scholarly journals Impacts of Tropical North Atlantic SST on Western North Pacific Landfalling Tropical Cyclones

2018 ◽  
Vol 31 (2) ◽  
pp. 853-862 ◽  
Author(s):  
Si Gao ◽  
Zhifan Chen ◽  
Wei Zhang
Keyword(s):  
Tropical Cyclones ◽  
North Atlantic ◽  
North Pacific ◽  
Korean Peninsula ◽  
Western North Pacific ◽  
Vertical Wind Shear ◽  
Relative Vorticity ◽  
Steering Flow ◽  
Tropical North Atlantic ◽  
Landfalling Tropical Cyclones

This study examines the impacts of tropical North Atlantic (TNA) sea surface temperature anomaly (SSTA) on western North Pacific (WNP) landfalling tropical cyclones (TCs). The authors find that TNA SSTA has significant negative correlations with the frequency of TCs making landfall in China, Vietnam, the Korean Peninsula and Japan, and the entirety of East Asia. TNA SSTA influences the frequency of TC landfalls in these regions by regulating TC genesis location and frequency associated with modulated environmental conditions. During cold TNA SST years, larger low-level relative vorticity and weaker vertical wind shear lead to more TC formations over the South China Sea (SCS) and western Philippine Sea (WPS), and larger low-level relative vorticity, higher midlevel relative humidity, and weaker vertical wind shear result in more TC formations over the eastern part of WNP (EWNP). More TCs forming over different regions are important for more TC landfalls in Vietnam (mainly forming over the SCS and WPS), south China (predominantly forming over the SCS), Taiwan (mostly forming over the WPS), and the Korean Peninsula and Japan (forming over the WPS and EWNP). Tracks of these landfalling TCs basically follow the mean steering flow in spite of different directions of steering flow anomalies in the vicinity. The modulation of large-scale environments by TNA SSTA may be through two possible pathways proposed in previous studies: the Indian Ocean relaying effect and the subtropical eastern Pacific relaying effect. The results of this study suggest that TNA SSTA is a potential predictor for the frequency of TCs making landfall in China, Vietnam, the Korean Peninsula and Japan, and the entirety of East Asia.

Modulation of North Pacific and North Atlantic tropical cyclones by tropical trans-basin variability and ENSO during May-October

2020 ◽  
pp. 1
Author(s):  
Shaohua Chen ◽  
Haikun Zhao ◽  
Graciela B. Raga ◽  
Philip J. Klotzbach
Keyword(s):  
Tropical Cyclones ◽  
North Atlantic ◽  
North Pacific ◽  
Large Scale ◽  
Vertical Wind Shear ◽  
Relative Vorticity ◽  
Low Level ◽  
Scale Factors ◽  
Frequency Changes ◽  
Dipole Modulation

AbstractThis study highlights the distinct modulation of May-October tropical cyclones (TCs) in the western North Pacific (WNP), eastern North Pacific (ENP) and North Atlantic (NATL) basins by tropical trans-basin variability (TBV) and ENSO. The pure TBV significantly modulates total TC counts in all three basins, with more TCs in the WNP and ENP and fewer TCs in the NATL during warm TBV years and fewer TCs in the WNP and ENP and more TCs in the NATL during cold TBV years. By contrast, the pure ENSO signal shows no impact on total TC count over any of the three basins. These results are consistent with changes in large scale factors associated with TBV and ENSO. Low-level relative vorticity (VOR) is an important driver of WNP TC genesis frequency, with broad agreement between the observed spatial distribution of TC genesis and TBV/ENSO-associated VOR anomalies. TBV significantly affects ENP TC frequency due to changes in basin wide vertical wind shear and sea surface temperatures, while the modulation in TC frequency by ENSO is primarily caused by a north-south dipole modulation of large-scale atmospheric and oceanic factors. The pure TBV-related low-level VOR changes appear to be the most important factor modulating NATL TC frequency. Changes in large-scale factors compare well with the budget of synoptic-scale eddy kinetic energy. Possible physical processes associated with pure TBV and pure ENSO that modulate TC frequency are further discussed. This study contributes to the understanding of TC inter-annual variability and could thus be helpful for seasonal TC forecasting.

scholarly journals What Caused The Increase of Tropical Cyclones In The Western North Pacific During The Period of 2011-2020?

2021 ◽  
Author(s):  
Haili Wang ◽  
Chunzai Wang
Keyword(s):  
Tropical Cyclones ◽  
North Pacific ◽  
High Frequency ◽  
Western North Pacific ◽  
Large Scale ◽  
Low Frequency ◽  
Vertical Wind Shear ◽  
Significant Negative Correlation ◽  
Relative Vorticity ◽  
The Pacific

Abstract Based on satellite era data after 1979, we find that the tropical cyclone (TC) variations in the Western North Pacific (WNP) can be divided into three-periods: a high-frequency period from 1979-1997 (P1), a low-frequency period from 1998-2010 (P2), and a high-frequency period from 2011-2020 (P3). Previous studies have focused on WNP TC activity during P1 and P2. Here we use observational data to study the WNP TC variation and its possible mechanisms during P3. Compared with P2, more TCs during P3 are due to the large-scale atmospheric environmental conditions of positive relative vorticity, negative vertical velocity and weak vertical wind shear. Warmer SST is found during P3, which is favorable for TC genesis. The correlation between the WNP TC frequency and SST shows a significant positive correlation around the equator and a significant negative correlation around 36°N, which is similar to the warm phase of the Pacific Decadal Oscillation (PDO). The correlation coefficient between the PDO and TC frequency is 0.71, significant at 99% confidence level. The results indicate that the increase of the WNP TC frequency during 2011-2020 is associated with the phase transition of the PDO and warmer SST. Therefore, more attention should be given to the warmer SST and PDO phase when predicting WNP TC activity.

Characteristics of Binary Tropical Cyclones Observed in the Western North Pacific for 62 Years (1951–2012)

2015 ◽  
Vol 143 (5) ◽  
pp. 1749-1761 ◽  
Author(s):  
Wook Jang ◽  
Hye-Yeong Chun
Keyword(s):  
Tropical Cyclones ◽  
North Pacific ◽  
Western North Pacific ◽  
Vertical Wind Shear ◽  
Temporal Variations ◽  
Reanalysis Data ◽  
Track Density ◽  
The North ◽  
Steering Flow ◽  
Analysis Technique

Abstract The statistical and dynamical characteristics of binary tropical cyclones (TCs) observed in the western North Pacific (WNP) for 62 years (1951–2012) are investigated by using best track and reanalysis data. A total of 98 binary TCs occurred with an annual average of 1.58. The occurrence frequency of binary TCs shows significant year-to-year variations and there are two peaks in the mid-1960s and early 1990s. Three-fourths (76.3%) of the binary TCs occurred between July and September, which is consistent with the high activity season of TCs in general. A relatively higher track density for binary TCs is present to the east of the maximum track density for total TCs. This result is likely due to the differences in the locations of genesis and environmental steering flow between binary and total TCs. The poleward steering flow, weaker vertical wind shear, and warmer sea surface temperature are pronounced for binary TCs, and these result in a longer lifetime of TCs, which can increase the chances that they would be detected as binary TCs. By applying the clustering analysis technique, six representative trajectories of the binary TCs are obtained. The transitional speed and recurving location are significantly different with respect to the clustered types. The trajectories of each type are strongly related to the temporal variations in the environmental steering flow and the location of the North Pacific high.

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

2018 ◽  
Vol 31 (19) ◽  
pp. 7739-7749 ◽  
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.

Seasonal forecasting of intense tropical cyclones over the North Atlantic and the western North Pacific basins

2016 ◽  
Vol 47 (9-10) ◽  
pp. 3063-3075 ◽  
Author(s):  
Woosuk Choi ◽  
Chang-Hoi Ho ◽  
Chun-Sil Jin ◽  
Jinwon Kim ◽  
Song Feng ◽  
...  
Keyword(s):  
Tropical Cyclones ◽  
North Atlantic ◽  
North Pacific ◽  
Western North Pacific ◽  
Seasonal Forecasting ◽  
The North ◽  
The North Atlantic

scholarly journals Seasonal Prediction of Tropical Cyclones over the North Atlantic and Western North Pacific

2021 ◽  
pp. 1-42
Author(s):  
Kevin I. Hodges ◽  
Antje Weisheimer
Keyword(s):  
Tropical Cyclones ◽  
North Atlantic ◽  
North Pacific ◽  
Western North Pacific ◽  
Seasonal Prediction ◽  
Seasonal Forecasting ◽  
Forecasting Models ◽  
The North ◽  
Forecast Models ◽  
Coarse Model

Abstract In this study, Tropical Cyclones (TC) over the Western North Pacific (WNP) and North Atlantic (NA) basins are analysed in seasonal forecasting models from five European modelling centres. Most models are able to capture the observed seasonal cycle of TC frequencies over both basins; however, large differences for numbers and spatial track densities are found. In agreement with previous studies, TC numbers are often underestimated, which is likely related to coarse model resolutions. Besides shortcomings in TC characteristics, significant positive skill (deterministic and probabilistic) in predicting TC numbers and accumulated cyclone energy is found over both basins. Whereas the predictions of TC numbers over the WNP basin are mostly unreliable, most seasonal forecast provide reliable predictions for the NA basin. Besides positive skill over the entire NA basin, all seasonal forecasting models are skillful in predicting the interannual TC variability over a region covering the Caribbean and North American coastline, suggesting that the models carry useful information, e.g. for adaptation and mitigation purposes ahead of the upcoming TC season. However, skill in all forecast models over a smaller region centred along the Asian coastline is smaller compared to their skill in the entire WNP basin.

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

2018 ◽  
Vol 31 (3) ◽  
pp. 1015-1028 ◽  
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.

Riverine Flooding and Landfalling Tropical Cyclones over China

2020 ◽  
Author(s):  
Long Yang ◽  
Maofeng Liu ◽  
Lachun Wang ◽  
Xiaomin Ji ◽  
Xiang Li ◽  
...  
Keyword(s):  
Tropical Cyclones ◽  
North Pacific ◽  
Flood Risk ◽  
Western North Pacific ◽  
Flood Control ◽  
East Asian ◽  
Wrf Model ◽  
Asian Countries ◽  
Spatial And Temporal Patterns ◽  
Landfalling Tropical Cyclones

<p>Riverine flooding associated with landfalling tropical cyclones (TCs) in the Western North Pacific basin is responsible for some of the most severe socioeconomic losses in East Asian countries. However, little is known about the spatial and temporal patterns of TC flooding and its synoptic controls, which constrain predictive understandings of flood risk in this highly populated region. In this study, we investigate hydrology, hydrometeorology, and hydroclimatology of riverine flooding over China induced by landfalling tropical cyclones, based on empirical analysis of dense networks of stream gauging and rainfall stations as well as downscaling simulations using the Weather Research and Forecasting (WRF) model driven by 20th Century Reanalysis fields. The most extreme floods in central and northeastern China are associated with TCs despite infrequent TC visits in these regions. Inter-annual variations in TC flooding demonstrate a mixture of climate controls tied to surface temperature anomalies in central tropical Pacific, western North Pacific and north Atlantic. We implement numerical modelling analysis of typhoon Nina (1975), typhoon Andy (1982) and typhoon Herb (1996) to further shed light on key hydro-meteorological features of landfalling TCs that are responsible for severe flooding over China. We highlight the important role of interactions of storm circulations with mid-latitude synoptic systems (e.g., upper-level trough) and complex terrains in producing extreme rain rates and flooding. Analytical framework developed in this study aims to explore utilization of hydro-meteorological approach in flood-control engineering designs by providing details on the key elements of flood-producing storms. We also highlight potential challenges of developing predictive tools of TC flood risk in east Asian countries.</p>

Are Tropical Cyclones Less Effectively Formed by Easterly Waves in the Western North Pacific than in the North Atlantic?

2008 ◽  
Vol 136 (11) ◽  
pp. 4527-4540 ◽  
Author(s):  
Tsing-Chang Chen ◽  
Shih-Yu Wang ◽  
Ming-Cheng Yen ◽  
Adam J. Clark
Keyword(s):  
Tropical Cyclones ◽  
North Atlantic ◽  
North Pacific ◽  
Western North Pacific ◽  
Monsoon Trough ◽  
Easterly Waves ◽  
The North ◽  
Easterly Wave ◽  
Monsoon Gyre ◽  
The North Atlantic

Abstract It has been observed that the percentage of tropical cyclones originating from easterly waves is much higher in the North Atlantic (∼60%) than in the western North Pacific (10%–20%). This disparity between the two ocean basins exists because the majority (71%) of tropical cyclogeneses in the western North Pacific occur in the favorable synoptic environments evolved from monsoon gyres. Because the North Atlantic does not have a monsoon trough similar to the western North Pacific that stimulates monsoon gyre formation, a much larger portion of tropical cyclogeneses than in the western North Pacific are caused directly by easterly waves. This study also analyzed the percentage of easterly waves that form tropical cyclones in the western North Pacific. By carefully separating easterly waves from the lower-tropospheric disturbances generated by upper-level vortices that originate from the tropical upper-tropospheric trough (TUTT), it is observed that 25% of easterly waves form tropical cyclones in this region. Because TUTT-induced lower-tropospheric disturbances often become embedded in the trade easterlies and resemble easterly waves, they have likely been mistakenly identified as easterly waves. Inclusion of these “false” easterly waves in the “true” easterly wave population would result in an underestimation of the percentage of easterly waves that form tropical cyclones, because the TUTT-induced disturbances rarely stimulate tropical cyclogenesis. However, an analysis of monsoon gyre formation mechanisms over the western North Pacific reveals that 82% of monsoon gyres develop through a monsoon trough–easterly wave interaction. Thus, it can be inferred that 58% (i.e., 82% × 71%) of tropical cyclones in this region are an indirect result of easterly waves. Including the percentage of tropical cyclones that form directly from easterly waves (∼25%), it is found that tropical cyclones formed directly and indirectly from easterly waves account for over 80% of tropical cyclogeneses in the western North Pacific. This is more than the percentage that has been documented by previous studies in the North Atlantic.

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