Increasing Influence of Central Pacific El Niño on the Interdecadal Variation of Spring Rainfall in Northern Taiwan and Southern China Since 1980

2020 ◽  
Author(s):  
Pei-ken Kao ◽  
Chi-Cherng Hong ◽  
Chih-wen Hung
Keyword(s):  
North Pacific ◽  
Transition Period ◽  
Southern China ◽  
Interdecadal Variation ◽  
Decadal Variation ◽  
Central Pacific ◽  
Circulation Anomaly ◽  
The Pacific ◽  
Sst Anomaly ◽  
Northern Taiwan

<p>Decadal variation of spring (February–April) rainfall in Northern Taiwan and Southern China was significantly related to the Pacific Decadal Oscillation (PDO) during the twentieth century. However, this interdecadal relationship subsequently weakened, and the sea surface temperature (SST) associated with the central Pacific El Niño (CPEN) has determined the interdecadal variation of spring rainfall in Northern Taiwan and Southern China since the 1980s. In this study, the effect of CPEN-SST on the interdecadal variation of spring rainfall in Northern Taiwan and Southern China was investigated. We found that a CPEN-associated positive SST anomaly in the eastern North Pacific forced an east–west overturning circulation anomaly in the subtropical North Pacific, the descending motion of which may have generated an anticyclonic circulation anomaly in the Philippine Sea. Simultaneously, the anticyclone associated southerly winds anomaly may enhance the southwesterly in northwest of the anticyclone, which in term enhance the trough extending from Japan to Northern Taiwan. The anticyclone and trough associated with the respective southwesterly and northeasterly anomalies created a convergence environment in Northern Taiwan. In turn, this convergence environment contributed substantially to an interdecadal rainfall enhancement in Northern Taiwan and Southern China. Our results suggest that the effect of CPEN-SST on the interdecadal variation of spring rainfall in Northern Taiwan and Southern China has increased since 1980, especially during the transition period from the termination of a warm PDO phase to a cold phase in the late 1990s</p>

scholarly journals Synoptic–Dynamic Climatology of Large-Scale Cyclones in the North Pacific

2006 ◽  
Vol 134 (12) ◽  
pp. 3567-3587 ◽  
Author(s):  
Linda M. Keller ◽  
Michael C. Morgan ◽  
David D. Houghton ◽  
Ross A. Lazear
Keyword(s):  
North Pacific ◽  
Large Scale ◽  
The United States ◽  
Height Anomaly ◽  
Maximum Frequency ◽  
Mean Flow ◽  
Central Pacific ◽  
The North ◽  
The Pacific ◽  
The North Pacific

Abstract A climatology of large-scale, persistent cyclonic flow anomalies over the North Pacific was constructed using the National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP–NCAR) global reanalysis data for the cold season (November–March) for 1977–2003. These large-scale cyclone (LSC) events were identified as those periods for which the filtered geopotential height anomaly at a given analysis point was at least 100 m below its average for the date for at least 10 days. This study identifies a region of maximum frequency of LSC events at 45°N, 160°W [key point 1 (KP1)] for the entire period. This point is somewhat to the east of regions of maximum height variability noted in previous studies. A second key point (37.5°N, 162.5°W) was defined as the maximum in LSC frequency for the period after November 1988. The authors show that the difference in location of maximum LSC frequency is linked to a climate regime shift at about that time. LSC events occur with a maximum frequency in the period from November through January. A composite 500-hPa synoptic evolution, constructed relative to the event onset, suggests that the upper-tropospheric precursor for LSC events emerges from a quasi-stationary long-wave trough positioned off the east coast of Asia. In the middle and lower troposphere, the events are accompanied by cold thickness advection from a thermal trough over northeastern Asia. The composite mean sea level evolution reveals a cyclone that deepens while moving from the coast of Asia into the central Pacific. As the cyclone amplifies, it slows down in the central Pacific and becomes nearly stationary within a day of onset. Following onset, at 500 hPa, a stationary wave pattern, resembling the Pacific–North American teleconnection pattern, emerges with a ridge immediately downstream (over western North America) and a trough farther downstream (from the southeast coast of the United States into the western North Atlantic). The implications for the resulting sensible weather and predictability of the flow are discussed. An adjoint-derived sensitivity study was conducted for one of the KP1 cases identified in the climatology. The results provide dynamical confirmation of the LSC precursor identification for the events. The upper-tropospheric precursor is seen to play a key role not only in the onset of the lower-tropospheric height falls and concomitant circulation increases, but also in the eastward extension of the polar jet across the Pacific. The evolution of the forecast sensitivities suggest that LSC events are not a manifestation of a modal instability of the time mean flow, but rather the growth of a favorably configured perturbation on the flow.

scholarly journals Role of Low-Frequency Wind Variability in Inducing WWBs during the onset of super El Niños

2021 ◽  
Author(s):  
Yi-Kai Wu ◽  
Chi-Cherng Hong ◽  
Tim Li ◽  
An-Yi Huang
Keyword(s):  
El Niño ◽  
North Pacific ◽  
El Nino ◽  
Low Frequency ◽  
Wind Fields ◽  
Wind Variability ◽  
The Pacific ◽  
Sst Anomaly ◽  
Wind Bursts

Abstract In this study, the effect of multiple timescale wind fields on the westerly wind bursts (WWBs) was investigated during the onset of super (1982, 1997, and 2015) and moderate El Niño events. The results revealed that extreme WWBs during the onset of the super El Niño group were attributed to low-frequency westerly (≥90 days, LFW), medium-frequency westerly (20–90 days, MFW, or intraseasonal) and high-frequency westerly (≤10 days, HFW) components, accounting for approximately 51%, 33% and 16%, respectively. Thus, the extreme WWBs during the onset of super El Niños were primarily contributed by LFWs and MFWs. By contrast, the WWBs during the onset of moderate El Niños were determined primarily by MFWs (38%) and HFWs (35%), whereas the LFW contribution is relatively small (27%). A further analysis indicated that LFWs during the onset of the super El Niños were primarily a response to a positive SST anomaly in the tropical to eastern North Pacific resembling the Pacific Meridional Mode (PMM), which had persisted during the preceding 9–12 months in the extratropical eastern North Pacific. A significant lagged correlation between the tropical and extratropical North Pacific SST was identified, and their correlation has become stronger since the late 1980s. MFWs during the onset of the super El Niños were primarily associated with the Madden-Julian Oscillation.

Different Impacts of Northern, Tropical, and Southern Volcanic Eruptions on the Tropical Pacific SST in the Last Millennium

2018 ◽  
Vol 31 (17) ◽  
pp. 6729-6744 ◽  
Author(s):  
Meng Zuo ◽  
Wenmin Man ◽  
Tianjun Zhou ◽  
Zhun Guo
Keyword(s):  
El Niño ◽  
El Nino ◽  
Volcanic Eruptions ◽  
Enso Cycle ◽  
Last Millennium ◽  
Westerly Wind ◽  
Central Pacific ◽  
The Pacific ◽  
Sst Anomaly ◽  
The Impact

The impact of northern, tropical, and southern volcanic eruptions on the Pacific sea surface temperature (SST) and the different response mechanisms arising due to differences in the volcanic forcing structure are investigated using the Community Earth System Model Last Millennium Ensemble (CESM-LME). Analysis of the simulations indicates that the Pacific features a significant El Niño–like SST anomaly 5–10 months after northern and tropical eruptions, and with a weaker such tendency after southern eruptions, possibly reflective of the weaker magnitude of these eruptions. The Niño-3 index peaks with a lag of one and a half years after northern and tropical eruptions. Two years after all three types of volcanic eruptions, a La Niña–like SST anomaly pattern over the equatorial Pacific is observed, which seems to form an El Niño–Southern Oscillation (ENSO) cycle. The westerly wind anomaly over the western to central Pacific plays an essential role in favoring the development of an El Niño following all three types of eruptions. Thus, the key point of the question is to find the causes of the westerly wind enhancement. The shift of the intertropical convergence zone (ITCZ) can explain the El Niño–like response to northern eruptions, which is not applicable for tropical or southern eruptions. The ocean dynamical thermostat mechanism is the fundamental cause of the anomalous westerly wind for all three types of eruptions.

scholarly journals Recent increase in the occurrences of Christmas typhoons in the Western North Pacific

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Joseph Basconcillo ◽  
Il-Ju Moon
Keyword(s):  
North Pacific ◽  
Western North Pacific ◽  
Large Scale ◽  
Relative Vorticity ◽  
Central Pacific ◽  
Active Season ◽  
Recent Increase ◽  
The Pacific ◽  
Poleward Shift ◽  
Research Gap

AbstractTo imply the gravity of their impact on Christmas celebration, the term Christmas typhoon recently became more popular to refer to tropical cyclones (TC) in the Western North Pacific (WNP) during its less active season. The past 9 years from 2012 to 2020 saw more than 70% (210%) increases in Christmas typhoon occurrences in the WNP (Philippines). Furthermore, Mindanao Island, which is located in southern Philippines, has experienced an unprecedented 480% increase in TC passage in the same period. Here we show that the detected recent increase in Christmas typhoons are mainly associated with the shift of the Pacific Decadal Oscillation to its positive phase in early 2010s, which led to favorable changes in the large-scale environment for TC development such as higher relative vorticity, anomalous low-level westerlies, warmer sea surface temperatures in the central Pacific, and extended WNP subtropical high. We also found that the poleward shift of the Intertropical Convergence Zone and possibly, the recent recovery of the Siberian High contributed to such increased occurrences. As opposed to the more active TC season, there is a wide research gap during the less active season. We aim to fill in this knowledge gap to gain better insights on TC risk reduction.

Troposphere-Stratosphere Coupling In S2S Models and Its Importance for a Realistic Extratropical Response to the Madden-Julian Oscillation

2020 ◽  
Author(s):  
Chen Schwartz ◽  
Chaim Garfinkel
Keyword(s):  
North Atlantic ◽  
North Pacific ◽  
Madden Julian Oscillation ◽  
Central Pacific ◽  
The West ◽  
The North ◽  
The Pacific ◽  
The North Atlantic ◽  
European Sector ◽  
The North Pacific

<p>The representation of upward and downward stratosphere-troposphere coupling and its influence on the teleconnections of the Madden Julian oscillation (MJO) to the European sector is examined in five subseasonal-to-seasonal (S2S) models. We show that while the models simulate a realistic stratospheric response to transient anomalies in troposphere, they overestimate the downward coupling. The models with a better stratospheric resolution capture a more realistic stratospheric response to the MJO, particularly after the first week of the integration. However, in all models examined here the connection between the MJO and vortex variability is weaker than that observed. Finally, we focus on the MJO-SSW teleconnection in the NCEP model, and specifically initializations during the MJO phase with enhanced convection in the west/central pacific (i.e. 6 and 7) that preceded observed SSW. The integrations that simulated a SSW (as observed) can be distinguished from those that failed to simulate a SSW by the realism of the Pacific response to MJO 6/7, with only the simulations that successfully simulate a SSW capturing the North Pacific low. Furthermore, only the simulations that capture the SSW, subsequently simulate a realistic surface response over the North Atlantic and Europe.</p>

scholarly journals Recent Strengthening of the Relationship between the Western North Pacific Monsoon and Western North Pacific Tropical Cyclone Activity during the Boreal Summer

2019 ◽  
Vol 32 (23) ◽  
pp. 8283-8299 ◽  
Author(s):  
Haikun Zhao ◽  
Shaohua Chen ◽  
Philip J. Klotzbach
Keyword(s):  
Tropical Cyclone ◽  
North Pacific ◽  
Western North Pacific ◽  
Southern Oscillation ◽  
Phase Relationship ◽  
Boreal Summer ◽  
Central Pacific ◽  
Enso Events ◽  
The Pacific ◽  
Phase Out

Abstract This study examines the association between the western North Pacific (WNP) summer monsoon (WNPSM) and WNP tropical cyclone (TC) frequency during June–August from 1979 to 2016. The interannual relationship between the WNPSM and the total number of WNP TCs has strengthened since 1998. There has also been a significant reduction in the number of TCs forming within the WNP monsoon trough (WNPMT)—hereafter called ITCs, for internal or inside TCs—since 1998. These two important features are found to be closely associated with the climate regime shift that occurred around 1998. During 1998–2016, the Pacific decadal oscillation (PDO) tended to be in a cold phase, with an increasing occurrence of central Pacific–type El Niño–Southern Oscillation (ENSO) events, whereas the 1979–97 period tended to be characterized by a warm phase of the PDO and east Pacific–type ENSO events. During 1998–2016, the tropical Pacific was characterized by enhanced easterlies, which led to a westward-retreated WNPMT that caused a significant decrease in ITCs over the WNP basin. However, there was little change in TCs outside of the WNPMT region (hereafter called OTCs) compared to that before 1998. A significant in-phase (out-of-phase) relationship between the WNPSM and the number of ITCs (OTCs) is observed before 1998, thus greatly weakening the WNPSM–TC relationship. The recent enhanced relationship between the WNPSM and TCs is mainly due to a strong in-phase relationship between the WNPSM and ITCs. The interannual change in ITCs is mainly controlled by WNPSM changes since 1998, while OTC changes are mainly modulated by changes in the tropical upper-tropospheric trough.

scholarly journals Interdecadal Variations in Extreme High–Temperature Events over Southern China in the Early 2000s and the Influence of the Pacific Decadal Oscillation

Atmosphere ◽  
2020 ◽  
Vol 11 (8) ◽  
pp. 829
Author(s):  
Baoyan Zhu ◽  
Bo Sun ◽  
Hua Li ◽  
Huijun Wang
Keyword(s):  
Water Vapor ◽  
High Temperature ◽  
Pacific Decadal Oscillation ◽  
Southern China ◽  
Walker Circulation ◽  
Interdecadal Variation ◽  
Water Vapor Content ◽  
Negative Phase ◽  
The Pacific ◽  
Extreme High Temperature

This study documents a sudden interdecadal variation in the frequency of extreme high–temperature events (FEHE) over southern China during summer in the early 2000s, which is characterized by a relatively small (large) FEHE during 1991–2000 (2003–2018). The composite analysis on the extreme high–temperature events (EHEs) over southern China indicates that the occurrence of EHEs is mainly influenced by increased downward surface net shortwave radiation, which is induced by the cloud–forced radiation anomalies associated with reduced cloud; the reduced cloud is attributed to anomalous descent motion and decreased water vapor content in the troposphere. Compared to the situation during 1991–2000, anomalous descent motion and decreased atmospheric water vapor content occurred over southern China in summer during 2003–2018, providing a more favorable climatic condition for EHEs. This interdecadal variation is associated with the strengthened Pacific Walker circulation after 2003. The Pacific decadal oscillation (PDO) is suggested to be an important driver for the above interdecadal variation, which shifted from a positive phase towards a negative phase after 2003. Numerical experiments demonstrate that a negative phase of PDO may induce a strengthened Walker circulation and anomalous atmospheric descent motion as well as water vapor divergence over Southern China.

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