Abstract
In 2010, Supertyphoon Megi experienced an abrupt track deflection in the South China Sea (SCS) after traversing Luzon Island. To reveal the physical processes responsible for the timing and location of the sudden track deflection, the potential vorticity (PV) diagnosis and numerical simulations with initial strength perturbations are applied to investigate the individual and combined effects of environmental systems on Megi’s motion based on the steering flow theory. Results indicate that Megi’s northward track deflection was mainly determined by the effect of the midlatitude circulation, or rather, the break of the high pressure belt joined by the continental high (CH) and the Pacific subtropical high (SH). The retraction of CH played a particularly critical role in the break of the high pressure belt, making it the most important feature of the midlatitude circulation to determine Megi’s deflection. In addition, a small low-latitude anticyclone (SA) southeast of Megi was crucial in affecting the timing and location of the deflection, although the steering effect provided by SA itself was relatively weak. The development of SA was associated with both the tropical cyclone energy dispersion and the activity of an easterly wave. This study suggests that the abrupt track deflection of Megi was attributed to the combined effect of the midlatitude and low-latitude systems, in addition to the combined effects of the large-scale and small-scale systems.
