Interdecadal changes in the genesis activity of the first tropical cyclones over the western North Pacific from 1979 to 2016

• Published in: Climate dynamics 2023-03, Vol.60 (5-6), p.1885-1906
• Main Authors: Cha, Yumi, Choi, JaeWon, Ahn, Joong-Bae
• Format: Article
• Language: English
• Subjects: Anticyclonic circulation; Atmospheric circulation; Atmospheric circulation anomalies; Circulation; Circulation patterns; Climate cycles; Climatology; Cloud cover; Cyclones; Cyclonic circulation; Earth and Environmental Science; Earth Sciences; Environmental aspects; Equatorial circulation; Geophysics/Geodesy; Hurricanes; Long wave radiation; Oceanography; Pacific Decadal Oscillation; Precipitable water; Precipitation (Meteorology); Radiation; Radiation-cloud interactions; Relative vorticity; Sea surface; Sea surface temperature; Statistical analysis; Stream discharge; Stream flow; Surface temperature; Trade winds; Tropical cyclones; Vertical wind shear; Vorticity; Walker circulation; Westerlies; Wind shear
• ISSN: 0930-7575; 1432-0894
• DOI: 10.1007/s00382-022-06382-2

This study analyzes time series data on the genesis latitude, longitude, and date of the first tropical cyclone (TC) each year during the 38 years between 1979 and 2016. Statistical change-point analysis applied to these three variables shows that a shift in climate regime occurred around 1998. More specifically, the first TCs in the western North Pacific (WNP) tend to occur later and more northwest area since 1998. Also, we compared differences between 1998 and 2016 (post-1998) and between 1979 and 1997 (pre-1998) in terms of outgoing longwave radiation (OLR), total cloud cover, precipitable water, precipitation, vertical wind shear, 850 hPa relative vorticity, and sea surface temperature. Our results show that a favorable environment for TC genesis formed near the South China Sea (SCS) and the Philippines, and an unfavorable environment for TC genesis formed in the southeastern portion of the WNP during the post-1998. Analysis of stream flow shows that an anomalous cyclonic circulation at 850 hPa formed in the SCS, and a large, anomalous, anticyclonic circulation formed in the North Pacific. From these circulations, a ridge extended to the east sea of the Philippines, and consequently, anomalous trade winds strengthened in the equatorial Pacific. Such an anomalous atmospheric circulation seems to be associated with the cold Pacific Decadal Oscillation (PDO) phase. At 200 hPa, the anomalous anticyclonic circulation strengthened in the SCS, and an anomalous cyclonic circulation formed in the east sea of the Philippines, which strengthened anomalous westerlies in the equatorial Pacific. Furthermore, this circulation pattern is related to a strengthening of the Walker circulation. Therefore, post-1998, when trade winds strengthened from development of the Walker circulation, the cold PDO phase strengthened, the locations for TC genesis moved toward the northwestern portion of the WNP, and the TC genesis day tended to be delayed.