Azimuthal Variations of the Convective-scale Structure in a Simulated Tropical Cyclone Principal Rainband
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• Original Paper •
Azimuthal Variations of the Convective-scale Structure in a Simulated Tropical Cyclone Principal Rainband Yue JIANG1,2, Liguang WU*3, Haikun ZHAO1, Xingyang ZHOU3, and Qingyuan LIU4 1Key
Laboratory of Meteorological Disaster of Ministry of Education,
Nanjing University of Information Science and Technology, Nanjing 210044, China 2State
Key Laboratory of Severe Weather, Chinese Academy of Meteorological Sciences, Beijing 100081, China 3Department
of Atmospheric and Oceanic Sciences and Institute of Atmospheric Sciences, Fudan University, Shanghai 200433, China
4Nanjing
Joint Institute for Atmospheric Sciences, Nanjing 210009, China
(Received 5 November 2019; revised 1 July 2020; accepted 17 July 2020) ABSTRACT Previous numerical simulations have focused mainly on the mesoscale structure of the principal rainband in tropical cyclones with a relatively coarse model resolution. In this study, the principal rainband was simulated in a semi-idealized experiment at a horizontal grid spacing of 1/9 km and its convective-scale structure was examined by comparing the convective elements of the simulated principal rainband with previous observational studies. It is found that the convective scale structure of the simulated principal rainband is well comparable to the observation. The azimuthal variations of the convective scale structure were examined by dividing the simulated principal rainband into the upwind, middle and downwind portions. Some new features are found in the simulated principal rainband. First, the overturning updraft contains small-scale rolls aligned along the inward side of the outward-leaning reflectivity tower in the middle portion. Second, the inner-edge downdraft is combined with a branch of inflow from the upper levels in middle and downwind portions, carrying upper-level dry air to the region between the overturning updrafts and eyewall, and the intrusion of the upper-level dry air further limits the altitude of the overturning updrafts in the middle and downwind portions of the principal rainband. Third, from the middle to downwind portions, the strength of the secondary horizontal wind maximum is gradually replaced by a low-level maximum of the tangential wind collocated with the low-level downdraft. Key words: azimuthal variations, principal rainband, tropical cyclone, WRF-LES simulation Citation: Jiang, Y., L. G. Wu, H. K. Zhao, X. Y. Zhou, and Q. Y. Liu, 2020: Azimuthal variations of the convective-scale structure in a simulated tropical cyclone principal rainband. Adv. Atmos. Sci., 37(11), 1239−1255, https://doi.org/10. 1007/s00376-020-9248-x. Article Highlights:
• The overturning updraft of the principal rainband contains small-scale rolls aligned along the inward side of the outwardleaning reflectivity tower.
• The inner-edge downdraft is combined with the upper-level inflow carrying dry air to the region between the rainband
and eyewall.
1. Introduction A tropical cyclone (TC) usually exhibits an eyewall and a set of spiral rainbands. In the i
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