Author Archives: Claudia Hinz
Artificial St. Elmo’s Fire
by Reinhard Nitze
What it is about
St. Elmo’s fire is a natural form of electrostatic discharge. It belongs to the so-called electrometeors and appears as a self-luminous corona discharge. It usually occurs during thunderstorms, but can also appear in winter weather conditions (especially during solid precipitation).
Direct observations of St. Elmo’s fire have become very rare in recent decades due to increasing light pollution and sometimes unpleasant or even dangerous weather conditions. However, it is frequently recorded by automated photo webcams. There, it often appears as small blue glowing tufts. These are always attached to pointed objects, usually at the ends of poles, masts, antennas, and similar structures.
If such a mast is covered with ice crystals, these act as attractors and can, in extreme cases, form a kind of “flag” of St. Elmo’s fire. It has also been observed on sharp rock ridges and at the tips of tree branches [1].
Background
At the spring seminar 2022 of the “Arbeitskreis Meteore,” the phenomenon described above was the subject of two presentations (“News about St. Elmo’s Fire” by Rainer Timm and “Unusual St. Elmo’s Fire during the night of 03/04 November 2021 over the Alps” by Claudia Hinz). These talks, together with images of electrostatic discharges on clothing and blankets shown afterwards, inspired the idea of artificially generating and photographing St. Elmo’s fire.
Back home, Reinhard Nitze (the author) began experimenting. After some initial thoughts and preliminary tests, the first results appeared when a PVC pipe was rubbed with a piece of cotton cloth in complete darkness. Weak, colorless, lightning-like emissions became visible (through the cloth), accompanied by the typical crackling sounds of electrical discharge.
Capturing these discharges with a digital camera proved difficult. Only long exposure with a high ISO setting made the “St. Elmo’s fire” visible as a diffuse blue “force field,” caused by motion blur. However, the first test images were mostly not convincing, with one exception.
Left: This PVC pipe was used for the first successful “St. Elmo’s fire” tests.
Middle: One of the first successful images of artificial St. Elmo’s fire in these experiments, appearing as a blue “force field.”
Right: The exception: Numerous individual discharges recorded indirectly under a cloth while rubbing the PVC pipe. The only directly visible discharge is the slightly violet tip originating from a finger holding the pipe (faintly visible).
Improving the experiment
Acrylic glass provided a solution. A sheet covered with protective film on both sides was used. A short test by rubbing the sheet with a cloth produced audible crackling, proving electrostatic discharges.
After dark, experiments began. The sheet was electrically charged by rubbing and then held above or moved along a test object. Depending on the shape and material of the object, the desired light emissions appeared—mostly as individual feather-like flashes or small bundles of flashes. The results were significantly better than those achieved with the PVC pipe. This made it possible to create a proper photo series. The first images of artificial St. Elmo’s fire comparable to natural observations were produced.
After many experiments, the protective film on the sheet began to peel off at the corners. When it was removed in the dark, continuous electrostatic light phenomena appeared along the separation line between film and sheet—vertical, parallel, constantly flickering light fibers accompanied by typical crackling sounds.
This observation led to the method still used by the author today, described below.
The best method
In the “forearm–thigh clamping method,” an acrylic glass sheet is pressed against bare skin between the forearm and thigh so that it can still be moved back and forth. When performing this motion, electrostatic charging usually occurs after a short time. This is noticeable through tingling on the skin, hair standing up, audible crackling, and—most importantly—light emissions along the contact line between the sheet and the skin.
These emissions typically appear as small, tuft-like flashes. Their strength and frequency depend on the level of charge, the pressure between arm and leg, and the speed of movement. With the right combination, the “St. Elmo’s fire” can even appear continuously during motion. It takes some time to reach full intensity. A dry environment and low humidity are essential. If charging does not occur, sweating or high humidity is usually the cause. Ventilating the room often helps.
Grease films (fingerprints, skin oils) also reduce effectiveness and should be removed regularly. Floor conditions and shoe soles (if standing) may also influence charging. If no charging occurs, changing location or footwear (especially if antistatic) may help.
Because the light emissions are very faint, they are only visible in darkness—the darker, the better. They are typically colorless, sometimes slightly greenish or bluish after dark adaptation. Strong discharges may briefly show pink or violet tones. In long-exposure digital photography, however, intense colors appear—mainly blue, with violet, pink, and white in the center of the discharge tufts. The discharges can reach several centimeters in length and often originate where body hairs are present. They frequently form tufted or flame-like structures.structures.
Variations of the experiment
To create this “St. Elmo’s fire” on other objects, several methods can be used:
Method 1: Hold the charged sheet and move it close (max. ~10 cm) to the object.
Advantage: Any accessible object can be tested; photography is relatively easy.
Disadvantage: Some loss of charge reduces effectiveness.
Method 2: Move the object over the charged sheet.
Advantage: Easy for small objects; slightly more efficient.
Disadvantage: Difficult to photograph.
Method 3 (best): Place the object next to the thigh and expose it directly during charging.
Advantage: Minimal energy loss; best for photography.
Disadvantage: Object size is limited; risk of contact with the sheet.
Experimental goals / observations
The main question—whether St. Elmo’s fire can be artificially produced—can clearly be answered: yes.
Various materials can be tested:
- Natural objects:
- Stones
- Plants
- Self-experiment
- Artificial objects:
- Metallic objects
- Non-metallic objects
All test objects should have sharp points or edges, as these act as attractors for electrostatic energy.
Description of experiments
Artificial St. Elmo’s fire on stones and minerals:
Left: Lava from Tenerife · Right: Rock crystal tip
Calcite (crystalline limestone), with and without additional lighting
Left: Fluorite with quartz, dry and moistened · Right: Galena (lead ore)
Artificial St. Elmo’s fire on plants and plant parts:
Chestnuts in their spiky husks are excellent for producing artificial St. Elmo’s fire. Multiple “flames” can often appear simultaneously. Both positive and negative St. Elmo’s fire can be observed. Literature describes positive discharge as tufted or flame-like, and negative as point-like glowing. In the chestnut images, the positive discharge appears at the top, while the negative appears as glowing points near the ground. Positive discharge is generally more visually impressive, but negative discharge is also interesting and best observed in macro photography.
All four images show negative St. Elmo’s fire in macro view on chestnut spikes. It appears spherical or candle-like. The last image is unusual, likely showing a polarity reversal during exposure.
Pear stem with St. Elmo’s fire
Apple stem with St. Elmo’s fire
Bouquet with St. Elmo’s fire
Turkish hazelnut
Acorn on flint from Rügen
Oak leaves
Fir branch
Artificial St. Elmo’s fire on metallic objects
Left: copper wire; Right: cut ends of galvanized chicken wire
Close-up (macro) of cut chicken wire
Left: Created “in a moment of beer inspiration”
Right: Natural St. Elmo’s fire on a metal rod (likely with ice crystals), photographed on 03 Nov 2021 in Axamer Lizum near Innsbruck, Tyrol (Photo: panomax.com)
Artificial St. Elmo’s fire on non-metallic objects
Left: Negative and positive discharge on the magazine “Meteoros” · Right: On the spout of a plastic measuring cup
Conclusion
With the right technique, it is quite easy to generate St. Elmo’s fire or similar corona discharges. The required equipment is minimal: an acrylic glass sheet (other plastics may also work, but were not tested) and proper handling.
Surprisingly, many materials proved suitable, including ones not expected due to their electrical properties—such as quartz crystals and paper.
Electrical conductivity influenced the behavior:
- Poor conductors produced stronger but more isolated discharges.
- Good conductors produced more continuous but weaker-looking discharges in long exposures.
Most generated discharges were positive (tufted), while only a small fraction were negative (point-like glowing). The reason is unclear but likely related to humidity.
Higher humidity (e.g., due to sweating) can reduce charging and lead to weaker glow discharges.
Side effects / Disclaimer
These experiments are generally harmless, but electrostatic voltages of several thousand volts can occur. There is always a risk of electric shocks, which can sometimes be surprisingly strong.
People who are sensitive, have pre-existing health conditions, or rely on electronic medical devices (e.g., pacemakers) should not perform these experiments.
Additionally:
- Static electricity can ignite flammable gases, vapors, or dust mixtures.
- Electronic components may be damaged by electrostatic discharge (ESD).
Anyone repeating these experiments does so at their own risk. The author assumes no responsibility for any damage or consequences.
References
[1] Obermayer, A. v. (1889) Elmsfeuererscheinungen in den Alpen. Zeitschrift des Deutschen und (des) Österreichischen Alpenvereins, Jahrgang 1889, (Band XX), S. 94–101.
[2] Elster, J. & Geitel, H. (1892) Elmsfeuerbeobachtungen auf dem Sonnblick. Akademie d. Wissenschaften Wien 1892
[3] Bosshard, E. (1897) Elmsfeuer und Blitzgefahr im Gebirge. SAC-Jahrbuch 1897
[4] Hinz, C. & Timm, R. (2021) Elmsfeuer in der Geschichte und der Gegenwart. METEOROS 11-12/2021
[5] Hinz, C. & Timm, R. (2022) Fachausschuss Amateurmeteorologie: Elmsfeuer in der Geschichte und der Gegenwart. Mitteilungen DMG 1/2022
[6] Timm, R. & Hinz, C. (2022) Neues vom Elmsfeuer. METEOROS 04/2022
A Look Back at the May 10–11, 2024 Aurora Display Featuring RAGDA
An extreme geomagnetic storm brought spectacular auroral displays on the night of May 10–11, 2024, which were photographed as far south as Mexico, Florida, and Algeria. In the Southern Hemisphere, the “Aurora Australis” reached unusually far north, being visible from Australia, Argentina, Chile, and New Zealand. The storm was triggered by a so-called “cannibal CME” – a phenomenon that occurs when a later, faster coronal mass ejection (CME) overtakes and collides with an earlier one, compressing plasma density and velocity into a massive shock front.
We observed the aurora from Schwarzenberg, Ore Mountains, Germany (50° 32′ 43″ N, 12° 46′ 45″ E). By the end of twilight, faint reddish beams were already visible, intensifying as darkness fell and sweeping from north to west, where the waxing crescent Moon appeared to be “dancing” within the auroral glow. Around 22:45 local time, the characteristic rays gave way to a diffuse crimson glow that stretched photographically far into the southern sky. A further outburst shortly after midnight sent red-violet rays to the zenith, where they converged in a Corona. In the south, green patches pulsed with vivid intensity, with upward-shooting red rays fanning out like flower petals – a breathtaking sight unlike anything we had ever seen before.
This rare event was identified as a RAGDA (Red Arc with Green Diffuse Aurora), a phenomenon occurring at the southern edge of the auroral oval and characterized by deep red arcs accompanied by green, pulsating spots. However, the sharply defined, upward-shooting rays we observed have not been described in connection with RAGDA before.
Research led by Toshi Nishimura in collaboration with Finnish amateur astronomers has shed light on this phenomenon. While typical auroras are caused by solar-wind electrons, RAGDA is driven by solar-wind protons colliding with atmospheric atoms, initiating a chain reaction. These collisions liberate electrons, which then excite other particles, producing the distinctive two-tone auroral display and, occasionally, transient rays such as those we captured. To date, this specific phenomenon has only been documented twice, and in both cases the rays were more diffuse and less sharply defined. Intriguingly, these rays appear to suppress the green diffuse glow while leaving the red arc intact. (→ Link to article)
There are now several dedicated reporting platforms for unusual auroral forms. Such reports are scientifically valuable, as they have revealed that some auroral emissions are not solely driven by particles from solar storms but also by protons originating within Earth’s magnetosphere, funneled downward along magnetic field lines. A key indicator is that aurora-producing particles often carry hundreds to thousands of times more energy than particles within a CME striking Earth. Anyone who photographs unusual auroras is encouraged to share their images with scientists—precise time and location metadata are more important than precise classification.
Aurora Reporting Platforms for Scientific Collaboration:
- Project Solarmax: www.solarmaxmission.com
- Skywarden (Finland): www.taivaanvahti.fi
- Aurorasaurus: www.aurorasaurus.org
Curiosity Captures First Crepuscular Rays and Noctilucent Clouds on Mars
Source: NASA/JPL-Caltech/MSSS/SSI, compiled by Claudia Hinz
On February 2, 2023, the 3,730th Martian sol, NASA’s Curiosity rover successfully captured images of noctilucent clouds and crepuscular rays shortly after sunset, projected onto thin clouds in the Martian atmosphere. The composite image is made up of 28 individual frames taken by the rover’s Mast Camera (Mastcam) and enhanced to improve the visibility of the phenomenon. This marked the first time such atmospheric features had been observed on Mars with such clarity.
The image was taken as part of an ongoing investigation into “noctilucent clouds” on Mars, which began in 2021. While most Martian clouds form no higher than 60 kilometers above the surface and are composed primarily of water ice, these clouds appear at much higher altitudes and within extremely cold atmospheric layers. This suggests that they are composed of carbon dioxide ice, or dry ice. The initial detection of a Martian halo on December 15, 2021, already indicated the presence of tenuous clouds in the Martian atmosphere consisting of fine ice crystals.
Unusual Twilight Phenomena in Europe
Between August 21 and September 3, 2017, unusual twilight phenomena could be observed in widespread parts of Germany. In most cases, the sky turned into a bright yellow short after sunset. Some observers reported an increase of brightness when this yellow glow appeared. During the following 20 minutes, the colour changed into orange and later into red with the coloured part of the sky shrinking towards the western horizon. At the end, only a narrow red stripe directly above the horizon remained. Additionally, there was a very intense purple light even during the “orange phase”. Many observers reported that the landscape also appeared in a bright yellow or orange coloured light.
At daytime, the sky appeared in a pale blue as if there was a layer of thin cirrostratus clouds. At low sun elevations, stripes and ripples appeared in this layer. Some observers felt reminded of noctilucent clouds by these structures.
In the mornings, these phenomena also appeared in reversed order.
Similar phenomena were also reported from observers in Austria, Hungary, the United Kingdom, Danmark and Iceland and showed up in several pictures by webcams in the Czech Republic.
More pictures and time lapses (e.g. 1–2) you can find in the Forum of “Arbeitskreis Meteore e.V.
These strange twilight phenomena were caused by the smoke of huge wildfires in Canada. The plumes of these fires ascended up to the stratosphere reaching altitudes of about 15 kilometres. Then they were transported over the Atlantic Ocean by the wind.
When travelling through the northeastern parts of the USA to observe the total solar eclipse which ocurred on August 21, Andreas Möller could take photographs of these plumes of smoke.
Author: Peter Krämer, Bochum, Germany
Searching for Sub-Visual Atmospheric Structures in the Daytime Sky
On sunny, warm days the sun heats the Earth’s surface and the air close to it. Periodically a parcel of air will rise from this area due to the warmed air being buoyant. This parcel is thought to rise in an elongated column of fairly large size such that several hundred tons of air are lofted skyward. In doing so many of the particles generated by Earth-bound processes (pollen, smoke, dust, pollution, water vapor, etc.) are brought with it. These particles are commonly known as aerosols. If the column reaches an altitude where the contained water vapor condenses then a cumulus cloud will form.
It is known that aerosols have a large effect on polarization of light, up to 30% or so. My first experiment in photographing these columns of air was to take 2 sequential photos of the sky with a linear polarization filter set to 90 degrees apart. Then in accordance with the article excerpt shown below and using an image processing program (Image Magik) I calculated the degree of linear polarization (DOLP) of each pixel from the formula given in the article. The resulting pictures are interesting and strange but do not show the expected structures.
I encourage others to make their own attempt at this goal as I am really a novice at image processing. No doubt there are many other ways of looking at this problem and I welcome all comments, thoughts and ideas. Thanks!
Excerpt from the article “Digital All-Sky Polarization Imaging of Partly Cloudy Skies” from Nathan J. Pust and Joseph A. Shaw
“It is our feeling that unseen aerosols and possibly thin clouds in what has recently been called the “twilight zone” between a cloud and the clear sky are reducing the DOLP in what appears to be clear sky. We believe that this effect on the sky polarization is directly related to the recently described observations of enhanced optical depth near clouds. In partially cloudy skies, we see DOLP reductions in clear sky areas between clouds that appear to be caused by subvisual aerosols and/or clouds. (Even though clouds appear to have hard edges, they are in fact surrounded by thin clouds.) Furthermore, these DOLP reductions show up in the clear sky long before we can physically see clouds in the sky.”
To determine Degree of Linear Polarization (DOLP) in each pixel he uses this formula:
(Image1pixel value – Image2pixelvalue) / (Image1pixel value + Image2pixelvalue)
Then he normalizes and stretches the result so it fills the whole 8 bit range of 0 to 255 pixel brightness values.
Some of my resulting pictures:
Author: Deane Williams, Connecticut, USA
Green-rimmed cloud at sunrise
On June 14th, 2014, I could observe green flamelets at the upper rim of an altocumulus cloud from Mt. Zugspitze (2963 m above sea level). The cloud was located left from the rising sun, and the phenomenon lasted from two minutes before the visible sunrise until shortly after it. At the moment of the astronomical sunrise the green flamelets at the cloud vanished. Additionally, green and blue rims appeared at the sun’s disk (see pictures 1 – 2).
I already observed a similar phenomenon a few seconds after sunset on September 24th, 2013, from Mt. Zugspitze. However, I could only take a single photograph of it. As there were seemingly no other reports about green cloud rims I decided to let the matter rest at that time. It was only after the second occurrence that I re-visited the case of the older observation.
When doing a new search for similar reports I encountered an observation from by Robert Wagner, January 7th, 2008, who also recorded green cloud rims during sunset on La Palma (2136 m above sea level).
No other documented observations could be found on the internet so far.
We cannot offer a complete explanation yet. It may be that the cloud edge, when illuminated from behind, acts as a separate light source and the green flamelets are then caused by the refractive dispersion of a weak mirage effect. This is consistent with the presence of blue and green rims at the sun, which indeed have been observed in all three cases. Furthermore, all observations were carried out from high mountains, from where the true geographic horizon already lies below zero elevation, and even the ordinary elevation shift due to refraction is already pretty high due to the long light path through the atmosphere.
More ideas and reports of similar observations are welcome in any case.
Author: Claudia Hinz
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Edit 21th March, 2017:
I would like to add a video to this article, in which I was record the green rimmed clouds on the Mt. Fichtelberg/Ore Mountains on 20-12-2016.
Gloridescent clouds
As “Gloridescence” I define colored clouds in the antisolar area, where there is no visible connection to a glory.
The first observation of colored clouds at the antisolar point was made by Stefan Rubach on Mt. Großer Arber at Jan. 26, 2007. We suspected fragments of a glory, but we were not sure.
Jan. 26, 2007: Glorydescence on Mt. Großer Arber. Photo: Stefan Rubach
On Nov. 18, 2007, I made the first observation of my own and on Mar. 1, 2010 my second observation at Mt. Wendelstein (1835m).
At Mt. Zugspitze (2963m) I observed these colored clouds a few times and named them „gloridescent clouds“ (and so far no one ever challenged this name).
On Apr. 25, 2015 I made my first observation of „gloridescent clouds“ at Mt. Fichtelberg (1215m). Meanwhile we received more observations, one from the valley of Neckar river, one photo by Eva Beatrix Bora from Stavanger, Norway and some from an aircraft (1 – 2). From these we conclude that:
- Just as glories become more frequent with increasing observing levels (see this article), the frequency of “Gloridescence” also increases.
- At lower altitudes (i.e. in the area of low clouds), “Gloridescence” originates mainly from underneath of stratocumulus clouds.
- At higher mountains (e.g. Zugspitze, 2963m) and on airplanes, “gloridescent clouds” are more frequent and appear mainly in deeper cloud layers or single shreds of clouds.
Author: Claudia Hinz, Schwarzenberg, Germany
Frequency of glories from different observation levels
Glory and Fogbow with interferences at Mt. Zugspitze
The combination of spectre of Brocken with glory and fog bow is named after the German Brocken mountain, even though it cannot be observed there too often. My colleagues from the weather station estimated a frequency of 2 or 3 observations per year at the top of the mountain. The phenomena much more frequently observed at higher mountains.
Since there is no reliable statistics about the frequency of Glories to date, I tried to obtain some tendencies from my own observations on various mountain tops.
I observed at three different mountain tops where I worked for a longer amount of time:
- Mount Fichtelberg, Ore mountains, 1214m (similar height as Mt. Brocken)
- Mount Wendelstein, Alps, 1838m (standalone rock)
- Mount Zugspitze, Alps, 2963m (main mountain chain of the Alps)
Fichtelberg I observed most frequently in the early morning hours without interferences. On Mt. Wendelstein the Glories often long duration phenomena, sometimes very colorful with impressive interferences. On top of Mt. Zugspitze the Glory was visible at every solar altitude, in most cases long duration, with impressive interferences an colors.
I tried to capture the frequency of glory statistically. Since I could not look at the same time periods, the statistics is an approximation.
These observations lead to the following conclusions:
- The frequency of glories increases with altitude (at my observing sites the number of glories increased by a factor of three for every 1000m altitude)
- The higher the altitude of the observation point, the more impressive are the glories! With increasing altitude of the cloud, the size of the droplet in the clouds decreases and interferences become more frequent. Because the smaller and more uniform the droplet size, the more impressive becomes the glory (Simulation of Les Cowley). In the best case, the glory transforms into interferences of a cloud bow.
- The duration of the phenomenon increases with the altitude, too. If the local conditions allow observations well below the horizon, the glory is possible at every solar altitude.
Author: Claudia Hinz, Schwarzenberg, Germany
Binary double rainbows
In past years I have done spot light rainbows when the rain was a fine mist. After seeing the results of a nice fog bow my LED flashlight made and since I had two I thought why don’t I try doing two at once. So I turned both lights on the hi-power mode which yielded a very bright beam of light and both lights were placed on fence posts 2 meters apart. I angled the lights so the beams crossed and at the point where they crossed is where I placed the camera. I took a shot was blown away by the results! There it was two full circle double rainbows crossing one another. I took quite a few shots before I was getting chill and wet. Just think if you landed on an Earth like exo-planet orbiting a binary star system and upon exiting your space craft you look up and see twin suns shining above then you hear a rumble of thunder. You retreat into your ship for shelter and later the storm moves on but its still raining but you look on the opposite side of the sky and see two double rainbows displaced a few degrees apart and the bows would cross one another. These flashlight binary double rainbows show how rainbows would look to civilizations living on Earth like Exo-planets orbiting double, triple, or even quadruple star systems. Next time I will use 3 and 4 LED flashlights. On the nights I was doing these bows the wind was blowing and I could see the primary bow in particular would move from side to side and one pic even shows that it could be twinned!!!
Author: Michael Ellestad, USA
Commonly spread Ice Wool
On February 2nd, 2016, we made an excursion to the Anna Tower together with my daughter´s form. The Anna Tower is located in the Deister hills, a small range of hills at about 20 kilometres southwest of Hanover. Its highest elevation ist Mt Bröhn near the Anna Tower with about 405 metres above sea level. We startet from the Nienstädter Pass at 277 metres above sea level. The car park there is covered with gravel and normally rather muddy, but that day it was frozen and hoar frost glittered everywhere. When we startet our excursion, the weather was bright and sunny. But as soon as we left the car park, I noticed a fibrous thing of brilliant white just beside the path which leads along the top of the range. At first sight, it looked like a sheared piece of wool from a sheep. But for me it was clear what it was: ice wool!
The first ice wool I ever found
Up to then, I knew ice wool only from descriptions, and although I had been looking for it for years everytimes there was a light frost, I never found some. And now I found it right beside the path, without having searched for it! After having given others a hint on that phenomenon and explaining it, I took some photographs and then continued my way – slowly and even slower, because there were more and more tree branches which showed ice wool. After having found 10 of these ice wool formations, I roughly counted them, but when I reached 50, I stopped counting. It made no sense, because there was too much. I found a place where at least 20 branches and twigs with ice wool laid around. Not every ice wool formation was well defined, but there were also some very bizarre ones among them!
Large accumulation of branches with ice wool
I arrived at the Anna Tower about one hour delayed. The weather was nice, but it was not really clear. There was a distinct inversion with a pronounced layer of mist, but without any mirages. I think, for this the hill is not high enough. (At really clear conditions you can see Mt Brocken in the east and the Porta Westfalica in the west from the Anna Tower).
Three weeks later, on February 27, I succeeded in finding ice wool at the Nienstädter Pass again. This time I was prepared better and brought a retro adapter to make macro photographs. Thus it was possible to take detailed pictures of the ice wool. Some parts of it had structures which reminded of chains of bacilli. Other parts just looked like shiny and transparent hair. The augmentation effect of the lens with retro adapter was not strong enough to unravel the structures here.
Background information:
Ice wool is a physical and biological phenomenon which mainly appears on rotten and decayed wood in deciduous forest with mixed types of trees. It forms hairy ice curls of a brilliant white which remind of candyfloss. Sometimes it looks like paintbrushs with the uppermost parts cut away, others look like wool from a sheep, others remind of minerals or lichen. And sometimes it looks just like a thrown away paper tissue and is often mixed up with this from the distance. But it has always this hairy and cristalline structure which sometimes looks like chains or if it was covered with sugar.
Ice wool is caused by the activity of funguses which decompose rotten wood. During this process, water is set free which gets out of the dead wood through capillaries and freezes at temperatures around or slightly below 0 °C, forming these hairy ice structures. This works as long as the wood itself does not freeze. Contrary to hoar frost crystals, ice wool is formed by liquid water from the wood freezing outside while the atmosphere is not involved. It is not long ago that the process could really be clarified.
Ideal conditions for the formation of ice wool are given when after a period of mild weather with (light) rain the sky clears off at night allowing frost on the ground. So, when you have to scratch the ice off your car windows, there is also a chance of encountering ice wool in the forests. It can be found from October until the beginning of March, except during very cold periods. Best places to find ice wool are under oak and beech trees and maybe also under some larches. Other conifers are not suitable.
But you also need some good luck when looking for ice wool, just as it normally is not wide spread. Similar to the appearing of mushrooms and toadstools, there seem to be good and bad years. Even if the conditions may apparently be perfect, you will not automatically find ice wool. Locations also seem to play an important role as I could see for myself a short time ago. While ice wool was rather abundant up there along the path on the top of the range, I could not find any of it in the Deister forest near my home, although the tree population there is not very different from that at the Nienstädter Pass. Also here lots of branches and twigs in all stages of rotting are lying around, but there is not a single trace of ice wool to be found.
Author: Reinhard Nitze, Barsinghausen, Germany
Atmospheric Phenomena