A case study of the cutoff process and latent heating effect in an upper-level cold-core low during the Mei-Yu season in East Asia

Compared with conceptual models based on dry dynamics, the formation process of this cutoff low (COL) was inconsistent with the model of migratory jet streak-trough interaction, but the evolution of the upper-level trough (including its narrowing and rotation of axis) and the scale of the resultant COL generally agreed with the theory of interaction between trough and mean westerly flow with anticyclonic background shear.

East/southeast of the trough, active and persistent convection appeared and induced 1) divergent ageostrophic flow near the tropopause, 2) an increase in mid- to upper-level thickness due to effective heating, and 3) amplification of an upper-level ridge downstream. Through a model sensitivity test, the diabatic heating is suggested to play a key role in the formation of the current CCL as the trough moved and extended southeastward to approach the amplifying ridge.