scholarly journals Variability of Tropical Cyclone Landfalls in China

2021 ◽  
pp. 1-26
Author(s):  
Kaiyue Shan ◽  
Xiping Yu
Keyword(s):  
Tropical Cyclone ◽  
20Th Century ◽  
Southern China ◽  
Vertical Wind Shear ◽  
Relative Vorticity ◽  
Ocean Basin ◽  
Abrupt Increase ◽  
Southeastern China ◽  
Southeastern Part ◽  
Abrupt Decrease

AbstractThe reported decreasing trend of the annual tropical cyclone (TC) landfalls in Southern China and increasing trend in Southeastern China in recent decades are confirmed to be an abrupt shift occurred at the end of the 20th century, based on a statistical analysis. The opposite trends in the two adjacent regions are often considered as a result of tropical cyclone landfalls in southern China being deflected northward. However, it is demonstrated in this study that they are phenomenally independent. In fact, the abrupt decrease of TC landfalls in Southern China occurs due to an abrupt decrease of the westward events in the post-peak season (October-December), as the consequence of a significant decrease of the TC genesis frequency in the southeastern part of the western North Pacific (WNP) ocean basin. On the other hand, the abrupt increase of TC landfalls in Southeastern China occurs due to an abrupt increase of the northwest events in the peak season (July-September), as the consequence of a statistically westward shift of the TC genesis. The relevant variations of the TC genesis are shown to be mainly caused by the decreased relative vorticity and the increased vertical wind shear, which, however, are intrinsically related to the accelerated zonal atmospheric circulation driven by a La Niña-like sea surface warming pattern over WNP developed after the end of 20th century.

scholarly journals Slowdown in the Decay of Western North Pacific Tropical Cyclones Making Landfall on the Asian Continent

2021 ◽  
Vol 9 ◽  
Author(s):  
Jinjie Song ◽  
Philip J. Klotzbach ◽  
Haikun Zhao ◽  
Yihong Duan
Keyword(s):  
North Pacific ◽  
Western North Pacific ◽  
Southern China ◽  
Vertical Wind Shear ◽  
Relative Vorticity ◽  
Asian Continent ◽  
Southeastern China ◽  
Increasing Trend ◽  
Thermodynamic Variables ◽  
Dynamic Variables

This study finds an increasing trend in the decay timescale (τ) of western North Pacific (WNP) tropical cyclone (TCs) making landfall on the Asian continent from 1966–2018. Statistical analysis of individual landfalling TCs shows that τ is significantly positively linked to soil wetness, 850-hPa relative vorticity and 200-hPa divergence, whereas it is weakly correlated with 700–500-hPa relative humidity and 850–200-hPa vertical wind shear. For TCs hitting southeastern China, the observed increasing τ is likely caused by enhanced 850-hPa vorticity and 200-hPa divergence. For TCs hitting southern China, increasing τ is likely driven by increased 850-hPa vorticity. By comparison, there are no significant trends in environmental variables over the eastern Indo-China Peninsula, and τ has not significantly changed in this region. Our results imply that the increasing τ of WNP landfalling TCs on the Asian continent are more likely caused by changes in dynamic variables than changes in thermodynamic variables.

scholarly journals Observational Analysis of Tropical Cyclone Formation Associated with Monsoon Gyres

2013 ◽  
Vol 70 (4) ◽  
pp. 1023-1034 ◽  
Author(s):  
Liguang Wu ◽  
Huijun Zong ◽  
Jia Liang
Keyword(s):  
Tropical Cyclone ◽  
Tropical Cyclones ◽  
Western North Pacific ◽  
Large Scale ◽  
Vertical Wind Shear ◽  
Relative Vorticity ◽  
Monsoon Trough ◽  
Cyclonic Circulation ◽  
Tropical Cyclone Formation ◽  
Monsoon Gyre

Abstract Large-scale monsoon gyres and the involved tropical cyclone formation over the western North Pacific have been documented in previous studies. The aim of this study is to understand how monsoon gyres affect tropical cyclone formation. An observational study is conducted on monsoon gyres during the period 2000–10, with a focus on their structures and the associated tropical cyclone formation. A total of 37 monsoon gyres are identified in May–October during 2000–10, among which 31 monsoon gyres are accompanied with the formation of 42 tropical cyclones, accounting for 19.8% of the total tropical cyclone formation. Monsoon gyres are generally located on the poleward side of the composited monsoon trough with a peak occurrence in August–October. Extending about 1000 km outward from the center at lower levels, the cyclonic circulation of the composited monsoon gyre shrinks with height and is replaced with negative relative vorticity above 200 hPa. The maximum winds of the composited monsoon gyre appear 500–800 km away from the gyre center with a magnitude of 6–10 m s−1 at 850 hPa. In agreement with previous studies, the composited monsoon gyre shows enhanced southwesterly flow and convection on the south-southeastern side. Most of the tropical cyclones associated with monsoon gyres are found to form near the centers of monsoon gyres and the northeastern end of the enhanced southwesterly flows, accompanying relatively weak vertical wind shear.

scholarly journals Tropical Cyclone Activity in the Fiji Region: Spatial Patterns and Relationship to Large-Scale Circulation

2009 ◽  
Vol 22 (14) ◽  
pp. 3877-3893 ◽  
Author(s):  
Savin S. Chand ◽  
Kevin J. E. Walsh
Keyword(s):  
Tropical Cyclone ◽  
El Niño ◽  
Large Scale ◽  
El Nino ◽  
Southern Oscillation ◽  
Vertical Wind Shear ◽  
Relative Vorticity ◽  
La Niña ◽  
Factors Affecting ◽  
La Nina

Abstract This study examines the variations in tropical cyclone (TC) genesis positions and their subsequent tracks for different phases of the El Niño–Southern Oscillation (ENSO) phenomenon in the Fiji, Samoa, and Tonga region (FST region) using Joint Typhoon Warning Center best-track data. Over the 36-yr period from 1970/71 to 2005/06, 122 cyclones are observed in the FST region. A large spread in the genesis positions is noted. During El Niño years, genesis is enhanced east of the date line, extending from north of Fiji to over Samoa, with the highest density centered around 10°S, 180°. During neutral years, maximum genesis occurs immediately north of Fiji with enhanced genesis south of Samoa. In La Niña years, there are fewer cyclones forming in the region than during El Niño and neutral years. During La Niña years, the genesis positions are displaced poleward of 12°S, with maximum density centered around 15°S, 170°E and south of Fiji. The cyclone tracks over the FST region are also investigated using cluster analysis. Tracks during the period 1970/71–2005/06 are conveniently described using three separate clusters, with distinct characteristics associated with different ENSO phases. Finally, the role of large-scale environmental factors affecting interannual variability of TC genesis positions and their subsequent tracks in the FST region are investigated. Favorable genesis positions are observed where large-scale environments have the following seasonal average thresholds: (i) 850-hPa cyclonic relative vorticity between −16 and −4 (×10−6 s−1), (ii) 200-hPa divergence between 2 and 8 (×10−6 s−1), and (iii) environmental vertical wind shear between 0 and 8 m s−1. The subsequent TC tracks are observed to be steered by mean 700–500-hPa winds.

scholarly journals Statistical Analysis of Tropical Cyclones in the Solomon Islands

2018 ◽  
Author(s):  
Edward Maru ◽  
Taiga Shibata ◽  
Kosuke Ito
Keyword(s):  
Tropical Cyclone ◽  
El Niño ◽  
Large Scale ◽  
El Nino ◽  
Southern Oscillation ◽  
Solomon Islands ◽  
Climatic Variability ◽  
Vertical Wind Shear ◽  
Longwave Radiation ◽  
Relative Vorticity

This paper examines the tropical cyclone (TC) activity in Solomon Islands (SI) using the best track data from Tropical Cyclone Warning Centre Brisbane and Regional Specialized Meteorological Centre Nadi. The long-term trend analysis showed that the frequency of TCs has been decreasing in this region while average TC intensity becomes strong. Then, the datasets were classified according to the phase of Madden-Julian Oscillation (MJO) and the index of El Nino Southern Oscillation (ENSO) provided by Bureau of Meteorology. The MJO has sufficiently influenced TC activity in the SI region with more genesis occurring in phases 6-8, in which the lower outgoing longwave radiation indicates enhanced convective activity. In contrast, TC genesis occurs less frequently in phases 1, 2, and 5. As for the influence of ENSO, more TCs are generated in El Nino period. The TC genesis locations during El Nino (La Nina) period were significantly displaced to the north (south) over SI region. TCs generated during El Nino condition tended to be strong. This paper also argues the modulation in terms of seasonal climatic variability of large-scale environmental conditions such as sea surface temperature, low level relative vorticity, vertical wind shear, and upper level divergence.

scholarly journals Interannual Shift of the Tropical Upper-Tropospheric Trough and Its Influence on Tropical Cyclone Formation over the Western North Pacific

2016 ◽  
Vol 29 (11) ◽  
pp. 4203-4211 ◽  
Author(s):  
Chao Wang ◽  
Liguang Wu
Keyword(s):  
Tropical Cyclone ◽  
North Pacific ◽  
Time Scale ◽  
Western North Pacific ◽  
Vertical Wind Shear ◽  
Relative Vorticity ◽  
Physical Factors ◽  
Interannual Time Scale ◽  
Core System ◽  
East West

Abstract The east–west migration of the tropical upper-tropospheric trough (TUTT) on the interannual time scale and its influence on tropical cyclone (TC) formation over the western North Pacific (WNP) is investigated in this study. Climatologically, the TUTT can be identified from 100 to 400 hPa with a relative vorticity maximum between 150 and 200 hPa. In addition to the strong westerly vertical wind shear in the south flank of the TUTT, this study shows that the cold-core system is associated with low relative humidity and subsidence to the east of the trough axis. As a result, the TC formation is enhanced (suppressed) in the eastern portion of the WNP when the TUTT shifts eastward (westward) on the interannual time scale. The interannual TUTT shift is closely associated with the SST anomalies in the central and eastern tropical Pacific or ENSO phases. The warm (cold) phase of ENSO corresponds to the eastward (westward) shift of the TUTT. The physical factors found to be responsible for the influence of ENSO on TC formation can be associated with the east–west shift of the TUTT. It is shown that the interannual variations of TC formation in the eastern part of the WNP basin are closely associated with the east–west shift of the TUTT due to the associated environmental conditions that are generally not favorable for TC formation.

scholarly journals Reexamining the Near-Core Radial Structure of the Tropical Cyclone Primary Circulation: Implications for Vortex Resiliency

2005 ◽  
Vol 62 (2) ◽  
pp. 408-425 ◽  
Author(s):  
Kevin J. Mallen ◽  
Michael T. Montgomery ◽  
Bin Wang
Keyword(s):  
Tropical Cyclone ◽  
Vertical Wind Shear ◽  
Relative Vorticity ◽  
Core Region ◽  
Vertical Shear ◽  
Theoretical Studies ◽  
True Nature ◽  
Radial Profiles ◽  
Tangential Wind ◽  
Radial Structure

Abstract Recent theoretical studies, based on vortex Rossby wave (VRW) dynamics, have established the importance of the radial structure of the primary circulation in the response of tropical cyclone (TC)–like vortices to ambient vertical wind shear. Linear VRW theory suggests, in particular, that the degree of broadness of the primary circulation in the near-core region beyond the radius of maximum wind strongly influences whether a tilted TC vortex will realign and resist vertical shear or tilt over and shear apart. Fully nonlinear numerical simulations have verified that the vortex resiliency is indeed sensitive to the initial radial structure of the idealized vortex. This raises the question of how well the “true” nature of a TC’s primary circulation is represented by idealized vortices that are commonly used in some theoretical studies. In this paper the swirling wind structure of TCs is reexamined by utilizing flight-level observations collected from Atlantic and eastern Pacific storms during 1977–2001. Hundreds of radial profiles of azimuthal-mean tangential wind and relative vorticity are constructed from over 5000 radial flight leg segments and compared with some standard idealized vortex profiles. This analysis reaffirms that real TC structure in the near-core region is characterized by relatively slow tangential wind decay in conjunction with a skirt of significant cyclonic relative vorticity possessing a negative radial gradient. This broadness of the primary circulation is conspicuously absent in some idealized vortices used in theoretical studies of TC evolution in vertical shear. The relationship of the current findings to the problem of TC resiliency is discussed.

scholarly journals The Influence of the Madden–Julian Oscillation on Tropical Cyclone Activity in the Fiji Region

2010 ◽  
Vol 23 (4) ◽  
pp. 868-886 ◽  
Author(s):  
Savin S. Chand ◽  
Kevin J. E. Walsh
Keyword(s):  
Tropical Cyclone ◽  
Large Scale ◽  
Vertical Wind Shear ◽  
Active Phase ◽  
Relative Vorticity ◽  
Convective Activity ◽  
Madden Julian Oscillation ◽  
Steering Flow ◽  
Upper Level ◽  
Cluster Analysis Technique

Abstract This study examines the modulation of tropical cyclone (TC) activity by the Madden–Julian oscillation (MJO) in the Fiji, Samoa, and Tonga regions (FST region), using Joint Typhoon Warning Center best-track cyclone data and the MJO index developed by Wheeler and Hendon. Results suggest strong MJO–TC relationships in the FST region. The TC genesis patterns are significantly altered over the FST region with approximately 5 times more cyclones forming in the active phase than in the inactive phase of the MJO. This modulation is further strengthened during El Niño periods. The large-scale environmental conditions (i.e., low-level relative vorticity, upper-level divergence, and vertical wind shear) associated with TC genesis show a distinct patterns of variability for the active and inactive MJO phases. The MJO also has a significant effect on hurricane category and combined gale and storm category cyclones in the FST region. The occurrences of both these cyclone categories are increased in the active phase of the MJO, which is associated with enhanced convective activity. The TCs in the other MJO phases where convective activity is relatively low, however, show a consistent pattern of increase in hurricane category cyclones and a concomitant decrease in gale and storm category cyclones. Finally, TC tracks in different MJO phases are also objectively described using a cluster analysis technique. Patterns seen in the clustered track regimes are well explained here in terms of 700–500-hPa mean steering flow.

Trends in Landfalling Tropical Cyclone–Induced Precipitation over China

2020 ◽  
Vol 33 (6) ◽  
pp. 2223-2235
Author(s):  
Lu Liu ◽  
Yuqing Wang
Keyword(s):  
Spatial Distribution ◽  
Water Vapor ◽  
Tropical Cyclone ◽  
Environmental Conditions ◽  
Average Duration ◽  
Southern China ◽  
Mainland China ◽  
Southeastern China ◽  
Precipitation Frequency ◽  
Increasing Trend

AbstractIn this study, trends in landfalling tropical cyclone (TC)-induced precipitation over China during 1980–2017 and the involved possible mechanisms are analyzed. Consistent with previous studies, it is found that the total annual TC precipitation shows a distinct spatial distribution with a significant increasing trend in southeastern China but a decreasing trend in southern China. This characteristic is found to be related to the increase in both the annual TC precipitation frequency and the precipitation intensity per TC over southeastern China but to the decrease in the annual TC precipitation frequency over southern China. A noticeable northward shift of total landfalling TC-induced annual precipitation has been identified. It is shown that the precipitation induced by strong TCs (STCs) significantly increased in southern China, whereas that induced by weak TCs (WTCs) increased in southeastern China, with the latter dominating the northward shift of total landfalling TC-induced precipitation over mainland China. The increasing trend of STC-induced precipitation in southern China is found to be closely related to sufficient water vapor supply and the increase in average duration and intensity of STCs after landfall. The increasing trend of WTC-induced precipitation in southeastern China is related to the northward shift of the average landfalling position of WTCs and changes in the environmental conditions that are more favorable for TC maintenance and precipitation.

Seasonal Prediction of Tropical Cyclone Activity Near Taiwan Using the Bayesian Multivariate Regression Method

2010 ◽  
Vol 25 (6) ◽  
pp. 1780-1795 ◽  
Author(s):  
Mong-Ming Lu ◽  
Pao-Shin Chu ◽  
Yun-Ching Lin
Keyword(s):  
Tropical Cyclone ◽  
Regression Model ◽  
Large Scale ◽  
Model Development ◽  
Vertical Wind Shear ◽  
Western Pacific Subtropical High ◽  
Seasonal Prediction ◽  
Relative Vorticity ◽  
Bayesian Regression ◽  
Easterly Waves

Abstract A Poisson generalized linear regression model cast within a Bayesian framework is applied to forecast the seasonal tropical cyclone (TC) counts in the vicinity of Taiwan. The TC season considered is June–November and the data period used for model development is 1979–2007. A stepwise regression procedure is applied for predictor selection. Three large-scale climate variables, namely, relative vorticity at 850 hPa (Vor850), vertical wind shear, and sea level pressure over the western and central North Pacific from the antecedent May, are selected as predictors. Leave-one-out cross validation is performed and forecast skill is thoroughly evaluated. The skill level of the Bayesian regression model is better than what can be achieved by climatology and persistence methods. Most importantly, the Bayesian probabilistic inference can provide an uncertainty expression in the parameter estimation. Among the three predictors, Vor850 is found to be the most important because it reflects the variation of the ridge position of the westward extension of the western Pacific subtropical high. The model shows negative bias during the years with successive TCs, which are generated by easterly waves before approaching Taiwan. Recommendations for real-time operational forecast and future development are discussed.

scholarly journals Impact of Different ENSO Regimes on Southwest Pacific Tropical Cyclones

2013 ◽  
Vol 26 (2) ◽  
pp. 600-608 ◽  
Author(s):  
Savin S. Chand ◽  
John L. McBride ◽  
Kevin J. Tory ◽  
Matthew C. Wheeler ◽  
Kevin J. E. Walsh
Keyword(s):  
Tropical Cyclone ◽  
El Niño ◽  
El Nino ◽  
Function Analysis ◽  
Vertical Wind Shear ◽  
Relative Vorticity ◽  
La Niña ◽  
Pacific Region ◽  
Southwest Pacific ◽  
La Nina

Abstract The influence of different types of ENSO on tropical cyclone (TC) interannual variability in the central southwest Pacific region (5°–25°S, 170°E–170°W) is investigated. Using empirical orthogonal function analysis and an agglomerative hierarchical clustering of early tropical cyclone season Pacific sea surface temperature, years are classified into four separate regimes (i.e., canonical El Niño, canonical La Niña, positive-neutral, and negative-neutral) for the period between 1970 and 2009. These regimes are found to have a large impact on TC genesis over the central southwest Pacific region. Both the canonical El Niño and the positive-neutral years have increased numbers of cyclones, with an average of 4.3 yr−1 for positive-neutral and 4 yr−1 for canonical El Niño. In contrast, during a La Niña and negative-neutral events, substantially fewer TCs (averages of ~2.2 and 2.4 yr−1, respectively) are observed in the central southwest Pacific. The enhancement of TC numbers in both canonical El Niño and positive-neutral years is associated with the extension of favorable low-level cyclonic relative vorticity, and low vertical wind shear eastward across the date line. Relative humidity and SST are also very conducive for genesis in this region during canonical El Niño and positive-neutral events. The patterns are quite different, however, with the favorable conditions concentrated in the date line region for the positive-neutral, as compared with conditions farther eastward for the canonical El Niño regime. A significant result of the study is the demonstration that ENSO-neutral events can be objectively clustered into two separate regimes, each with very different impacts on TC genesis.

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