FR author Christian Satorius worries about autumnal weather phenomena – and whether people also grow a winter coat
It not only gives the wind its spurs, as Erich Kästner once wrote, but also gives the days their very own magic: Autumn is here! The clouds fly over the land, squirrels nibble and bury nut after nut. But the third season not only throws a drape of gold over the woods, it also raises some seemingly mundane questions that we’ll quickly answer here before winter gives the spurs to fall.
Are we growing a winter coat? In nature, the animals prepare for the winter by changing their fur and shedding their summer fur. But what about us humans? Do we also lose more hair in autumn than usual? In fact, a number of studies have found evidence of seasonality in hair growth and increased hair loss in the fall – in both men and women! One of the larger studies on the subject is the one that Ralph M. Trüeb and his team began in the early 2000s and conducted over a period of six years. 823 women between the ages of 18 and 78 took part in the study at the University Hospital Zurich. The result of the study, which was published in the journal Dermatology: Similar to animals, there is also a kind of coat change in humans. Or, to put it more scientifically: “The fact that human hair follicles, like those of other mammals, are subject to cyclical activity and are influenced by hormones implies that human hair is not unaffected by these phenomena.”
How heavy is a cloud? They seem to float through the air as light as a feather, but are mountains of water and correspondingly heavy. Claudia Stephan from the Max Planck Institute for Meteorology (MPI-M) in Hamburg is a cloud expert and knows: “How heavy a cloud is depends on how much water it contains and how big it is.” Size can usually only be estimated, since the shape of the cloud varies greatly in its three-dimensionality.” The water content of a cloud, in turn, depends heavily on the temperature. Warm air can hold more water vapor than cold air. When the air is saturated with water vapor, the invisible water vapor condenses into droplets, creating a visible cloud. “However,” says Claudia Stephan, “the condensed proportion of water is usually only about one gram per cubic meter.” As an example, she cites a fair-weather cloud “with a height, width and depth of one kilometer each”. The water it contains therefore weighs “one million kilograms, which corresponds to 1000 tons”. Of course, there are no square clouds in nature; the most precise measurements of the droplet quantity and droplet size are obtained “when flying through a cloud with appropriately equipped aircraft,” says the head of the cloud-wave coupling working group at the MPI-M. But there are “only a few instruments that can measure the three-dimensional structure when flying over it.”
Despite their enormous weight, clouds can stay in the air for a long time because the water droplets that make them up are small and light. These fall to the ground so slowly that they are, as it were, in the air. In addition, updrafts and air turbulence can prevent the drops from falling. However, if the drops in the cloud become too large and heavy, they fall to the ground as rain.
Why are large nuts always on top of muesli? This so-called Brazil nut effect has nothing to do with the convenience of the manufacturer, but is rather due to physical processes. But what exactly is going on? A number of researchers have already tried to crack the Brazil nut effect, but it is not so easy to find out exactly how it works. What is certain is that the mixture has to be shaken or at least slightly agitated so that the Brazil nut effect can take place. On the one hand, smaller nuts, such as peanuts, slip down into the gaps between the larger nuts when shaken. On the other hand, shaking opens up smaller gaps in the peanut mixture into which the large Brazil nuts can penetrate, while the resulting cavity behind the Brazil nuts is immediately filled with peanuts again. In this way, the large nuts gradually reach the surface of the nut mixture. Researchers from the University of Manchester also found that the Brazil nuts first have to stand up in the mixture in order to be able to migrate to the surface. The nuts that were not raised by accidental small collisions remained on the ground even after 181 shakes.
Why is blowing cold and breath warm? If we have cold hands, we like to breathe on them with our breath to warm them up a bit. Since the warm breathing air only has to travel a relatively short distance and is also expelled relatively slowly, it hardly ever mixes with the cold outside air and our fingers get warm.
Quite different when blowing. Even if the air you breathe has the same temperature as when you breathe, it is expelled relatively quickly. It swirls and mixes with the outside air. In addition, we blow away the insulating warm layer of air that surrounds our skin, so that the skin cools down and the whole thing feels colder in an instant.