Vorticity budget in Typhoon Nuri

Introduction Conclusions References Tables Figures Back Close Full Screen / Esc Atmospheric Chemistry and Physics Discussions This discussion paper is/has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP if available. Abstract Introduction Conclusions References Tables Figures Back Close Full Screen / Esc Abstract The formation of west Pacific tropical cyclone Nuri (2008) was observed over four days from easterly wave to typhoon stage by aircraft using scanning Doppler radar and drop-sonde data. This typhoon intensified rapidly in a significantly sheared environment. In spite of the shear, overlapping closed circulations existed in the storm frame of refer-5 ence in the boundary layer and at 5 km elevation, providing a deep region protected from environmental influences. The vorticity budget was analyzed and it was found that vorticity convergence dominated vortex tilting on the storm scale in the lower tro-posphere. At times vorticity convergence also greatly exceeded frictional spindown in the boundary layer. Thus, the Ekman pumping hypothesis was found to be a poor ap-10 proximation in the early stages of the development of this typhoon. As Nuri developed, convective sources of boundary layer vorticity became fewer but more intense, culminating in a single nascent eyewall at the tropical storm stage. A non-developing tropical wave case was also analyzed. This system started with much weaker circulations in the boundary layer and aloft, leaving it unprotected against environmental intrusion. 15 This may explain its failure to develop.