The Controlling of the Subtropical High Leading Modes on the Spatial Pattern of Tropical Cyclone Genesis in the Western North Pacific and Tracks Landing on the East Coast of China

As a prime circulation system, the western Pacific subtropical high (WPSH) significantly impacts tropical cyclone (TC) activities over the western North Pacific (WNP), especially TCs landing on the east coast of China; however, the associated mechanism is not firmly established. This study investigates the underlying dynamic impact of the first two empirical orthogonal function (EOF) modes of the WPSH on the interannual variability in the genesis and number of TCs landing over the WNP. The results show that these two dominant modes control the WNP TC activity over different subregions via different environmental factors. The first mode (EOF1) affects the TC genesis number over region I (105°–128° E, 5°–30° N) (r = −0.49) and region II (130°–175° E, 17°–30° N) (r = −0.5) and controls the TCs landing on the east coast of China, while the second mode (EOF2) affects the TC genesis number over region III (128°–175° E, 5°–17° N) (r = −0.69). The EOF1 mode, a southwest-northeast-oriented enhanced pattern, causes the WPSH to expand (retreat) along the southwest-northeast direction, which makes both mid-low-level relative humidity and low-level vorticity unfavorable (favorable) for TC genesis in region I and region II and steers fewer (more) TC tracks to land on the coast of China. The EOF2 mode features a strengthened WPSH over the southeast quarter of the WNP region. The active (inactive) phases of this mode control the low-level vorticity and vertical wind shear in region III, which lead to less (more) TC genesis over this region. The prediction equations combining the two modes of the WPSH for the total number of TCs and TCs that make landfall show high correlation coefficients. Our findings verify the high prediction skill of the WPSH on WNP TC activities, provide a new way to predict TCs that will make landfall on the east coast of China, and help to improve the future projection of WNP TC activity.

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Inactive Period of Western North Pacific Tropical Cyclone Activity in 1998–2011

Journal of Climate ◽

10.1175/jcli-d-12-00053.1 ◽

2013 ◽

Vol 26 (8) ◽

pp. 2614-2630 ◽

Cited By ~ 92

Author(s):

Kin Sik Liu ◽

Johnny C. L. Chan

Keyword(s):

Tropical Cyclone ◽

North Pacific ◽

Wind Shear ◽

Western North Pacific ◽

Vertical Wind Shear ◽

Vertical Wind ◽

Subtropical High ◽

Atmospheric Conditions ◽

Inactive Period ◽

Genesis Frequency

Abstract Tropical cyclone (TC) activity over the western North Pacific (WNP) exhibits a significant interdecadal variation during 1960–2011, with two distinct active and inactive periods each. This study examines changes in TC activity and atmospheric conditions in the recent inactive period (1998–2011). The overall TC activity shows a significant decrease, which is partly related to the decadal variation of TC genesis frequency in the southeastern part of the WNP and the downward trend of TC genesis frequency in the main development region. The investigation on the factors responsible for the low TC activity mainly focuses on the effect of vertical wind shear and subtropical high on multidecadal time scales. A vertical wind shear index, defined as the mean magnitude of the difference of the 200- and 850-hPa horizontal zonal winds (10°–17.5°N, 150°E–180°) averaged between June and October, is highly correlated with the annual TC number and shows a significant interdecadal variation. Positive anomalies of vertical wind shear are generally found in the eastern part of the tropical WNP during this inactive period. A subtropical high area index, calculated as the area enclosed by the 5880-gpm line of the June–October 500-hPa geopotential height (0°–40°N, 100°E–180°), shows a significant upward trend. A high correlation is also found between this index and the annual TC number, and a stronger-than-normal subtropical high is generally observed during this inactive period. The strong vertical wind shear and strong subtropical high observed during 1998–2011 together apparently lead to unfavorable atmospheric conditions for TC genesis and hence the low TC activity during the period.

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Interannual and interdecadal impact of Western North Pacific Subtropical High on tropical cyclone activity

Climate Dynamics ◽

10.1007/s00382-019-05110-7 ◽

2020 ◽

Vol 54 (3-4) ◽

pp. 2237-2248 ◽

Cited By ~ 2

Author(s):

Qiong Wu ◽

Xiaochun Wang ◽

Li Tao

Keyword(s):

Tropical Cyclone ◽

North Pacific ◽

Western North Pacific ◽

Southern Oscillation ◽

Subtropical High ◽

Interdecadal Change ◽

Steering Flow ◽

The Pacific ◽

Sea Surface Temperature Anomalies ◽

Peak Phase

AbstractIn this study, we analyzed the impacts of Western North Pacific Subtropical High (WNPSH) on tropical cyclone (TC) activity on both interannual and interdecadal timescales. Based on a clustering analysis method, we grouped TCs in the Western North Pacific into three clusters according to their track patterns. We mainly focus on Cluster 1 (C1) TCs in this work, which is characterized by forming north of 15° N and moving northward. On interannual timescale, the number of C1 TCs is influenced by the intensity variability of the WNPSH, which is represented by the first Empirical Orthogonal Function (EOF) of 850 hPa geopotential height of the region. The WNPSH itself is modulated by the El Niño–Southern Oscillation at its peak phase in the previous winter, as well as Indian and Atlantic Ocean sea surface temperature anomalies in following seasons. The second EOF mode shows the interdecadal change of WNPSH intensity. The interdecadal variability of WNPSH intensity related to the Pacific climate regime shift could cause anomalies of the steering flow, and lead to the longitudinal shift of C1 TC track. Negative phases of interdecadal Pacific oscillation are associated with easterly anomaly of steering flow, westward shift of C1 TC track, and large TC impact on the East Asia coastal area.

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Future Change in Tropical Cyclone Activity over the Western North Pacific in CORDEX-East Asia Multi-RCMs Forced by HadGEM2-AO

Journal of Climate ◽

10.1175/jcli-d-18-0575.1 ◽

2019 ◽

Vol 32 (16) ◽

pp. 5053-5067 ◽

Cited By ~ 4

Author(s):

Hyeonjae Lee ◽

Chun-Sil Jin ◽

Dong-Hyun Cha ◽

Minkyu Lee ◽

Dong-Kyou Lee ◽

...

Keyword(s):

Tropical Cyclone ◽

East Asia ◽

North Pacific ◽

Western North Pacific ◽

Climate Models ◽

Regional Climate ◽

Vertical Wind Shear ◽

Coastal Regions ◽

The Future ◽

Cordex East Asia

AbstractFuture changes in tropical cyclone (TC) activity over the western North Pacific (WNP) are analyzed using four regional climate models (RCMs) within the Coordinated Regional Climate Downscaling Experiment (CORDEX) for East Asia. All RCMs are forced by the HadGEM2-AO under the historical and representative concentration pathway (RCP) 8.5 scenarios, and are performed at about 50-km resolution over the CORDEX-East Asia domain. In the historical simulations (1980–2005), multi-RCM ensembles yield realistic climatology for TC tracks and genesis frequency during the TC season (June–November), although they show somewhat systematic biases in simulating TC activity. The future (2024–49) projections indicate an insignificant increase in the total number of TC genesis (+5%), but a significant increase in track density over East Asia coastal regions (+17%). The enhanced TC activity over the East Asia coastal regions is mainly related to vertical wind shear weakened by reduced meridional temperature gradient and increased sea surface temperature (SST) at midlatitudes. The future accumulated cyclone energy (ACE) of total TCs increases significantly (+19%) because individual TCs have a longer lifetime (+6.6%) and stronger maximum wind speed (+4.1%) compared to those in the historical run. In particular, the ACE of TCs passing through 25°N increases by 45.9% in the future climate, indicating that the destructiveness of TCs can be significantly enhanced in the midlatitudes despite the total number of TCs not changing greatly.

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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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Environmental Factors Affecting Tropical Cyclone Power Dissipation

Journal of Climate ◽

10.1175/2007jcli1571.1 ◽

2007 ◽

Vol 20 (22) ◽

pp. 5497-5509 ◽

Cited By ~ 190

Author(s):

Kerry Emanuel

Keyword(s):

Tropical Cyclone ◽

Surface Temperature ◽

Sea Surface Temperature ◽

Time Scales ◽

North Pacific ◽

Wind Shear ◽

Western North Pacific ◽

Vertical Wind Shear ◽

Sea Surface ◽

Strongly Correlated

Abstract Revised estimates of kinetic energy production by tropical cyclones in the Atlantic and western North Pacific are presented. These show considerable variability on interannual-to-multidecadal time scales. In the Atlantic, variability on time scales of a few years and more is strongly correlated with tropical Atlantic sea surface temperature, while in the western North Pacific, this correlation, while still present, is considerably weaker. Using a combination of basic theory and empirical statistical analysis, it is shown that much of the variability in both ocean basins can be explained by variations in potential intensity, low-level vorticity, and vertical wind shear. Potential intensity variations are in turn factored into components related to variations in net surface radiation, thermodynamic efficiency, and average surface wind speed. In the Atlantic, potential intensity, low-level vorticity, and vertical wind shear strongly covary and are also highly correlated with sea surface temperature, at least during the period in which reanalysis products are considered reliable. In the Pacific, the three factors are not strongly correlated. The relative contributions of the three factors are quantified, and implications for future trends and variability of tropical cyclone activity are discussed.

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Strong Modulation of the Pacific Meridional Mode on the Occurrence of Intense Tropical Cyclones over the Western North Pacific

Journal of Climate ◽

10.1175/jcli-d-17-0833.1 ◽

2018 ◽

Vol 31 (19) ◽

pp. 7739-7749 ◽

Cited By ~ 14

Author(s):

Si Gao ◽

Langfeng Zhu ◽

Wei Zhang ◽

Zhifan Chen

Keyword(s):

Tropical Cyclones ◽

North Pacific ◽

Western North Pacific ◽

Vertical Wind Shear ◽

Low Level ◽

The Pacific ◽

Main Development ◽

Development Region ◽

Meridional Mode ◽

Pacific Meridional Mode

This study finds a significant positive correlation between the Pacific meridional mode (PMM) index and the frequency of intense tropical cyclones (TCs) over the western North Pacific (WNP) during the peak TC season (June–November). The PMM influences the occurrence of intense TCs mainly by modulating large-scale dynamical conditions over the main development region. During the positive PMM phase, anomalous off-equatorial heating in the eastern Pacific induces anomalous low-level westerlies (and cyclonic flow) and upper-level easterlies (and anticyclonic flow) over a large portion of the main development region through a Matsuno–Gill-type Rossby wave response. The resulting weaker vertical wind shear and larger low-level relative vorticity favor the genesis of intense TCs over the southeastern part of the WNP and their subsequent intensification over the main development region. The PMM index would therefore be a valuable predictor for the frequency of intense TCs over the WNP.

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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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Tropical Cloud Cluster Environments and Their Importance for Tropical Cyclone Formation

Journal of Climate ◽

10.1175/jcli-d-18-0679.1 ◽

2019 ◽

Vol 32 (13) ◽

pp. 4069-4088 ◽

Cited By ~ 3

Author(s):

Hsu-Feng Teng ◽

Cheng-Shang Lee ◽

Huang-Hsiung Hsu ◽

James M. Done ◽

Greg J. Holland

Keyword(s):

Tropical Cyclone ◽

Environmental Conditions ◽

North Pacific ◽

Western North Pacific ◽

Subtropical High ◽

Low Latitude ◽

Brightness Temperatures ◽

Cloud Cluster ◽

Potential Index ◽

Circulation Patterns

Abstract This study uses a nonhierarchical cluster analysis to identify the major environmental circulation patterns associated with tropical cloud cluster (TCC) formation in the western North Pacific. All TCCs that formed in July–October 1981–2009 are examined based on their 850-hPa wind field around TCC centers. Eight types of environmental circulation patterns are identified. Of these, four are related to monsoon systems (trough, confluence, north of trough, and south of trough), three are related to easterly systems (low-latitude zone, west of subtropical high, and southwest of subtropical high), and one is associated with low-latitude cross-equatorial flow. The genesis potential index (GPI) is analyzed to compare how favorable the environmental conditions are for tropical cyclone (TC) formation when TCCs form. Excluding three cluster types with the GPI lower than the climatology of all samples, TCCs formed in monsoon environments have larger sizes, lower brightness temperatures, longer lifetimes, and higher GPIs than those of TCCs formed in easterly environments. However, for TCCs formed in easterly environments, the average GPI for those TCCs that later develop into TCs (developing TCCs) is higher than that for other TCCs (nondeveloping TCCs). This difference is nonsignificant for TCCs formed in monsoon environments. Conversely, the average magnitudes of GPI are similar for developing TCCs, regardless of whether TCCs form in easterly or monsoon environments. In summary, the probability of a TCC to develop into a TC is more sensitive to the environmental conditions for TCCs formed in easterly environments than those formed in monsoon environments.

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Rapid Weakening of Tropical Cyclones in Monsoon Gyres over the Tropical Western North Pacific

Journal of Climate ◽

10.1175/jcli-d-16-0784.1 ◽

2018 ◽

Vol 31 (3) ◽

pp. 1015-1028 ◽

Cited By ~ 9

Author(s):

Jia Liang ◽

Liguang Wu ◽

Guojun Gu

Keyword(s):

Tropical Cyclone ◽

Tropical Cyclones ◽

North Pacific ◽

Western North Pacific ◽

Large Scale ◽

Vertical Wind Shear ◽

Tropical Cyclone Intensity ◽

Cyclone Intensity ◽

Operational Forecasts ◽

Tropical Western North Pacific

Abstract As one major source of forecasting errors in tropical cyclone intensity, rapid weakening of tropical cyclones [an intensity reduction of 20 kt (1 kt = 0.51 m s−1) or more over a 24-h period] over the tropical open ocean can result from the interaction between tropical cyclones and monsoon gyres. This study aims to examine rapid weakening events occurring in monsoon gyres in the tropical western North Pacific (WNP) basin during May–October 2000–14. Although less than one-third of rapid weakening events happened in the tropical WNP basin south of 25°N, more than 40% of them were associated with monsoon gyres. About 85% of rapid weakening events in monsoon gyres occurred in September and October. The rapid weakening events associated with monsoon gyres are usually observed near the center of monsoon gyres when tropical cyclone tracks make a sudden northward turn. The gyres can enlarge the outer size of tropical cyclones and tend to induce prolonged rapid weakening events with an average duration of 33.2 h. Large-scale environmental factors, including sea surface temperature changes, vertical wind shear, and midlevel environmental humidity, are not primary contributors to them, suggesting the possible effect of monsoon gyres on these rapid weakening events by modulating the tropical cyclone structure. This conclusion is conducive to improving operational forecasts of tropical cyclone intensity.

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A Physical Basis for the Probabilistic Prediction of the Accumulated Tropical Cyclone Kinetic Energy in the Western North Pacific

Journal of Climate ◽

10.1175/jcli-d-12-00679.1 ◽

2013 ◽

Vol 26 (20) ◽

pp. 7981-7991 ◽

Cited By ~ 14

Author(s):

Hye-Mi Kim ◽

Myong-In Lee ◽

Peter J. Webster ◽

Dongmin Kim ◽

Jin Ho Yoo

Keyword(s):

Tropical Cyclone ◽

Kinetic Energy ◽

El Niño ◽

North Pacific ◽

Wind Shear ◽

Western North Pacific ◽

El Nino ◽

Vertical Wind Shear ◽

Tropical Storm ◽

Probabilistic Prediction

Abstract The relationship between El Niño–Southern Oscillation (ENSO) and tropical storm (TS) activity over the western North Pacific Ocean is examined for the period from 1981 to 2010. In El Niño years, TS genesis locations are generally shifted to the southeast relative to normal years and the passages of TSs tend to recurve to the northeast. TSs of greater duration and more intensity during an El Niño summer induce an increase of the accumulated tropical cyclone kinetic energy (ACE). Based on the strong relationship between the TS properties and ENSO, a probabilistic prediction for seasonal ACE is investigated using a hybrid dynamical–statistical model. A statistical relationship is developed between the observed ACE and large-scale variables taken from the ECMWF seasonal forecast system 4 hindcasts. The ACE correlates positively with the SST anomaly over the central to eastern Pacific and negatively with the vertical wind shear near the date line. The vertical wind shear anomalies over the central and western Pacific are selected as predictors based on sensitivity tests of ACE predictive skill. The hybrid model performs quite well in forecasting seasonal ACE with a correlation coefficient between the observed and predicted ACE at 0.80 over the 30-yr period. A relative operating characteristic analysis also indicates that the ensembles have significant probabilistic skill for both the above-normal and below-normal categories. By comparing the ACE prediction over the period from 2003 to 2011, the hybrid model appears more skillful than the forecast from the Tropical Storm Risk consortium.

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