scholarly journals Interdecadal change in the genesis activity of the first tropical cyclone of each year over the western North Pacific

2021 ◽  
Author(s):  
Yumi Cha ◽  
JaeWon Choi ◽  
Joong-Bae Ahn
Keyword(s):  
Tropical Cyclone ◽  
North Pacific ◽  
Western North Pacific ◽  
Walker Circulation ◽  
The Philippines ◽  
Cyclonic Circulation ◽  
Equatorial Pacific ◽  
Trade Winds ◽  
Anticyclonic Circulation ◽  
Anomalous Cyclonic Circulation

Abstract This study analyzed time series of the genesis latitude, longitude, and date of the first tropical cyclone (TC) each year over the 38 years between 1979 and 2016. Statistical change-point analysis applied to these three variables showed that a shift in climate regime occurred around 1998. More specifically, recent TCs have shown a strong tendency to occur more northwest in the western North Pacific (WNP), and day of TC genesis tend to be delayed. Also, we compared differences between the periods 1998 to 2016 (post-1998) and 1979–1997 (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 (SST). Our results showed that a favorable environment for TC genesis was formed near the South China Sea (SCS) and the Philippines and an unfavorable environment for TC genesis was formed in the southeastern part of the WNP. Analysis of stream flow showed that an anomalous cyclonic circulation at 850 hPa was formed in the SCS and an anomalous large anticyclonic circulation was formed in the North Pacific. From these circulations, a ridge extended to the east sea of the Philippines, and consequently, anomalous trade winds were strengthened in the equatorial Pacific. Such anomalous atmospheric circulation seems to be associated with the cold Pacific Decadal Oscillation (PDO) phase. At 200 hPa, the anomalous anticyclonic circulation was 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 found to be related with a strengthening of Walker circulation. Therefore, during the post-1998, when trade winds were strengthened by the development of Walker circulation, the cold PDO phase was strengthened, the location of TC genesis moved toward the northwestern WNP, and TC genesis day tended to be delayed.

scholarly journals Differences in Western North Pacific Tropical Cyclone Activity among Three El Niño Phases

2020 ◽  
Vol 33 (18) ◽  
pp. 7983-8002
Author(s):  
Jinjie Song ◽  
Philip J. Klotzbach ◽  
Yihong Duan
Keyword(s):  
Tropical Cyclone ◽  
El Niño ◽  
North Pacific ◽  
Western North Pacific ◽  
El Nino ◽  
Walker Circulation ◽  
The Philippines ◽  
Central Pacific El Niño ◽  
Low Level ◽  
Sst Anomalies

AbstractThe impacts of El Niño on tropical cyclone (TC) activity over the western North Pacific (WNP) are examined through investigation of three types of tropical Pacific warming episodes according to where the maximum sea surface temperature (SST) anomalies occur in the equatorial Pacific: the eastern Pacific El Niño (EPE), the central Pacific El Niño (CPE), and the mixed El Niño (ME). More TCs form over the eastern part of the WNP in all three El Niño types, whereas the frequency of TCs over the western part of the WNP increases as the peak SST anomalies migrate from east to west. Although TCs more frequently recurve at higher latitudes during EPE and CPE, the most frequent region for recurving is much closer to the East Asian continent in CPE years than in EPE years. In contrast, more TCs track westward and threaten the Philippines in ME years. The increased TC genesis over the western part of the WNP can be explained by enhanced low-level relative vorticity, reduced vertical wind shear, and increased maximum potential intensity during CPE and increased midlevel moisture during EPE and ME. This increase is further related to updraft anomalies near the date line driven by an anomalous Walker circulation and an anomalous low-level cyclonic circulation over the WNP. The TC track differences among the different El Niño types are linked to the east–west shift of the western Pacific subtropical high, possibly caused by an anomalous Hadley circulation from 120° to 130°E that is strongly coupled with the anomalous Walker circulation.

scholarly journals Change in Tropical Cyclone Activity during the Break of the Western North Pacific Summer Monsoon in Early August

2016 ◽  
Vol 29 (7) ◽  
pp. 2457-2469 ◽  
Author(s):  
Ke Xu ◽  
Riyu Lu
Keyword(s):  
Tropical Cyclone ◽  
Summer Monsoon ◽  
North Pacific ◽  
Western North Pacific ◽  
Cyclonic Circulation ◽  
Tropical Cyclone Activity ◽  
Upward Motion ◽  
Mariana Islands ◽  
Cyclone Activity

Abstract The modulation of tropical cyclone (TC) activity by the western North Pacific (WNP) monsoon break is investigated by analyzing the subseasonal evolution of TCs and corresponding circulations, based on 65 years of data from 1950 to 2014. The monsoon break has been identified as occurring over the WNP in early August. The present results show that TC occurrence decreases (increases) remarkably to the east of the Mariana Islands (southeast of Japan) during the monsoon break, which is closely related to local anomalous midtropospheric downward (upward) motion and lower-tropospheric anticyclonic (cyclonic) circulation, in comparison with the previous and subsequent convective periods in late July and mid-August. These changes of TC activity and the corresponding circulation during the monsoon break are more significant in typical monsoon break years when the monsoon break phenomenon is predominant. The reverse changes of TC activity to the east of the Mariana Islands and to the southeast of Japan during the monsoon break are closely associated with the out-of-phase subseasonal evolutions over these two regions from late July to mid-August, which are both contributed to greatly by 10–25-day oscillations. Finally, the roles of midlatitude and tropical disturbances on 10–25-day oscillations are also discussed.

scholarly journals Improved Simulation of Tropical Cyclone Responses to ENSO in the Western North Pacific in the High-Resolution GFDL HiFLOR Coupled Climate Model*

2016 ◽  
Vol 29 (4) ◽  
pp. 1391-1415 ◽  
Author(s):  
Wei Zhang ◽  
Gabriel A. Vecchi ◽  
Hiroyuki Murakami ◽  
Thomas Delworth ◽  
Andrew T. Wittenberg ◽  
...  
Keyword(s):  
High Resolution ◽  
Tropical Cyclone ◽  
El Niño ◽  
North Pacific ◽  
Western North Pacific ◽  
El Nino ◽  
Walker Circulation ◽  
La Niña ◽  
Sea Surface ◽  
La Nina

Abstract This study aims to assess whether, and the extent to which, an increase in atmospheric resolution of the Geophysical Fluid Dynamics Laboratory (GFDL) Forecast-Oriented Low Ocean Resolution version of CM2.5 (FLOR) with 50-km resolution and the High-Resolution FLOR (HiFLOR) with 25-km resolution improves the simulation of the El Niño–Southern Oscillation (ENSO)–tropical cyclone (TC) connections in the western North Pacific (WNP). HiFLOR simulates better ENSO–TC connections in the WNP including TC track density, genesis, and landfall than FLOR in both long-term control experiments and sea surface temperature (SST)- and sea surface salinity (SSS)-restoring historical runs (1971–2012). Restoring experiments are performed with SSS and SST restored to observational estimates of climatological SSS and interannually varying monthly SST. In the control experiments of HiFLOR, an improved simulation of the Walker circulation arising from more realistic SST and precipitation is largely responsible for its better performance in simulating ENSO–TC connections in the WNP. In the SST-restoring experiments of HiFLOR, more realistic Walker circulation and steering flow during El Niño and La Niña are responsible for the improved simulation of ENSO–TC connections in the WNP. The improved simulation of ENSO–TC connections with HiFLOR arises from a better representation of SST and better responses of environmental large-scale circulation to SST anomalies associated with El Niño or La Niña. A better representation of ENSO–TC connections in HiFLOR can benefit the seasonal forecasting of TC genesis, track, and landfall; improve understanding of the interannual variation of TC activity; and provide better projection of TC activity under climate change.

scholarly journals Attribution of Decadal Variability in Tropical Cyclone Passage Frequency over the Western North Pacific: A New Approach Emphasizing the Genesis Location of Cyclones

2013 ◽  
Vol 26 (3) ◽  
pp. 973-987 ◽  
Author(s):  
Satoru Yokoi ◽  
Yukari N. Takayabu
Keyword(s):  
Tropical Cyclone ◽  
Time Scales ◽  
North Pacific ◽  
Western North Pacific ◽  
Decadal Variability ◽  
The Philippines ◽  
Ocean Basin ◽  
New Approach ◽  
Equal Degree ◽  
Analysis Application

Abstract Variability in tropical cyclone (TC) activity is a matter of direct concern for affected populations. On interannual and longer time scales, variability in TC passage frequency can be associated with total TC frequency over the concerned ocean basin [basinwide frequency (BF)], the spatial distribution of TC genesis in the basin [genesis distribution (GD)], and the preferable track (PT) that can be considered as a function of genesis locations. To facilitate investigation of mechanisms responsible for the variability, the authors propose an approach of decomposing anomalies in the passage frequency into contributions of variability in BF, GD, and PT, which is named the Integration of Statistics on TC Activity by Genesis Location (ISTAGL) analysis. Application of this approach to TC best track data in the western North Pacific (WNP) basin reveals that overall distribution of the passage frequency trends over the 1961–2010 period is mainly due to the PT trends. On decadal time scales, passage frequency variability in midlatitudes is primarily due to PT variability, while the BF and GD also play roles in the subtropics. The authors further discuss decadal variability over the East China Sea in detail. The authors demonstrate that northward shift of the PT for TCs generated around the Philippines Sea and westward shift for TCs generated in the eastern part of the WNP contribute the variability with almost equal degree. The relationships between these PT shifts and anomalies in environmental circulation fields are also discussed.

scholarly journals Western North Pacific Tropical Cyclone Characteristics Stratified by Genesis Environment

2018 ◽  
Vol 146 (2) ◽  
pp. 435-446 ◽  
Author(s):  
Hironori Fudeyasu ◽  
Ryuji Yoshida
Keyword(s):  
Tropical Cyclone ◽  
North Pacific ◽  
Western North Pacific ◽  
Convective Available Potential Energy ◽  
The Philippines ◽  
Vertical Shear ◽  
Occurrence Rate ◽  
Tropical Cyclone Heat Potential ◽  
Heat Potential ◽  
Confluence Region

Abstract The characteristics of tropical cyclones (TCs) in the summer and autumn seasons over the western North Pacific that are associated with different environmental factors that influence TC genesis (TCG) were studied. The authors objectively categorized factors into the five TCG factors classified by Ritchie and Holland: monsoon shear line (SL), monsoon confluence region (CR), monsoon gyre (GY), easterly wave (EW), and the Rossby wave energy dispersion from a preexisting TC (PTC). The GY-TCs tended to develop slowly, and the highest rates of occurrence of rapid intensification (RI) were found for the CR-TCs, whereas the GY-TCs rarely experienced RI. The average storm size of the GY-TCs at the time of formation was the largest of the averages among the TC types, while the EW- and PTC-TCs were smaller, although these differences disappeared at the mature time. There were no significant differences in the sea surface temperature (SST) beneath the TCs, but the tropical cyclone heat potential (TCHP) of the PTC-TCs was higher. The PTC-TCs tended to develop as intense TCs and exhibited favorable environmental characteristics, such as high TCHP, high convective available potential energy, and weak vertical shear. The occurrence rate of the PTC-TCs that made landfall in the Philippines was higher than the averages of the other TC types, whereas those of the EW-TCs (PTC-TCs) that made landfall in Japan (China) were lower. These results provide important information for use in disaster prevention.

Tropical cyclone genesis and trajectory characteristics in the western north Pacific

2020 ◽  
Author(s):  
Rui Xiong ◽  
Mengqian Lu
Keyword(s):  
Tropical Cyclone ◽  
Zonal Wind ◽  
Environmental Conditions ◽  
North Pacific ◽  
Western North Pacific ◽  
Data Science ◽  
Clustering Algorithm ◽  
The Philippines ◽  
Vertical Shear ◽  
Gaussian Kernel

<p>The western North Pacific (WNP) is one of the most active tropical cyclone (TC) regions, which can inflict enormous death and massive property damage to surrounding areas. Although many studies about tropical cyclone activities on multi-timescales have been done, most of them focus on the entire basin, variations within the basin deserve more investigations. Besides TC characteristics on different timescales, to investigate the impacts of environment variables on TC and provide informative factors for prediction is another concern in the research community. In this study, we adopt several data science techniques, including Gaussian kernel estimator, wavelet, cross-wavelet coherence and regression analyses, to explore the spatiotemporal variations of TC genesis and associated environmental conditions. Significant semiannual and annual variations of TC genesis have been found in the northern South China Sea (NSCS) and oceanic areas east of the Philippines (OAEP). In the southeast part of WNP (SEWNP), TC genesis shows prominent variations on ENSO time scale. With reconstructed TC series on those frequencies, we further quantify the influences of environmental variables on the primary TC signals over WNP. About 40% of the identified TC variance over NSCS and OAEP can be explained by variability in vertical shear of zonal wind and relative humidity. In the SEWNP, TC genesis reveals strong nonlinear and non-stationary relationships with vertical shear of zonal wind and absolute vorticity. Besides, A probabilistic clustering algorithm is used to describe the TC tracks in the WNP. The best track dataset from JMA is decomposed into three clusters based on genesis location and curvature. For each cluster, we analyze the relationships between TC properties, such as genesis location, trajectory and intensity, and associated environmental conditions using the self-organizing map. The spatial patterns of sea surface temperature have huge impacts on TC genesis location, while the trajectory is largely influenced by geopotential height.</p>

A Global View of Equatorial Waves and Tropical Cyclogenesis

2012 ◽  
Vol 140 (3) ◽  
pp. 774-788 ◽  
Author(s):  
Carl J. Schreck ◽  
John Molinari ◽  
Anantha Aiyyer
Keyword(s):  
Tropical Cyclone ◽  
Tropical Cyclones ◽  
North Pacific ◽  
Western North Pacific ◽  
The Philippines ◽  
Tropical Cyclogenesis ◽  
Equatorial Waves ◽  
Wave Type ◽  
The North ◽  
Equatorial Wave

Abstract This study investigates the number of tropical cyclone formations that can be attributed to the enhanced convection from equatorial waves within each basin. Tropical depression (TD)-type disturbances (i.e., easterly waves) were the primary tropical cyclone precursors over the Northern Hemisphere basins, particularly the eastern North Pacific and the Atlantic. In the Southern Hemisphere, however, the number of storms attributed to TD-type disturbances and equatorial Rossby waves were roughly equivalent. Equatorward of 20°N, tropical cyclones formed without any equatorial wave precursor most often over the eastern North Pacific and least often over the western North Pacific. The Madden–Julian oscillation (MJO) was an important tropical cyclone precursor over the north Indian, south Indian, and western North Pacific basins. The MJO also affected tropical cyclogenesis by modulating the amplitudes of higher-frequency waves. Each wave type reached the attribution threshold 1.5 times more often, and tropical cyclogenesis was 3 times more likely, within positive MJO-filtered rainfall anomalies than within negative anomalies. The greatest MJO modulation was observed for storms attributed to Kelvin waves over the north Indian Ocean. The large rainfall rates associated with tropical cyclones can alter equatorial wave–filtered anomalies. This study quantifies the contamination over each basin. Tropical cyclones contributed more than 20% of the filtered variance for each wave type over large potions of every basin except the South Pacific. The largest contamination, exceeding 60%, occurred for the TD band near the Philippines. To mitigate the contamination, the tropical cyclone–related anomalies were removed before filtering in this study.

scholarly journals Systematic Variation of Summertime Tropical Cyclone Activity in the Western North Pacific in Relation to the Madden–Julian Oscillation

2008 ◽  
Vol 21 (6) ◽  
pp. 1171-1191 ◽  
Author(s):  
Joo-Hong Kim ◽  
Chang-Hoi Ho ◽  
Hyeong-Seog Kim ◽  
Chung-Hsiung Sui ◽  
Seon Ki Park
Keyword(s):  
Tropical Cyclone ◽  
South China ◽  
North Pacific ◽  
Western North Pacific ◽  
Large Scale ◽  
Function Analysis ◽  
Equatorial Indian Ocean ◽  
The Philippines ◽  
Madden Julian Oscillation ◽  
Enso Events

Abstract The variability of observed tropical cyclone (TC) activity (i.e., genesis, track, and landfall) in the western North Pacific (WNP) is examined in relation to the various categories of the Madden–Julian oscillation (MJO) during summer (June–September) for the period 1979–2004. The MJO categories are defined based on the empirical orthogonal function analysis of outgoing longwave radiation data. The number of TCs increases when the MJO-related convection center is located in the WNP. The axis of a preferable genesis region systematically shifts like a seesaw in response to changes in the large-scale environments associated with both the eastward and northward propagation of the MJO and the intraseasonal variability of the WNP subtropical high. Furthermore, the authors show that the density of TC tracks in each MJO category depends on the systematic shift in the main genesis regions at first order. Also, the shift is affected by the prevailing large-scale steering flows in each MJO category. When the MJO-related convection center is found in the equatorial Indian Ocean (the tropical WNP), a dense area of tracks migrates eastward (westward). The effects of extreme ENSO events and the variations occurring during ENSO neutral years are also examined. A statistical analysis of TC landfalls by MJO category is applied in seven selected subareas: the Philippines, Vietnam, South China, Taiwan, East China, Korea, and Japan. While a robust and significant modulation in the number of TC landfalls is observed in south China, Korea, and Japan, the modulation is marginal in the remaining four subareas.

scholarly journals Response of Tropical Cyclone Tracks to Sea Surface Temperature in the Western North Pacific

2016 ◽  
Vol 29 (5) ◽  
pp. 1955-1975 ◽  
Author(s):  
Kotaro Katsube ◽  
Masaru Inatsu
Keyword(s):  
Tropical Cyclone ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
North Pacific ◽  
Linear Response ◽  
Western North Pacific ◽  
Lower Troposphere ◽  
Cyclonic Circulation ◽  
Sea Surface ◽  
The West

Abstract A set of short-term experiments using a regional atmospheric model (RAM) were carried out to investigate the response of tropical cyclone (TC) tracks to sea surface temperature (SST) in the western North Pacific. For 10 selected TC cases occurring during 2002–07, a warm and a cold run are performed with 2 and −2 K added to the SSTs uniformly over the model domain, respectively. The cases can be classified into three groups in terms of recurvature: recurved tracks in the warm and cold runs, a recurved track in the warm run and a nonrecurved track in the cold run, and nonrecurved tracks in both runs. Commonly the warm run produced northward movement of the TC faster than the cold run. The rapid northward migration can be mainly explained by the result that cyclonic circulation to the west of the TC is found in the steering flow in the warm run and it is not in the cold run. The beta effect is also activated under the warm SST environment. For the typical TC cases, a linear baroclinic model experiment is performed to examine how the cyclonic circulation is intensified in the warm run. The stationary linear response to diabatic heating obtained from the RAM experiment reveals that the intensified TC by the warm SST excites the cyclonic circulation in the lower troposphere to the west of the forcing position. The vorticity and thermodynamic equation analysis shows the detailed mechanism. The time scale of the linear response and the teleconnection are also discussed.

scholarly journals Cluster Analysis of Tropical Cyclone Tracks over the Western North Pacific Using a Self-Organizing Map

2016 ◽  
Vol 29 (10) ◽  
pp. 3731-3751 ◽  
Author(s):  
Han-Kyoung Kim ◽  
Kyong-Hwan Seo
Keyword(s):  
Tropical Cyclone ◽  
North Pacific ◽  
Western North Pacific ◽  
The Philippines ◽  
Self Organizing Map ◽  
Central Pacific ◽  
Philippine Sea ◽  
Genesis Frequency ◽  
Sst Anomalies ◽  
Self Organizing

Abstract Tropical cyclone (TC) tracks over the western North Pacific (WNP) in 1979–2013 are classified by a self-organizing map technique. A false detection rate method identifies five optimal TC clusters. Physical mechanisms of the intraseasonal and interannual variations in the TC genesis frequency are investigated for each cluster. The five clusters are separated by genesis location, from the westernmost area (east of the Philippines, C1) to the easternmost (~150°E, C5) onset area over the WNP. The intraseasonal Madden–Julian oscillation (MJO) significantly affects the genesis frequency for all clusters except for C5. In particular, MJO phases 5 and 6 (1 and 2) provide significantly favorable (unfavorable) large-scale conditions for TC genesis. Two types of El Niño–Southern Oscillation influence the interannual variation of the genesis frequency for only C2 (generated over the western Philippine Sea and East China Sea) and C4 (formed near the eastern Philippine Sea). Enhanced eastern Pacific sea surface temperature (SST) anomalies lead to a ~40% decrease in the C2 TC frequency through a reversed Walker circulation with downward motion over the WNP. Conversely, increased central Pacific SST anomalies generate a cyclonic Rossby wave northwest of the forcing, inducing a significant increase (~50%) in the C4 TC frequency. The interannual variability for the C5 TCs is strongly controlled by the variation of the western Pacific subtropical high (WPSH). A positive WPSH variation reduces the C5 TC genesis frequency by 66%, while negative WPSH anomalies enhance the frequency by 50%. A prediction scheme using information from the first four 6-h TC locations demonstrates a skillful determination of TC clusters.

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