航空機観測で捉えられた2017年台風第21号の暖気核構造の維持に関わる熱力学的特徴

Abstract

Upper-tropospheric aircraft reconnaissance was carried out for Typhoon Lan (2017) using a civil jet with a newly developed dropsonde system. This paper describes the warm-core structure in the eye during the mature stage of this typhoon and the thermodynamic characteristics associated with the maintenance of the warm core. Dropsondes, released from the upper troposphere, captured a double warm-core structure with a higher perturbation temperature in the middle (3~4 km) and upper troposphere (> 12 km). The two warm cores showed a difference in equivalent potential temperature (θe) of more than 10 K, suggesting different air origins. Saturation-point analysis suggests that the air observed in the upper warm core was entrained from the eyewall. The eyewall updraft in the left-of-shear semicircle had a two-layer structure with a higher θe and lower absolute angular momentum on the inner side of the updraft core. Analyses of the saturation point and parcel method suggest that the warmer air with a θe exceeding 370 K on the inner side of the updrafts originated from the eye boundary layer and was eventually transported into the upper warm core. These results led us to hypothesize that the vertical transport of high-θe air from the eye boundary layer contributed to the continuous eye warming in the upper troposphere against the negative effect of strengthening environmental wind shear on storm intensity.