scholarly journals A Region-Dependent Seasonal Forecasting Framework for Tropical Cyclone Genesis Frequency in the Western North Pacific

2019 ◽  
Vol 32 (23) ◽  
pp. 8415-8435 ◽  
Author(s):  
Chao Wang ◽  
Bin Wang ◽  
Liguang Wu
Keyword(s):  
Tropical Cyclone ◽  
North Pacific ◽  
Western North Pacific ◽  
Large Scale ◽  
Prediction Models ◽  
Temporal Correlation ◽  
Tropical Cyclone Genesis ◽  
Regional Variability ◽  
Empirical Prediction ◽  
Genesis Frequency

ABSTRACT It has been a common practice to predict total tropical cyclone (TC) genesis frequency over the entire western North Pacific (WNP). Here we show that TC genesis (TCG) exhibits distinct regional variability and sources of predictability. Therefore, we divide the WNP into four quadrants with 140°E and 17°N being dividing lines plus the South China Sea (SCS) to predict five subregional TCG frequencies as well as the entire WNP TCG frequency. Besides the well-known ENSO-induced seesaw relationship between the TCGs in the southeast and northwest quadrants, we found that 1) an enhanced TCG in the northeast WNP is associated with a pronounced anomalous cyclonic circulation, which is maintained through its interaction with the underlying sea surface temperature (SST) anomalies; 2) an active TCG in the southwest WNP is accompanied by a zonally elongated positive vorticity anomaly and SST warming over the equatorial eastern Pacific; and 3) the SCS TCG is influenced by the upper-level South Asia high through modulating large-scale environmental parameters. Physically meaningful predictors are identified and a set of empirical prediction models for TCG frequency is established for each subregion. Both the cross-validated reforecast for 1965–2000 and independent forecast for 2001–16 show significant temporal correlation skills. Moreover, the sum of the predicted TCG frequency in five subregions yields a basinwide TCG frequency prediction with a temporal correlation skill of 0.76 for the independent forecast period of 2001–16. The results indicate its potential utility to improve the TC forecasting in the WNP.

scholarly journals Possible Cause of Seasonal Inhomogeneity in Interdecadal Changes of Tropical Cyclone Genesis Frequency over the Western North Pacific

2021 ◽  
Vol 34 (2) ◽  
pp. 635-642
Author(s):  
Minhee Chang ◽  
Doo-Sun R. Park ◽  
Chang-Hoi Ho
Keyword(s):  
Tropical Cyclone ◽  
North Pacific ◽  
Western North Pacific ◽  
Large Scale ◽  
Tropical Cyclone Genesis ◽  
Easterly Wind ◽  
Sst Warming ◽  
Cyclone Genesis ◽  
Interdecadal Changes ◽  
Genesis Frequency

AbstractAn abrupt decrease in annual tropical cyclone genesis frequency (TCGF), which is statistically significant only from October to December (OND), has been noticed over the western North Pacific Ocean. However, the seasonal inhomogeneity of interdecadal changes in TCGF between OND and the other seasons (from January to September) and the associated mechanisms are not clearly documented. This study examines and compares the different interdecadal changes in OND and in January–September from 1979 to 2018. According to our analysis, the TCGF decrease in OND (2.2) accounts for 79% of the total decrease (2.8) in annual TCGF after 1998, whereas the TCGF in January to September remains unchanged. The key differences in large-scale environment are found from the extension of equatorial easterly wind anomalies and attendant anticyclone anomalies in the subtropics. Under similar sea surface temperature (SST) warming pattern in the tropical Indo-Pacific region (i.e., the La Niña–like SST warming), tropical precipitation is significantly enhanced over the area where its seasonal peak occurs: the tropical Indian Ocean in OND and the tropical western Pacific in January–September. Thus, the equatorial easterly wind anomalies extend westward to 110°E in OND and to 145°E in January–September. Different extension of easterly wind anomalies results in different expansion of attendant large-scale anticyclone anomaly over the subtropical western Pacific, which dominates the entire main development region in OND but not in January–September. To summarize, the different extensions of easterly wind anomalies under similar La Niña–like SST warming are responsible for the seasonal inhomogeneity of interdecadal changes in TCGF.

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

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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