Analysis of the Rapid Intensification Mechanism for a Super Arctic Cyclone Based on a New Surface Pressure Tendency Equation

The synoptic process of a super Arctic cyclone in August 2016 (AC16) is investigated based on the Weather Research and Forecasting (WRF) model, and the key factors affecting the rapid intensification (RI) of AC16 and their relative contributions are analyzed by diagnosing a new surface pressure tendency equation (SPTE). The major physical mechanisms behind the two RI stages of AC16 are revealed. The trajectory, intensity changes, and structural characteristics of AC16 are well simulated by the WRF model. A diagnosis based on the SPTE promisingly reproduces the two RI stages of AC16. The leading factor that influenced the intensity of AC16 was identified to be the air-column potential temperature tendency, while the pressure change at the upper boundary had less of an impact. Further analysis reveals that the horizontal potential temperature advection was the decisive factor in a warming of the air column. Specifically, the upper-level warm advection generated by the strong wind field of the upper-level jet played a dominant role in warming the air column, which caused the initial RI of AC16. The AC16 movement into a strong potential temperature gradient generated by tropopause polar vortices increased the upper-level warm advection, which warmed the air column and thereby induced the second RI of AC16. However, the net effect of vertical potential temperature advection and latent heating, as well as radiation processes, caused a cooling of the air column and thereby negatively contributed to the RI of AC16.