In search of snow’s secrets
Nature is full of genius, full of divinity; so that not a snowflake escapes its fashioning hand.
Henry David Thoreau
By Katrin Henneberg and Katarina Werneburg
Translation by Matthew Rockey
Where the peaks almost touch the sky
High up in the majestic Rocky Mountains, where the peaks seem to touch the sky and the wilderness shines in all its splendour, four researchers from Leipzig embarked on an ambitious adventure. The meteorologists took part in a major measurement campaign as part of the international research project SAIL, a huge field experiment that involved almost two years of interdisciplinary measurements of the hydrological cycle.
In this inspiring scientific setting, in the midst of an overwhelming landscape and against the breathtaking backdrop of the 3,850-metre-high Gothic Mountain, the meteorologists opened a new chapter in the history of snow research: their measurements, unprecedented in their wealth and complexity, have allowed them to delve deep into the mysteries of snow and its formation.
The best way to understand complex snowfall processes is with a large amount of data. The Rocky Mountains receive many times more snow than Germany. Ten metres of snow fell on Gothic last winter.
Junior Professor Heike Kalesse-Los, Leipzig Institute for Meteorology
A love of snow
On her way to the Rocky Mountains in June 2023: Junior Professor Heike Kalesse-Los travelled to Gothic (Colorado, US) to dismantle and send home the Leipzig Institute for Meteorology’s snowfall cameras and cloud radar after seven months of measurements. While changing planes in Denver, the meteorologist checked the current weather in Gothic as recorded by these instruments.
In the SAIL sub-project CORSIPP, a quartet of scientists from the Institute for Meteorology at Leipzig University is investigating orography-influenced riming of ice crystal particles, the associated secondary ice production and its effects on precipitation rates.
- Junior Professor Heike Kalesse-Los, co-lead CORSIPP sub-project
- Dr Maximilian Maahn, research assistant, co-lead CORSIPP sub-project
- Dr Veronika Ettrichrätz, postdoctoral researcher
- Anton Kötsche, doctoral researcher
The brains behind the measurement campaign
High in the mountains, where the land and atmosphere are intimately linked
Junior Professor Heike Kalesse-Los explains the background of the international SAIL field experiment.
Dr Maximilian Maahn on the process of secondary ice production, a key aspect of the CORSIPP measurement campaign.
Mountains are the planet’s natural water reservoirs. They play a key role in the global water balance. In their complex, rugged landscapes, the land and the atmosphere are intimately linked and interact in many ways.
Until now, relatively few atmospheric and hydrological measurements have taken place in mountain environments. As a result, scientists have not fully understood the key processes involved in the water cycle.
The interdisciplinary SAIL campaign and the CORSIPP sub-project have collected vast amounts of usable data to map and describe the key processes of the hydrological cycle and to improve previously inadequate computer models.
How does snowfall form?
When it snows, the following mechanisms are often at work:
- Initially, small droplets of water freeze on ice crystals, which greatly increases the mass of the snow. This is called riming.
- There is also the process of secondary ice production. This can lead to a higher number of ice crystals in the clouds than the number of actual ice nuclei would suggest.
Secondary ice production is for example triggered when ice crystal fragments break off during riming and form new snow particles.
This process explains why we often measure more snowflakes on the ground than the number of original ice nuclei would suggest. The question of how often snowflake riming occurs is a complex one. For example, it depends on whether the clouds contain layers of liquid water through which the snowflakes can fall, and how fast the snowflakes fall.
Junior Professor Heike Kalesse-Los, Leipzig Institute for Meteorology
The images show, from left to right: pristine (untouched) snowflake dendrites, their increasing riming and, at the end, graupel or soft hail.
The images show pristine (untouched) snowflake plates and so-called sectored snowflake plates.
Images of non-rimed snowflakes taken by a snowfall camera on 3 December 2022.
Until now, the weather and climate models used by scientists have not been able to accurately model the complex processes involved in snow formation.
To significantly improve the quality and quantity of data, the research team used a combination of state-of-the-art technologies:
- A radar system for remote sensing of clouds
- And two snowfall cameras to document in detail what actually lands on the ground and the extent of particle riming.
The data obtained is really exciting. The snowfall cameras allowed us to clearly see the shape and size of the particles, while the cloud radar measured variables from which we could deduce the size of the particles, how many there were and how fast they were falling.
Junior Professor Heike Kalesse-Los, Leipzig Institute for Meteorology
From mining town to research village:
metres above sea level
The village of Gothic, at an altitude of 2,891 metres, is set in stunning countryside at the foot of the 3,850-metre-high Gothic Mountain. The majestic mountain landscape is characterised by snow-capped peaks, deep gorges and dense forests. Built in 1879 as a silver mining town, this remote village consists of a handful of modest log cabins. Today, it is mainly used for research.
Arrival in Gothic: the research team from Leipzig explore where they’ll be staying for the next few days.
Rocky Mountain Biological Laboratory – RMBL for short – is the name of the field station near the abandoned mining town of Gothic. It has been in existence since 1928 and has hosted the entire SAIL campaign.
Winter in Gothic in November 2022.
Doctoral researcher Anton Kötsche helped set up the measuring equipment.
When the researchers from Leipzig returned to the Rocky Mountains in June to dismantle their station, the only snow left was on much higher ground.
About to leave for Leipzig, Junior Professor Heike Kalesse-Los sits on top of her carefully packed “suitcase”.
The beating heart of the research
The SAIL campaign’s meteorological and hydrological monitoring stations were set up on all the slopes and in the valley around Gothic.
Back at the institute in Leipzig, the meteorologists have long since unpacked their LIMRAD94 cloud radar and two snowfall cameras.
Their task now is to combine the data collected by the instruments, which promises new insights.
The great thing about radar is that it can see into clouds. This will give us an idea of exactly what processes are going on in a cloud at any given time.
Dr Maximilian Maahn, Leipzig Institute for Meteorology
What exactly happens in clouds? The cloud radar recorded this for seven months.
The cloud radar in winter 2022/23.
At the same time, the snowfall cameras filmed snowflakes hitting the ground from two different angles.
The snowfall cameras shortly before being dismantled in June 2023.
Containers with the SAIL campaign instruments.
View of the SAIL containers from above.
The cloud radar
Junior Professor Heike Kalesse-Los explains how the Leipzig cloud radar works.
The snowfall cameras
Filming the snowflakes with two cameras from two angles was helpful in seeing the riming process directly in the images. When riming has taken place on the so-called dendrites, the snowflakes look much denser and more compact – and they then fall faster.
Dr Veronika Ettrichrätz, Leipzig Institute for Meteorology
Visualising the shape of the flakes, their size, the number of particles and how fast they fall – snowfall cameras can do all of this. Dr Veronika Ettrichrätz shows how the snowflakes are photographed and filmed.
The radiosonde
In addition, technicians from the Atmospheric Radiation Measurement (ARM) user facility used a weather balloon for radiosonde ascents twice a day, always at the same time.
This allowed us to measure air temperature, humidity, pressure and wind speed at different altitudes in order to create another profile with high-resolution weather data directly from the atmosphere. It will also be used in weather and climate models.
Junior Professor Heike Kalesse-Los,
Leipzig Institute for Meteorology
Day one of shutting down and dismantling the cloud radar: Junior Professor Heike Kalesse-Los first takes a look at the latest data recorded by the system.
A 3D puzzle in reverse
Struggling to loosen long, thick screws, patiently disconnecting countless cables and packing each part securely for transport – for the researchers, dismantling the instrumentation was a laborious, fiddly and sometimes physically demanding task.
When it came to packing and loading the valuable, sometimes very heavy and highly sensitive equipment, every move had to be just right. Fortunately, there were plenty of people to help.
A data set of particular value
The south-west of the United States, where the Rocky Mountains are located, has been suffering from a severe water shortage for several years. The results of the CORSIPP campaign provide an essential piece of the puzzle in understanding the entire water cycle in the region.
In the next step, new evaluation and visualisation algorithms programmed by the meteorologists themselves will play a decisive role in penetrating the formation of snow – and precipitation in general – in detail. Ultimately, this will also allow for more accurate precipitation forecasts.
The knowledge gained by the researchers from Leipzig also benefits from the other measurements of the SAIL campaign, which used a wide range of remote sensing instruments. All this data, combined with the Leipzig meteorologists’ measurements, makes the final data set particularly comprehensive and valuable – and the first link in a long chain of research.
A better understanding of how snow and precipitation form in clouds will help to make weather and climate models more accurate in the future. This will allow more reliable predictions of precipitation and provide insights into how precipitation patterns may change in a warming world. The results of our research are an important first step in this direction.
Dr Maximilian Maahn, Leipzig Institute for Meteorology
An impressive wealth of data, surprising findings, exciting conclusions:
the researchers talk about the possibilities that the measurements they have recorded are now opening up for the science of snow.
The number of snowflakes observed by the meteorologists from Leipzig
Each snowflake is unique. Many resemble beautiful poinsettias, while others look like hexagonal discs, columns or very thin needles. There are countless types and forms.
Dr Veronika Ettrichrätz, Leipzig Institute for Meteorology
Published by: Office for University Communications Katrin Henneberg (Text, layout and design) Dr Katarina Werneburg (Editing, layout and design) Translation: Matthew Rockey Email: presse@uni-leipzig.de
The photos and videos of the site were taken by the scientists from the Leipzig Institute for Meteorology. Email: heike.kalesse@uni-leipzig.de; maximilian.maahn@uni-leipzig.de
Publication date: 1 December 2023