Ill winds

When you think about it, wind is a strange phenomenon.

In its simplest form, wind occurs when uneven heating of the surface of the Earth causes higher pressure in some places than in others, and the air flows from highs to lows.  But it's considerably more complex (and interesting) than that, because as surface-dwellers we often forget that there's a third dimension -- and that air can move vertically as well as horizontally.

I got to thinking of this because I've been reading Eric Pinder's fascinating, often lyrical, book Tying Down the Wind: Adventures in the Worst Weather on Earth.  Pinder is a meteorologist who was stationed as a weather observer on Mount Washington, New Hampshire, which one in every three days clocks hurricane-force winds (greater than 119 kilometers per hour) and is the spot that holds second place for the highest anemometer-clocked wind speed ever recorded on the Earth's surface (an almost unimaginable 372 kilometers per hour; the only higher one was on Barrow Island, Australia, which on April 10, 1996, during Cyclone Olivia, hit 407 kilometers per hour).

The fact that air moves vertically, of course, is why air moves horizontally.  When the Sun heats a patch of ground, the air above it warms and becomes less dense, causing it to rise.  This creates an area of low pressure, and air moves in from the side to replace the air moving upward.  This process, writ large, is what causes hurricanes; the heat source is the ocean, and the convection caused by that tremendous reservoir of heat energy not only generates wind, but when the water-vapor-laden air rises high enough, it undergoes adiabatic cooling, triggering condensation, cloud formation -- and torrential rain.

The process can go the other direction, though.  A weather phenomenon that has long fascinated me is the convective microburst, something that most often happens in hot, dry climates in midsummer, like the American Midwest.  The process goes something like this.  Rising air triggers cloud formation, and ultimately rain clouds.  When the droplets of water become heavy enough that the downward force of gravity exceeds the upward force of the air updrafts, they fall, but they drop into the layer of warm, dry air near the surface, so they evaporate on the way down, often not making it to the ground as rain.  Evaporation cools the air that surrounds them, making it denser -- and if the process happens fast enough, it creates a blob of air so much denser than the air surrounding it that it literally falls out of the sky, hits the ground, and explodes outward.  Windspeeds can go from nothing to 100 kilometers per hour in a matter of fifteen seconds.  Then -- a couple of minutes later -- it's all over, the dust (and any airborne objects) settle back to Earth, and everyone in the vicinity staggers around trying to figure out what the hell just happened.

A convective microburst in Nebraska [Image licensed under the Creative Commons Couch-scratching-cats, Downburst 1, CC BY-SA 4.0]

Microbursts aren't the only weird weather phenomenon having to do with density flow.  Have you heard of katabatic winds?  If you haven't, it's probably because you live in an area where they don't happen, because they're really dramatic where they do.  Katabatic winds (from the Greek κατάβασις, "falling down") occurs when you have significant chilling of a layer of air aloft -- on top of a mountain, for example, or (even better) over an ice sheet.  This raises the density of the air mass, creating a huge difference in gravitational potential energy from high to low.  The superchilled air pours downward, funneling through any gaps in the terrain; the effect is accentuated when there's a low pressure center nearby.  The katabatic winds off Antarctica (nicknamed "Herbies," for no reason I could find) and the ones off Greenland (known by the Inuit name piteraq) can be unpredictable, fast, and frigid, often driving layers of snow horizontally and creating sudden whiteout conditions.

Then there's the foehn (or föhn) wind, created when onshore air flow is pushed up against a mountain range.  This occurs in the southern Alps, central Washington and Oregon, parts of Greece and Turkey, and south-central China.  On the windward side of the mountains, the air rises and cools; this causes condensation and higher rainfall.  But when the air piles up and gets pushed over the mountain passes, it warms for two reasons -- the pressure increases as it goes downhill on the other side, and the condensation of water vapor releases heat energy.  The result is a warm, dry wind that pours downhill on the leeward side of the mountains -- the source of the "Chinook winds" that desiccate the northwestern United States east of the Cascades.

Interestingly, foehn winds are associated with physiological problems -- headaches, sinus problems, and mood swings.  It's documented that prescriptions for anxiolytic medications go up when the foehn is blowing; and a study at the Ludwig Maximilians Universität München found that suicide and accident rates both go up by about ten percent during periods when there's a strong foehn, and no one knows why exactly.

In any case, there are a few interesting tidbits about a phenomenon we usually don't think about unless we're in the path of a hurricane or tornado.  Something to think about next time your face is brushed by a warm breeze.  We live at the bottom of a layer of moving fluid, driven by invisible forces that usually are benign.  Only occasionally do we see how powerful that fluid can be -- preferably, from a safe distance.

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Thunderstorms on Titan

Sometimes I bump into a piece of research that's just so cool I have to tell you about it.

Yesterday when I was casting about for a topic for today's post, I found a link to a paper in the Journal of Geophysical Research called "The Physics of Falling Raindrops in Diverse Planetary Atmospheres," by Kaitlyn Loftus and Robin Wordsworth, of Harvard University's Department of Earth and Planetary Sciences.  In it, they consider the models of how raindrops alter as they fall -- evaporating, changing shape because of atmospheric drag, interacting with nearby drops -- and how that might differ not only in different environments on Earth, but on other planets.

You may already know that raindrops aren't as they're usually pictured, with a teardrop shape that's bulbous on the bottom and tapers to a point at the top; they're more or less spherical.  Large raindrops, or drops in high winds, will sometimes be deformed into fat ellipses, but modeling raindrop shapes as spheres is going to be a pretty good approximation most of the time.  Where things get interesting, though, is the fact that they sometimes coalesce with other drops, or partially evaporate as they fall.  In fact, it's the evaporation of rain on the way down, especially when falling into warm, dry air, that gives rise to my all-time favorite atmospheric phenomenon: a convective microburst.

Microbursts don't occur where I live, here in central New York, which I'm disappointed about because it'd be cool to experience one, and relieved about because having your stuff blown into the next time zone is kind of inconvenient.  They're much more common in areas that have turbulent updrafts from a layer of warm air near the surface -- like the American Midwest.  (It's no coincidence that places with microbursts are usually also prone to tornados.)

What happens is something like this.  A moisture-laden cloud reaches the point where the droplets of water are heavy enough to fall, so they do, dropping into the layer of warm, dry air underneath.  This makes the drops begin to evaporate.  Evaporation cools the air layer, and if the gradient -- the temperature difference between the blob of rain-cooled air and the hot, dry air below it -- gets big enough, the cool air literally falls out of the sky like an Acme anvil in a Roadrunner and Coyote cartoon.

If you're underneath this, all you know is that it's lightly raining, and then all of a sudden, WHAM.  The winds go from zero to a hundred kilometers per hour in thirty seconds flat.  Then equally quickly, it's all over, leaving you to pick yourself up and wander around trying to figure out where your trash cans and patio furniture went.

A microburst near Denver, Colorado in 2006. There aren't many good photographs of them because they're over so quickly, and also because if you're in one, the last thing you'll be thinking about is taking pictures. [Image licensed under the Creative Commons Unixluv, Denver-microburst, CC BY 3.0]

Anyhow, raindrops are way more interesting than a lot of people realize, as is weather in general.  If I hadn't become a science teacher I think I'd have been a tornado chaser.  As things stand, I have to content myself with frequently updating my wife about such critical information as the status of frontal systems in North Dakota, usually eliciting a comment of, "Yes, dear," which I choose to interpret as a sign of breathless fascination.

But back to the study.  What Loftus and Wordsworth did was to model raindrop behavior, and then extrapolate that model to other, less familiar environments -- like the thunderstorms on Titan, which are made of droplets of ammonia.  The authors write:

The behavior of clouds and precipitation on planets beyond Earth is poorly understood, but understanding clouds and precipitation is important for predicting planetary climates and interpreting records of past rainfall preserved on the surfaces of Earth, Mars, and Titan.  One component of the clouds and precipitation system that can be easily understood is the behavior of individual raindrops.  Here, we show how to calculate three key properties that characterize raindrops: their shape, their falling speed, and the speed at which they evaporate.  From these properties, we demonstrate that, across a wide range of planetary conditions, only raindrops in a relatively narrow size range can reach the surface from clouds.  We are able to abstract a very simple expression to explain the behavior of falling raindrops from more complicated equations, which should facilitate improved representations of rainfall in complex climate models in the future.

Which I think is amazingly cool.  The idea that we could use information about rainfall here on Earth to make some guesses about what weather is like on other planets is astonishing.  I'm sure if we ever get real data from extrasolar planets, or better data from places like Titan and Enceladus here in our own Solar System, we'll still be in for plenty of surprises; I'm reminded of the cyclic violent downpours of liquid methane on the planet where the Robinsons are stranded in the remake of Lost in Space (which, unlike the original series, is actually good).

But even having a start at understanding the weather on exoplanets, based upon speculation about the conditions and knowledge of how raindrops behave on Earth, is nothing short of fascinating.

So who knows.  Maybe soon I'll be able to update my wife about what the low-pressure systems are doing on Titan.  With luck, that will produce a better reaction than "Yes, dear." 

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This week's Skeptophilia book-of-the-week is a bit of a departure from the usual science fare: podcaster and author Rose Eveleth's amazing Flash Forward: An Illustrated Guide to the Possibly (and Not-So-Possible) Tomorrows.

Eveleth looks at what might happen if twelve things that are currently in the realm of science fiction became real -- a pill becoming available that obviates the need for sleep, for example, or the development of a robot that can make art.  She then extrapolates from those, to look at how they might change our world, to consider ramifications (good and bad) from our suddenly having access to science or technology we currently only dream about.

Eveleth's book is highly entertaining not only from its content, but because it's in graphic novel format -- a number of extremely talented artists, including Matt Lubchansky, Sophie Goldstein, Ben Passmore, and Julia Gförer, illustrate her twelve new worlds, literally drawing what we might be facing in the future.  Her conclusions, and their illustrations of them, are brilliant, funny, shocking, and most of all, memorable.

I love her visions even if I'm not sure I'd want to live in some of them.  The book certainly brings home the old adage of "Be careful what you wish for, you may get it."  But as long as they're in the realm of speculative fiction, they're great fun... especially in the hands of Eveleth and her wonderful illustrators.

[Note: if you purchase this book from the image/link below, part of the proceeds goes to support Skeptophilia!]

The hexagons of doom

New from the Woo-Woo Bullshit That Would Not Die department, we have: stories popping up all over the place claiming that the discovery of hexagonal clouds "solves the mystery of the Bermuda Triangle."

There are dozens of these articles all over the place, many at clickbait sites like the Daily Mail Fail, so I will only post one link -- to a dubiously-less-clickbaitish site called the Mother News Network.  In it, we find that a meteorologist named Randy Cerveny has been studying atmospheric turbulence patterns, and found that a phenomenon that creates hexagonal-shaped clouds is also likely to create the proper conditions for a microburst -- a sudden downdraft that can reach hurricane-speed in a matter of seconds (and usually dissipates just as fast).  "These types of hexagonal shapes over the ocean are in essence air bombs," Cerveny said.  "They are formed by what are called microbursts, blasts of air that come down out of the bottom of a cloud and then hit the ocean and then create waves that can sometimes be massive in size as they start to interact with each other."

Which is all well and good, and of obvious interest to weather nerds like myself.  I'm fascinated by weather, which is why I'm always updating my poor long-suffering wife about the status of low-pressure systems in Saskatchewan.  So I think the discovery is cool.

But.

You may want to back slowly away from your screen, 'cuz I'm gonna yell.

THERE IS NO SUCH THING AS "THE BERMUDA TRIANGLE PHENOMENON."

I dealt with this in a post way back in 2011.  Let me quote for you the relevant paragraph:

[T]he whole preposterous idea [of the Bermuda Triangle] was brought to the public's attention by a fellow named Charles Berlitz, who wrote a bestselling book on the subject in 1974.  Berlitz's book, upon examination, turns out to be full of sensationalized hype, reports taken out of context, omitted information, and outright lies.  Larry Kusche, whose painstaking collection of data finally proved once and for all that there were proportionally no more ships and planes going down there than anywhere else in the world, said about Berlitz, "If Berlitz were to report that a ship was red, the chances of it being some other color is almost a certainty."

So the Bermuda Triangle Mystery is actually the Bermuda Triangle Ordinary Patch Of Ocean.  But far be it from the woo-woos of the world to say, "Well, I guess we were wrong after all.  There's nothing to see here, folks."  No.  We have to keep hearing about how ancient aliens built the Pyramids, that ley lines determined the siting of Stonehenge, how you can heal yourself with crystals, and that homeopathy works.

And, heaven help us all, that there's a mysterious "Bermuda Triangle" where ships and airplanes vanish regularly, never to be seen again.

So poor Randy Cerveny has joined the rank of scientists who have had their legitimate (and interesting) research co-opted by wingnuts who then use it to support a loony claim.  I don't know how he feels about this.  Maybe he's just laughing it off.  Me, I'd be pissed.

In fact, I'm pissed enough just reading about it.  I better go check the weather forecast for Quito, Ecuador and calm down a little.  It'll also give me something to tell my wife about over dinner tonight.