Factors Controlling Multiple Tropical Cyclone Events in the Western North Pacific*

Abstract The statistical feature of occurrence of multiple tropical cyclone (MTC) events in the western North Pacific (WNP) is examined during summer (June–September) for the period of 1979–2006. The number of MTC events ranged from one to eight per year, experiencing a marked interannual variation. The spatial distance between the TCs associated with MTC events is mostly less than 3000 km, which accounts for 73% of total samples. The longest active phase of an MTC event lasts for nine days, and about 80% of the MTC events last for five days or less. A composite analysis of active and inactive MTC phases reveals that positive low-level (negative upper-level) vorticity anomalies and enhanced convection and midtropospheric relative humidity are the favorable large-scale conditions for MTC genesis. About 77% of the MTC events occurred in the region where either the atmospheric intraseasonal (25–70 day) oscillation (ISO) or biweekly (10–20 day) oscillation (BWO) is in a wet phase. The overall occurrence of the MTC events is greatly regulated by the combined large-scale impact of BWO, ISO, and the lower-frequency (90 days or longer) oscillation. On the interannual time scale, the MTC frequency is closely related to the seasonal mean anomalies of 850-hPa vorticity, outgoing longwave radiation (OLR), and 500-hPa humidity fields. The combined ISO and BWO activity is greatly strengthened (weakened) in the WNP region during the MTC active (inactive) years.

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Association of the Poleward Shift of East Asian Subtropical Upper-Level Jet with Frequent Tropical Cyclone Activities over the Western North Pacific in Summer

Journal of Climate ◽

10.1175/jcli-d-16-0334.1 ◽

2017 ◽

Vol 30 (14) ◽

pp. 5597-5603 ◽

Cited By ~ 6

Author(s):

Xian Chen ◽

Zhong Zhong ◽

Wei Lu

Keyword(s):

Tropical Cyclone ◽

North Pacific ◽

Western North Pacific ◽

Large Scale ◽

East Asian ◽

Teleconnection Pattern ◽

Reanalysis Dataset ◽

Poleward Shift ◽

Upper Level ◽

Upper Level Jet

The NCEP–NCAR reanalysis dataset and the tropical cyclone (TC) best-track dataset from the Regional Specialized Meteorological Center (RSMC) Tokyo Typhoon Center were employed in the present study to investigate the possible linkage of the meridional displacement of the East Asian subtropical upper-level jet (EASJ) with the TC activity over the western North Pacific (WNP). Results indicate that summertime frequent TC activities would create the poleward shift of the EASJ through a stimulated Pacific–Japan (PJ) teleconnection pattern as well as the changed large-scale meridional temperature gradient. On the contrary, in the inactive TC years, the EASJ is often located more southward than normal with an enhanced intensity. Therefore, TC activities over the WNP are closely related to the location and intensity of the EASJ in summer at the interannual time scale.

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Possible Linkage between the Monsoon Trough Variability and the Tropical Cyclone Activity over the Western North Pacific

Monthly Weather Review ◽

10.1175/mwr-d-11-00078.1 ◽

2012 ◽

Vol 140 (1) ◽

pp. 140-150 ◽

Cited By ~ 104

Author(s):

Liang Wu ◽

Zhiping Wen ◽

Ronghui Huang ◽

Renguang Wu

Keyword(s):

Tropical Cyclone ◽

North Pacific ◽

Western North Pacific ◽

Large Scale ◽

Monsoon Trough ◽

Vertical Shear ◽

Mean Flow ◽

Tropical Eastern Pacific ◽

Barotropic Energy Conversion ◽

Upper Level

Abstract The present study investigates the influence of the monsoon trough (MT) on the interannual variability of tropical cyclone (TC) activity over the western North Pacific during July–November for the period 1979–2007. It is shown that the TC activity is closely related to the MT location. During the years when the MT extends eastward (retreats westward), more (less) TCs form within the southeastern quadrant of the western North Pacific. Such a relationship can be explained by the changes in large-scale environmental factors associated with the movement of the MT. An eastward extension of the MT coincides with warmed ocean surface, enhanced convection, increased relative humidity in the lower and midtroposphere, reduced vertical shear of zonal wind, intensified upper-level divergence, and low-level anomalous cyclonic vorticity over the southeast quadrant of the western North Pacific. These conditions associated with the eastern extension of the MT are favorable for TC genesis, while those associated with the westward retreat of the MT are not. Diagnosis of the barotropic energy conversion indicates that synoptic-scale disturbances moving westward from tropical eastern Pacific will gain the energy from the mean flow when they meet with the eastward-extending MT. This is an important reason for the linkage between MT variability and TC genesis over the western North Pacific.

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Evaluation of Simulation Capability for Multiple Tropical Cyclone Events in the Western North Pacific of the UH_HCM Model

Frontiers in Earth Science ◽

10.3389/feart.2020.598473 ◽

2021 ◽

Vol 8 ◽

Author(s):

Tianhang Li ◽

Hong-Li Ren ◽

Yujie Wu ◽

Jianyun Gao

Keyword(s):

Tropical Cyclone ◽

North Pacific ◽

Western North Pacific ◽

Large Scale ◽

Intraseasonal Variability ◽

Coupled Model ◽

Active Phase ◽

Monsoon Trough ◽

Factors Affecting ◽

Potential Index

The intraseasonal variability of multiple tropical cyclone (MTC) events in the western North Pacific (WNP) during 1979–2015 is analyzed using the best-track dataset archived at the Joint Typhoon Warning Center. MTC events are divided into three phases according to the time intervals of the tropical cyclone (TC) genesis, that is, active, normal, and inactive phases. Composite analysis results indicate that MTC events tend to occur in the active phase when the monsoon trough is stronger and located farther north than at other times. Initialized by the data from a 10-year stable running result, a 12-year control experiment is carried out using the hybrid atmosphere–ocean coupled model developed at the University of Hawaii (UH_HCM model) to evaluate its simulation capability. Compared with the climate observations, the model shows good skill in simulating the large-scale environmental conditions in the WNP, especially the subtropical high and the monsoon trough. In addition, the model can well simulate the climate characteristics of TCs in the WNP, as well as the differences in each MTC phase. However, the simulated frequency of TCs is less and their locations are more northeast, compared with the observations. The vorticity and moisture in the model appear to be the two main factors affecting MTC activity based on analyses of the genesis potential index.

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Mesoscale Features Associated with Tropical Cyclone Formations in the Western North Pacific

Monthly Weather Review ◽

10.1175/2007mwr2267.1 ◽

2008 ◽

Vol 136 (6) ◽

pp. 2006-2022 ◽

Cited By ~ 32

Author(s):

Cheng-Shang Lee ◽

Kevin K. W. Cheung ◽

Jenny S. N. Hui ◽

Russell L. Elsberry

Keyword(s):

Tropical Cyclone ◽

North Pacific ◽

Western North Pacific ◽

Large Scale ◽

North Pacific Ocean ◽

Deep Convection ◽

Mesoscale Convective System ◽

Convective System ◽

Synoptic Patterns ◽

The Mean

Abstract The mesoscale features of 124 tropical cyclone formations in the western North Pacific Ocean during 1999–2004 are investigated through large-scale analyses, satellite infrared brightness temperature (TB), and Quick Scatterometer (QuikSCAT) oceanic wind data. Based on low-level wind flow and surge direction, the formation cases are classified into six synoptic patterns: easterly wave (EW), northeasterly flow (NE), coexistence of northeasterly and southwesterly flow (NE–SW), southwesterly flow (SW), monsoon confluence (MC), and monsoon shear (MS). Then the general convection characteristics and mesoscale convective system (MCS) activities associated with these formation cases are studied under this classification scheme. Convection processes in the EW cases are distinguished from the monsoon-related formations in that the convection is less deep and closer to the formation center. Five characteristic temporal evolutions of the deep convection are identified: (i) single convection event, (ii) two convection events, (iii) three convection events, (iv) gradual decrease in TB, and (v) fluctuating TB, or a slight increase in TB before formation. Although no dominant temporal evolution differentiates cases in the six synoptic patterns, evolutions ii and iii seem to be the common routes taken by the monsoon-related formations. The overall percentage of cases with MCS activity at multiple times is 63%, and in 35% of cases more than one MCS coexisted. Most of the MC and MS cases develop multiple MCSs that lead to several episodes of deep convection. These two patterns have the highest percentage of coexisting MCSs such that potential interaction between these systems may play a role in the formation process. The MCSs in the monsoon-related formations are distributed around the center, except in the NE–SW cases in which clustering of MCSs is found about 100–200 km east of the center during the 12 h before formation. On average only one MCS occurs during an EW formation, whereas the mean value is around two for the other monsoon-related patterns. Both the mean lifetime and time of first appearance of MCS in EW are much shorter than those developed in other synoptic patterns, which indicates that the overall formation evolution in the EW case is faster. Moreover, this MCS is most likely to be found within 100 km east of the center 12 h before formation. The implications of these results to internal mechanisms of tropical cyclone formation are discussed in light of other recent mesoscale studies.

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Large-Scale Environmental Parameters Associated with Tropical Cyclone Formations in the Western North Pacific

Journal of Climate ◽

10.1175/1520-0442(2004)017<0466:lepawt>2.0.co;2 ◽

2004 ◽

Vol 17 (3) ◽

pp. 466-484 ◽

Cited By ~ 42

Author(s):

Kevin K. W. Cheung

Keyword(s):

Tropical Cyclone ◽

North Pacific ◽

Western North Pacific ◽

Large Scale ◽

Environmental Parameters

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Developing versus Nondeveloping Disturbances for Tropical Cyclone Formation. Part II: Western North Pacific

Monthly Weather Review ◽

10.1175/2011mwr3618.1 ◽

2012 ◽

Vol 140 (4) ◽

pp. 1067-1080 ◽

Cited By ~ 63

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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Multidecadal Variability of Tropical Cyclone Rapid Intensification in the Western North Pacific

Journal of Climate ◽

10.1175/jcli-d-14-00400.1 ◽

2015 ◽

Vol 28 (9) ◽

pp. 3806-3820 ◽

Cited By ~ 36

Author(s):

Xidong Wang ◽

Chunzai Wang ◽

Liping Zhang ◽

Xin Wang

Keyword(s):

Tropical Cyclone ◽

North Pacific ◽

Wind Shear ◽

Western North Pacific ◽

Large Scale ◽

Vertical Wind Shear ◽

Trade Wind ◽

Rapid Intensification ◽

Multidecadal Variability ◽

Heat Potential

Abstract This study investigates the variation of tropical cyclone (TC) rapid intensification (RI) in the western North Pacific (WNP) and its relationship with large-scale climate variability. RI events have exhibited strikingly multidecadal variability. During the warm (cold) phase of the Pacific decadal oscillation (PDO), the annual RI number is generally lower (higher) and the average location of RI occurrence tends to shift southeastward (northwestward). The multidecadal variations of RI are associated with the variations of large-scale ocean and atmosphere variables such as sea surface temperature (SST), tropical cyclone heat potential (TCHP), relative humidity (RHUM), and vertical wind shear (VWS). It is shown that their variations on multidecadal time scales depend on the evolution of the PDO phase. The easterly trade wind is strengthened during the cold PDO phase at low levels, which tends to make equatorial warm water spread northward into the main RI region rsulting from meridional ocean advection associated with Ekman transport. Simultaneously, an anticyclonic wind anomaly is formed in the subtropical gyre of the WNP. This therefore may deepen the depth of the 26°C isotherm and directly increase TCHP over the main RI region. These thermodynamic effects associated with the cold PDO phase greatly support RI occurrence. The reverse is true during the warm PDO phase. The results also indicate that the VWS variability in the low wind shear zone along the monsoon trough may not be critical for the multidecadal modulation of RI events.

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A Survey on the Relationship between Ocean Subsurface Temperature and Tropical Cyclone over the Western North Pacific

Advances in Meteorology ◽

10.1155/2020/9290837 ◽

2020 ◽

Vol 2020 ◽

pp. 1-14

Author(s):

Difu Sun ◽

Junqiang Song ◽

Kaijun Ren ◽

Xiaoyong Li ◽

Guangjie Wang

Keyword(s):

Tropical Cyclone ◽

Water Temperature ◽

Negative Correlation ◽

North Pacific ◽

Western North Pacific ◽

Vertical Wind Shear ◽

Longwave Radiation ◽

Subsurface Water ◽

Subsurface Temperature ◽

The Relationship

The relationship between ocean subsurface temperature and tropical cyclone (TC) over the western North Pacific (WNP) is studied based on the TC best-track data and global reanalysis data during the period of 1948–2012. Here the TC frequency (TCF), lifespan, and genesis position of TCs are analysed. A distinctive negative correlation between subsurface water temperature and TCF is observed, especially the TCF in the southeastern quadrant of the WNP (0–15°N, 150–180°E). According to the detrended subsurface temperature anomalies of the 125 m depth layer in the main TC genesis area (0–30°N, 100–180°E), we selected the subsurface cold and warm years. During the subsurface cold years, TCs tend to have a longer mean lifespan and a more southeastern genesis position than the subsurface warm years in general. To further investigate the causes of this characteristic, the TC genesis potential indexes (GPI) are used to analyse the contributions of environmental factors to TC activities. The results indicate that the negative correlation between subsurface water temperature and TCF is mainly caused by the variation of TCF in the southeastern quadrant of the WNP, where the oceanic and atmospheric environments are related to ocean subsurface conditions. Specifically, compared with the subsurface warm years, there are larger relative vorticity, higher relative humidity, smaller vertical wind shear, weaker net longwave radiation, and higher ocean mixed layer temperature in the southeastern quadrant during cold years, which are all favorable for genesis and development of TC.

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Interannual Variability of Summer Tropical Cyclone Rainfall in the Western North Pacific Depicted by CFSR and Associated Large-Scale Processes and ISO Modulations

Journal of Climate ◽

10.1175/jcli-d-16-0805.1 ◽

2018 ◽

Vol 31 (5) ◽

pp. 1771-1787 ◽

Cited By ~ 5

Author(s):

Jau-Ming Chen ◽

Pei-Hua Tan ◽

Liang Wu ◽

Hui-Shan Chen ◽

Jin-Shuen Liu ◽

...

Keyword(s):

Tropical Cyclone ◽

Interannual Variability ◽

El Niño ◽

North Pacific ◽

Western North Pacific ◽

Large Scale ◽

El Nino ◽

Southern Oscillation ◽

Monsoon Trough ◽

Tropical Eastern Pacific

This study examines the interannual variability of summer tropical cyclone (TC) rainfall (TCR) in the western North Pacific (WNP) depicted by the Climate Forecast System Reanalysis (CFSR). This interannual variability exhibits a maximum region near Taiwan (19°–28°N, 120°–128°E). Significantly increased TCR in this region is modulated by El Niño–Southern Oscillation (ENSO)-related large-scale processes. They feature elongated sea surface temperature warming in the tropical eastern Pacific and a southeastward-intensified monsoon trough. Increased TC movements are facilitated by interannual southerly/southeasterly flows in the northeastern periphery of the intensified monsoon trough to move from the tropical WNP toward the region near Taiwan, resulting in increased TCR. The coherent dynamic relations between interannual variability of summer TCR and large-scale environmental processes justify CFSR as being able to reasonably depict interannual characteristics of summer TCR in the WNP. For intraseasonal oscillation (ISO) modulations, TCs tend to cluster around the center of a 10–24-day cyclonic anomaly and follow its northwestward propagation from the tropical WNP toward the region near Taiwan. The above TC movements are subject to favorable background conditions provided by a northwest–southeasterly extending 30–60-day cyclonic anomaly. Summer TCR tends to increase (decrease) during El Niño (La Niña) years and strong (weak) ISO years. By comparing composite TCR anomalies and correlations with TCR variability, it is found that ENSO is more influential than ISO in modulating the interannual variability of summer TCR in the WNP.

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Changes in the Past and Projected Western North Pacific Tropical Cyclone Activity in a Warmed Climate

10.5194/egusphere-egu2020-7521 ◽

2020 ◽

Author(s):

Liang Wu

Keyword(s):

Tropical Cyclone ◽

North Pacific ◽

Western North Pacific ◽

Large Scale ◽

Climate Models ◽

Rapid Development ◽

Current Trend ◽

Coupled Model ◽

Rcp 8.5 ◽

Projected Changes

Two high-resolution climate models (the HiRAM and MRI-AGCM3.2) are used to simulate present-day western North Pacific (WNP) tropical cyclone (TC) activity and investigate the projected changes for the late 21st century. Compared toobservations, the models are able to realistically simulate many basic features of the WNP TC activity climatology. Future projections with the coupled model inter-comparison project phase 5 (CMIP5) under Representative Concentration Pathway (RCP) 8.5 scenario show a tendency for decreases in the number of WNP TCs, and of increases in the more intense TCs. It is unknown to what cause this inverse variation with number and intensity should be generally linked to similar large-scale environmental conditions. To examine the WNP TC genesis and intensity with environmental variables, we show that most of the current trend of decreasing genesis of TCs can be attributed to weakened dynamic environments and the current trend of increasing intensity of TCs might be linked to increased thermodynamic environments. Thus, the future climate warms under RCP 8.5 will likely lead to strong reductions in TC genesis frequency over the WNP, with project decreases of 36-63% by the end of the twenty-first century, but lead to greater TC intensities with rapid development of thermodynamic environments.

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