What actually is freezing rain and how it impacts infrastructure?
The freezing rain process cannot be understood without the prior know- how of the term super cooled water. As we can see in the picture below of a melting ice chunk, the surrounding appears to be at 0 degree Celsius.
We all know ice melts at 0 c but many people incorrectly believe 0 c to be the freezing point of water as well. There are many other factors which catalyzes the icing process.
Be care full! The process of conversion from solid to liquid state at a particular temperature does not mean its reversal at exactly the same temperature.
What happens is:
Liquid water requires impurities (cloud condensation nucleus) such as soot; dust etc. in the surroundings which are used as ice forming nuclei.
Generally speaking, in normal circumstances, there are too few of these nuclei in the atmosphere and while in a rain event, the sky is cleared off of any pollutants or aerosols to facilitate ice formation.
Furthermore, even if those nuclei were present, they would tend to be least effective between -1 to – 10 c.
Therefore, Most of ice forming process begins when the temperature in the atmosphere drops below – 10 c .
People at homes experience the same phenomenon, when they find water bottles hours after putting those in the freezer at -10 c, still in the liquid state.
Now we can easily understand what freezing rain is :
Freezing rain is a precipitation process in which super cooled liquid falls on earth, but it is hazardous upon impact with a cold terrain or infrastructure.
As the rain drops touch surface, it immediately builds up into ice hill like structure and adds up weight on the low lying infrastructure by each passing instant.
Such massive weighing down of load have, in the past, crumbled down trees, electric poles in some regions of the world.
Read further : What is freezing rain?
We discuss below an experiment which you can do at your homes to notice the freezing rain phenomenon:
Fill a bottle with refined water( pure of any contaminants), tightly capped and put it into a freezer for 6 hours.
Put an empty bowl too in the freezer for the same duration of time. This is done to prepare a cooler surface in a room temperature environment, on which super cooled liquid would later be poured down on.
After the elapsed time, take out the water bottle and bowl from the freezer and pour down below 0 c water onto the bowl.
You would notice a surprising build up of ice, immediately after the water drops encounters the bowl surface.
As the experiment is being carried out in a room temperature, you would notice the built up ice starts to melt too and shoves off the weight.