A Direct Observation study on the Horizontal Helical Rolls in the Typhoon Boundary Layer

Helical convective rolls has been known to play a significant role in the evolution of the tropical cyclone boundary layer (TCBL) and take a considerable amount in the turbulence flux between in the air-sea interaction. In this study, analyses of data from an aircraft situ observation of the Hongkong Observation (HKO) are presented. In this study, we proved the existence of boundary rolls and investigated the prevalence of helical rolls within different scale in TCBL by the direct observation method. The rolls detected in Typhoon Kalmaegi (1415) and Typhoon Nida (1604) were found have several different remarkable wavelength: the sub-kilometer-scale streaks and kilometer-scale roll vortices respectively. Further analysis showed that these horizontal helical rolls are not rare to be found and have a remarkbly larger than the observation samples without rolls. Our airborne observation of this paper qualified that the prevalence and roles of helical rolls and this may help to understand the air–sea turbulence exchange in TCBL.It is hoped that the findings of this study about the roll and turbulence flux could contribute to the knowledge about turbulent mixing schemes so that the turbulent mixing and transport processes in the TCBL and thus help to modify parameterized in scheme of boundary scheme of numerical models