scholarly journals Inter-annual variation of chlorophyll in the northern South China Sea observed at the SEATS Station and its asymmetric responses to climate oscillation

2013 ◽  
Vol 10 (11) ◽  
pp. 7449-7462 ◽  
Author(s):  
K.-K. Liu ◽  
L.-W. Wang ◽  
M. Dai ◽  
C.-M. Tseng ◽  
Y. Yang ◽  
...  
Keyword(s):  
Time Series ◽  
Wind Speed ◽  
South China Sea ◽  
El Niño ◽  
El Nino ◽  
La Niña ◽  
Wind Forcing ◽  
Sea Surface ◽  
La Nina ◽  
Asymmetric Responses

Abstract. It is widely recognised that the variation of average surface chlorophyll a concentration (Chl) in the South China Sea (SCS) is closely related to wind forcing, especially during the intense winter monsoon. In this study, we demonstrate that after removal of the seasonal cycles, the variation of Chl showed strong asymmetric responses to wind speed under El Niño or La Niña conditions. The analysis was based on a time-series of Chl in the study area (115–117° E, 17–19° N) around the SEATS (South-East Asian Time-series Study) station located in the central northern SCS from September 1997 to the end of 2011, which was constructed by merging the SeaWiFS data (1997–2006) and MODIS data (2003–2011). The merged daily data were validated by shipboard observations at the SEATS station. The non-seasonal variations of monthly mean Chl, wind speed, sea surface height (SSH) and sea surface temperature (SST) were examined against the multivariate ENSO index (MEI). The analysis reveals strongly asymmetric correlations of Chl and SST with positive MEI (El Niño) or negative MEI (La Niña). Under El Niño conditions, both showed significant correlations with MEI or wind speed; under La Niña conditions, both showed weak or insignificant correlations. The contrast was more pronounced for Chl than for SST. The subdued responses of Chl to wind forcing under La Niña conditions were attributable to a deepened thermocline, for which wind driven nutrient pumping is less efficient. A deeper thermocline, which was observed during the 1999–2000 La Niña event and inferred by positive SSH anomalies during other La Niña events, was probably caused by reduced SCS throughflow under La Niña conditions. Intrusion of the nutrient-depleted Kuroshio water in the surface layer as observed during the 1999–2000 La Niña could be partially responsible for the suppressed Chl response.

scholarly journals Inter-annual variation of chlorophyll in the northern South China Sea observed at the SEATS Station and its asymmetric responses to climate oscillation

2013 ◽  
Vol 10 (4) ◽  
pp. 6899-6938 ◽  
Author(s):  
K.-K. Liu ◽  
L.-W. Wang ◽  
M. Dai ◽  
C.-M. Tseng ◽  
Y. Yang ◽  
...  
Keyword(s):  
Time Series ◽  
Wind Speed ◽  
South China Sea ◽  
El Niño ◽  
El Nino ◽  
La Niña ◽  
Wind Forcing ◽  
Sea Surface ◽  
La Nina ◽  
Asymmetric Responses

Abstract. It is widely recognized that the variation of average surface chlorophyll a concentration (Chl) in the South China Sea (SCS) is closely related to wind forcing, especially during the intense winter monsoon. In this study we demonstrate that, after removal of the seasonal cycles, the variation of Chl showed strong asymmetric responses to wind speed under El Niño or La Niña conditions. The analysis was based on a time-series of Chl in the study area (115–117° E, 17–19° N) around the SEATS (South-East Asian Time-series Study) station located in the central northern SCS from September 1997 to the end of 2011, which was constructed by merging the SeaWiFS data (1997–2006) and MODIS data (2003–2011). The merged daily data were validated by shipboard observations at the SEATS station. The non-seasonal variations of monthly mean Chl, wind speed, sea surface height (SSH) and sea surface temperature (SST) were examined against the multivariate ENSO index (MEI). The analysis reveals strongly asymmetric correlations of Chl and SST with positive MEI (El Niño) or negative MEI (La Niña). Under El Niño conditions, both showed significant correlations with MEI or wind speed; under La Niña conditions, both showed weak or insignificant correlations. The contrast was more pronounced for Chl than for SST. The subdued responses of Chl to wind forcing under La Niña conditions were probably attributed to a deepened thermocline, for which wind driven nutrient pumping is less efficient. A deeper thermocline, which was observed during the 1999–2000 La Niña event and inferred by positive SSH anomalies during other La Niña events, was probably caused by reduced SCS throughflow under La Niña conditions. Intrusion of the nutrient-depleted Kuroshio water in the surface layer as observed during the 1999–2000 La Niña could be partially responsible for the suppressed Chl response.

scholarly journals Improved Simulation of Tropical Cyclone Responses to ENSO in the Western North Pacific in the High-Resolution GFDL HiFLOR Coupled Climate Model*

2016 ◽  
Vol 29 (4) ◽  
pp. 1391-1415 ◽  
Author(s):  
Wei Zhang ◽  
Gabriel A. Vecchi ◽  
Hiroyuki Murakami ◽  
Thomas Delworth ◽  
Andrew T. Wittenberg ◽  
...  
Keyword(s):  
High Resolution ◽  
Tropical Cyclone ◽  
El Niño ◽  
North Pacific ◽  
Western North Pacific ◽  
El Nino ◽  
Walker Circulation ◽  
La Niña ◽  
Sea Surface ◽  
La Nina

Abstract This study aims to assess whether, and the extent to which, an increase in atmospheric resolution of the Geophysical Fluid Dynamics Laboratory (GFDL) Forecast-Oriented Low Ocean Resolution version of CM2.5 (FLOR) with 50-km resolution and the High-Resolution FLOR (HiFLOR) with 25-km resolution improves the simulation of the El Niño–Southern Oscillation (ENSO)–tropical cyclone (TC) connections in the western North Pacific (WNP). HiFLOR simulates better ENSO–TC connections in the WNP including TC track density, genesis, and landfall than FLOR in both long-term control experiments and sea surface temperature (SST)- and sea surface salinity (SSS)-restoring historical runs (1971–2012). Restoring experiments are performed with SSS and SST restored to observational estimates of climatological SSS and interannually varying monthly SST. In the control experiments of HiFLOR, an improved simulation of the Walker circulation arising from more realistic SST and precipitation is largely responsible for its better performance in simulating ENSO–TC connections in the WNP. In the SST-restoring experiments of HiFLOR, more realistic Walker circulation and steering flow during El Niño and La Niña are responsible for the improved simulation of ENSO–TC connections in the WNP. The improved simulation of ENSO–TC connections with HiFLOR arises from a better representation of SST and better responses of environmental large-scale circulation to SST anomalies associated with El Niño or La Niña. A better representation of ENSO–TC connections in HiFLOR can benefit the seasonal forecasting of TC genesis, track, and landfall; improve understanding of the interannual variation of TC activity; and provide better projection of TC activity under climate change.

Sea Surface Temperature in the Subtropical Pacific Boosted the 2015 El Niño and Hindered the 2016 La Niña

2018 ◽  
Vol 31 (2) ◽  
pp. 877-893 ◽  
Author(s):  
Jingzhi Su ◽  
Renhe Zhang ◽  
Xinyao Rong ◽  
Qingye Min ◽  
Congwen Zhu
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
El Niño ◽  
El Nino ◽  
Heat Content ◽  
Equatorial Region ◽  
La Niña ◽  
Sea Surface ◽  
La Nina ◽  
Super El Niño

After the quick decaying of the 2015 super El Niño, the predicted La Niña unexpectedly failed to materialize to the anticipated standard in 2016. Diagnostic analyses, as well as numerical experiments, showed that this ENSO evolution of the 2015 super El Niño and the hindered 2016 La Niña may be essentially caused by sea surface temperature anomalies (SSTAs) in the subtropical Pacific. The self-sustaining SSTAs in the subtropical Pacific tend to weaken the trade winds during boreal spring–summer, leading to anomalous westerlies along the equatorial region over a period of more than one season. Such long-lasting wind anomalies provide an essential requirement for ENSO formation, particularly before a positive Bjerknes feedback is thoroughly built up between the oceanic and atmospheric states. Besides the 2015 super El Niño and the hindered La Niña in 2016, there were several other El Niño and La Niña events that cannot be explained only by the oceanic heat content in the equatorial Pacific. However, the questions related to those eccentric El Niño and La Niña events can be well explained by suitable SSTAs in the subtropical Pacific. Thus, the leading SSTAs in the subtropical Pacific can be treated as an independent indicator for ENSO prediction, on the basis of the oceanic heat content inherent in the equatorial region. Because ENSO events have become more uncertain under the background of global warming and the Pacific decadal oscillation during recent decades, thorough investigation of the role of the subtropical Pacific in ENSO formation is urgently needed.

Asymmetric Responses of the Western Tropical Pacific Sea Level to El Niño and La Niña

2020 ◽  
Author(s):  
Fan WANG ◽  
Qiuping Ren ◽  
Yuanlong Li ◽  
Fei Zheng ◽  
Jing Duan
Keyword(s):  
Sea Level ◽  
El Niño ◽  
El Nino ◽  
Tropical Pacific ◽  
La Niña ◽  
Western Tropical Pacific ◽  
La Nina ◽  
Asymmetric Responses

North Australian Sea Surface Temperatures and the El Niño–Southern Oscillation in the CMIP5 Models

2012 ◽  
Vol 25 (18) ◽  
pp. 6375-6382 ◽  
Author(s):  
Jennifer L. Catto ◽  
Neville Nicholls ◽  
Christian Jakob
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
La Niña ◽  
Sea Surface ◽  
Cmip5 Models ◽  
Sea Surface Temperatures ◽  
The North ◽  
La Nina ◽  
Surface Temperatures

Abstract Aspects of the climate of Australia are linked to interannual variability of the sea surface temperatures (SSTs) to the north of the country. SST anomalies in this region have been shown to exhibit strong, seasonally varying links to ENSO and tropical Pacific SSTs. Previously, the models participating in phase 3 of the Coupled Model Intercomparison Project (CMIP3) have been evaluated and found to vary in their abilities to represent both the seasonal cycle of correlations between the Niño-3.4 and north Australian SSTs and the evolution of SSTs during composite El Niño and La Niña events. In this study, the new suite of models participating in the CMIP5 is evaluated using the same method. In the multimodel mean, the representation of the links is slightly improved, but generally the models do not capture the strength of the negative correlations during the second half of the year. The models also still struggle to capture the SST evolution in the north Australian region during El Niño and La Niña events.

scholarly journals The influence of interannual and decadal Indo-Pacific sea surface temperature variability on Australian monsoon rainfall

2021 ◽  
pp. 1-58
Author(s):  
Hanna Heidemann ◽  
Joachim Ribbe ◽  
Tim Cowan ◽  
Benjamin J. Henley ◽  
Christa Pudmenzky ◽  
...  
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
El Niño ◽  
El Nino ◽  
La Niña ◽  
Sea Surface ◽  
Northern Australia ◽  
Central Pacific ◽  
Cp El Niño ◽  
La Nina

AbstractMonsoonal rainfall varies substantially in Northern Australia (AUMR) on interannual, decadal and longer time scales, profoundly impacting natural systems and agricultural communities. Some of this variability arises in response to sea surface temperature (SST) variability in the Indo-Pacific linked to both the El Niño-Southern Oscillation (ENSO) and the Interdecadal Pacific Oscillation (IPO). Here we use observations to investigate unresolved issues regarding the influence of the IPO and ENSO on AUMR. Specifically, we show that during negative IPO phases, central Pacific (CP) El Niño events are associated with below average rainfall over northeast Australia, an anomalous anticyclonic pattern to the northwest of Australia, and eastward moisture advection towards the Dateline. In contrast, CP La Niña events (distinct from eastern Pacific La Niña events) during negative IPO phases drive significantly wet conditions over much of northern Australia, a strengthened Walker Circulation, and large-scale moisture flux convergence. During positive IPO phases, the impact of CP El Niño and CP La Niña events on AUMR is weaker. The influence of central Pacific SSTs on AUMR has been stronger during the recent (post-1999) negative IPO phase. The extent to which this strengthening is associated with climate change or merely natural, internal variability is not known.

scholarly journals Diversity of Marine Heatwaves in the South China Sea regulated by the ENSO phase

2021 ◽  
pp. 1-51
Author(s):  
Kai Liu ◽  
Kang Xu ◽  
Congwen Zhu ◽  
Boqi Liu
Keyword(s):  
South China Sea ◽  
Latent Heat ◽  
South China ◽  
El Niño ◽  
El Nino ◽  
The South China Sea ◽  
La Niña ◽  
The South ◽  
China Sea ◽  
La Nina

Abstract Marine heatwaves (MHWs) in the South China Sea (SCS) have dramatic impacts on local ecosystems, fisheries, and aquacultures. Our results show that SCS MHWs were strongly regulated by El Niño-Southern Oscillation (ENSO) with a distinct life cycle during 1982–2018. Based on the ENSO-associated sea surface temperature anomaly (SSTA) warming peaks in the SCS, we can classify SCS MHWs into three categories, namely, El Niño-P1 during the first warming peak of El Niño from September to the following February, El Niño-P2 during the second warming peak of El Niño from the following June to September, and La Niña-P1 during the single warming peak of La Niña from the following February to May. The three types of SCS MHWs are all affected by the lower-level enhanced anticyclone over the western North Pacific (WNP), but their physical mechanisms are quite different. In El Niño-P1, SCS MHWs are mostly induced by enhanced net downward shortwave radiation and reduced latent heat flux loss over the southwestern and northern SCS, respectively. In El Niño-P2, SCS MHWs are primarily attributed to weaker entrainment cooling caused by a local enhanced anticyclone and stronger Ekman downwelling in the central-northern SCS. However, in La Niña-P1, SCS MHWs are mainly contributed by the reduced latent heat loss due to the weaker WNP anticyclone centered east of the Philippines on the pentad timescale. The distinct spatial distributions of MHWs show phase locking with ENSO-associated SCS SSTA warming, which provides a potential seasonal forecast of SCS MHWs according to the ENSO phase.

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