scholarly journals Trends in Western North Pacific Tropical Cyclone Intensity Change Before Landfall

2021 ◽  
Vol 9 ◽  
Author(s):  
Qingyuan Liu ◽  
Jinjie Song ◽  
Philip J. Klotzbach
Keyword(s):  
South China Sea ◽  
South China ◽  
North Pacific ◽  
Western North Pacific ◽  
Large Scale ◽  
Northern South China Sea ◽  
The Philippines ◽  
Intensity Change ◽  
China Sea ◽  
Heat Potential

This study investigates the long-term trend in the average 24-h intensity change (ΔV24) of western North Pacific (WNP) tropical cyclones (TCs) before landfall during June-November for the period from 1970–2019. We find a significant increasing trend in basin-averaged ΔV24 during 1970–2019. The increase in ΔV24 is significant over the northern South China Sea (17.5°-25°N, 107.5°-120°E) and to the east of the Philippines (7.5°-15°N, 122.5°-132.5°E), implying a slower weakening rate before landfall for the South China Sea and an increased intensification rate before landfall for the region east of the Philippines. We find a significant linkage between changes in ΔV24 and several large-scale environmental conditions. The increased ΔV24 before landfall in the above two regions is induced by a warmer ocean (e.g., higher sea surface temperatures, maximum potential intensity and TC heat potential) and greater upper-level divergence, with a moister mid-level atmosphere also aiding the ΔV24 increase east of the Philippines. Our study highlights an increasing tendency of ΔV24 before landfall, consistent with trends in ΔV24 over water and over land as found in previous publications.

scholarly journals Evaluation of the ability of the Chinese stalagmite δ<sup>18</sup>O to record the variation in atmospheric circulation during the second half of the 20th century

2014 ◽  
Vol 10 (3) ◽  
pp. 975-985 ◽  
Author(s):  
S. Nan ◽  
M. Tan ◽  
P. Zhao
Keyword(s):  
Water Vapor ◽  
South China Sea ◽  
South China ◽  
Bay Of Bengal ◽  
North Pacific ◽  
Western North Pacific ◽  
Large Scale ◽  
The South China Sea ◽  
The South ◽  
China Sea

Abstract. The Chinese stalagmite δ18O (δ18Ocs) has provoked debate worldwide over the past few years due to its lack of quantitative calibration, leading us to questions of whether δ18Ocs records a local or large-scale signal and whether δ18Ocs records the signal of a single remote water vapor source or multiple water vapor sources. In this study, we observe all of the δ18Ocs trends within the instrumental period to verify whether they possess a common trend, which could be used as a basis to determine whether the trends reflect the large-scale signal together or whether each trend reflects the local signal. The results show that most of the δ18Ocs experienced a linear increase from 1960 to 1994, which may indicate that the δ18Ocs could record a trend occurring in large-scale atmosphere circulations. We then quantitatively describe the proportion of water vapor transport (WVT) from different source regions. Using the NCEP/NCAR (National Centers for Environmental Protection/National Center for Atmospheric Research) reanalysis data from 1960 to 1994, the ratios of the intensities of three WVTs from the Bay of Bengal, the South China Sea, and the western North Pacific during the summer are calculated. We define RSCS/BOB as the ratio of the WVT intensities from the South China Sea to those from the Bay of Bengal, RWNP/BOB as the ratio of the WVT intensities from the western North Pacific to those from the Bay of Bengal, and RWNP/SCS as the ratio of the WVT intensities from the western North Pacific to those from the South China Sea. The significant decadal increase occurs in the time series of RWNP/BOB and RWNP/SCS, most likely resulting from the strengthening of the WVT from the western North Pacific in the late 1970s due to the western Pacific subtropical high that extended westward. Further analysis indicates that when the equatorial central and eastern Pacific is in the El Niño phase, the sea surface temperature (SST) in the tropical Indian Ocean, the Bay of Bengal, and the South China Sea is high, and the SST at the middle latitudes in the North Pacific is low, then the RWNP/BOB and RWNP/SCS values tend to be high. After the late 1970s, the equatorial central and eastern Pacific have often been in the El Niño phase. Therefore, we confirm that the δ18Ocs primarily records the variation in atmospheric circulation during the second half of the 20th century.

scholarly journals The Philippines–Taiwan Oscillation: Monsoonlike Interannual Oscillation of the Subtropical–Tropical Western North Pacific Wind System and Its Impact on the Ocean

2012 ◽  
Vol 25 (5) ◽  
pp. 1597-1618 ◽  
Author(s):  
Y.-L. Chang ◽  
L.-Y. Oey
Keyword(s):  
South China Sea ◽  
South China ◽  
North Pacific ◽  
Western North Pacific ◽  
The Philippines ◽  
The South China Sea ◽  
The South ◽  
China Sea ◽  
Interannual Oscillation ◽  
Tropical Western North Pacific

Tide gauge and satellite data reveal an interannual oscillation of the ocean’s thermoclines east of the Philippines and Taiwan, forced by a corresponding oscillation in the wind stress curl. This so-called Philippines–Taiwan Oscillation (PTO) is shown to control the interannual variability of the circulation of the subtropical and tropical western North Pacific. The PTO shares some characteristics of known Pacific indices, for example, Niño-3.4. However, unlike PTO, these other indices explain only portions of the western North Pacific circulation. The reason is because of the nonlinear nature of the forcing in which mesoscale (ocean) eddies play a crucial role. In years of positive PTO, the thermocline east of the Philippines rises while east of Taiwan it deepens. This results in a northward shift of the North Equatorial Current (NEC), increased vertical shear of the Subtropical Countercurrent (STCC)/NEC system, increased eddy activity dominated by warm eddies in the STCC, increased Kuroshio transport off the northeastern coast of Taiwan into the East China Sea, increased westward inflow through Luzon Strait into the South China Sea, and cyclonic circulation and low sea surface height anomalies in the South China Sea. The reverse applies in years of negative PTO.

The carbonate system of the northern South China Sea: Seasonality and exchange with the western North Pacific

2020 ◽  
pp. 102464
Author(s):  
Elliott G. Roberts ◽  
Minhan Dai ◽  
Zhimian Cao ◽  
Weidong Zhai ◽  
Liguo Guo ◽  
...  
Keyword(s):  
South China Sea ◽  
South China ◽  
North Pacific ◽  
Western North Pacific ◽  
Northern South China Sea ◽  
Carbonate System ◽  
China Sea

scholarly journals Eddy characteristics in the northern South China Sea as inferred from Lagrangian drifter data

Ocean Science ◽  
2011 ◽  
Vol 7 (5) ◽  
pp. 661-669 ◽  
Author(s):  
◽  
◽  
Keyword(s):  
South China Sea ◽  
South China ◽  
Large Scale ◽  
Northern South China Sea ◽  
Temporal Distribution ◽  
Height Anomaly ◽  
Spatial And Temporal Patterns ◽  
China Sea ◽  
Eddy Characteristics ◽  
Anticyclonic Eddies

Abstract. Cyclonic and anticyclonic eddies from large scale to submesoscale in the northern South China Sea (NSCS) have been statistically characterized based on the satellite-tracked Lagrangian drifters using our developed geometric eddy identification method. There are in total 2208 eddies identified, 70% of which are anticyclonic eddies. If the submesoscale eddies are eliminated, the other eddies in the NSCS will show a 1.2:1 ratio of the number of anticyclones (210) to the number of cyclones (171). The spatial distribution of the eddies is regional: in southwest of Taiwan, the number of anticyclones dominates the number of cyclones, and most of them are the submesoscale anticyclones with small radii; in contrast, the large and medium cyclonic eddies are a little more than the same scale anticyclonic eddies in northwest of Luzon. The temporal distribution of eddy number in the NSCS has a close relation with the Asian monsoon. The number of the large and medium eddies peaks during the winter monsoon, while the submesoscale eddies are apt to generate in the summer monsoon. The spatial and temporal patterns have a good agreement with the results of the sea surface height anomaly (SSHA). The maximum and mean tangential velocities of anticyclones (cyclones) are 40 (30) cm s−1 and 25 (15) cm s−1, respectively. The calculated normalized vorticities from drifters suggest that although the mesoscale eddies may be considered in geostrophic balance, ageostrophic dynamics and centrifugal effects may play an important role for the growth and decay of the mesoscale cores.

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 Two Distinctive Processes for Abnormal Spring to Summer Transition over the South China Sea

2017 ◽  
Vol 30 (23) ◽  
pp. 9665-9678 ◽  
Author(s):  
Renguang Wu ◽  
Zhuoqi He
Keyword(s):  
South China Sea ◽  
South China ◽  
North Pacific ◽  
Western North Pacific ◽  
The South China Sea ◽  
The South ◽  
Maritime Continent ◽  
China Sea ◽  
Tropical Western North Pacific ◽  
Sst Anomalies

The period from April to June signifies the transition from spring to summer over the South China Sea (SCS). The present study documents two distinct processes for abnormal spring to summer transition over the SCS. One process is related to large-scale sea surface temperature (SST) anomalies in the tropical Indo-Pacific region. During spring of La Niña decaying years, negative SST anomalies in the equatorial central Pacific (ECP) and the southwestern tropical Indian Ocean (TIO) coexist with positive SST anomalies in the tropical western North Pacific. Negative ECP SST anomalies force an anomalous Walker circulation, negative southwestern TIO SST anomalies induce anomalous cross-equatorial flows from there, and positive tropical western North Pacific SST anomalies produce a Rossby wave–type response to the west. Together, they contribute to enhanced convection and an anomalous lower-level cyclone over the SCS, leading to an advanced transition to summer there. The other process is related to regional air–sea interactions around the Maritime Continent. Preceding positive ECP SST anomalies induce anomalous descent around the Maritime Continent, leading to SST increase in the SCS and southeast TIO. An enhanced convection region moves eastward over the south TIO during spring and reaches the area northwest of Australia in May. This enhances descent over the SCS via an anomalous cross-equatorial overturning circulation and contributes to further warming in the SCS. The SST warming in turn induces convection over the SCS, leading to an accelerated transition to summer. Analysis shows that the above two processes are equally important during 1979–2015.

scholarly journals Climate shift of the South China Sea summer monsoon onset in 1993/1994 and its physical causes

2019 ◽  
Vol 54 (3-4) ◽  
pp. 1819-1827
Author(s):  
Ailan Lin ◽  
Renhe Zhang
Keyword(s):  
South China Sea ◽  
South China ◽  
North Pacific ◽  
Early Onset ◽  
Western North Pacific ◽  
The South China Sea ◽  
The South ◽  
Climate Shift ◽  
China Sea ◽  
Zonal Winds

AbstractThe characteristics of anomalous circulations during spring associated with the climate shift of the South China Sea summer monsoon (SCSSM) onset in 1993/1994 and its physical causes are investigated. It is found that the interdecadal shift of SCSSM onset happened in 1993/1994 is related closely to the 850 hPa zonal wind anomalies over the area around Kalimantan Island. Easterly (westerly) anomalies over Kalimantan Island enhance (weaken) subtropical high over the western North Pacific, leading to the late (early) onset of SCSSM in 1979–1993 (1994–2013). The sea surface temperature anomalies (SSTAs) in the key region 140°–150° E, 5° S–2.5° N influence the interdecadal change of zonal winds over Kalimantan Island. The positive SSTAs over this key region in 1994–2013 force convergence toward the region at low-level and form significant westerly anomalies near Kalimantan Island located to the west of the key region. The negative anomalies of meridional gradient of zonal winds over the South China Sea region increase the atmospheric vorticity over there significantly and result in the weakening and retreating eastward of the subtropical high over the western North Pacific, which is conducive to the early onset of SCSSM.

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