Recent decrease in genesis productivity of tropical cloud clusters over the Western North Pacific

2018 ◽  
Vol 52 (9-10) ◽  
pp. 5819-5831 ◽  
Author(s):  
Haikun Zhao ◽  
Shaohua Chen ◽  
G. B. Raga ◽  
Philip J. Klotzbach ◽  
Liguang Wu
Keyword(s):  
North Pacific ◽  
Western North Pacific ◽  
Cloud Clusters

scholarly journals Tropical Cyclogenesis Detection in the North Pacific Using the Deviation Angle Variance Technique

2015 ◽  
Vol 30 (6) ◽  
pp. 1663-1672 ◽  
Author(s):  
Kimberly M. Wood ◽  
Oscar G. Rodríguez-Herrera ◽  
Elizabeth A. Ritchie ◽  
Miguel F. Piñeros ◽  
Ivan Arias Hernández ◽  
...  
Keyword(s):  
False Alarm ◽  
False Alarm Rate ◽  
Tropical Cyclones ◽  
Median Time ◽  
North Pacific ◽  
Western North Pacific ◽  
Tropical Cyclogenesis ◽  
Deviation Angle ◽  
Variance Technique ◽  
Cloud Clusters

Abstract The deviation angle variance technique (DAV-T) for genesis detection is applied in the western and eastern North Pacific basins. The DAV-T quantifies the axisymmetric organization of cloud clusters using infrared brightness temperature. Since axisymmetry is typically correlated with intensity, the technique can be used to identify relatively high levels of organization at early stages of storm life cycles associated with tropical cyclogenesis. In addition, the technique can be used to automatically track cloud clusters that exhibit signs of organization. In the western North Pacific, automated tracking results for the 2009–11 typhoon seasons show that for a false alarm rate of 25.6%, 96.8% of developing tropical cyclones are detected with a median time of 18.5 h before the cluster reaches an intensity of 30 knots (kt; 1 kt = 0.51 m s−1) in the Joint Typhoon Warning Center best track at a DAV threshold of 1750°2. In the eastern North Pacific, for a false alarm rate of 38.0%, the system detects 92.9% of developing tropical cyclones with a median time of 1.25 h before the cluster reaches an intensity of 30 kt in the National Hurricane Center best track during the 2009–11 hurricane seasons at a DAV threshold of 1650°2. A significant decrease in tracked nondeveloping clusters occurs when a second organization threshold is introduced, particularly in the western North Pacific.

The Characteristics of Tropical Cyclone Formation in an Environment with Large Low-Level Low-Frequency (More than 10 days) Vorticity in the Western North Pacific

2020 ◽  
Vol 148 (10) ◽  
pp. 4101-4116
Author(s):  
Yi-Huan Hsieh ◽  
Cheng-Shang Lee ◽  
Hsu-Feng Teng
Keyword(s):  
Tropical Cyclone ◽  
Tropical Cyclones ◽  
North Pacific ◽  
High Frequency ◽  
Lead Time ◽  
Western North Pacific ◽  
Initial Conditions ◽  
Surface Wind ◽  
Low Frequency ◽  
Cloud Clusters

AbstractA total of 14 tropical cyclones (TCs) that formed from 2008 to 2009 over the western North Pacific are simulated to examine the effects that environmental low-frequency and high-frequency vorticity (more than 10 days and less than 10 days, respectively) have on the formations of TCs [where the maximum surface wind ~25 kt (≈13 m s−1)]. Results show that all the simulations can reproduce the formation of a TC in an environment with a large 850-hPa low-frequency vorticity, even if the high-frequency parts are removed from the initial conditions. High-frequency vorticity mainly affects the timing and location of TC formation in such an environment. The 850-hPa vorticity is also analyzed in 3854 tropical cloud clusters that developed in 1981–2009 and may or may not have formed TCs; this reveals that the strength of the low-frequency vorticity is a crucial factor in TC formation. A tropical cloud cluster is expected to develop into a TC in an environment favorable for TC formation in the presence of a large 850-hPa low-frequency vorticity. The lead time for forecasting the formation of a TC can probably be extended under such conditions.

scholarly journals A Contrast of Recent Changing Tendencies in Genesis Productivity of Tropical Cloud Clusters over the Western North Pacific in May and October

Atmosphere ◽  
2021 ◽  
Vol 12 (9) ◽  
pp. 1177
Author(s):  
Xugang Peng ◽  
Lei Wang ◽  
Minmin Wu ◽  
Qiuying Gan
Keyword(s):  
Kinetic Energy ◽  
North Pacific ◽  
Western North Pacific ◽  
Large Scale ◽  
Eddy Kinetic Energy ◽  
Boreal Summer ◽  
Cloud Clusters ◽  
Sst Warming ◽  
Atmospheric Circulation Anomalies ◽  
Anomalous Anticyclonic Circulation

Tropical cloud clusters (TCCs) are embryos of tropical cyclones (TCs) and may have the potential to develop into TCs. The genesis productivity (GP) of TCCs is used to quantify the proportion of TCCs that can evolve into TCs. Recent studies have revealed a decrease in GP of western North Pacific (WNP) TCCs during the extended boreal summer (July–October) since 1998. Here, we show that the changing tendencies in GP of WNP TCCs have obvious seasonality. Although most months could see recent decreases in GP of WNP TCCs, with October experiencing the strongest decreasing trend, May is the only month with a significant recent increasing trend. The opposite changing tendencies in May and October could be attributed to different changes in low-level atmospheric circulation anomalies triggered by different sea surface temperature (SST) configurations across the tropical oceans. In May, stronger SST warming in the tropical western Pacific could prompt increased anomalous westerlies associated with anomalous cyclonic circulation, accompanied by the weakening of the WNP subtropical high and the strengthening of the WNP monsoon. Such changes in background atmospheric circulations could favor the enhancement of atmospheric eddy kinetic energy and barotropic energy conversions, resulting in a recent intensified GP of WNP TCCs in May. In October, stronger SST warming in the tropical Atlantic and Indian Oceans contributed to anomalous easterlies over the tropical WNP associated with anomalous anticyclonic circulation, giving rise to the suppressed atmospheric eddy kinetic energy and recent weakened GP of WNP TCCs. These results highlight the seasonality in recent changing tendencies in the GP of WNP TCCs and associated large-scale atmospheric-oceanic conditions.

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