scholarly journals Intermodel Uncertainty in the Projection of the Anomalous Western North Pacific Anticyclone Associated With El Niño Under Global Warming

2020 ◽  
Vol 47 (2) ◽  
Author(s):  
Mingna Wu ◽  
Tianjun Zhou ◽  
Xiaolong Chen ◽  
Bo Wu
Keyword(s):  
Global Warming ◽  
El Niño ◽  
North Pacific ◽  
Western North Pacific ◽  
El Nino

scholarly journals Global Warming and Western North Pacific Typhoon Activity from an Observational Perspective

2004 ◽  
Vol 17 (23) ◽  
pp. 4590-4602 ◽  
Author(s):  
Johnny C. L. Chan ◽  
Kin Sik Liu
Keyword(s):  
Global Warming ◽  
El Niño ◽  
North Pacific ◽  
Western North Pacific ◽  
Large Scale ◽  
Climate Model ◽  
El Nino ◽  
Interannual Variations ◽  
Model Simulations ◽  
Climate Model Simulations

Abstract Based on results from climate model simulations, many researchers have suggested that because of global warming, the sea surface temperature (SST) will likely increase, which will then lead to an increase in the intensity of tropical cyclones (TCs). This paper reports results of a study of the relationship between SST and observed typhoon activity (which is used as a proxy for the intensity of TCs averaged over a season) over the western North Pacific (WNP) for the past 40 yr. The average typhoon activity over a season is found to have no significant relationship with SST in the WNP but increases when the SST over the equatorial eastern Pacific Ocean is above normal. The mean annual typhoon activity is generally higher (lower) during an El Niño (La Niña) year. Such interannual variations of typhoon activity appear to be largely constrained by the large-scale atmospheric factors that are closely related to the El Niño–Southern Oscillation (ENSO) phenomenon. These large-scale dynamic and thermodynamic factors include low-level relative vorticity, vertical wind shear, and moist static energy. Such results are shown to be physically consistent with one another and with those from previous studies on the interannual variations of TC activity. The results emphasize the danger of drawing conclusions about future TC intensity based on current climate model simulations that are not designed to make such predictions.

scholarly journals Intensification of the Western North Pacific Anticyclone Response to the Short Decaying El Niño Event due to Greenhouse Warming

2016 ◽  
Vol 29 (10) ◽  
pp. 3607-3627 ◽  
Author(s):  
Wei Chen ◽  
June-Yi Lee ◽  
Kyung-Ja Ha ◽  
Kyung-Sook Yun ◽  
Riyu Lu
Keyword(s):  
Global Warming ◽  
El Niño ◽  
North Pacific ◽  
Western North Pacific ◽  
Climate Models ◽  
El Nino ◽  
Coupled Model ◽  
Precipitation Anomaly ◽  
Historical Period ◽  
Central Pacific

Abstract Two types of El Niño evolution have been identified in terms of the lengths of their decaying phases: the first type is a short decaying El Niño that terminates in the following summer after the mature phase, and the second type is a long decaying one that persists until the subsequent winter. The responses of the western North Pacific anticyclone (WNPAC) anomaly to the two types of evolution are remarkably different. Using experiments from phase 5 of the Coupled Model Intercomparison Project (CMIP5), this study investigates how well climate models reproduce the two types of El Niño evolution and their impacts on the WNPAC in the historical period (1950–2005) and how they will change in the future under anthropogenic global warming. To reduce uncertainty in future projection, the nine best models are selected based on their performance in simulating El Niño evolution. In the historical run, the nine best models’ multimodel ensemble (B9MME) well reproduces the enhanced (weakened) WNPAC that is associated with the short (long) decaying El Niño. The comparison between results of the historical run for 1950–2005 and the representative concentration pathway 4.5 run for 2050–99 reveals that individual models and the B9MME tend to project no significant changes in the two types of El Niño evolution for the latter half of the twenty-first century. However, the WNPAC response to the short decaying El Niño is considerably intensified, being associated with the enhanced negative precipitation anomaly response over the equatorial central Pacific. This enhancement is attributable to the robust increase in mean and interannual variability of precipitation over the equatorial central Pacific under global warming.

Response of western North Pacific anomalous anticyclone in the summer of decaying El Niño to global warming: Diverse projections based on CMIP6 and CMIP5 models

2021 ◽  
pp. 1-41
Author(s):  
Chao He ◽  
Zhenyuan Cui ◽  
Chunzai Wang
Keyword(s):  
Global Warming ◽  
El Niño ◽  
North Pacific ◽  
Western North Pacific ◽  
El Nino ◽  
Southern Oscillation ◽  
Tropical Indian Ocean ◽  
Cmip5 Models ◽  
Kelvin Wave ◽  
Anomalous Anticyclone

AbstractThe anomalous anticyclone over the western North Pacific (WNPAC) is a key atmospheric bridge through which El Niño-Southern Oscillation (ENSO) affects East Asian climate. In this study, the response of the anomalous WNPAC to global warming under the high-emission scenario is investigated based on 40 models from CMIP6 and 30 models from CMIP5. Despite low inter-model consensus, the multi-model median (MMM) of CMIP6 models projects an enhanced anomalous WNPAC but the MMM of CMIP5 models projects a weakened anomalous WNPAC, both of which reach about 0.5 standard deviation of the decadal internal variability derived from the pre-industrial control experiment. As consistently projected by CMIP6 and CMIP5 models, a same magnitude of sea surface temperature anomaly (SSTA) over the tropical Indian Ocean (TIO) stimulates a weaker anomalous WNPAC under a warmer climate, and this mechanism is responsible for the weakened anomalous WNPAC based on the CMIP5-MMM. However, the above mechanism is overwhelmed by another mechanism related to the changes in tropical SSTA based on the CMIP6-MMM. As a result of the enhanced warm SSTA over the TIO and the eastward shift of the warm SSTA over the equatorial Pacific during the decaying El Niño, the warm Kelvin wave emanating from the TIO is enhanced along with the stronger zonal SSTA gradient based on the CMIP6-MMM, enhancing the anomalous WNPAC. The diverse changes in the zonal SSTA gradient between the TIO and the equatorial western Pacific also explain the inter-model diversity of the changes in anomalous WNPAC.

scholarly journals The source of uncertainty in projecting the anomalous western North Pacific anticyclone during El Niño–decaying summers

2021 ◽  
pp. 1-49
Author(s):  
Mingna Wu ◽  
Tianjun Zhou ◽  
Xiaolong Chen
Keyword(s):  
Global Warming ◽  
El Niño ◽  
North Pacific ◽  
Decomposition Method ◽  
Western North Pacific ◽  
Climate Models ◽  
El Nino ◽  
East Asian ◽  
Climate Projections ◽  
Amplitude Change

AbstractThe western North Pacific anomalous anticyclone (WNPAC) is a key bridge that links El Niño and East Asian climate variability. Future projections of ENSO-related WNPAC changes under global warming are highly uncertain across climate models. Based on a 40-member ensemble from the Community Earth System Model Large Ensemble (CESM-LE) project, we investigate the effects of internal variability on the El Niño-related WNPAC projection. Here, we first develop a decomposition method to separate the contributions of El Niño amplitude change and non-amplitude change from the leading uncertainty in the El Niño-related WNPAC projection. Based on the decomposition, approximately 23% of the uncertainty in the El Niño-related WNPAC projection is attributed to the El Niño amplitude change, while the remaining 77% is from the non-amplitude change, which is mainly related to the change in the El Niño decaying pace. A larger (smaller) El Niño amplitude can enhance (weaken) the WNPAC through a stronger (weaker) tropical Indian Ocean (TIO) capacitor effect. For non-amplitude change, a faster (slower) El Niño decaying pace can also enhance (weaken) the WNPAC through descending Rossby waves in response to cold sea surface temperature anomalies (SSTA) over the tropical central-eastern Pacific. The decomposition method can be generalized to investigate the sources of uncertainty related to El Niño properties in climate projections and to help improve the understanding of changes in the interannual variability of East Asian-western Pacific climate under global warming.

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 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 Reintensification of the Anomalous Western North Pacific Anticyclone during the El Niño Modoki Decaying Summer: Relative Importance of Tropical Atlantic and Pacific SST Anomalies

2020 ◽  
Vol 33 (8) ◽  
pp. 3271-3288
Author(s):  
Juan Feng ◽  
Wen Chen ◽  
Xiaocong Wang
Keyword(s):  
El Niño ◽  
North Pacific ◽  
General Circulation ◽  
Western North Pacific ◽  
El Nino ◽  
Central Pacific ◽  
El Niño Modoki ◽  
Sst Cooling ◽  
Sst Warming ◽  
Sst Anomalies

AbstractThe El Niño Modoki–induced anomalous western North Pacific anticyclone (WNPAC) undergoes an interesting reintensification process in the El Niño Modoki decaying summer, the period when El Niño Modoki decays but warm sea surface temperature (SST) anomalies over the tropical North Atlantic (TNA) and cold SST anomalies over the central-eastern Pacific (CEP) dominate. In this study, the region (TNA or CEP) in which the SST anomalies exert a relatively important influence on reintensification of the WNPAC is investigated. Observational analysis demonstrates that when only anomalous CEP SST cooling occurs, the WNPAC experiences a weak reintensification. In contrast, when only anomalous TNA SST warming emerges, the WNPAC experiences a remarkable reintensification. Numerical simulation analysis demonstrates that even though the same magnitude of CEP SST cooling and TNA warming is respectively set to force the atmospheric general circulation model, the response of the WNPAC is still much stronger in the TNA warming experiment than in the CEP cooling experiment. Further analysis demonstrates that this difference is caused by the distinct location of the effective tropical forcing between the CEP SST cooling and TNA SST warming for producing a WNPAC. The CEP cooling-induced effective anomalous diabatic cooling is located in the central Pacific, by which the forced anticyclone becomes gradually weak from the central Pacific to the western North Pacific. Thus, a weak WNPAC is produced. In contrast, as the TNA SST warming–induced effective anomalous diabatic cooling is just located in the western North Pacific via a Kelvin wave–induced Ekman divergence process, the forced anticyclone is significant and powerful in the western North Pacific.

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