scholarly journals Influence of Track Changes on the Poleward Shift of LMI Location of Western North Pacific Tropical Cyclones

2019 ◽  
Vol 32 (23) ◽  
pp. 8437-8445
Author(s):  
Ruifang Wang ◽  
Liguang Wu
Keyword(s):  
Tropical Cyclones ◽  
North Pacific ◽  
Western North Pacific ◽  
Large Scale ◽  
North Pacific Ocean ◽  
Mixed Layer Depth ◽  
Vertical Wind Shear ◽  
Environmental Parameters ◽  
Ocean Basin ◽  
The Mean

Abstract The annual mean latitude at which tropical cyclones (TCs) reach their lifetime maximum intensity (LMI) over the western North Pacific Ocean basin has shifted northward since the early 1980s, and it is suggested that the shift is due to the northward migration of the mean TC formation location. In this study, the TC intensity is simulated with an intensity model to assess the historical records of TC intensity. During the period 1980–2015, the simulated poleward trend in the mean latitude of LMI is 0.44° (10 yr)−1, which agrees well with the one [0.48° (10 yr)−1] derived from the Joint Typhoon Warning Center (JTWC) dataset. This suggests that the observed poleward trend in the mean latitude of LMI is physically consistent with changes in the large-scale ocean–atmosphere environment and TC track. This study also demonstrates that the temporal change in the environmental parameters (sea surface temperature, outflow temperature, vertical wind shear, and ocean mixed layer depth) has little influence on the observed shift of the mean LMI latitude. The poleward migration of the mean LMI latitude is mainly due to the TC track shift, which results primarily from the change in the large-scale steering flow.

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

2008 ◽  
Vol 136 (6) ◽  
pp. 2006-2022 ◽  
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.

scholarly journals The roles of ENSO on the occurrence of abruptly recurving tropical cyclones over the Western North Pacific Ocean Basin

2006 ◽  
Vol 6 ◽  
pp. 139-148 ◽  
Author(s):  
N. K. W. Cheung
Keyword(s):  
Tropical Cyclones ◽  
El Niño ◽  
North Pacific ◽  
Western North Pacific ◽  
Pressure Field ◽  
El Nino ◽  
North Pacific Ocean ◽  
Ocean Basin ◽  
La Niña ◽  
La Nina

Abstract. The abruptly recurving tropical cyclones over the Western North Pacific Ocean Basin during El Niño and La Niña events are studied. Temporal and spatial variations of these anomalous tracks under different phases of ENSO are shown. The anomalies of the pressure field in relation to ENSO circulation for the occurrence of the abruptly recurving cyclone tracks are investigated using fuzzy method. These are supplemented by wind field analyses. It is found that the occurrence of recurving-left (RL) and recurving-right (RR) tropical cyclones under the modification of the steering currents, including the re-adjustment of the westerly trough, the expansion or contraction of the sub-tropical high pressure, the intensifying easterly flow and the strengthening of the cross-equatorial flow, can be in El Niño or La Niña events. Evidently, there is a higher chance of occurrence of anomalous tropical cyclone trajectories in El Niño rather than La Niña events, but there is not any pronounced spatial pattern of anomalous tropical cyclone tracks. By analyzing the pressure-field, it is seen RL (RR) tropical cyclones tend to occur when the subtropical high pressure is weak (strong) in El Niño and La Niña events. More importantly, how the internal force of tropical cyclones changed by the steering current, which relies upon the relative location of tropical cyclones to the re-adjustment of the weather systems, shows when and where RL and RR tropical cyclones occur in El Niño and La Niña events.

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 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.

scholarly journals Satellite Air–Sea Enthalpy Flux and Intensity Change of Tropical Cyclones over the Western North Pacific

2016 ◽  
Vol 55 (2) ◽  
pp. 425-444 ◽  
Author(s):  
Si Gao ◽  
Shunan Zhai ◽  
Long S. Chiu ◽  
Dong Xia
Keyword(s):  
Heat Flux ◽  
Tropical Cyclones ◽  
North Pacific ◽  
Western North Pacific ◽  
North Pacific Ocean ◽  
Sensible Heat Flux ◽  
Vertical Wind Shear ◽  
Intensity Change ◽  
Rapid Intensification ◽  
Sea Temperature

AbstractAn improved high-resolution satellite enthalpy flux dataset is employed to study the composites of initial (i.e., t = 0 h) latent heat flux (LHF), sensible heat flux (SHF), and their bulk variables associated with four intensity-change categories of tropical cyclones (TCs) over the western North Pacific Ocean—rapidly intensifying (RI), slowly intensifying, neutral, and weakening—in a vertical wind shear–relative coordinate system with horizontal dimensions normalized by the radius of maximum wind. Results show that RI TCs are associated with significantly higher LHF and SHF in all TC environments than non-RI TCs, which are mainly attributable to the air–sea humidity difference (DQ) and the air–sea temperature difference (DT), respectively. Higher DQ and DT are primarily due to significantly higher sea surface temperature (SST) underlying RI TCs, emphasizing the crucial role of SST in supplying more energy to TCs that undergo rapid intensification, in which LHF plays a more important role than SHF. Relative to non-RI TCs, LHF and SHF for RI TCs show a more symmetric pattern. The magnitude and pattern of air–sea enthalpy flux could serve as potential predictors for rapid intensification of TCs.

scholarly journals Rainfall Characteristics of Recurving Tropical Cyclones over the Western North Pacific

2018 ◽  
Vol 31 (2) ◽  
pp. 575-592 ◽  
Author(s):  
Difei Deng ◽  
Elizabeth A. Ritchie
Keyword(s):  
Tropical Cyclones ◽  
North Pacific ◽  
Western North Pacific ◽  
Large Scale ◽  
Motion Vector ◽  
Vertical Wind Shear ◽  
Rainfall Characteristics ◽  
Group 2 ◽  
Baroclinic Zone ◽  
Group 1

A dataset of 88 recurving western North Pacific tropical cyclones from 2004 to 2015 is investigated for rainfall characteristics during their period of recurvature. The TCs are categorized into two groups based on different large-scale patterns from empirical orthogonal function analysis. Group 1 is characterized by an intense midlatitude baroclinic zone and close distance between the zone and TC, while Group 2 is characterized by a weaker midlatitude baroclinic zone and more remote distance between the zone and TC at the time of recurvature. The results show the large-scale environment has substantial impact on TC rainfall patterns. In Group 1, as the TC approaches and is embedded into the baroclinic zone, a relatively strong interaction between the TC and midlatitudes occurs, which is reflected by a rapid increase of environmental vertical wind shear and TC translation speed, the alignment of the shear vector and motion vector, and a sharp contrast of temperature and moisture. Higher rainfall and wider coverage of rainfall tends to be produced along the track after recurvature, and the rainfall pattern turns from a right-of-track (ROT) to a left-of-track (LOT) preference. Conversely, in Group 2, a relatively weak interaction between the TC and midlatitude circulation occurs, which is reflected by weaker vertical wind shear and slower TC motion, a separation of the shear vector and motion vector, and a weak gradient of temperature and moisture. The corresponding rainfall swath for Group 2 exhibits a narrower rainfall swath after recurvature. The rain pattern changes from a LOT to ROT preference.

scholarly journals Rapid Weakening of Tropical Cyclones in Monsoon Gyres Over the Western North Pacific: A Revisit

2021 ◽  
Vol 9 ◽  
Author(s):  
Kexin Song ◽  
Li Tao ◽  
Jianyun Gao
Keyword(s):  
Environmental Factors ◽  
Tropical Cyclones ◽  
North Pacific ◽  
Western North Pacific ◽  
Large Scale ◽  
Inner Core ◽  
Vertical Wind Shear ◽  
Reanalysis Data ◽  
Monsoon Gyre

The low-level monsoon trough over the western North Pacific (WNP) can evolve into a large cyclonic circulation, which is often termed a monsoon gyre (MG). Previous studies have revealed that tropical cyclones (TCs) embedded in MGs can experience rapid weakening (RW) and such RW might be attributed to the convective activity in the southeastern quadrant of the MG, which could induce asymmetries in a TC’s inner core structure, while the environmental factors, including the sea surface temperature (SST) and vertical wind shear (VWS), were not primary contributors to RW events. In this study, the possible role of large-scale environmental factors in association with the RW of TCs in MGs over the WNP is revisited based on the best-track TC and global reanalysis data during 2000–2018. Results indicate that TCs tend to weaken rapidly when they are embedded in the eastern semicircle of a MG, with the extreme RW events often occurring in the southeastern quadrant of a MG. However, different from previous studies, results from this study demonstrated that lower SST and strong large-scale VWS in the eastern semicircle of a MG are two major environmental factors contributing to the RW of TCs in MGs over the WNP. The different findings in this study from those in previous studies could be partly due to the different methods used to obtain the MG circulations and partly due to the environmental factors being analyzed in different quadrants of MG in this study.

scholarly journals Large-Scale Conditions for Reintensification after the Extratropical Transition of Tropical Cyclones in the Western North Pacific Ocean

2020 ◽  
Vol 33 (23) ◽  
pp. 10039-10053
Author(s):  
Wataru Yanase ◽  
Udai Shimada ◽  
Nao Takamura
Keyword(s):  
Tropical Cyclones ◽  
North Pacific ◽  
Western North Pacific ◽  
Large Scale ◽  
North Pacific Ocean ◽  
Japan Meteorological Agency ◽  
Horizontal Gradient ◽  
Extratropical Transition ◽  
Planetary Scale ◽  
Upper Level

AbstractTropical cyclones that complete extratropical transition (ETTCs) in the western North Pacific are statistically analyzed to clarify the large-scale conditions for their reintensification. A dataset of ETTCs is grouped into intensifying, dissipating, and neutral classes based on the best track data documented by the Japan Meteorological Agency during the period 1979–2018. Intensifying ETTCs are most frequent in September–October, whereas dissipating ETTCs are most frequent in the later season, October–November. Intensifying ETTCs occur at higher latitudes than dissipating ETTCs, where the upper levels are characterized by high potential vorticity (PV) and a steep horizontal gradient of PV. The composite analysis demonstrates that intensifying ETTCs are associated with deep upper-level troughs to their northwest, intense ridge building to their northeast, and strong updrafts to their north associated with vorticity advection and warm-air advection. These results statistically support the findings of previous studies. Furthermore, an analysis using a time filter demonstrates the relationship between planetary-scale environments and synoptic-scale dynamics in the upper levels. The high PV to the northwest of ETTCs is attributed not only to eastward-moving troughs, but also to the environmental PV. The low PV to the northeast of ETTCs results from the negative PV formation associated with ridge building, which almost cancels the environmental PV. Thus, the environmental PV at relatively high latitudes enhances the intensity of positive PV to the northwest of ETTCs, and increases the upper limit of the magnitude of ridge building to the northeast.

scholarly journals High-Resolution Seeded Simulations of Western North Pacific Ocean Tropical Cyclones in Two Future Extreme Climates

2018 ◽  
Vol 32 (2) ◽  
pp. 309-334
Author(s):  
J. G. McLay ◽  
E. A. Hendricks ◽  
J. Moskaitis
Keyword(s):  
High Resolution ◽  
Pacific Ocean ◽  
Tropical Cyclones ◽  
North Pacific ◽  
Western North Pacific ◽  
North Pacific Ocean ◽  
Weather Prediction ◽  
Bootstrap Analysis ◽  
Western North Pacific Ocean ◽  
The Future

ABSTRACT A variant of downscaling is devised to explore the properties of tropical cyclones (TCs) that originate in the open ocean of the western North Pacific Ocean (WestPac) region under extreme climates. This variant applies a seeding strategy in large-scale environments simulated by phase 5 of the Coupled Model Intercomparison Project (CMIP5) climate-model integrations together with embedded integrations of Coupled Ocean–Atmosphere Mesoscale Prediction System for Tropical Cyclones (COAMPS-TC), an operational, high-resolution, nonhydrostatic, convection-permitting numerical weather prediction (NWP) model. Test periods for the present day and late twenty-first century are sampled from two different integrations for the representative concentration pathway (RCP) 8.5 forcing scenario. Then seeded simulations for the present-day period are contrasted with similar seeded simulations for the future period. Reinforcing other downscaling studies, the seeding results suggest that the future environments are notably more conducive to high-intensity TC activity in the WestPac. Specifically, the future simulations yield considerably more TCs that exceed 96-kt (1 kt ≈ 0.5144 m s−1) intensity, and these TCs exhibit notably greater average life cycle maximum intensity and tend to spend more time above the 96-kt intensity threshold. Also, the future simulations yield more TCs that make landfall at >64-kt intensity, and the average landfall intensity of these storms is appreciably greater. These findings are supported by statistical bootstrap analysis as well as by a supplemental sensitivity analysis. Accounting for COAMPS-TC intensity forecast bias using a quantile-matching approach, the seeded simulations suggest that the potential maximum western North Pacific TC intensities in the future extreme climate may be approximately 190 kt.

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