The Influence of Environments on the Intensity Change of Typhoon Soudelor

Leo Oey,Yuchen Lin

doi:10.3390/atmos12020162

Abstract

Previous studies have shown that background oceanic and atmospheric environments can influence not only the formation but also the intensity of tropical cyclones. Typhoon Soudelor in August 2015 is notable in that it underwent two rapid intensifications as the storm passed over the Philippine Sea where the 26 °C isotherm (Z26) was deeper than 100 m and warm eddies abounded. At the same time, prior to the storm’s arrival, an anomalous upper-level anticyclone developed south of Japan and created a weakened vertical wind shear (Vs) environment that extended into the Philippine Sea. This study examines how the rapid intensification of Typhoon Soudelor may be related to the observed variations of Z26, Vs and other environmental fields as the storm crossed over them. A regression analysis indicates that the contribution to Soudelor’s intensity variation from Vs is the largest (62%), followed by Z26 (27%) and others. Further analyses using composites then indicate that the weak vertical wind shear produced by the aforementioned anomalous anticyclone is a robust feature in the western North Pacific during the developing summer of strong El Ninos with Oceanic Nino Index (ONI) > 1.5.

Highlights

It is well documented that large-scale environmental conditions exert strong controls upon tropical cyclone formation [1]
This study examines how the vertical wind shear (Vs), Z26 and other environmental parameters may be related to the intensity change of Typhoon Soudelor in August 2015 in the Philippine Sea
This paper uses observations to examine the environmental influences on the intensity change of Typhoon Soudelor in the western North Pacific

Summary

Introduction

It is well documented that large-scale environmental conditions exert strong controls upon tropical cyclone formation [1]. A number of case studies have suggested that warm eddies with deep Z26 may trigger the intensification and rapid intensification of typhoons in the western North Pacific (for example, see [7]). We find that Soudelor’s intensity change is related more to Vs than Z26 and other parameters This is due to the presence of a small area—a “pocket”, roughly 1500 km × 1500 km, of very weak environmental wind shear (Vs < 4 m/s) south of Japan and into the central Philippine Sea, which the storm crossed. The result suggests that small pockets of vertical wind shear field embedded in the aforementioned favorable climatology in the western North Pacific in (cyclonic low-level wind vorticity, high humidity and MPI) may have influenced the rapid intensification of Soudelor and may play a role in the intensity change of other typhoons. A further analysis indicates that the low-Vs pocket is a consistent feature of the atmospheric conditions in the western North Pacific in the summer, preceding a strong El Nino

Data Sources

Along-Track Environmental Values

Results

Conclusions