SUPERCELL
Supercell
"Supercells produce mostly great tornadoes and hail. That's not to say it's very big. It's relatively small, up to 20 miles (32 kilometers) wide, but it's very powerful. I always compare it to peanuts. They're very small but rich in protein, fat, calories and energy."
-Walker Ashley / Professor of Meteorology & Disaster Geography, University of Northern Illinois
Concepts and Structures
Structure of Supercell Outside
McMurdie, L., & Houze, R. A. (2006). Weather Systems. In J. M. Wallace & P. V. Hobbs (Eds.), Atmospheric Science (Second Edition) (pp. 313-373).
Academic Press. doi:10.1016/B978-0-12-732951-2.50013-2
A supercell is an extremely hazardous form of convective storm that can produce strong winds, large hail, and long-lasting tornadoes. In its simplest form, it is composed of a single rotating updraft and downdraft system. The primary updraft typically includes a rapidly growing cloud top and often exhibits strong cyclonic rotation, while the downdraft appears to spread out farther due to intense rainfall. Strong supercells often feature an overshooting top. Moreover, when developing from multicell storm systems, supercells can have multiple smaller cores within a larger cell structure.
Structure of Supercell Inside
Denton, S. (2018, October 17). Breakdown: Why wind shear is necessary for tornado development. Action News 5.
The rotating air within the updraft of a supercell is known as a mesocyclone, usually forming at middle altitudes and spreading out about 5-10 kilometers from its center. The formation of a tornado within a mesocyclone is determined by a delicate balance between converging airstreams, and not every mature mesocyclone results in a tornado.
Supercell Splitting
Trapp, R. J. (2003). Thunderstorms, Severe. In R. A. Meyers (Ed.), Encyclopedia of Physical Science and Technology (Third Edition) (pp. 735-749). Academic Press. doi:10.1016/B0-12-227410-5/00685-2
Houze, R. A. (2014). Cumulonimbus and Severe Storms. In R. A. Houze (Ed.), International Geophysics (Vol. 104), (pp. 187-236). Academic Press. doi:10.1016/B978-0-12-374266-7.00008-1
During the process of storm splitting, where two updraft cores propagate in different directions, a vortex couplet is generated. This occurs as horizontal rotation associated with unidirectional environmental shear is tilted into vertical rotation during the ascent of the downdraft, creating a horizontal rotation in the updraft. The characteristic organization of a supercell in the cloud layer is facilitated by strong mid-level vortices on the storm flanks, induced by crosswise environmental shear.
Formation Step of Supercell
The biggest reason for supercell formation is the reverse layer, and the atmosphere where supercells occur frequently is hot and humid air on the surface. The middle layer takes the form of hot and dry dense air, and the upper layer takes the form of cold air.
(Step 1) The air near the surface is hot and humid, so a lot of energy is accumulated. However, the dense air layer in the middle layer suppresses the upward movement of the surface air.
(Step 2) The reverse layer disappears due to surface radiation heating. Strong heat and moist air continue to accumulate on the surface.
(Step 3) The reverse layer is completely dissipated, disappears, and the energy accumulated in the lower layer explodes. As the temperature difference between the upper and lower floors increases, so does the instability.
(Step 4) The elevated air expands adiabatically and condenses to form a turbulent cloud.
(Step 5) By the law of mass conservation, a descending airflow is formed in the side of a turbulent cloud. The mixing effect is generated by the descending airflow.
(Step 6) All the remaining unsaturated air by the mixing effect reaches a saturated state.
(Step 7) On the cloud side, a clear state is maintained by the descending airflow. At the midpoint, a very strong turbulent cloud develops.
Motivation
Supercell Case in South Korea
On June 10, 2014, a tornado accompanied by a supercell occurred unusually in Ilsan, Goyang-si, Gyeonggi-do, located inland on the Korean Peninsula. More than 40 flower farms and plastic houses were damaged. The National Emergency Management Agency estimated property and casualties of about 1.5 billion won. Unlike previous Yongoreum cases, tornadoes in Goyang can utilize ground observation data, especially X-band dual-polarization radar operated by the Korea Institute of Civil Engineering and Building Technology (KICT) for about 18 minutes from formation to extinction.
Supercell Case in United States
A supercell occurred in Russell Springs, Kansas, U.S., on June 8, 2019. On May 21, 2020, a supercell also occurred in Satanta, Kansas. It also occurred in Alexander, North Dakota on June 10, 2021. Supercell recently devastated the Rolling Fork in Mississippi. Meteorologists are speculating that more supercells with tornadoes will occur in the southern part of the U.S. due to the warming effect.