Does the Antarctic Oscillation modulate tropical cyclone rapid intensification over the western North Pacific?

Abstract

This study investigates the modulation of tropical cyclone (TCs) rapid intensification (RI) over the western North Pacific by the Antarctic Oscillation. There is a significant inverse relationship between basinwide RI number during July–November from 1982 to 2020 and the simultaneous Antarctic Oscillation index. During positive Antarctic Oscillation years, RI occurrence is significantly suppressed over the main RI region (10°–20° N and 125°–150° E) and slightly enhanced over the South China Sea. By contrast, during negative Antarctic Oscillation years, RI is significantly enhanced over the main RI region and slightly suppressed over the South China Sea. The Antarctic Oscillation influences western North Pacific RI occurrence mainly through modulation of the large-scale dynamic environment. During positive Antarctic Oscillation years, increases in 850–200 hPa vertical wind shear and decreases in both low-level vorticity and upper-level divergence all suppress RI occurrence over the main RI region, while thermodynamic variables (e.g. TC heat potential, maximum potential intensity and low-to-middle level relative humidity) show mostly weak changes. These changes in dynamic factors can be linked to a low-level anomalous western North Pacific anticyclone triggered by the positive phase of the Antarctic Oscillation and a low-level anomalous western North Pacific cyclone generated by a negative phase of the Antarctic Oscillation.

Keywords

• tropical cyclone
• rapid intensification
• Antarctic Oscillation