scholarly journals Maximum wind radius estimated by the 50 kt radius: improvement of storm surge forecasting over the western North Pacific

2016 ◽  
Vol 16 (3) ◽  
pp. 705-717 ◽  
Author(s):  
Hiroshi Takagi ◽  
Wenjie Wu
Keyword(s):  
Storm Surge ◽  
North Pacific ◽  
Western North Pacific ◽  
Estimation Method ◽  
Storm Surges ◽  
The Philippines ◽  
Estimation Methods ◽  
Central Pressure ◽  
Estimation Errors ◽  
Maximum Wind

Abstract. Even though the maximum wind radius (Rmax) is an important parameter in determining the intensity and size of tropical cyclones, it has been overlooked in previous storm surge studies. This study reviews the existing estimation methods for Rmax based on central pressure or maximum wind speed. These over- or underestimate Rmax because of substantial variations in the data, although an average radius can be estimated with moderate accuracy. As an alternative, we propose an Rmax estimation method based on the radius of the 50 kt wind (R50). Data obtained by a meteorological station network in the Japanese archipelago during the passage of strong typhoons, together with the JMA typhoon best track data for 1990–2013, enabled us to derive the following simple equation, Rmax  =  0.23 R50. Application to a recent strong typhoon, the 2015 Typhoon Goni, confirms that the equation provides a good estimation of Rmax, particularly when the central pressure became considerably low. Although this new method substantially improves the estimation of Rmax compared to the existing models, estimation errors are unavoidable because of fundamental uncertainties regarding the typhoon's structure or insufficient number of available typhoon data. In fact, a numerical simulation for the 2013 Typhoon Haiyan as well as 2015 Typhoon Goni demonstrates a substantial difference in the storm surge height for different Rmax. Therefore, the variability of Rmax should be taken into account in storm surge simulations (e.g., Rmax  =  0.15 R50–0.35 R50), independently of the model used, to minimize the risk of over- or underestimating storm surges. The proposed method is expected to increase the predictability of major storm surges and to contribute to disaster risk management, particularly in the western North Pacific, including countries such as Japan, China, Taiwan, the Philippines, and Vietnam.

scholarly journals Maximum wind radius estimated by the 50 kt radius: improvement of storm surge forecasting over the Western North Pacific

2015 ◽  
Vol 3 (10) ◽  
pp. 6431-6457 ◽  
Author(s):  
H. Takagi ◽  
W. Wu
Keyword(s):  
Storm Surge ◽  
North Pacific ◽  
Western North Pacific ◽  
Estimation Error ◽  
Estimation Method ◽  
Storm Surges ◽  
Estimation Methods ◽  
Maximum Wind ◽  
Japanese Archipelago ◽  
The Japanese Archipelago

Abstract. Even though the maximum wind radius (Rmax) is an important parameter in determining the intensity and size of tropical cyclones, it has been overlooked in previous storm surge studies. This research reviewed the existing estimation methods of Rmax based on the central pressure or maximum wind speed. These over or underestimated Rmax because of the substantial variety of the data, though an average radius could be moderately estimated. Alternatively, we proposed an Rmax estimation method based on the radius of the 50 knot wind (R50). The data obtained during the passage of strong typhoons by a meteorological station network in the Japanese archipelago enabled us to derive the following formula, Rmax = 0.23R50. Although this new method substantially improved the estimation of Rmax compared to the existing models, an estimation error was unavoidable because of fundamental uncertainties regarding the typhoon's structure or insufficient number of available typhoon data. In fact, a numerical simulation from 2013 Typhoon Haiyan demonstrated a substantial difference in the storm surge height for different Rmax. Therefore, the variability of Rmax should be taken into account in storm surge simulations, independently of the model used, to minimize the risk of over or underestimation of storm surges. The proposed method is expected to increase the reliability of storm surge prediction and contribute to disaster risk management, particularly in the Western North Pacific, including countries such as Japan, China, Taiwan, Philippines, and Vietnam.

Dropsonde Observations of Intense Typhoons in 2017 and 2018 in the T-PARCII Project

2020 ◽  
Author(s):  
Kazuhisa Tsuboki ◽  
Hiroyuki Yamada ◽  
Tadayasu Ohigashi ◽  
Taro Shinoda ◽  
Kosuke Ito ◽  
...  
Keyword(s):  
Wind Speed ◽  
Tropical Cyclone ◽  
North Pacific ◽  
Western North Pacific ◽  
Maximum Wind Speed ◽  
Central Pressure ◽  
The South ◽  
Main Island ◽  
Maximum Wind ◽  
Typhoon Intensity

<p>Typhoon is a tropical cyclone in the western North Pacific and the South China Sea. It is the most devastating weather system in East Asia. Strong winds and heavy rainfalls associated with a typhoon often cause severe disasters in these regions. There are many cases of typhoon disasters even in the recent decades in these regions. Furthermore, future projections of typhoon activity in the western North Pacific show that its maximum intensity will increase with the climate change. However, the historical data of typhoon (best track data) include large uncertainty after the US aircraft reconnaissance of typhoon was terminated in 1987. Another problem is that prediction of typhoon intensity has not been improved for the last few decades. To improve these problems, in situ observations of typhoon using an aircraft are indispensable. The T-PARCII (Tropical cyclone-Pacific Asian Research Campaign for Improvement of Intensity estimations/forecasts) project is aiming to improve estimations and forecasts of typhoon intensity as well as storm track forecasts.</p><p>In 2017, the T-PARCII team performed dropsonde observations of intense Typhoon Lan in collaboration with Taiwan DOTSTAR, which was the most intense typhoon in 2017 and caused huge disaster over the central Japan. It was categorized as a supertyphoon by JTWC and as a very intense and huge typhoon by JMA. Typhoon Lan moved northeastward to the east of the Okinawa main island and it was located around 23 N on 21 and 28 N on 22 October. In these two days, we made dropsonde observations at the center of the eye and in the surrounding area of the eyewall. The observations showed that the central pressure of Lan slightly increases from 926 hPa on 21 to 928 hPa on 22 October with the northward movement. On the other hand, The JMA best track data indicate that the central pressure decreases from 935 hPa on 21 to 915 hPa on 22 October. The observations also showed a significant double warm core structure in the eye and the maximum wind speed along the eyewall. The dropsonde data were used for forecast experiments. The result shows an improvement of typhoon track prediction.</p><p>The T-PARCII team also made aircraft observations of Typhoon Trami during the period from 25 to 28 September 2018 in collaboration with the SATREPS ULAT group and DOTSTAR. Trami was almost stationary during the period to the south of the Okinawa main island. Then, it moved northward and finally made a landfall over the central part of Japan. This also caused a big disaster and electricity was shut down for several days in the central part of Japan. Typhoon Trami showed a drastic change of intensity from 25 to 26 September with a large change of eye size from about a diameter of 60 km to 200 km. Dropsonde observations showed the change of central pressure and maximum wind speed as well as the thermodynamic structure of the eye.</p>

scholarly journals Modeling Study on the Asymmetry of Positive and Negative Storm Surges along the Southeastern Coast of China

2021 ◽  
Vol 9 (5) ◽  
pp. 458
Author(s):  
Dongdong Chu ◽  
Haibo Niu ◽  
Wenli Qiao ◽  
Xiaohui Jiao ◽  
Xilin Zhang ◽  
...  
Keyword(s):  
Storm Surge ◽  
Pressure Field ◽  
Three Dimensional ◽  
Storm Surges ◽  
Ocean Model ◽  
Central Pressure ◽  
Linear Interaction ◽  
Southeastern Coast ◽  
Zhoushan Archipelago ◽  
Wind Intensity

In this paper, a three-dimensional storm surge model was developed based on the Finite Volume Community Ocean Model (FVCOM) by the hindcasts of four typhoon-induced storm surges (Chan-hom, Mireille, Herb, and Winnie). After model validation, a series of sensitivity experiments were conducted to explore the effects of key parameters in the wind and pressure field (forward speed, radius of maximum wind (RMW), inflow angle, and central pressure), typhoon path, wind intensity, and topography on the storm surge and surge asymmetry between sea level rise (positive surge) and fall (negative surge) along the southeastern coast of China (SCC). The model results show that lower central pressure and larger RMW could lead to stronger surge asymmetry. A larger inflow angle results in a stronger surge asymmetry. In addition, the path of Chan-hom is the most dangerous path type for the Zhoushan Archipelago area, and that of Winnie follows next. The model results also indicate that the non-linear interaction between wind field and pressure field tends to weaken the peak surge elevation. The effect of topography on storm surges indicates that the peak surge elevation and its occurrence time, as well as the surge asymmetry, increase with a decreasing slope along the SCC.

Biennial and Lower-Frequency Variability Observed in the Early Summer Climate in the Western North Pacific

2004 ◽  
Vol 17 (21) ◽  
pp. 4254-4266 ◽  
Author(s):  
Tomohiko Tomita ◽  
Takao Yoshikane ◽  
Tetsuzo Yasunari
Keyword(s):  
North Pacific ◽  
Western North Pacific ◽  
Southern Oscillation ◽  
The Philippines ◽  
Early Summer ◽  
Tropical Pacific ◽  
Western Pacific ◽  
Spatial Phase ◽  
Summer Climate ◽  
Baiu Front

Abstract Early summer climate in the western North Pacific is largely represented by the baiu phenomenon. The meridional fluctuations of the baiu front on interannual time scales and the associated large-scale circulations are examined using the empirical orthogonal function (EOF) analysis and composite or correlation analyses based on the EOF time coefficients. The first EOF mode indicates a 5- or 6-yr low-frequency fluctuation (LF mode) appearing south of 35°N. The development is concurrent with horseshoe sea surface temperature anomalies (SSTAs) in the entire tropical Pacific that are associated with the El Niño–Southern Oscillation (ENSO). SSTAs in the western North Pacific control the anomalous southward expansion of the baiu front through a modification of the convection at around 20°–35°N. The LF mode is negatively correlated with the south-southeast Asian summer monsoon. The second EOF mode is characterized by a meridional seesawlike fluctuation with a node at around 28°N and a time scale of biennial oscillation (BO mode). The horseshoe SSTAs again control the anomalous meridional circulations, but with a different spatial phase through a convection off the Philippines. The spatial phase difference between the two horseshoe patterns is about 90° in both the zonal and meridional directions. The BO mode is negatively correlated with the tropical western North Pacific monsoon. SSTAs associated with the BO mode tend to be confined to the tropical western Pacific, while the signals of the LF mode extend rather broadly in the tropical Pacific–Indian Ocean sector, suggesting that the tropical BO is an aborted ENSO in the tropical central–western Pacific. The spatial phase of horseshoe SSTAs adjusts the interannual variability of the meridional fluctuation of the baiu front in the western North Pacific.

scholarly journals Attribution of Decadal Variability in Tropical Cyclone Passage Frequency over the Western North Pacific: A New Approach Emphasizing the Genesis Location of Cyclones

2013 ◽  
Vol 26 (3) ◽  
pp. 973-987 ◽  
Author(s):  
Satoru Yokoi ◽  
Yukari N. Takayabu
Keyword(s):  
Tropical Cyclone ◽  
Time Scales ◽  
North Pacific ◽  
Western North Pacific ◽  
Decadal Variability ◽  
The Philippines ◽  
Ocean Basin ◽  
New Approach ◽  
Equal Degree ◽  
Analysis Application

Abstract Variability in tropical cyclone (TC) activity is a matter of direct concern for affected populations. On interannual and longer time scales, variability in TC passage frequency can be associated with total TC frequency over the concerned ocean basin [basinwide frequency (BF)], the spatial distribution of TC genesis in the basin [genesis distribution (GD)], and the preferable track (PT) that can be considered as a function of genesis locations. To facilitate investigation of mechanisms responsible for the variability, the authors propose an approach of decomposing anomalies in the passage frequency into contributions of variability in BF, GD, and PT, which is named the Integration of Statistics on TC Activity by Genesis Location (ISTAGL) analysis. Application of this approach to TC best track data in the western North Pacific (WNP) basin reveals that overall distribution of the passage frequency trends over the 1961–2010 period is mainly due to the PT trends. On decadal time scales, passage frequency variability in midlatitudes is primarily due to PT variability, while the BF and GD also play roles in the subtropics. The authors further discuss decadal variability over the East China Sea in detail. The authors demonstrate that northward shift of the PT for TCs generated around the Philippines Sea and westward shift for TCs generated in the eastern part of the WNP contribute the variability with almost equal degree. The relationships between these PT shifts and anomalies in environmental circulation fields are also discussed.

scholarly journals Western North Pacific Tropical Cyclone Characteristics Stratified by Genesis Environment

2018 ◽  
Vol 146 (2) ◽  
pp. 435-446 ◽  
Author(s):  
Hironori Fudeyasu ◽  
Ryuji Yoshida
Keyword(s):  
Tropical Cyclone ◽  
North Pacific ◽  
Western North Pacific ◽  
Convective Available Potential Energy ◽  
The Philippines ◽  
Vertical Shear ◽  
Occurrence Rate ◽  
Tropical Cyclone Heat Potential ◽  
Heat Potential ◽  
Confluence Region

Abstract The characteristics of tropical cyclones (TCs) in the summer and autumn seasons over the western North Pacific that are associated with different environmental factors that influence TC genesis (TCG) were studied. The authors objectively categorized factors into the five TCG factors classified by Ritchie and Holland: monsoon shear line (SL), monsoon confluence region (CR), monsoon gyre (GY), easterly wave (EW), and the Rossby wave energy dispersion from a preexisting TC (PTC). The GY-TCs tended to develop slowly, and the highest rates of occurrence of rapid intensification (RI) were found for the CR-TCs, whereas the GY-TCs rarely experienced RI. The average storm size of the GY-TCs at the time of formation was the largest of the averages among the TC types, while the EW- and PTC-TCs were smaller, although these differences disappeared at the mature time. There were no significant differences in the sea surface temperature (SST) beneath the TCs, but the tropical cyclone heat potential (TCHP) of the PTC-TCs was higher. The PTC-TCs tended to develop as intense TCs and exhibited favorable environmental characteristics, such as high TCHP, high convective available potential energy, and weak vertical shear. The occurrence rate of the PTC-TCs that made landfall in the Philippines was higher than the averages of the other TC types, whereas those of the EW-TCs (PTC-TCs) that made landfall in Japan (China) were lower. These results provide important information for use in disaster prevention.

Tropical cyclone genesis and trajectory characteristics in the western north Pacific

2020 ◽  
Author(s):  
Rui Xiong ◽  
Mengqian Lu
Keyword(s):  
Tropical Cyclone ◽  
Zonal Wind ◽  
Environmental Conditions ◽  
North Pacific ◽  
Western North Pacific ◽  
Data Science ◽  
Clustering Algorithm ◽  
The Philippines ◽  
Vertical Shear ◽  
Gaussian Kernel

<p>The western North Pacific (WNP) is one of the most active tropical cyclone (TC) regions, which can inflict enormous death and massive property damage to surrounding areas. Although many studies about tropical cyclone activities on multi-timescales have been done, most of them focus on the entire basin, variations within the basin deserve more investigations. Besides TC characteristics on different timescales, to investigate the impacts of environment variables on TC and provide informative factors for prediction is another concern in the research community. In this study, we adopt several data science techniques, including Gaussian kernel estimator, wavelet, cross-wavelet coherence and regression analyses, to explore the spatiotemporal variations of TC genesis and associated environmental conditions. Significant semiannual and annual variations of TC genesis have been found in the northern South China Sea (NSCS) and oceanic areas east of the Philippines (OAEP). In the southeast part of WNP (SEWNP), TC genesis shows prominent variations on ENSO time scale. With reconstructed TC series on those frequencies, we further quantify the influences of environmental variables on the primary TC signals over WNP. About 40% of the identified TC variance over NSCS and OAEP can be explained by variability in vertical shear of zonal wind and relative humidity. In the SEWNP, TC genesis reveals strong nonlinear and non-stationary relationships with vertical shear of zonal wind and absolute vorticity. Besides, A probabilistic clustering algorithm is used to describe the TC tracks in the WNP. The best track dataset from JMA is decomposed into three clusters based on genesis location and curvature. For each cluster, we analyze the relationships between TC properties, such as genesis location, trajectory and intensity, and associated environmental conditions using the self-organizing map. The spatial patterns of sea surface temperature have huge impacts on TC genesis location, while the trajectory is largely influenced by geopotential height.</p>

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 Systematic Variation of Summertime Tropical Cyclone Activity in the Western North Pacific in Relation to the Madden–Julian Oscillation

2008 ◽  
Vol 21 (6) ◽  
pp. 1171-1191 ◽  
Author(s):  
Joo-Hong Kim ◽  
Chang-Hoi Ho ◽  
Hyeong-Seog Kim ◽  
Chung-Hsiung Sui ◽  
Seon Ki Park
Keyword(s):  
Tropical Cyclone ◽  
South China ◽  
North Pacific ◽  
Western North Pacific ◽  
Large Scale ◽  
Function Analysis ◽  
Equatorial Indian Ocean ◽  
The Philippines ◽  
Madden Julian Oscillation ◽  
Enso Events

Abstract The variability of observed tropical cyclone (TC) activity (i.e., genesis, track, and landfall) in the western North Pacific (WNP) is examined in relation to the various categories of the Madden–Julian oscillation (MJO) during summer (June–September) for the period 1979–2004. The MJO categories are defined based on the empirical orthogonal function analysis of outgoing longwave radiation data. The number of TCs increases when the MJO-related convection center is located in the WNP. The axis of a preferable genesis region systematically shifts like a seesaw in response to changes in the large-scale environments associated with both the eastward and northward propagation of the MJO and the intraseasonal variability of the WNP subtropical high. Furthermore, the authors show that the density of TC tracks in each MJO category depends on the systematic shift in the main genesis regions at first order. Also, the shift is affected by the prevailing large-scale steering flows in each MJO category. When the MJO-related convection center is found in the equatorial Indian Ocean (the tropical WNP), a dense area of tracks migrates eastward (westward). The effects of extreme ENSO events and the variations occurring during ENSO neutral years are also examined. A statistical analysis of TC landfalls by MJO category is applied in seven selected subareas: the Philippines, Vietnam, South China, Taiwan, East China, Korea, and Japan. While a robust and significant modulation in the number of TC landfalls is observed in south China, Korea, and Japan, the modulation is marginal in the remaining four subareas.

scholarly journals Interchange and movements of humpback whales (Megaptera novaeangliae) between western North Pacific winter breeding grounds in northern Luzon, Philippines and Okinawa, Japan

2021 ◽  
Vol 22 (1) ◽  
pp. 39-53
Author(s):  
Jo Marie Acebes ◽  
Haruna Okabe ◽  
Nozomi Kobayashi ◽  
Shotaro Nakagun ◽  
Naoto Higashi ◽  
...  
Keyword(s):  
North Pacific ◽  
Western North Pacific ◽  
The Philippines ◽  
Humpback Whales ◽  
Distinct Population Segment ◽  
Breeding Grounds ◽  
Different Seasons ◽  
The Relationship ◽  
Population Segment ◽  
Winter Breeding

Humpback whales wintering in the northern Philippines and Okinawa, Japan, belong to the western North Pacific subpopulation, now recognised as a distinct population segment. The numbers for this subpopulation are low hence it is being proposed to be listed as endangered. Although previous research revealed movements between breeding grounds, the relationship between these areas remain little understood. Recent survey efforts in the Philippines resulted in a total of 234 photo-identified individuals from 1999-2016 while Okinawa had 1,445 from 1991-2014. Within the seasons a total of 100 matches were found between the two breeding grounds including 38 males and 24 females while the rest were unknown. Within these matches, eight individuals were recorded moving within seasons, including two individuals moving across seasons multiple times. The two whales were both males, where one was recorded in both breeding grounds in three different seasons (2005, 2008 and 2012). The shortest duration of recorded sightings between grounds was one whale seen in the Philippines in late March 2012 and in Okinawa 13 days later. More females with calves were sighted in the Philippines than in Okinawa and this may indicate the Philippines as a preferred nursing ground.

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