In winter, when looking out the window, several questions related to precise measurements may arise, most of which belong to the field of temperature. This year, before Christmas, we at Metrosert had a question: is it possible to weigh snowflakes, and how heavy are they?

It turns out that this is a research problem that scientists have already been working on. The exact determination of snowflake mass is important to understand how snow affects microwave* scattering in the atmosphere. This is necessary to more accurately assess whether snowfall impacts remote sensing and communication connections, which depend on microwaves. Therefore, for certain communication fields, evaluating the ice content of snow clouds and the intensity of snowfall is of critical importance.

So, how are snowflakes weighed? Traditionally, the mass of snowflakes has been determined either by measuring the meltwater of manually collected flakes or using imaging techniques that assess the total volume of the flakes and correlate it with the snow water content. However, these methods are labor-intensive and often limited to calculating average values for a sample.

Some time ago, scientists from the University of Utah developed an innovative automatic method that measures the mass of individual snowflakes using a heated plate. The method is based on determining the amount of energy required to evaporate the flake when it comes into contact with a heated aluminum plate. The flake’s mass is calculated based on the temperature drop of the heating plate. Preliminary field results show that the device can measure the mass of flakes starting from 0.4 milligrams and record successive measurements at intervals of 2 to 10 seconds, depending on the size of the flakes and the wind impact.

This new method can be used both independently during snowstorms to study the distribution of snowflake masses and alongside high-resolution imaging techniques to analyze the mass and shape of the flakes simultaneously. This metrological development could provide significant advances in both meteorology and remote sensing.

To form a snowflake, a dust particle is required to which a water droplet attaches in cold air. As a result, a hexagonal structure of an ice crystal forms, as this shape requires the least energy to form. When more water molecules freeze onto the crystal, they join at the corners, again forming a hexagonal structure. All ice crystals are star-shaped, or hexagram-shaped, but their shapes can vary. They can collide with each other and form snowflakes of different shapes. Snowflakes can vary in size, from nearly invisible crystals to snowflakes with a diameter of 2.5 cm or more. A typical small ice crystal may contain 10¹⁸ water molecules, which are scattered throughout the crystal. The mass of a water molecule is 2.992 × 10⁻²⁶ kg. Therefore, the mass of a typical ice crystal may be about 2.9 × 10⁻⁸ kg. A typical snowflake, made up of 100 ice crystals, weighs about 2.9 mg.

It is said that no two snowflakes are alike. Factors such as relative humidity, wind, and temperature affect the growth of each snowflake during its descent. A crystal requires growth conditions where the temperature does not exceed -15 °C. These star-shaped crystals form in high-altitude clouds. In mid-altitude clouds, ice crystals form in needle-like or flat star-shaped forms. In low-altitude clouds, many different star-shaped structures form. The lower the temperature, the sharper the ice crystals’ tips. At higher temperatures, ice crystals grow more slowly and smoothly. When a snowflake melts, its intricate design disappears, and it becomes a water droplet.

Metrosert has not yet measured snowflake mass in the state reference laboratory, because the temperature in the state reference laboratory is constantly 20 °C, which is not favorable for snowflakes. However, we could calibrate the Metrosert laboratories’ elf scales so that all children would still get the right amount of candy during Christmas.

*Microwaves are part of the electromagnetic wave spectrum, with wavelengths ranging from about 1 millimeter to 1 meter (frequency range 300 MHz to 300 GHz). In the atmosphere, microwaves play an important role primarily in remote sensing and communication.

References:

A Novel Technique for Automated Mass Measurements of Individual Snowflakes, Gergely, M ; Shkurko, K ; Simon, E, 2016, https://ui.adsabs.harvard.edu/abs/2016AGUFM.A23A0177G/abstract

Measurement report: Mass and Density of Individual Frozen Hydrometeors, Karlie N. Rees ; Dhiraj K. Singh ; Eric R. Pardyjak ; and Timothy J. Garrett, 2021, https://acp.copernicus.org/articles/21/14235/2021/acp-21-14235-2021.pdf