scholarly journals How Significant are Low-Level Flow Patterns in Tropical Cyclone Genesis over the Western North Pacific?

2020 ◽  
Vol 148 (2) ◽  
pp. 559-576 ◽  
Author(s):  
Ryuji Yoshida ◽  
Hironori Fudeyasu
Keyword(s):  
Tropical Cyclone ◽  
Flow Pattern ◽  
North Pacific ◽  
Western North Pacific ◽  
Flow Patterns ◽  
Lower Latitude ◽  
Boreal Summer ◽  
Tropical Cyclone Genesis ◽  
Low Level ◽  
Cyclone Genesis

Abstract The low-level flow pattern characteristics of the tropical cyclone genesis (TCG) environment over the western North Pacific (WNP) were investigated not only for the periods during which TCG occurred, but also for the periods during which no TCG occurred. The flow patterns investigated were the shear line (SL), confluence region (CR), and easterly wave (EW) patterns. Although these flow patterns are recognized as favorable environmental conditions for TCG, their general characteristics, such as the climatological horizontal distribution, have not been previously investigated and there has been no comparison of the significance of the TCG cases to the climatological mean. We examined flow patterns using flow pattern indices defined by the modified semiobjective analysis method. SL and CR were broadly distributed over the WNP east of the Philippines during the boreal summer season. There was a peak in the EW from summer to autumn and it was distributed in a band running in an east–west direction at a lower latitude. Flow pattern indices of all three flow patterns gradually intensified until the TCG date was reached. The SL and EW indices became more intense compared to the climatological mean one day before the TCG, while that of the CR did not exceed the climatological mean. TCG occurred at the eastern edge of the area with a high genesis potential index and relative humidity and a weak vertical shear over flow patterns. This determination of the general characteristics of favorable flow pattern conditions improves our understanding of the TCG process.

scholarly journals Environmental Factors Contributing to Tropical Cyclone Genesis over the Western North Pacific

2013 ◽  
Vol 141 (2) ◽  
pp. 451-467 ◽  
Author(s):  
Ryuji Yoshida ◽  
Hirohiko Ishikawa
Keyword(s):  
Tropical Cyclone ◽  
North Pacific ◽  
Western North Pacific ◽  
Flow Patterns ◽  
Reanalysis Data ◽  
Occurrence Frequency ◽  
Tropical Cyclone Genesis ◽  
Defined Contribution ◽  
Cyclone Genesis ◽  
Confluence Region

Abstract The flow environment associated with tropical cyclone genesis (TCG) over the western North Pacific was assessed via categorization into five flow patterns: monsoon shear line (SL), monsoon confluence region (CR), monsoon gyre (GY), easterly wave (EW), and preexisting tropical cyclone (PTC). Using reanalysis data and an objective algorithm, the authors defined “contribution scores” for the five flow patterns. Each score represents the contribution to TCG from each flow pattern, and scores were calculated for 908 TCG cases from 1979 to 2008 (30 yr). Of the major contribution flow patterns, SL accounted for 42% of TCGs, EW for 18%, CR for 16%, PTC for 11%, and GY for 6%. Seasonal variations in the occurrence frequency of these five patterns were clear, but interannual variations were not as apparent. Tropical cyclones often appear to be generated in conditions with multiple flow patterns. Thus, relationships between multiple flow patterns were investigated by comparing contribution scores. The SL and CR patterns were strongly correlated to each other, which can be explained by the monsoon southwesterly that organizes both patterns. The EW pattern tends to be independent of the other flow patterns. The PTC pattern has a relatively high correlation with CR, but does not have a correlation with SL or EW. Thus, the characteristics of flow patterns for the occurrence frequency of TCG are derived for a longer period than in previous studies, and correlations among flow patterns are also investigated.

scholarly journals Multi-model Projection of Tropical Cyclone Genesis Frequency over the Western North Pacific: CMIP5 Results

SOLA ◽  
2012 ◽  
Vol 8 (0) ◽  
pp. 137-140 ◽  
Author(s):  
Satoru Yokoi ◽  
Chiharu Takahashi ◽  
Kazuaki Yasunaga ◽  
Ryuichi Shirooka
Keyword(s):  
Tropical Cyclone ◽  
North Pacific ◽  
Western North Pacific ◽  
Tropical Cyclone Genesis ◽  
Model Projection ◽  
Cyclone Genesis ◽  
Genesis Frequency

Impact of the cross-tropopause wind shear on tropical cyclone genesis over the Western North Pacific in May

2018 ◽  
Vol 52 (7-8) ◽  
pp. 3845-3855 ◽  
Author(s):  
Jingliang Huangfu ◽  
Wen Chen ◽  
Maoqiu Jian ◽  
Ronghui Huang
Keyword(s):  
Tropical Cyclone ◽  
North Pacific ◽  
Wind Shear ◽  
Western North Pacific ◽  
Tropical Cyclone Genesis ◽  
The Cross ◽  
Cyclone Genesis

Developing versus Nondeveloping Disturbances for Tropical Cyclone Formation. Part II: Western North Pacific

2012 ◽  
Vol 140 (4) ◽  
pp. 1067-1080 ◽  
Author(s):  
Bing Fu ◽  
Melinda S. Peng ◽  
Tim Li ◽  
Duane E. Stevens
Keyword(s):  
Tropical Cyclone ◽  
North Pacific ◽  
Western North Pacific ◽  
Large Scale ◽  
Relative Vorticity ◽  
Tropical Cyclone Genesis ◽  
Horizontal Shear ◽  
The North ◽  
Thermodynamic Variables ◽  
Cyclone Genesis

Global daily reanalysis fields from the Navy Operational Global Atmospheric Prediction System (NOGAPS) are used to analyze Northern Hemisphere summertime (June–September) developing and nondeveloping disturbances for tropical cyclone (TC) formation from 2003 to 2008. This is Part II of the study focusing on the western North Pacific (WNP), following Part I for the North Atlantic (NATL) basin. Tropical cyclone genesis in the WNP shows different characteristics from that in the NATL in both large-scale environmental conditions and prestorm disturbances. A box difference index (BDI) is used to identify parameters in differentiating between the developing and nondeveloping disturbances. In order of importance, they are 1) 800-hPa maximum relative vorticity, 2) rain rate, 3) vertically averaged horizontal shear, 4) vertically averaged divergence, 5) 925–400-hPa water vapor content, 6) SST, and 7) translational speed. The study indicates that dynamic variables are more important in TC genesis in the WNP, while in Part I of the study the thermodynamic variables are identified as more important in the NATL. The characteristic differences between the WNP and the NATL are compared.

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