Analysis
III. Cloud zones with Temperatures
According to a pilot weather report on the ice accretion of aircraft, over 70 % of ice accretion occurs at temperatures above -10 °C and rarely below -15 °C.
Since there is about 90% of the supercooled water droplets above -15 °C, ice accretion happens easily with water freezing to the gas in wet layers at temperatures above -15 °C. If the ice nuclei and supercooled water droplets
coexist, the ice crystal can grow rapidly, snow can fall easily on the ground, and there is a lot of snow fall compared to precipitation.
However, if the highest temperature of the wet layer is lower than -15°C, ice crystals do not grow much because there is few supercooled water droplet, making it difficult for snow with large volumes, such as large snowflakes, to fall on the ground.
The following figures are model diagrams of the type of the snow according to the location of the cloud zone by temperature distribution.
Like Figure (a), if the temperature inside the cloud is lower than 0 ℃ but higher than -4 ℃ with a thin wet layer at a low altitude, snow is not easy to be created. This is because ice crystals are difficult to be created since most particles that make up the ice nuclei do not serve their roles in this section.
On the other hand, if the temperature of the upper cloud is around -10℃, as shown in (b),
it is easy for the ice crystals to grow rapidly and fall as snow because the ice nuclei are active and the supercooled water droplets are distributed in this section.
As shown in (c), if the temperature of the upper cloud is around -15℃ or lower and that of the lower cloud is higher than -10℃, ice crystals stick together like branches from the top of the cloud. Moving to the bottom of the cloud, they meet supercooled water droplet layer and grow rapidly with condensing water droplets. As a result, the snow of large volume like large snowflakes of wet snow can fall to the ground.
However, although the cloud layer is developed highly as shown in (d), it is difficult to have bulky snow as there is little supercooled water droplet layer when the temperature of the lower part of the cloud is around -15℃.
With reference to this information, we decided to draw the diagrams ourselves.
The followings are the data obtained for January 4, 2010 and January 12, 2021.
January 12, 2021 18:00 (KST)
Cloud Type: ScAs
Sc (Stratocumulus): 1.5~3 km
As (Altostratus): 3~6 km
Cloud top height: about 3km (pink~red)
January 4, 2010 12:00 (KST)
Cloud Type: StNs
St (Stratus): ~1.5 km
Ns (Nimbostratus): ~3km
Considering cloud types, the cloud top height is similar to that of January 12th, 2021.
January 4, 2010 12:00 (KST)
Ground Temperature: - 5.2 °C
850hpa (1.5km): - 11 °C
700hpa (3km): - 21 °C
January 12, 2021 18:00 (KST)
Ground Temperature: - 0.8 °C
850hpa (1.5km): - 7 °C
700hpa (3km): - 15 °C
Diagrams of Cloud zones
January 4, 2010
January 12, 2021
We drew our diagrams of cloud zones with the temperatures for each day with the data above. Comparing them, the size of the supercooled water droplets layer of January 12 is larger than that of January 4, making snowflakes larger.
In addition, the relatively high ground temperature on January 12 makes snowflakes melt and congeal together when they fall. It also contributes to the larger size of snowflakes. Therefore, we can say that January 12, 2021 was more suitable for snowmen building than January 4, 2010.