Atmos. Chem. Phys. Discuss., 13, 26795-26840, 2013
www.atmos-chem-phys-discuss.net/13/26795/2013/
doi:10.5194/acpd-13-26795-2013
© Author(s) 2013. This work is distributed
under the Creative Commons Attribution 3.0 License.
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
The genesis of Typhoon Nuri as observed during the Tropical Cyclone Structure 2008 (TCS-08) field experiment – Part 3: Dynamics of low-level spin-up during the genesis
L. L. Lussier III1, M. T. Montgomery1, and M. M. Bell2
1Naval Postgraduate School, Monterey, California, USA
2University of Hawaii at Manoa, Honolulu, Hawaii, USA

Abstract. Aircraft reconnaissance data collected during the Tropical Cyclone Structure 2008 field campaign are used to examine further kinematical, dynamical and thermodynamical aspects of the genesis of Typhoon Nuri. Data from the first two missions into the pre-Nuri disturbance document the transition from a tropical wave to a tropical depression. Dropwindsonde-derived tangential wind profiles at several radii from the low-level circulation center indicate that the magnitude of low-level circulation increases and that the corresponding tangential velocity maximum moves inward from the first to second reconnaissance mission. To compliment these findings, a three-dimensional variational analysis incorporating both dropwindsonde and aircraft Doppler radar data is conducted. These data are used to perform circulation tendency calculations at multiple distances from the low-level circulation center. The results demonstrate a net spin-up of the system-scale circulation in the low-levels near the center and in the outer regions of the recirculating Kelvin cat's eye circulation. In these regions, the spin-up tendency due to the influx of cyclonic absolute vorticity exceeds the frictional spin-down tendency for both Nuri missions. The system-scale spin up is found to be accompanied by areas of low-level vorticity concentration through vortex-tube stretching associated with cumulus convection. The areal coverage and intensity of these high-vorticity regions increase between the first and second Nuri missions.

The findings of this study are consistent in some respects to the Nuri observational analysis carried out by Raymond and Lopez (2011), but differ in their suggested key result and related scientific implication that the pre-Nuri disturbance was spinning down on the first day of observations. The findings herein strongly support a recent tropical cyclogenesis model positing that the Kelvin cat's eye circulation of the parent wave-like disturbance provides a favorable environment for convective-vorticity organization and low-level spin-up on the mesoscale.


Citation: Lussier III, L. L., Montgomery, M. T., and Bell, M. M.: The genesis of Typhoon Nuri as observed during the Tropical Cyclone Structure 2008 (TCS-08) field experiment – Part 3: Dynamics of low-level spin-up during the genesis, Atmos. Chem. Phys. Discuss., 13, 26795-26840, doi:10.5194/acpd-13-26795-2013, 2013.
 
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