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 Changes in Characteristics of Rapidly Intensifying Western North Pacific Tropical Cyclones Related to Climate Regime Shifts

2018 ◽  
Vol 31 (19) ◽  
pp. 8163-8179 ◽  
Author(s):  
Haikun Zhao ◽  
Xingyi Duan ◽  
G. B. Raga ◽  
Philip J. Klotzbach
Keyword(s):  
Tropical Cyclones ◽  
North Pacific ◽  
Wind Shear ◽  
Western North Pacific ◽  
Regime Shift ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Rapid Intensification ◽  
Climate Regime ◽  
Climate Regime Shift

A significant increase in the proportion of tropical cyclones undergoing rapid intensification at least once during their lifetime (RITCs) over the western North Pacific (WNP) is observed since 1998 when an abrupt climate regime shift occurred. Changes of large-scale atmospheric and oceanic conditions affecting TC activity are compared between two subperiods: one before and one since 1998. Results suggest that both a significant decrease in the number of TCs and a nearly unchanged number of RITCs since 1998 caused a significant increase in the frequency of RITCs. The decrease in TC numbers is likely driven by considerably increased vertical wind shear and decreased low-level vorticity. In contrast, the unchanged RITC counts and thus increased ratio of RITCs during the recent decades are largely attributed to the dominance of a more conducive ocean environment with increased TC heat potential and warmer sea surface temperature anomalies. These associated decadal changes are closely associated with the recent climate regime shift. During the recent decades with a mega–La Niña–like pattern, stronger easterly trade winds have caused increased vertical wind shear and a weakened monsoon trough, thus hampering TC formation ability over the WNP. In addition, a steeper thermocline slope that hampered the eastward migration of warm water along the equatorial Pacific has generated a more favorable thermodynamic environment supporting TC rapid intensification over the WNP.

New Probabilistic Forecast Models for the Prediction of Tropical Cyclone Rapid Intensification

2011 ◽  
Vol 26 (5) ◽  
pp. 677-689 ◽  
Author(s):  
Christopher M. Rozoff ◽  
James P. Kossin
Keyword(s):  
Logistic Regression ◽  
North Atlantic ◽  
North Pacific ◽  
North Pacific Ocean ◽  
Vertical Wind Shear ◽  
Intensity Change ◽  
Rapid Intensification ◽  
The North ◽  
Skill Scores ◽  
The North Atlantic

Abstract The National Hurricane Center currently employs a skillful probabilistic rapid intensification index (RII) based on linear discriminant analysis of the environmental and satellite-derived features from the Statistical Hurricane Intensity Prediction Scheme (SHIPS) dataset. Probabilistic prediction of rapid intensity change in tropical cyclones is revisited here using two additional models: one based on logistic regression and the other on a naïve Bayesian framework. Each model incorporates data from the SHIPS dataset over both the North Atlantic and eastern North Pacific Ocean basins to provide the probability of exceeding the standard rapid intensification thresholds [25, 30, and 35 kt (24 h)−1] for 24 h into the future. The optimal SHIPS and satellite-based predictors of rapid intensification differ slightly between each probabilistic model and ocean basin, but each set of optimal predictors incorporates thermodynamic and dynamic aspects of the tropical cyclone’s environment (such as vertical wind shear) and its structure (such as departure from convective axisymmetry). Cross validation shows that both the logistic regression and Bayesian probabilistic models are skillful relative to climatology. Dependent testing indicates both models exhibit forecast skill that generally exceeds the skill of the present operational SHIPS-RII and a simple average of the probabilities provided by the logistic regression, Bayesian, and SHIPS-RII models provides greater skill than any individual model. For the rapid intensification threshold of 25 kt (24 h)−1, the three-member ensemble mean improves the Brier skill scores of the current operational SHIPS-RII by 33% in the North Atlantic and 52% in the eastern North Pacific.

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 Landfalls of Tropical Cyclones with Rapid Intensification in the Western North Pacific

2019 ◽  
Author(s):  
Jie Yang ◽  
Meixiang Chen
Keyword(s):  
Tropical Cyclones ◽  
North Pacific ◽  
Western North Pacific ◽  
Intensity Change ◽  
Moderate Intensity ◽  
Rapid Intensification ◽  
Southern Chinese ◽  
Chinese Coast ◽  
The Mean ◽  
Definition Of

Abstract. This study statistically investigates the seasonal and decadal variation of tropical cyclones (TCs) underwent rapid intensification (RI) and their landfalling cyclone energy in the western North Pacific using the satellite-era best track data from 1986 to 2017. Totally 31.2 % TCs have underwent at least one RI processes (RI TCs) and 341 made landfalls after RI from 946 historical TCs, using the definition of 95th percentile from the accumulative probability distribution of over-water 24-h TC intensity change. The frequent-occurrence region of RI is found in sea areas to the east of Philippines, and the mean genesis and on-set locations of landfalling TCs underwent RI had westward components compared with the ones did not made landfalls. The Philippine coast, the southern Chinese coast and the coast along the southern Japan are the three main regions affected by the landfalling RI TCs. The coasts in the latter two regions have increased trend of cyclone energy since 1986, which possibly correlates with the poleward migration of the mean latitude where TCs reach their lifetime maximum intensities (LMI). The frequency of the landfalling RI TCs have a significant upward trend with insignificant increase in their LMI, while both the LMI and landfalling cyclone energy by TCs that didn't undergo RI in the western North Pacific show downward trends in the period during 1986–2017. The changes of the LMI distribution in the western North Pacific are related tightly with these two types of TCs with different intensification rates: strong TCs are found become stronger mainly due to more active RI processes, while weak TCs have weakened in majority of moderate intensity TCs, which didn't experience RI processes.

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.

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 Multidecadal Variability of Tropical Cyclone Rapid Intensification in the Western North Pacific

2015 ◽  
Vol 28 (9) ◽  
pp. 3806-3820 ◽  
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.

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.

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