Analysis of Characteristics and Formation of "Train Effect" in the Spiral Cloud Belts of Typhoon "Fitow" (No. 1323)

The characteristics and formation of “train effect” in the spiral cloud belt of typhoon “Fitow” (No. 1323) are analyzed in this paper. The results show a “train effect” occurred during persistent rainfall over the south bank of the Qiantangjiang Bay in Zhejiang. According to the stable position of the rain belt, This rain process can be divided into two “train effect”. Each “train effect" last about 3–4 h, and the space span is 1–2 longitude distance. The rainstorm area shows the characteristics of band, with high precipitation efficiency. The precipitation exceeds 25 mm h⁻¹ and propagates forward linearly. The average reflectivity of radar echo in the spiral cloud belt of typhoon with over 35 dBZ also shows a linear band structure. The trend of precipitation belt and radar echo deviated from the typhoon center by more than 25° to the right. From the formation of the “train effect”, the direction of the high-altitude guided airflow and the direction of the surface meso-scale disturbance convergence zone are consistent with the movement direction of the convective cell in the “train effect” providing the basis for its nearly linear arrangement. The meso-scale disturbance convergence or vortex formed along the coast provides important conditions for the occurrence or development of convection in the spiral cloud belt in coastal areas. This convergence also forms the beginning and maintenance mechanism for the rapid growth and subsequent development of convective clouds, playing an important role in the formation, development, and maintenance of the “train effect”.