scholarly journals Interannual Variation of the Tropical Cyclone Activity over the Western North Pacific

2006 ◽  
Vol 19 (21) ◽  
pp. 5709-5720 ◽  
Author(s):  
Tsing-Chang Chen ◽  
Shih-Yu Wang ◽  
Ming-Cheng Yen
Keyword(s):  
Tropical Cyclone ◽  
Tropical Cyclones ◽  
North Pacific ◽  
Western North Pacific ◽  
Wave Train ◽  
Short Wave ◽  
Monsoon Trough ◽  
Anomalous Circulation ◽  
Group 3 ◽  
Group 1

Abstract An effort was made to search for relationships between interannual variations of population, lifetime, genesis locations, and intensity of named typhoons and numbered tropical depressions in the western North Pacific during the 1979–2002 period. To support this research task, climatological relationships of tropical cyclone characteristics were also investigated for these cyclones. Major findings of this study are summarized as follows:Climatology: Measured by the intensity scale of the Japan Meteorological Agency, three groups of tropical cyclones were identified in terms of population versus intensity: Group 1 [tropical depression (TD) + typhoon (TY)], Group 2 (strong + very strong TY), and Group 3 (catastrophic TY). This group division coincides with that formed in terms of lifetime of tropical cyclones versus intensity. Weak cyclones (Group 1) have a larger population than strong cyclones (Group 3), while the former group has shorter lifetime than the latter group. For genesis locations, the monsoon trough is established as a favorable region of tropical cyclone genesis because it provides an environment of large vorticity. Therefore, the northward latitudinal displacement of the maximum genesis frequency in the three groups of tropical cyclones follows that of the monsoon trough.Interannual variation: Any mechanism that can modulate the location and intensity of the monsoon trough affects the genesis location and frequency of tropical cyclones. In response to tropical Pacific sea surface temperature anomalies, a short wave train consisting of east–west oriented cells emanates from the Tropics and progresses along the western North Pacific rim. Population of the Group-1 tropical cyclones varies interannually in phase with the oscillation of the anomalous circulation cell northeast of Taiwan and south of Japan in this short wave train, while that of Group 3 fluctuates coherently with the tropical cell of this short wave train. Because these two anomalous circulation cells exhibit opposite polarity, the out-of-phase interannual oscillation between these two cells results in the opposite interannual variation of genesis frequency between tropical cyclones of Groups 1 and 3.

scholarly journals Extended Simulation of Tropical Cyclone Formation in the Western North Pacific Monsoon Trough

2015 ◽  
Vol 72 (12) ◽  
pp. 4469-4485 ◽  
Author(s):  
Liguang Wu ◽  
Jingjing Duan
Keyword(s):  
Tropical Cyclone ◽  
North Pacific ◽  
Western North Pacific ◽  
Large Scale ◽  
Global Analysis ◽  
Wave Train ◽  
Low Frequency ◽  
Monsoon Trough ◽  
Synoptic Scale ◽  
Environmental Prediction

Abstract Previous studies suggest that the low-frequency background makes an important contribution to the predictability of tropical cyclone (TC) activity on the intraseasonal time scale by providing large-scale conditions favorable for TC formation. Extended numerical experiments were conducted to demonstrate additional low-frequency influence on TC activity, which results from the development of a synoptic-scale wave train. The cyclonic circulation of the wave train provides low-level synoptic-scale disturbances for TC formation. The observed TC formation events over the western North Pacific during 14 August–10 September 2004 were first successfully simulated with the initial and lateral conditions derived from the National Centers for Environmental Prediction (NCEP) Final (FNL) Operational Global Analysis. Then the 27-day extended experiment was repeated only with the initial and lateral boundary conditions derived from the FNL low-frequency (longer than 20 days) background. It is found that the development of the synoptic-scale wave train can be well simulated with TCs forming in the cyclonic circulations of the wave train although the wavelength of the simulated wave train is substantially reduced in the absence of higher-frequency influences with periods shorter than 20 days. Sensitivity experiments indicate that the development of wave trains is sensitive to the initial monsoon trough structure. This study suggests that the synoptic-scale wave train can develop in situ and does not need upstream precursors.

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.

Five-day track forecast skills of WRF model for the western North Pacific tropical cyclones

2021 ◽  
Author(s):  
Jihong Moon ◽  
Jinyoung Park ◽  
Dong-Hyun Cha ◽  
Yumin Moon
Keyword(s):  
Tropical Cyclones ◽  
North Pacific ◽  
Western North Pacific ◽  
Forecast Error ◽  
Wrf Model ◽  
Analysis Data ◽  
Track Forecast ◽  
Steering Vector ◽  
Group 2 ◽  
Group 1

AbstractIn this study, the characteristics of simulated tropical cyclones (TCs) over the western North Pacific by a regional model (the WRF model) are verified. We utilize 12 km horizontal grid spacing, and simulations are integrated for 5 days from model initialization. One hundred and twenty-five forecasts are divided into five clusters through the k-means clustering method. The TCs in the cluster 1 and 2 (group 1), which includes many TCs moves northward in subtropical region, generally have larger track errors than for TCs in cluster 3 and 4 (group 2). The optimal steering vector is used to examine the difference in the track forecast skill between these two groups. The bias in the steering vector between the model and analysis data is found to be more substantial for group 1 TCs than group 2 TCs. The larger steering vector difference for group 1 TCs indicates that environmental fields tend to be poorly simulated in group 1 TC cases. Furthermore, the residual terms, including the storm-scale process, asymmetric convection distribution, or beta-related effect, are also larger for group 1 TCs than group 2 TCs. Therefore, it is probable that the large track forecast error for group 1 TCs is a result of unreasonable simulations of environmental wind fields and residual processes in the midlatitudes.

Tropical Cyclogenesis Associated with Kelvin Waves and the Madden–Julian Oscillation

2011 ◽  
Vol 139 (9) ◽  
pp. 2723-2734 ◽  
Author(s):  
Carl J. Schreck ◽  
John Molinari
Keyword(s):  
Tropical Cyclone ◽  
Tropical Cyclones ◽  
North Pacific ◽  
Western North Pacific ◽  
Diabatic Heating ◽  
Kelvin Waves ◽  
Tropical Cyclogenesis ◽  
Madden Julian Oscillation ◽  
Convective Envelope

The Madden–Julian oscillation (MJO) influences tropical cyclone formation around the globe. Convectively coupled Kelvin waves are often embedded within the MJO, but their role in tropical cyclogenesis remains uncertain. This case study identifies the influences of the MJO and a series of Kelvin waves on the formation of two tropical cyclones. Typhoons Rammasun and Chataan developed in the western North Pacific on 28 June 2002. Two weeks earlier, conditions had been unfavorable for tropical cyclogenesis because of uniform trade easterlies and a lack of organized convection. The easterlies gave way to equatorial westerlies as the convective envelope of the Madden–Julian oscillation moved into the region. A series of three Kelvin waves modulated the development of the westerlies. Cyclonic potential vorticity (PV) developed in a strip between the growing equatorial westerlies and the persistent trade easterlies farther poleward. Rammasun and Chataan emerged from the apparent breakdown of this strip. The cyclonic PV developed in association with diabatic heating from both the MJO and the Kelvin waves. The tropical cyclones also developed during the largest superposition of equatorial westerlies from the MJO and the Kelvin waves. This chain of events suggests that the MJO and the Kelvin waves each played a role in the development of Rammasun and Chataan.

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

2018 ◽  
Vol 31 (5) ◽  
pp. 1771-1787 ◽  
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.

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 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.

scholarly journals Seasonal Modulation of Tropical Intraseasonal Oscillations on Tropical Cyclone Geneses in the Western North Pacific

2011 ◽  
Vol 24 (24) ◽  
pp. 6339-6352 ◽  
Author(s):  
Ping Huang ◽  
Chia Chou ◽  
Ronghui Huang
Keyword(s):  
Tropical Cyclone ◽  
North Pacific ◽  
Western North Pacific ◽  
Asian Summer Monsoon ◽  
North Pacific Ocean ◽  
Intraseasonal Oscillation ◽  
Monsoon Trough ◽  
Intraseasonal Oscillations ◽  
Asian Summer ◽  
Primary Contribution

Abstract The seasonal modulation of tropical intraseasonal oscillation (TISO) on tropical cyclone (TC) geneses over the western North Pacific Ocean (WNP) is investigated in three periods of the WNP TC season: May–June (MJ), July–September (JAS), and October–December (OND). The modulation of the TISO–TC geneses over the WNP is strong in MJ, while it appears weaker in JAS and OND. In MJ, TISO propagates northward via two routes, the west route through the South China Sea and the east route through the WNP monsoon trough region, which are two clustering locations of TC geneses. TISO can synchronously influence most TC geneses over these two regions. In JAS, however, the modulation is out of phase between the monsoon trough region and the East Asian summer monsoon region, as well as the WNP subtropical high region, as a result of further northward propagation of TISO and scattered TC geneses. The TISO–TC genesis modulation in each individual region is comparable to that in MJ, although the modulation over the entire WNP in JAS appears weaker. In OND, TISO has a stronger influence on TC geneses west than east of 150°E because TISO decays and its convection center located at the equator is out of the TC genesis region when propagating eastward into east of 150°E. Midlevel relative humidity is the primary contribution to the modulations of TISO on the genesis environment, while vorticity could contribute to the modulation over the subtropics in JAS.

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