scholarly journals El Niño Impacts on Precipitation in the Western North Pacific–East Asian Sector

2009 ◽  
Vol 22 (8) ◽  
pp. 2039-2057 ◽  
Author(s):  
Chia Chou ◽  
Li-Fan Huang ◽  
Jien-Yi Tu ◽  
Lishan Tseng ◽  
Yu-Chieh Hsueh
Keyword(s):  
Wind Speed ◽  
El Niño ◽  
Western North Pacific ◽  
El Nino ◽  
Rainy Period ◽  
Rainfall Anomalies ◽  
Precipitation Anomalies ◽  
The Mean ◽  
Peak Phase ◽  
Mean State

Abstract In this study, the western North Pacific–East Asian (WNP–EA) rainfall anomaly induced by the strong El Niño in 1982–83, 1991–92, and 1997–98, and its association with the mean state, are examined. Over the northern part of the WNP–EA region (north of 20°N), which is dominated by southwest–northeast tilting frontal systems, positive rainfall anomalies from the fall before the El Niño peak phase (year 0) to the first wet period after the peak phase (year 1) are affected by low- and midlevel horizontal moisture convergence anomalies induced by low-level anticyclonic circulation anomalies over the WNP region that are associated with El Niño. Over the southern part of the WNP–EA region (south of 20°N), which is dominated by tropical convection, positive precipitation anomalies in the first and second wet periods of year 0 and negative precipitation anomalies from the fall of year 0 to the second wet period of year 1 are associated with the variation of the net energy into the atmosphere, which is mainly contributed to by local evaporation anomalies. The mechanisms for inducing the precipitation anomalies over both northern and southern parts of the WNP–EA region are similar to the mechanisms of the mean precipitation in each rainy period, but the detailed processes for the southern WNP–EA precipitation anomalies are more complicated, particularly in summer. In the first wet periods of years 0 and 1 and the fall of year 0, the precipitation anomalies are induced by evaporation anomalies that are contributed to by similar effects of sea surface temperature (SST) and wind speed anomalies. In the second wet period of years 0 and 1, on the other hand, near-surface wind speed anomalies affect precipitation via the process of evaporation. These wind speed anomalies are associated with the concurrence of the low-level circulation anomalies over the WNP region and the Asian summer monsoon trough. The SST anomalies are merely a response to evaporation and downward solar radiation anomalies. The dependence of the rainfall anomalies on the mean state, that is, similar causes for the rainfall mean and anomalies in each rainy period, implies that the mean state plays a key role in simulating the interannual variation over the WNP–EA region.

scholarly journals Impact of the mean state on El Niño induced western North Pacific anomalous anticyclone during its decaying summer in AMIP models

2021 ◽  
pp. 1-49
Author(s):  
Xieyuan Wang ◽  
Tim Li ◽  
Chao He
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
North Pacific ◽  
Western North Pacific ◽  
El Nino ◽  
Tropical Indian Ocean ◽  
Cp El Niño ◽  
Anomalous Anticyclone ◽  
The Mean ◽  
Mean State

AbstractThrough the diagnosis of 29 Atmospheric Model Inter-comparison Project (AMIP) experiments from the CMIP5 inter-comparison project, we investigate the impact of the mean state on simulated western North Pacific anomalous anticyclone (WNPAC) during El Niño decaying summer. The result indicates that the inter-model difference of the JJA mean precipitation in the Indo-western Pacific warm pool is responsible for the difference of the WNPAC. During the decaying summer of an Eastern Pacific (EP) type El Niño, a model that simulates excessive mean rainfall over the western North Pacific (WNP) reproduces a stronger WNPAC response, through an enhanced local convection-circulation-moisture feedback. The intensity of the simulated WNPAC during the decay summer of a Central Pacific (CP) type El Niño, on the other hand, depends on the mean precipitation over the tropical Indian Ocean. The distinctive WNPAC-mean precipitation relationships between the EP and CP El Niño result from different anomalous SST patterns in the WNP. While the local SST anomaly plays an active role in maintaining the WNPAC during the EP El Niño, it plays a passive role during the CP El Niño. As a result, only the mean-state precipitation/moisture field in the tropical Indian Ocean modulates the circulation anomaly in the WNP in the latter case.

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 Winter 2015/16 Atmospheric and Precipitation Anomalies over North America: El Niño Response and the Role of Noise

2018 ◽  
Vol 146 (3) ◽  
pp. 909-927 ◽  
Author(s):  
Mingyue Chen ◽  
Arun Kumar
Keyword(s):  
North America ◽  
El Niño ◽  
El Nino ◽  
Internal Variability ◽  
Precipitation Response ◽  
Sst Forcing ◽  
Precipitation Anomalies ◽  
The Mean ◽  
The U.S

Abstract The possible causes for the observed winter 2015/16 precipitation anomalies, which were opposite to the mean El Niño signal over the U.S. Southwest, are analyzed based on the ensemble of forecasts from the NCEP Climate Forecast System, version 2 (CFSv2). The analysis focuses on the role of anomalous sea surface temperature (SST) forcing and the contributions of atmospheric internal variability. The model-predicted ensemble mean forecast for December–January–February 2015/16 (DJF 2015/16) North American atmospheric anomalies compared favorably with the El Niño composite, although some difference existed. The predicted pattern was also like that in the previous strong El Niño events of 1982/83 and 1997/98. Therefore, the model largely predicted the teleconnection and precipitation response pattern in DJF 2015/16 like the mean El Niño signal. The observed negative precipitation anomalies over the U.S. Southwest in DJF 2015/16 were not consistent either with the observed or with the model-predicted El Niño composite. Analysis of the member-to-member variability in the ensemble of forecast anomalies allowed quantification of the contribution of atmospheric internal variability in shaping seasonal mean anomalies. There were considerable variations in the outcome of DJF 2015/16 precipitation over North America from one forecast to another even though the predicted SSTs were nearly identical. The observed DJF 2015/16 precipitation anomalies were well within the envelope of possible forecast outcomes. Therefore, the atmospheric internal variability could have played a considerable role in determining the observed DJF 2015/16 negative precipitation anomalies over the U.S. Southwest, and its role is discussed in the context of differences in response.

scholarly journals Regional impacts of ocean color on tropical Pacific variability

2009 ◽  
Vol 6 (1) ◽  
pp. 243-275 ◽  
Author(s):  
W. Anderson ◽  
A. Gnanadesikan ◽  
A. Wittenberg
Keyword(s):  
El Niño ◽  
El Nino ◽  
Pure Water ◽  
Ocean Color ◽  
Tropical Pacific ◽  
Shortwave Radiation ◽  
Penetration Length ◽  
The Mean ◽  
Mean State ◽  
The Tropical Pacific

Abstract. The role of the penetration length scale of shortwave radiation into the surface ocean and its impact on tropical Pacific variability is investigated with a fully coupled ocean, atmosphere, land and ice model. Previous work has shown that removal of all ocean color results in a system that tends strongly towards an El Niño state. Results from a suite of surface chlorophyll perturbation experiments show that the mean state and variability of the tropical Pacific is highly sensitive to the concentration and distribution of ocean chlorophyll. Setting the near-oligotrophic regions to contain optically pure water warms the mean state and suppresses variability in the western tropical Pacific. Doing the same above the shadow zones of the tropical Pacific also warms the mean state but enhances the variability. It is shown that increasing penetration can both deepen the pycnocline (which tends to damp El Niño) while shifting the mean circulation so that the wind response to temperature changes is altered. Depending on what region is involved this change in the wind stress can either strengthen or weaken ENSO variability.

scholarly journals Interdecadal Relationship between the Mean State and El Niño Types*

2013 ◽  
Vol 26 (2) ◽  
pp. 361-379 ◽  
Author(s):  
Pei-Hsuan Chung ◽  
Tim Li
Keyword(s):  
El Niño ◽  
El Nino ◽  
Atmospheric Precipitation ◽  
Frequent Occurrence ◽  
Central Pacific ◽  
Cp El Niño ◽  
Budget Analysis ◽  
Ep El Niño ◽  
The Mean ◽  
Mean State

Abstract The interdecadal change of the mean state and two types of El Niño was investigated based on the analysis of observational data from 1980 to 2010. It was found that easterly trades and sea surface temperature (SST) gradients across the equatorial Pacific undergo a regime change in 1998/99, with enhanced trades and a significant cooling (warming) over tropical eastern (western) Pacific in the later period. Accompanying this mean state change is more frequent occurrence of central Pacific (CP) El Niño during 1999–2010. The diagnosis of air–sea feedback strength showed that atmospheric precipitation and wind responses to CP El Niño are greater than those to the eastern Pacific (EP) El Niño for given a unit SST anomaly (SSTA) forcing. The oceanic response to the same wind forcing, however, is greater in the EP El Niño than in the CP El Niño. A mixed layer heat budget analysis reveals that zonal advection (thermocline change induced vertical advection) primarily contributes to the CP (EP) El Niño growth. The role of the mean SST zonal gradient in El Niño selection was investigated through idealized numerical experiments. With the increase of the background zonal SST gradient, the anomalous wind and convection response to a specified EP or CP SSTA shift to the west. Such a difference results in a bifurcation of maximum SSTA tendency, as shown from a simple ocean model. The numerical results support the notion that a shift to the La Niño–like interdecadal mean state is responsible for more frequent occurrence of CP-type El Niño.

scholarly journals El Niño in a Coupled Climate Model: Sensitivity to Changes in Mean State Induced by Heat Flux and Wind Stress Corrections

2007 ◽  
Vol 20 (10) ◽  
pp. 2273-2298 ◽  
Author(s):  
Hilary Spencer ◽  
Rowan Sutton ◽  
Julia M. Slingo
Keyword(s):  
Heat Flux ◽  
Wind Stress ◽  
El Niño ◽  
General Circulation ◽  
El Nino ◽  
Seasonal Forecasts ◽  
Coupled Models ◽  
The Mean ◽  
Flux Corrections ◽  
Mean State

Abstract Here the factors affecting the mean state and El Niño variability in the Third Hadley Centre Coupled Ocean–Atmosphere General Circulation Model (HadCM3) are examined with and without heat flux or wind stress corrections. There is currently little confidence in the prediction of El Niño for seasonal forecasts or climate change due to the inaccuracies in coupled models. If heat flux or wind stress corrections could reduce these biases then forecasts might be improved. Heat flux corrections have unexpected effects on both the mean state and variability of HadCM3. HadCM3 is found to be very sensitive to the corrections imposed. If heat flux corrections are imposed Tropics wide then easterlies in the eastern equatorial Pacific are increased leading to localized steep east–west gradients in the thermocline or “thermocline jumps,” which appear to suppress propagation of heat from the west to the east and hence suppress strong El Niños so that ENSO variability is weak. In contrast, if heat flux corrections are imposed only within 10° of the equator, an atmospheric teleconnection from the cold subtropical SST biases intensifies the ITCZ and weakens the equatorial easterlies. As a result, the thermocline jumps are flattened and strong El Niños occur very frequently. Neither heat flux correction procedure improves the representation of El Niño. Wind stress corrections alone have a small impact on the coupled model. Some of the SST warm biases are reduced, but the variability is not altered significantly.

scholarly journals Regional impacts of ocean color on tropical Pacific variability

Ocean Science ◽  
2009 ◽  
Vol 5 (3) ◽  
pp. 313-327 ◽  
Author(s):  
W. Anderson ◽  
A. Gnanadesikan ◽  
A. Wittenberg
Keyword(s):  
El Niño ◽  
El Nino ◽  
Pure Water ◽  
Ocean Color ◽  
Tropical Pacific ◽  
Shortwave Radiation ◽  
Penetration Length ◽  
The Mean ◽  
Mean State ◽  
The Tropical Pacific

Abstract. The role of the penetration length scale of shortwave radiation into the surface ocean and its impact on tropical Pacific variability is investigated with a fully coupled ocean, atmosphere, land and ice model. Previous work has shown that removal of all ocean color results in a system that tends strongly towards an El Niño state. Results from a suite of surface chlorophyll perturbation experiments show that the mean state and variability of the tropical Pacific is highly sensitive to the concentration and distribution of ocean chlorophyll. Setting the near-oligotrophic regions to contain optically pure water warms the mean state and suppresses variability in the western tropical Pacific. Doing the same above the shadow zones of the tropical Pacific also warms the mean state but enhances the variability. It is shown that increasing penetration can both deepen the pycnocline (which tends to damp El Niño) while shifting the mean circulation so that the wind response to temperature changes is altered. Depending on what region is involved this change in the wind stress can either strengthen or weaken ENSO variability.

scholarly journals Asymmetric Relationship between Indian Ocean SST and the Western North Pacific Summer Monsoon

2015 ◽  
Vol 28 (4) ◽  
pp. 1383-1395 ◽  
Author(s):  
Riyu Lu ◽  
Shu Lu
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
North Pacific ◽  
Western North Pacific ◽  
El Nino ◽  
Summer Precipitation ◽  
La Niña ◽  
La Nina ◽  
Precipitation Anomalies ◽  
Sst Anomalies

Abstract The summer precipitation anomalies over the tropical western North Pacific (WNP), which greatly affect East Asian climate, are closely related to Indian Ocean (IO) SST anomalies, and this WNP–IO relationship is widely assumed to be linear. This study indicates that the IO SST–WNP precipitation relationship is generally linear only when the IO SST anomalies are positive and not when the IO SST anomalies are negative, that is, a strongly cooler IO, in comparison with a moderately cooler IO, does not correspond to stronger precipitation enhancement over the WNP. Further analysis suggests that the phases of ENSO play a crucial role in modifying the impacts of IO SSTs on WNP anomalies. The reverse IO SST–WNP precipitation relationship, which exists without apparent ENSO development/decay, is intensified by El Niño decay through the enhancement of IO SST anomalies, but weakened by El Niño development and La Niña decay through the concurrence of SST anomalies in the tropical central and eastern Pacific. After removing El Niño developing and La Niña decaying cases, the IO SST and WNP precipitation anomalies show a clear linear relationship. Because of the effects of the phases of ENSO, the years of negative precipitation or anticyclonic anomalies over the WNP are highly concentrated over strongly warmer IO and El Niño decaying years, which is consistent with previous studies. However, the years of positive precipitation anomalies are scattered over cooler IO and moderately warmer IO years, implying a complexity of tropical SST forcing on positive WNP precipitation anomalies.

scholarly journals Enlarged Asymmetry of Tropical Pacific Rainfall Anomalies Induced by El Niño and La Niña under Global Warming

2017 ◽  
Vol 30 (4) ◽  
pp. 1327-1343 ◽  
Author(s):  
Ping Huang ◽  
Dong Chen
Keyword(s):  
Global Warming ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
La Niña ◽  
Cmip5 Models ◽  
Maximum Rainfall ◽  
La Nina ◽  
Rainfall Anomalies ◽  
Mean State

Abstract El Niño–Southern Oscillation (ENSO) is one of the most important sources of climate interannual variability. A prominent characteristic of ENSO is the asymmetric, or so-called nonlinear, local rainfall response to El Niño (EN) and La Niña (LN), in which the maximum rainfall anomalies during EN are located farther east than those during LN. In this study, the changes in rainfall anomalies during EN and LN are examined based on the multimodel ensemble mean results of 32 CMIP5 models under the representative concentration pathway 8.5 (RCP8.5) scenario. It is found that robust EN–LN asymmetric changes in rainfall anomalies exist. The rainfall anomalies during EN and LN both shift eastward and intensify under global warming, but the eastward shift during EN is farther east than that during LN. A simplified moisture budget decomposition method is applied to study the mechanism of the asymmetric response. The results show that the robust increase in mean-state moisture can enlarge the EN–LN asymmetry of the rainfall anomalies, and the spatial relative changes in mean-state SST with an El Niño–like pattern can shift the rainfall anomalies farther east during EN than during LN, enlarging the difference in the zonal locations of the rainfall response to EN and LN. The role of the relative changes in mean-state SST can also be interpreted as follows: the decreased zonal gradient of mean-state SST due to El Niño–like warming leads to a larger EN–LN asymmetry of rainfall anomalies under a future warming climate.

scholarly journals Distinct Influences of the ENSO-Like and PMM-Like SST Anomalies on the Mean TC Genesis Location in the Western North Pacific: The 2015 Summer as an Extreme Example

2018 ◽  
Vol 31 (8) ◽  
pp. 3049-3059 ◽  
Author(s):  
Chi-Cherng Hong ◽  
Ming-Ying Lee ◽  
Huang-Hsiung Hsu ◽  
Wan-Ling Tseng
Keyword(s):  
El Niño ◽  
North Pacific ◽  
Western North Pacific ◽  
El Nino ◽  
Southern Oscillation ◽  
Boreal Summer ◽  
The Pacific ◽  
Sea Surface Temperature Anomalies ◽  
The Mean ◽  
East West

Abstract This study reports the different effects of tropical and subtropical sea surface temperature anomalies (SSTAs) on the mean tropical cyclone (TC) genesis location in the western North Pacific (WNP), a TC–SSTA relationship that has been largely ignored. In the Pacific, the interannual variability of the tropical SSTA in the boreal summer is characterized by an El Niño–Southern Oscillation (ENSO)-like pattern, whereas the subtropical SSTA exhibits a Pacific meridional mode (PMM)-like structure. Partial correlation analysis reveals that the ENSO-like and PMM-like SSTAs dominate the south–north and east–west shift of mean TC genesis location, respectively. The 2015/16 El Niño was a strong event comparable with the 1997/98 event in terms of Niño-3.4 SSTA. However, the mean TC genesis location in the WNP during the summer of 2015 exhibited an unprecedented eastward shift by approximately 10 longitudinal degrees relative to that in 1997. Whereas the ENSO-like SSTAs in 1997 and 2015 were approximately equal, the amplitude of the PMM-like SSTA in 2015 was approximately twice as large as that in 1997. Numerical experiments forced by the ENSO-like and PMM-like SSTAs in June–August 2015 reveal that the positive PMM-like SSTA forces an east–west overturning circulation anomaly in the subtropical North Pacific with anomalously ascending (descending) motion in the subtropical central (western) Pacific. The mean TC genesis location in the WNP therefore shifts eastward when warmer SST occurs in the subtropical eastern Pacific. This finding supports the hypothesis that the extremely positive PMM-like SSTA in the summer of 2015 caused the unprecedented eastward shift of the TC genesis location in the WNP.

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