scholarly journals Dominant Mode of Climate Variability, Intermodel Diversity, and Projected Future Changes over the Summertime Western North Pacific Simulated in the CMIP3 Models

2011 ◽  
Vol 24 (15) ◽  
pp. 3935-3955 ◽  
Author(s):  
Yu Kosaka ◽  
Hisashi Nakamura
Keyword(s):  
North Pacific ◽  
Western North Pacific ◽  
Low Frequency ◽  
Coupled Model ◽  
Lower Troposphere ◽  
The Philippines ◽  
Dominant Mode ◽  
Intergovernmental Panel ◽  
Projected Change ◽  
Mean State

Abstract A set of multimodel twentieth-century climate simulations for phase 3 of the Coupled Model Intercomparison Project (CMIP3) is analyzed to assess the model reproducibility of the Pacific–Japan (PJ) teleconnection pattern. It is the dominant low-frequency anomaly pattern over the summertime western North Pacific (WNP), characterized by a meridional dipole of zonally elongated vorticity anomalies in the lower troposphere and by anomalous precipitation over the tropical WNP. Most of the models can reproduce the PJ pattern reasonably well as one of the leading anomaly patterns or their combination. The model reproducibility of the pattern tends to be higher for those models in which the climatological-mean state over the WNP is better reproduced. Furthermore, intermodel diversity in the summertime climatological-mean fields over the WNP, especially in the lower troposphere, is found to be large and projected most strongly onto the observed PJ pattern. Nevertheless, the multimodel ensemble (MME) mean of these climatological-mean states is close to the observations. Projected future changes in the summertime climatological-mean state under the Intergovernmental Panel on Climate Change’s (IPCC) Special Report on Emission Scenarios (SRES) A1B also bear certain similarities with the PJ pattern, in a manner consistent with the aforementioned sensitivity of the model climate to that pattern. The MME projection indicates an overall increase in precipitation over the entire tropics, but it is overwhelmed locally by the effects of the enhanced tropospheric stratification over the tropical WNP. A resultant local reduction of the mean ascent is dynamically consistent with the anticyclonic projection around the Philippines and the cyclonic projection around Japan in MME, as in the observed anomalous dipole associated with the PJ pattern. However, the polarity and magnitude of the PJ-like projected change vary substantially from one model to another.

scholarly journals Can a Regional Ocean–Atmosphere Coupled Model Improve the Simulation of the Interannual Variability of the Western North Pacific Summer Monsoon?

2013 ◽  
Vol 26 (7) ◽  
pp. 2353-2367 ◽  
Author(s):  
Liwei Zou ◽  
Tianjun Zhou
Keyword(s):  
Interannual Variability ◽  
North Pacific ◽  
Western North Pacific ◽  
Coupled Model ◽  
The Philippines ◽  
Ocean Model ◽  
Land System ◽  
Anomalous Anticyclone ◽  
Ocean Atmosphere ◽  
Sst Anomalies

Abstract A flexible regional ocean–atmosphere–land system coupled model [Flexible Regional Ocean Atmosphere Land System (FROALS)] was developed through the Ocean Atmosphere Sea Ice Soil, version 3 (OASIS3), coupler to improve the simulation of the interannual variability of the western North Pacific summer monsoon (WNPSM). The regionally coupled model consists of a regional atmospheric model, the Regional Climate Model, version 3 (RegCM3), and a global climate ocean model, the National Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics (LASG)/Institute of Atmospheric Physics (IAP) Climate Ocean Model (LICOM). The impacts of local air–sea interaction on the simulation of the interannual variability of the WNPSM are investigated through regionally ocean–atmosphere coupled and uncoupled simulations, with a focus on El Niño’s decaying summer. Compared with the uncoupled simulation, the regionally coupled simulation exhibits improvements in both the climatology and the interannual variability of rainfall over the WNP. In El Niño’s decaying summer, the WNP is dominated by an anomalous anticyclone, less rainfall, and enhanced subsidence, which lead to increases in the downward shortwave radiation flux, thereby warming sea surface temperature (SST) anomalies. Thus, the ocean appears as a slave to atmospheric forcing. In the uncoupled simulation, however, the atmosphere is a slave to oceanic SST forcing, with the warm SST anomalies located east of the Philippines unrealistically producing excessive rainfall. In the regionally coupled run, the unrealistic positive rainfall anomalies and the associated atmospheric circulations east of the Philippines are significantly improved, highlighting the importance of air–sea coupling in the simulation of the interannual variability of the WNPSM. One limitation of the model is that the anomalous anticyclone over the WNP is weaker than the observations in both the regionally coupled and the uncoupled simulations. This results from the weaker simulated climatological summer rainfall intensity over the monsoon trough.

scholarly journals Tropical Cyclone Footprints in Long-Term Mean State and Multiscale Climate Variability in the Western North Pacific as Seen in the JRA-55 Reanalysis

2021 ◽  
pp. 1-46
Author(s):  
Sho Arakane ◽  
Huang-Hsiung Hsu
Keyword(s):  
Climate Variability ◽  
North Pacific ◽  
Western North Pacific ◽  
Large Scale ◽  
Lower Troposphere ◽  
Monsoon Trough ◽  
Climate Projections ◽  
Anticyclonic Circulation ◽  
Mean State

AbstractThe monsoon trough and subtropical high have long been acknowledged to exert a substantial modulating effect on the genesis and development of TCs in the western North Pacific (WNP). However, the potential upscaling effect of TCs on large-scale circulation remains poorly understood. This study revealed the considerable contributions of TCs to the climate mean state and variability in the WNP between 1958 and 2019, characterized by a strengthened monsoon trough and weakened subtropical anticyclonic circulation in the lower troposphere, enhanced anticyclonic circulation in the upper troposphere, and warming throughout the troposphere. TCs constituted distinct footprints in the long-term mean states of the WNP summer monsoon, and their contributions increased intraseasonal and interannual variance by 50%–70%. The interdecadal variations and long-term trends in intraseasonal variance were mainly due to the year-to-year fluctuations in TC activity. The size of TC footprints was positively correlated with the magnitude of TC activity.Our findings suggest that the full understanding of climate variability and changes cannot be achieved simply on the basis of low-frequency, large-scale circulations. Rather, TCs must be regarded as a crucial component in the climate system, and their interactions with large-scale circulations require thorough exploration. The long-term dataset created in this study provides an opportunity to study the interaction between TCs and TC-free large-scale circulations to advance our understanding of climate variability in the WNP. Our findings also indicate that realistic climate projections must involve the accurate simulations of TCs.

scholarly journals Past and Projected Changes in Western North Pacific Tropical Cyclone Exposure

2016 ◽  
Vol 29 (16) ◽  
pp. 5725-5739 ◽  
Author(s):  
James P. Kossin ◽  
Kerry A. Emanuel ◽  
Suzana J. Camargo
Keyword(s):  
North Pacific ◽  
Western North Pacific ◽  
Southern China ◽  
Numerical Models ◽  
North Pacific Ocean ◽  
Eastern China ◽  
Coupled Model ◽  
The Philippines ◽  
Ryukyu Islands ◽  
The Past

Abstract The average latitude where tropical cyclones (TCs) reach their peak intensity has been observed to be shifting poleward in some regions over the past 30 years, apparently in concert with the independently observed expansion of the tropical belt. This poleward migration is particularly well observed and robust in the western North Pacific Ocean (WNP). Such a migration is expected to cause systematic changes, both increases and decreases, in regional hazard exposure and risk, particularly if it persists through the present century. Here, it is shown that the past poleward migration in the WNP has coincided with decreased TC exposure in the region of the Philippine and South China Seas, including the Marianas, the Philippines, Vietnam, and southern China, and increased exposure in the region of the East China Sea, including Japan and its Ryukyu Islands, the Korea Peninsula, and parts of eastern China. Additionally, it is shown that projections of WNP TCs simulated by, and downscaled from, an ensemble of numerical models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) demonstrate a continuing poleward migration into the present century following the emissions projections of the representative concentration pathway 8.5 (RCP8.5). The projected migration causes a shift in regional TC exposure that is very similar in pattern and relative amplitude to the past observed shift. In terms of regional differences in vulnerability and resilience based on past TC exposure, the potential ramifications of these future changes are significant. Questions of attribution for the changes are discussed in terms of tropical belt expansion and Pacific decadal sea surface temperature variability.

scholarly journals Factors of boreal summer latent heat flux variations over the tropical western North Pacific

2021 ◽  
Author(s):  
Yuqi Wang ◽  
Renguang Wu
Keyword(s):  
Heat Flux ◽  
Wind Speed ◽  
North Pacific ◽  
High Frequency ◽  
Western North Pacific ◽  
Surface Wind ◽  
Low Frequency ◽  
Boreal Summer ◽  
Wind Intensity ◽  
Tropical Western North Pacific

AbstractSurface latent heat flux (LHF) is an important component in the heat exchange between the ocean and atmosphere over the tropical western North Pacific (WNP). The present study investigates the factors of seasonal mean LHF variations in boreal summer over the tropical WNP. Seasonal mean LHF is separated into two parts that are associated with low-frequency (> 90-day) and high-frequency (≤ 90-day) atmospheric variability, respectively. It is shown that low-frequency LHF variations are attributed to low-frequency surface wind and sea-air humidity difference, whereas high-frequency LHF variations are associated with both low-frequency surface wind speed and high-frequency wind intensity. A series of conceptual cases are constructed using different combinations of low- and high-frequency winds to inspect the respective effects of low-frequency wind and high-frequency wind amplitude to seasonal mean LHF variations. It is illustrated that high-frequency wind fluctuations contribute to seasonal high-frequency LHF only when their intensity exceeds the low-frequency wind speed under which there is seasonal accumulation of high-frequency LHF. When high-frequency wind intensity is smaller than the low-frequency wind speed, seasonal mean high-frequency LHF is negligible. Total seasonal mean LHF anomalies depend on relative contributions of low- and high-frequency atmospheric variations and have weak interannual variance over the tropical WNP due to cancellation of low- and high-frequency LHF anomalies.

scholarly journals Tropical Cyclogenesis in the Western North Pacific as Revealed by the 2008–09 YOTC Data*

2013 ◽  
Vol 28 (4) ◽  
pp. 1038-1056 ◽  
Author(s):  
Yamei Xu ◽  
Tim Li ◽  
Melinda Peng
Keyword(s):  
Rossby Wave ◽  
Wave Energy ◽  
North Pacific ◽  
Western North Pacific ◽  
Large Scale ◽  
Lower Troposphere ◽  
Energy Dispersion ◽  
Reanalysis Dataset ◽  
Initial Development ◽  
Wave Trains

Abstract The Year of Tropical Convection (YOTC) high-resolution global reanalysis dataset was analyzed to reveal precursor synoptic-scale disturbances related to tropical cyclone (TC) genesis in the western North Pacific (WNP) during the 2008–09 typhoon seasons. A time filtering is applied to the data to isolate synoptic (3–10 day), quasi-biweekly (10–20 day), and intraseasonal (20–90 day) time-scale components. The results show that four types of precursor synoptic disturbances associated with TC genesis can be identified in the YOTC data. They are 1) Rossby wave trains associated with preexisting TC energy dispersion (TCED) (24%), 2) synoptic wave trains (SWTs) unrelated to TCED (32%), 3) easterly waves (EWs) (16%), and 4) a combination of either TCED-EW or SWT-EW (24%). The percentage of identifiable genesis events is higher than has been found in previous analyses. Most of the genesis events occurred when atmospheric quasi-biweekly and intraseasonal oscillations are in an active phase, suggesting a large-scale control of low-frequency oscillations on TC formation in the WNP. For genesis events associated with SWT and EW, maximum vorticity was confined in the lower troposphere. During the formation of Jangmi (2008), maximum Rossby wave energy dispersion appeared in the middle troposphere. This differs from other TCED cases in which energy dispersion is strongest at low level. As a result, the midlevel vortex from Rossby wave energy dispersion grew faster during the initial development stage of Jangmi.

scholarly journals Weakened Anomalous Western North Pacific Anticyclone during an El Niño–Decaying Summer under a Warmer Climate: Dominant Role of the Weakened Impact of the Tropical Indian Ocean on the Atmosphere

2018 ◽  
Vol 32 (1) ◽  
pp. 213-230 ◽  
Author(s):  
Chao He ◽  
Tianjun Zhou ◽  
Tim Li
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
North Pacific ◽  
Western North Pacific ◽  
El Nino ◽  
Tropical Indian Ocean ◽  
Tropospheric Temperature ◽  
Coupled Models ◽  
Subtropical Anticyclone ◽  
Mean State

Abstract The western North Pacific subtropical anticyclone (WNPAC) is the most prominent atmospheric circulation anomaly over the subtropical Northern Hemisphere during the decaying summer of an El Niño event. Based on a comparison between the RCP8.5 and the historical experiments of 30 coupled models from the CMIP5, we show evidence that the anomalous WNPAC during the El Niño–decaying summer is weaker in a warmer climate although the amplitude of the El Niño remains generally unchanged. The weakened impact of the sea surface temperature anomaly (SSTA) over the tropical Indian Ocean (TIO) on the atmosphere is essential for the weakened anomalous WNPAC. In a warmer climate, the warm tropospheric temperature (TT) anomaly in the tropical free troposphere stimulated by the El Niño–related SSTA is enhanced through stronger moist adiabatic adjustment in a warmer mean state, even if the SSTA of El Niño is unchanged. But the amplitude of the warm SSTA over TIO remains generally unchanged in an El Niño–decaying summer, the static stability of the boundary layer over TIO is increased, and the positive rainfall anomaly over TIO is weakened. As a result, the warm Kelvin wave emanating from TIO is weakened because of a weaker latent heating anomaly over TIO, which is responsible for the weakened WNPAC anomaly. Numerical experiments support the weakened sensitivity of precipitation anomaly over TIO to local SSTA under an increase of mean-state SST and its essential role in the weakened anomalous WNPAC, independent of any change in the SSTA.

scholarly journals Mass Footprints of the North Pacific Atmospheric Blocking Highs

2015 ◽  
Vol 28 (12) ◽  
pp. 4941-4949 ◽  
Author(s):  
Tae-Won Park ◽  
Yi Deng ◽  
Wenhong Li ◽  
Song Yang ◽  
Ming Cai
Keyword(s):  
Mass Loss ◽  
North Pacific ◽  
Three Dimensional ◽  
Low Frequency ◽  
Lower Troposphere ◽  
Decay Stage ◽  
The North ◽  
Detection And Attribution ◽  
Blocking High ◽  
The North Pacific

Abstract The mass footprints associated with atmospheric blocks over the North Pacific are evaluated by constructing daily tendencies of total mass over the blocking domain from three-dimensional mass fluxes throughout the life cycle of a composite blocking event. The results highlight the major role of mass convergence driven by low-frequency (with periods >1 week) atmospheric disturbances during both the development and decay stage of a block. Specifically, low-frequency eddies are responsible for the accelerated mass buildup 4 days prior to the peak intensity of a block, and they also account for the rapid mass loss afterward. High-frequency, subweekly scale disturbances have statistically significant positive contributions to the mass loss during the decay stage, and also show weak negative contributions to the development of the blocking high prior to the peak of the high. The majority of the mass convergence (divergence) responsible for the intensification (decay) of the blocking high occurs in the middle-to-lower troposphere and is largely attributed to mass flux driven by low-frequency meridional (zonal) winds. Also discussed are the implications of this new mass perspective of atmospheric blocks for understanding dynamics of blocking highs and for model bias detection and attribution.

Interdecadal variation of the wintertime precipitation in Southeast Asia and its possible causes

2021 ◽  
pp. 1-58
Author(s):  
Zizhen Dong ◽  
Lin Wang ◽  
Peiqiang Xu ◽  
Sittichai Pimonsree ◽  
Atsamon Limsakul ◽  
...  
Keyword(s):  
Sea Ice ◽  
Coupled Model ◽  
Walker Circulation ◽  
The Philippines ◽  
Dominant Mode ◽  
Arctic Sea Ice ◽  
Maritime Continent ◽  
Asian Winter Monsoon ◽  
Arctic Sea ◽  
The One

AbstractBased on several observational and reanalysis datasets for the winters 1901-2017, this study investigates the interdecadal (ID) variation of the Southeast Asian rainfall (SEAR) and its potential drivers. The dominant mode of the wintertime SEAR on the ID timescale features enhanced precipitation over the eastern Maritime Continent and the Philippines and a slight decrease of precipitation over the western Maritime Continent, or the opposite sign. The ID SEAR variability peaks at the 8-16-year period and explains more than 20% of the total variance regardless of the datasets and period considered, highlighting the importance of the ID variability of the SEAR. The atmospheric circulation that facilitates abundant ID SEAR is characterized by enhanced lower-tropospheric wind convergence and cyclonic anomalies over the South China Sea and the Philippines. On the one hand, this wind convergence is attributed to the enhanced Walker circulation induced by the negative phase of the Interdecadal Pacific Oscillation (IPO). On the other hand, it is attributed to the enhanced northerly anomalies along the coast of East Asia induced by strong East Asian winter monsoon (EAWM) and reduced autumn Arctic sea ice in the Barents-Kara Sea. These mechanisms are further confirmed by model experiments from the Coupled Model Intercomparison Project Phase 5. The effects of the IPO, EAWM, and Arctic sea ice on the SEAR are mostly independent. They together explain approximately 70% of the SEAR variance on the ID timescale.

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.

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