A Numerical study of clear-air turbulence (CAT) encounters occurred in Korea

CAT encounters reported in Korea are investigated using a non-hydrostatic and fully compressible Weather Research Forecast (WRF) model.

On 2 April 2007, 9 moderate or greater-level CATs were reported in three different regions of Korea: western coast, Jeju island, and eastern mountain areas. Locations and timings of the observed CATs in PIREPs are reasonably well simulated in a finest-resolution subdomain. In the western coast area, tropopause is deeply folded down to about 4-km level due to the strengthening of upper-level front, and maximized vertical wind shear below the jet core produces localized turbulences. In the Jeju island area, localized vertical mixings and turbulences are generated in the anticyclonic side of jet core since the streamwise vertical component of relative vorticity is perturbed by ageostrophically forced disturbances in inertial instability region. In the eastern mountain area, large-amplitude waves induced by complex terrain are vertically propagating and subsequently break down near 13 km level over the steepest regions of lee-side topography, and this causes localized turbulences.