People from countries with strong winters know something that many other people don‘t know. It doesn‘t have to be warm for snow to disappear. In fact, even if it is cold piles of snow in the yard are slowly decreasing in size. But how quickly? Does snow or water disappear into thin air quicker? Scientists from University of Amsterdam decided to find out.
You know how water disappears – it evaporates. However, most people think that higher temperatures are needed for this to happen, which is not the case. Solids can skip the state of being liquid and go immediately into vapour. This process is called sublimation and it is what makes piles of snow shrink in temperatures that are below the freezing point. That and the simple matter of compaction. Scientists did some testing and found that your perception of evaporating may be completely wrong – ice and water can evaporate at the same rate.
Let’s take two droplets of pure water. We freeze one and we leave the second one on the table. Which one will disappear quicker under the same conditions? Scientists say that they both will be gone around the same time. This is quite a bizarre phenomenon – it is hard to wrap your head around it. But it is very important to study. Ice in the clouds affects our climate greatly, because it reflects the sunlight. It is also important to be prepared for whatever the weather might bring, such as hail, blizzards and similar extreme weather events. Finally, sublimating snow leaves cavities on top of the mountains, which can cause a lot of different problems. But then why ice and liquid water disappears at the same speed? How can we explain this phenomenon?
Scientists say that the speed of evaporation of sublimation is determined by the rate of a single process, called diffusion. Water vapour slowly spreads through the air, making its concentration even. Water vapour in the air can only move so fast. This limits the speed of evaporation of both liquid and solid water. It also makes the structure of snow different. During the process of sublimation individual snowflakes become more rounded, which changes the feel of the snow. While these results may impact other studies of snow and weather, their implications are far more reaching.
Scientists say that the same knowledge can be applied to other crystalline structures, such as nanoparticles and salt crystals. Information gathered in this study will be important in studying the dissolution rate of pharmaceuticals as well. But, of course, it is nice to know that you are not just seeing things – fresh snow is different than one day old snow.
Source: University of Amsterdam