lurking over a patch of the Pacific Ocean, off the west coast of North America and, second, the quasi-biennial oscillation (QBO).

So there you have it. The British do have their fair share of rain, the west more than the east, higher ground more than the low-lying areas, but feel no pity because the British love the rain. Without it, there’d be less to moan about and fewer occasions to perfect their famous stiff upper lip.

rain walk or run

Is it better to run or walk in the rain to stay as dry as possible? A lifelong physics question

rain walk or runYou just got out of the office, looking to head home to a soothing dinner, only to find that it’s raining cats and dogs outside – and you forgot your umbrella of course. Do you walk or run to your car to stay as dry as possible? It might sound trivial, but this is a question that has gained a considerable amount of attention from physicists, and other scientists alike. Various suggestions have been made, the most recent of which comes from Franco Bocci of University of Brescia‘s Department of Mechanical and Industrial Engineering. Bocci used mathematics to describe the problem, and found that running is usually best during most situations, however concludes that there’s an optimal pace for particular conditions.

If you run in the rain, you get exposed to rain for a smaller interval of time than walking, however you also maximize the body surface that directly comes into contact with the rain droplets. Bocci take on the issue comes with a twist as he used simplified geometrical bodies, when previous attempts assumed people to be thin sheets or upright, rectangular boxes.

From his paper, which you can read here in its entirety, complete with equations and thorough statements, the author derived these conclusions:

  • “For rain falling vertically, the best strategy is to run as quickly as possible. The same is also true for motion into the wind.”
  • “For motion downwind, there may be an optimal speed, which equals the component along the direction of motion of the wind velocity. This happens only if the ratio between the cross-section of the body perpendicular to the motion and the horizontal one is large enough; otherwise, the best choice is again to run at the maximum speed one can reach.”

In short, the answer depends on the shape and orientation of the moving bod, as well as  the wind direction and intensity. You can say that in the majority of cases, when rain is joined by little to no wind, it is better to run if your intentions are of staying as dry as possible.

Bocci’s paper was published in the journal European Journal of Physics.

[Image credit / story source]

Raindrop imprints fossilized from 2.7 billion years ago in rock. (c) Sanjoy Som

Raindrops fossil 2.7-billion-year-old reveals secrets from Earth’s early atmosphere

Billions of years ago, the Earth was unrecognizable from the life supporting paradise it is today. Fossilized raindrops from some 2.7 billion years ago, conserved in time as rain dropped onto volcanic ash during an eruption, which eventually solidified into  rock known as tuff, has revealed some very interesting facts about Earth’s ancient atmosphere. The discovery will help scientists understand more about Earth’s early history and how it evolved in time, as well as aid research funneled towards finding life bearing exoplanets.

Raindrop imprints fossilized from 2.7 billion years ago in rock. (c) Sanjoy Som

Raindrop imprints fossilized from 2.7 billion years ago in rock. (c) Sanjoy Som

During this period, the sun burned as much as 30% less brighter. In those conditions, the Earth should have been covered in a thick layer of ice, however geologic evidence for rivers and ocean sediments testify otherwise. This is because, at the time, the planet had an atmosphere filled with greenhouse gases which warmed it – a thick haze filled with hydrocarbons which made the Earth resemble today’s Saturn’s moon Titan.

“Because the sun was so much fainter back then, if the atmosphere was the same as it is today the Earth should have been frozen,” says Sanjoy Som, a postdoctoral researcher at NASA’s Ames Research Center.

Scientists at University of Washington in Seattle scanned the raindrop craters engraved into the ancient rock sample with lasers, and compared them with similar marks left by raindrops in ash from present time. The sizes of raindrop impressions depend on their velocity, atmospheric pressure and the composition of the material into which they fall.

The maximum raindrop diameter is around 6.8 millimeters, anything larger breaks up in smaller droplets due to the laws of physics. Considering the same laws were in place billions of years ago, raindrops during the Archean period couldn’t have been larger than this either. After a careful analysis, the researchers concluded that Earth’s early atmosphere exerted at most twice as much pressure as the present day atmosphere. Most likely, it would have been similar to present day atmospheric pressure or as little as half present pressure.

The discovery and consequent research studying the raindrop fossils adds even more weight to the claim that Earth’s early atmosphere was covered in greenhouse gases, explaining the faint sun paradox from the time. Also, the finding could prove important in the search for life on planets orbiting other stars, called exoplanets. In all respects, ancient Earth was alien compared to present day, and studying its ancient history might hint scientists to what kind of planets might hold the potential for supporting life, even microbial.

“Setting limits on atmospheric pressure is the first step towards understanding what the atmospheric composition was then,” says Som. “Knowing this will double the known data points that we have for comparison to exoplanets that might support life.”

The scientists have reported their findings in the March 29 edition of the journal Nature.

[via Scientific American]

 

© Sebastiao Salgado

Two dazzling, yet discrepant sides of the Amazon [AMAZING PHOTOS]

A recent art photography exhibition, dubbed  Amazon, is currently on display at Somerset House in London, which brings together two remarkable, distinct bodies of photography to highlight the plight of the Amazonian rainforest and the people living within it. Thus, the work of Brazilian Sebastião Salgado depicts the virgin beauty of the largest and most species-rich tract of tropical rainforest in the world, while Swedish photographer Per Anders Pettersson chose to show the less serene side.

Salgado’s photo from below shows a largely unspoiled region in the state of Amazonas in north-west Brazil, part of his ongoing project called Genesis, in which he tries to capture the pristine beauty of the Amazon and its inhabitants in black and white.

© Sebastiao Salgado

© Sebastiao Salgado

In total opposition, yet still of a retched beauty, Pettersson’s photograph shows a huge heavily deforested area of the rain forest. The photographer captured the sight on 21 June this year,when  he flew over the Amazonian rainforest. What’s sad, maybe even stupid if you will, is that much of the deforestation was made to clear way for farmland. The problem is that the soil there is practically unusable, which results in poor crops.

© Per-Anders Pettersson

© Per-Anders Pettersson

Shorties: why can’t bats fly in the rain

Ever wondered why you never see bats flying in the rain? Well, maybe you’ve seen some skimming through trees in parks on light rain,  but that’s probably the most you’ll see. A new study published in Biology Letters yesterday tries to shed some light on why this exactly happens, the answer being that they have to burn more energy during rain.

For years it was thought that the main reason bats don’t fly in the rain is because the mass of rain droplets are obstructing their flight. As part of a series of trials in Costa Rica, scientists studied Sowell’s short-tailed fruit bats, which they exposed to rain like effects. They observed the rain itself though it’s droplets mass didn’t affect the bat’s mechanical flying behavior whatsoever. What made it really hard for them, however, was the fact their fur and wings were wet, and like most mammals, bats have to keep themselves warm by patting harder, coupled with the fact that water is mussing their silky fur and dampening their wings, bedraggled bats might also be less aerodynamic.

Study source/Photo Source.

It’s the methane rainy season on Titan

On Saturn’s largest moon, Titan, precipitations under the form of methane has scientists staggered. NASA’s Cassini spacecraft, through the use of its infrared camera, detected signs of heavy spring rain of the highly flammable liquefied natural gas sprinkling across vast fields of dunes near Titan’s equator.

“They see for the very first time evidence of rainfall at the equator of Titan,” said planetary meteorologist Tetsuya Tokano at the University of Koln in Germany, who studies the moon but wasn’t involved in the project.

As opposed to Earth, Titan’s cycles of precipitation, evaporation and cloud formation involve hydrocarbons such as methane and ethane. At its two poles, the moon features thousands of such hydrocarbon filled lakes, many as big as the ones you can find at the Great Lakes.

Using the Cassini probe, the scientists led by planetary geologist Elizabeth Turtle at Johns Hopkins University in Maryland compared images of Titan’s dunes between August 2009 and this past January. They realized there was a  sudden decreases in the brightness of the moon’s surface after clouds had swept over the region, and after a swift analysis they concluded that the ground there had darkened because it was wet.

“It may be a case of surface wetting,” Dr. Turtle said. “It wouldn’t take much. A millimeter of rain over this area would have done it.” Their research was published in Science.

Titan is one of the most fascinating space bodies in our solar system, mostly because it’s the only moon known to have a dense atmosphere capable of forming precipitation and because it has weather patterns resembling Earth. This latest study offers important insights regarding Titan’s climate.

The researchers’ observations may help explain the presence of dry river beds in Titan’s equatorial region. Scientists have been unsure if these channels formed during wetter climates in the past or from occasional methane storms that then dried out.

“Equatorial precipitation is likely to occur near equinoxes,” Tokano said. “The rain belt, while being intermittent, swings between the south and north pole, so every area on Titan could experience rainfall in the course of a Titan year.”

For the upcoming months up ahead, Turtle and his colleagues will be busy watching Titan for more climate change insights, particularly looking to see if the precipitation travels into Titan’s northern hemisphere, as predicted by atmospheric models.

More posts involving the extraordinary Cassini space-craft covered by ZME Science can be found here.