SCALES #30: mixed clouds
Hello!
In February 1922 Tor Bergeron was at a health resort outside of Oslo. He was on a multi-week break before starting a new position in Bergen, Norway, as a meteorologist at the Bergen Weather Service. The resort was on a hill, often immersed in a stratus cloud, and he frequently walked on a narrow road in the middle of a fir forest, with ice-coated branches visible in every direction. He noticed he traveled straight through the fog when the temperature was above 0 °C, but the fog, though present overhead, disappeared from ground level when the temperature dropped to -5 to -10 °C.
Bergeron had read a book by Alfred Wegener years previously that discussed "mixed clouds" containing both supercooled liquid droplets and ice crystals. Because ice crystals are a more stable form of water than liquid droplets at subzero temperatures, Wegener pointed out under these conditions the liquid droplets would evaporate and their vapors would cause the ice crystals to grow. Bergeron recalls "immediately" thinking of Wegener's theory to explain his observations in the foggy wood: in this case the liquid droplet-scavenging ice crystals weren't in the air, but rather were the rime-coated tree branches.
In the following years, Bergeron thought about how the transfer of water mass from liquid drops to ice crystals he observed in the woods above Oslo could also address the problem of how clouds lead to precipitation. If there are few enough ice crystals relative to the amount of liquid water in a mixed cloud, the ice crystals can grow heavy enough that they start to fall out of the sky. Bergeron's subsequent cloud-watching, including of fallstreak holes, was consistent with such a process; he hoped several times to fly by airplane or balloon through such a cloud system, but the plans always fell through.
Bergeron included his ideas in his doctoral thesis, which he started writing in 1927, but "the ice nucleus theory" didn't circulate widely until presented at an international meeting in Lisbon in 1933. He found the reception to his theory of precipitation varied, based, in part, on the climate the other meteorologists were accustomed to: those who lived further south were more concerned with precipitation from warm tropical clouds, in sharp contrast to Bergeron, who wrote he "then hardly had seen any weather or climate south of 50°N (except the winter of 1928/29 on Malta)."
Eventually, the theory became widely accepted as a key process in the physics of mixed clouds and known as the Wegener–Bergeron–Findeison process. As Bergeron wrote in 1971, "as often happens in science, the […] theory […] proved to be better and more fruitful than the partly doubtful or incorrect observations, and the somewhat daring conclusions on which it was founded."
I'm amazed how well Bergeron's story falls into the structure of scientific myth. It tidily knits together virtues—sensitivity to unexpected observation, possession of prior knowledge, courage to make intellectual leaps, patience to see through an idea over years of development—that are rewarded in the end. (Setting aside for the moment equally interesting broader questions: why this idea about cloud physics, at this time and place? A Vermont farmer named Bentley, for instance, had similar ideas about cloud physics decades earlier.)
(Much of this cribbed from a 1978 paper (free access) remembering Bergeron and printing his "Autobiographic Notes" on developing the ice nucleus theory.)
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Also foggy
Going through an old notebook, I remembered a talk by Kathleen Weathers about the role of coastal fogs in ecosystems such as redwood forests, particularly as an input of nitrogen. She called fog "a charismatic abiotic phenomenon".
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Noticing, remembering
Digging up the half-remembered Bergeron process from my memory of a talk about mixed clouds was brought to you by noticing holes in a dusting of snow around salt crystals on the pavement—a bit of a leap, since the physics can't possibly be exactly the same.
The salt also reminded me of how atmospheric chemists are thinking about the importance of road salt as a wintertime source of inorganic ions. Some researchers have argued that application of road salt can lead to atmospheric chloride concentrations in continental regions that match those on the sea spray-influenced coast.
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From salt to dust
I've been playing a lot of Dust, Laurel Halo's 2017 album. Shifting explorations of texture, rhythm, concrete poetry that reward careful listening and re-listening. (Album is on Bandcamp, including "Syzygy".)
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Dipping into the Instapaper backlog
"What exactly are we reading when we read The Doom of the Great City? Is it a forward-looking sci-fi tale about a dystopian future that may yet arrive? Or is it a fantasy of divine retribution that belongs with the ancient past?"
"(Wednesday is what she calls 'real-life night,' and she spends it watching reality television with her best friend.)"
"The very way of living, of art-making, of storytelling, that I have so long aspired to is one based on abuse, one that thrives on the blood of the vulnerable. All the art I love is essentially large-hearted, but maybe its heart is so large because it has eaten the hearts of others."
"Strangely enough, we Americans have made the decision to embrace a libertarian, devil-take-the-hindmost capitalist approach to labor and contracting on our public lands, the same lands that are perhaps our best remaining example of a shared national vision, a vision that defies the raw and bloody arithmetic of markets and bald statements of profit and loss. ... Swept into this vortex is the economic connection that small communities once had to the federally managed public lands that surround them, and that, increasingly, are seen as hampering, rather than encouraging, economic prosperity and quality of life in the West."
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The holes in the snow.
—Adam