So sánh fog mist và hoar frost năm 2024

When ice forms on a tree, it can make the perfect snap to post to Instagram or Facebook. There may be a tendency to simply call it hoarfrost, which for a social media posting probably doesn’t matter. But in the real world, on the roads, it does matter. A lot.

Both are great for photos, but one can be deadly

Rime ice vs. Hoarfrost: Can you spot the difference?

Rime ice vs. Hoarfrost: Can you spot the difference?

When ice forms on a tree, it can make the perfect snap to post to Instagram or Facebook.

However, there may be a tendency to simply call it hoarfrost, which for a social media posting probably doesn't matter.

But in the real world, on the roads, it does matter. A lot.

• You too can be an expert at identifying hoarfrost compared to rime ice and why it matters, just check out the video at the top of this story.
• And if you got good photos of the rime ice on the weekend, we'd love to see them! Email [email protected], or tag @CBCCalgary on Instagram, and we might feature your work on CBC Television, CBC.ca online, or CBC's social platforms.

"One is more dangerous than the other," explains Terri Lang, a meteorologist with Environment and Climate Change Canada.

"Looking at it, you may not be able to tell the difference. The difference is how it's formed."

Hoarfrost: clear skies

"Hoarfrost forms under clear skies, clear and cold. Any moisture that's in the air goes from the gaseous state, meaning there is water vapour in the air and you can't see it. It skips that liquid phase and it goes right into solids," Lang says.

"So it goes from a gas to a solid, it forms right onto the tree. There is no melting in between."

Rime ice: low cloud, foggy

"It usually forms when there is a lot of low cloud, foggy conditions. You can see the moisture particles in the air," Lang says.

"Those particles you see floating around in the fog are liquid. Those tiny particles can stay liquid up until –25 C. As soon as those liquid drops encounter something solid like a tree, a power line, a car, they immediately freeze onto it."

What's the difference?

"You have to go right up to the tree and look at the way the particles are," she says.

"Rime ice looks more like droplets. They are heavier, the trees are weighed down. They are harder to break off. Hoarfrost is usually a lot lighter, more feather-like. You can just blow it off."

Which one can be dangerous?

"What makes rime icing dangerous, when the fog stays for days, it can build up and it's really, really heavy, whereas hoarfrost on a branch, you can just blow on it and it blows away. Hoarfrost is so light. That's the big difference. Rime ice can cause big power outages or even bring down airplanes, when they fly through a cloud with a lot of these particles," Lang says.

"Rime icing can be quite dangerous because of the ice conditions. They can develop very, very quickly."

Hoarfrost is on the left, rime ice is on the right, according to meteorologist Terri Lang. (Environment and Climate Change Canada)

Where do you see each one?

"We tend to see hoarfrost where it gets colder, so you wouldn't see it as much on the [B.C.] Lower Mainland. We tend to see it more on the prairies," Lang explains.

"Rime icing can occur pretty much anywhere the temperature goes below freezing. We see the worst events when the temperatures are –4 C to –7 C. If it gets colder than that, the air gets drier and we don't see the fog banks as much."

Observing fog, dew, frost and mist may seem unimportant for some people. However, knowledge of these weather phenomenon can be useful and for some people crucial. For each to form, there must be the appropriate conditions to achieve condensation, (and sometimes sublimation in the case of frost).

It is a very common thing to see fog in the morning over the ocean that dissipates as sun comes up. Many boaters often wait to travel when the fog is thick, especially when cruising long distances in an expedition yacht. Another interesting phenomenon is sea smoke, which is essentially mist above the water that is moved by the wind.

Fog and dew can be measured despite the fine size of the water droplets. The dew gauge is used to measure the light droplets through weight.

Fog

Fog can be described as a cloud forming very close to or at ground level. It requires air with sufficient moisture to cool or to be cooled to a temperature to achieve condensation. Once condensation occurs, visibility decreases dramatically. It therefore becomes very hazardous.

Fog does not necessarily have to be uniform, or widespread. Some areas may have thick fog whilst others may miss out completely.

Fog is more common in valleys and near creeks or streams. It also most commonly occurs overnight and during the morning. However, in colder climates where fog is more common, it may last all day.

From a distance, fog is observed to be similar to a cloud on the ground especially when it is thick.

If the air is sufficiently warmed by the sun to raise the temperature above the temperature level needed for condensation or if wind begins to blow, the fog will begin to break into patches. It may rise to higher level in the form of fast moving low clouds and eventually clear.

Mist

Mist is similar to fog except it may appear more ragged and forms on rainy days with the air saturated due to the amount of moisture. Mist is more common in mountainous and forest regions.

Dew

Dew is moisture that condenses at the ground level. The layer of air within about a metre above the ground experiences rapid changes in temperature from day to night. Therefore the temperature may be cooler on the ground than the air above. Consequently, the air temperature close to the ground may cool to below the level needed for condensation. Moisture therefore is observed on grass and on the surface of some objects such as those with metal surfaces. If the air above also cools below the condensation level, fog will form.