scholarly journals Intraseasonal Modulation of Synoptic-Scale Disturbances and Tropical Cyclone Genesis in the Eastern North Pacific

2014 ◽  
Vol 27 (15) ◽  
pp. 5724-5745 ◽  
Author(s):  
Ewan Crosbie ◽  
Yolande Serra
Keyword(s):  
North Pacific ◽  
Vertical Wind Shear ◽  
Active Phase ◽  
Regional Model ◽  
Tropical Cyclogenesis ◽  
Tropical Cyclone Genesis ◽  
Synoptic Scale ◽  
Global Pattern ◽  
Cyclone Genesis ◽  
Neutral Conditions

Abstract The influence of the Madden–Julian oscillation (MJO) on synoptic-scale waves, important precursors to tropical cyclones and tropical cyclogenesis, is investigated using a regional model of the eastern North Pacific basin. Cyclogenesis frequency is evaluated with respect to the MJO using a combination of the regional model and the archive best-track data. The statistics of the regional model compare well to the data and suggest that the MJO predominantly deters cyclogenesis during the suppressed phase rather than enhances it during the active phase when compared to neutral conditions. Synoptic-scale variability of cloudiness and eddy kinetic energy and analysis of vortex track statistics show a consistent enhancement of wave strength during the active phases of the MJO supported by both barotropic energetics and tropospheric moisture availability. Vertical wind shear, of critical importance to cyclone development, also exhibits strong variability associated with the phase of the MJO but, contrary to synoptic activity and moisture, results in unfavorable conditions for cyclogenesis during the active phase of the MJO in the region. The result is for the MJO to enhance cyclogenesis frequency relative to neutral conditions during the early active phase but otherwise to result in suppressed activity. In addition to the basinwide longitudinal structure, the local MJO exhibits a distinct north–south structure not apparent in the global pattern but in agreement with recent studies of tropical eastern North Pacific subseasonal variability.

scholarly journals Impact of the Madden–Julian Oscillation on Western North Pacific Tropical Cyclogenesis Associated with Large-Scale Patterns

2015 ◽  
Vol 54 (7) ◽  
pp. 1413-1429 ◽  
Author(s):  
Haikun Zhao ◽  
Ryuji Yoshida ◽  
G. B. Raga
Keyword(s):  
North Pacific ◽  
Western North Pacific ◽  
Large Scale ◽  
Vertical Wind Shear ◽  
Active Phase ◽  
Relative Vorticity ◽  
Tropical Cyclogenesis ◽  
Unexpected Result ◽  
Positive Anomaly ◽  
Madden Julian Oscillation

AbstractThe intraseasonal variability of tropical cyclogenesis in the western North Pacific (WNP) basin is explored in this study. The relation of cyclogenesis in each of the five large-scale patterns identified in recent work by Yoshida and Ishikawa is associated with the Madden–Julian oscillation (MJO). Confirming previous results, more events of cyclogenesis are found during the active MJO phase in the WNP. Furthermore, results indicate that most of the tropical cyclogenesis is associated with the monsoon shear line large-scale pattern during the active phase. The genesis potential index (GPI) and its individual components are used to evaluate the environmental factors that most contribute toward cyclogenesis under the different phases of the MJO. GPI exhibits a large positive anomaly during the active phase of the MJO, and such an anomaly is spatially correlated with the events of cyclogenesis. The analysis of each factor indicates that low-level relative vorticity and midlevel relative humidity are the two dominant contributors to the MJO-composited GPI anomalies. The positive GPI anomalies during the active phase are partially offset by the negative contributions from vertical wind shear and potential intensity. This is valid for all five large-scale patterns. It is noteworthy that the easterly wave (EW) large-scale pattern, while exhibiting the same influence of relative vorticity and midlevel humidity contributing toward positive GPI anomalies, presents slightly more cyclogenesis events under the inactive phase of the MJO. This unexpected result suggests that other factors not included in the definition of the GPI and/or changes in environmental flows on other time scales contribute to the tropical cyclogenesis associated with the EW large-scale pattern.

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.

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.

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