| LOW-DEFORMATION VORTICITY AREAS IN SYNOPTIC-SCALE DISTURBANCES FOR TROPICAL CYCLOGENESIS: AN
OBSERVATIONAL ANALYSIS |
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| 作者姓名： | 段晶晶 吴立广 |
| |
| 摘 要： | It has long been known that incipient tropical cyclones (TCs) always occur in
synoptic-scale disturbances or tropical cyclogenesis precursors, and the disturbances can
intensify only within a limited area during tropical cyclogenesis. An observational analysis
of five tropical cyclogenesis events over the western North Pacific during 11 August to 10
September 2004 is conducted to demonstrate the role of synoptic-scale disturbances in
establishing a limited area of low-deformation vorticity for tropical cyclogenesis.
The analysis of the five tropical cyclogenesis events shows that synoptic-scale tropical
cyclogenesis precursors provide a region of low-deformation vorticity, which is measured with
large positive values of the Okubo-Weiss (OW) parameter. The OW concentrated areas are within
the tropical cyclogenesis precursors with a radius of about 400-500 km and can be found as
early as 72 hours prior to the formation of the tropical depression. When the TCs reached the
tropical storm intensity, the concentrated OW is confined to an area of 200-300 radius and the
storm centers are coincident with the centers of the maximum OW. This study indicates that the
tropical cyclogenesis occurs in the low-deformation 18-72 hours prior to the formation of
tropical depressions, suggesting the importance of low-deformation vorticity in pre-existent
synoptic-scale disturbances. Although the Rossby radius of deformation is reduced in TC
genesis precedes, the reduction does not sufficiently make effective conversion of convective
heating into kinetic energy within the low-deformation area. Further analysis indicates that
the initial development of four of the five disturbances is coupled with the counterclockwise
circulation of the mixed Rossby-Gravity (MRG) wave.
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| 关 键 词： | synoptic-scale disturbances low-deformation vorticity Okubo-Weiss parameter Rossby radius of deformation |
| 修稿时间： | 2017/3/29 0:00:00 |
LOW-DEFORMATION VORTICITY AREAS IN SYNOPTIC-SCALE DISTURBANCES FOR TROPICAL CYCLOGENESIS: AN
OBSERVATIONAL ANALYSIS |
| |
| DUAN Jing-jing and WU Li-guang.LOW-DEFORMATION VORTICITY AREAS IN SYNOPTIC-SCALE DISTURBANCES FOR TROPICAL CYCLOGENESIS: AN
OBSERVATIONAL ANALYSIS[J].Journal of Tropical Meteorology,2017,23(2):121-132. |
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| Authors: | DUAN Jing-jing and WU Li-guang |
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| Institution: | 1. Pacific Typhoon Research Center and Key Laboratory of Meteorological Disaster of Ministry
of Education, University of Information Science and Technology, Nanjing 210044 China; 2.
Ningbo Meteorological Observatory of Zhejiang Province, Ningbo 315012 China |
| |
| Abstract: | It has long been known that incipient tropical cyclones (TCs) always occur in
synoptic-scale disturbances or tropical cyclogenesis precursors, and the disturbances can
intensify only within a limited area during tropical cyclogenesis. An observational analysis
of five tropical cyclogenesis events over the western North Pacific during 11 August to 10
September 2004 is conducted to demonstrate the role of synoptic-scale disturbances in
establishing a limited area of low-deformation vorticity for tropical cyclogenesis.
The analysis of the five tropical cyclogenesis events shows that synoptic-scale tropical
cyclogenesis precursors provide a region of low-deformation vorticity, which is measured with
large positive values of the Okubo-Weiss (OW) parameter. The OW concentrated areas are within
the tropical cyclogenesis precursors with a radius of about 400-500 km and can be found as
early as 72 hours prior to the formation of the tropical depression. When the TCs reached the
tropical storm intensity, the concentrated OW is confined to an area of 200-300 radius and the
storm centers are coincident with the centers of the maximum OW. This study indicates that the
tropical cyclogenesis occurs in the low-deformation 18-72 hours prior to the formation of
tropical depressions, suggesting the importance of low-deformation vorticity in pre-existent
synoptic-scale disturbances. Although the Rossby radius of deformation is reduced in TC
genesis precedes, the reduction does not sufficiently make effective conversion of convective
heating into kinetic energy within the low-deformation area. Further analysis indicates that
the initial development of four of the five disturbances is coupled with the counterclockwise
circulation of the mixed Rossby-Gravity (MRG) wave. |
| |
| Keywords: | synoptic-scale disturbances low-deformation vorticity Okubo-Weiss parameter Rossby radius of deformation |
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