We create a Fog Index to classify the fog occurs in Incheon and Jeju airport.

There are various factors regarded to make this index.

    1.  Surface T - Td

• Calculation: T@1000 - Td@1000

• Fog is saturated on the ground because it is a weather phenomenon caused by condensation of water vapor on the surface.

    2. Surface Inversion

• Calculation: T@925 - T@1000

• And radiation fog is caused by condensation of water vapor due to radiant cooling of the ground, which forms an inversion layer near the ground due to its rapid cooling rate.

• It is an element to identify an inversion layer that is almost touching the ground. When it is , it means an inversion layer, and it also means that the larger the number is, the stronger the inversion layer is.

    3. Differences in T - Td between lower atmosphere and surface atmosphere.

• Calculation: 925hPa(T-Td) - surface(T-Td)

• These surface inversions of radiation fog are usually almost saturated. Accordingly, we considered that radiation fog has small temperature- differences between the ground and lower atmosphere, so it was believed that these elements could be used to distinguish the case of radiation fog.

    4. Vertical Shear: summer 500 hPa~1000 hPa, winter 700 hPa~1000 hPa

• Calculation: (cold season)1,2,3,10,11,12: Wind direction@700hPa-Wind direction@1000hPa

                  (warm season)4,5,6,7,8,9: Wind direction@500hPa-Wind direction@1000hPa​

• Advection fog is produced when air currents of different characteristics move.

• We used these elements because we thought that we could identify advection through a thermal wind. If you subtract the wind angle from the top to the bottom (starting from the north and with the right side of the north as a positive number), you will see a change in wind direction. As the altitude rises, clockwise rotation indicates warm advection, and counterclockwise rotation indicates cold advection.

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Case Selection Criteria: The classifying fog indexes applied to Incheon and Jeju are different.