scholarly journals Diagnosing and Predicting ENSO SSTA Development from Moored-Buoy and Scatterometer Winds

2019 ◽  
Vol 32 (24) ◽  
pp. 8755-8770 ◽  
Author(s):  
Andrew M. Chiodi
Keyword(s):  
Real Time ◽  
Wind Stress ◽  
Southern Oscillation ◽  
Tropical Pacific ◽  
Equatorial Pacific ◽  
Coupled Models ◽  
Simulation Accuracy ◽  
Enso Events ◽  
Moored Buoy ◽  
The Tropical Pacific

Abstract Accurate real-time knowledge of equatorial Pacific wind stress is critical for monitoring the state of the tropical Pacific Ocean and understanding sea surface temperature anomaly (SSTA) development associated with El Niño–Southern Oscillation (ENSO) events. The tropical Pacific moored-buoy array has been shown to adequately provide this knowledge when operating as designed. Ocean model simulation of equatorial Pacific SSTA by moored-buoy winds reveals that recent western Pacific buoy losses exceed the array’s minimal redundancy. Additional wind measurements are needed to adequately simulate ENSO-related SSTA development when large portions of the moored-buoy array have been lost or decommissioned. Prospects for obtaining this supplemental wind information in real time are evaluated from simulations of central equatorial Pacific SSTA development during 2017 and end-of-year Niño-3.4 conditions during the previous 25 years. Results show that filling multiple-buoy-dropout gaps with winds from a pair of scatterometers (2000–17) achieves simulation accuracy improving upon that available from the moored-buoy array in the case in which large portions of the array are out. Forcing with the reanalysis-product winds most commonly used in recent ENSO studies or the scatterometer measurements (without the buoy winds) degrades simulation accuracy. The utility of having accurate basinwide wind stress information is demonstrated in an examination of the role that easterly weather-scale wind events played in driving the unexpected development of La Niña in 2017 and by showing that wintertime Niño-3.4 conditions can be statistically forecast, with skill comparable to state-of-the-art coupled models, on the basis of accurate knowledge of equatorial Pacific wind variability over spring or summer.

scholarly journals Contribution of buoyancy fluxes to tropical Pacific sea level variability

Ocean Science ◽  
2021 ◽  
Vol 17 (4) ◽  
pp. 1103-1113
Author(s):  
Patrick Wagner ◽  
Markus Scheinert ◽  
Claus W. Böning
Keyword(s):  
Sea Level ◽  
Wind Stress ◽  
Southern Oscillation ◽  
Tropical Pacific ◽  
Sea Level Variability ◽  
Steric Sea Level ◽  
Enso Events ◽  
Freshwater Fluxes ◽  
Stress Changes ◽  
The Tropical Pacific

Abstract. Regional anomalies of steric sea level are either due to redistribution of heat and freshwater anomalies or due to ocean–atmosphere buoyancy fluxes. Interannual to decadal variability in sea level across the tropical Pacific is mainly due to steric variations driven by wind stress anomalies. The importance of air–sea buoyancy fluxes is less clear. We use a global, eddy-permitting ocean model and a series of sensitivity experiments with quasi-climatological momentum and buoyancy fluxes to identify the contribution of buoyancy fluxes for interannual to decadal sea level variability in the tropical Pacific. We find their contribution on interannual timescales to be strongest in the central tropical Pacific at around a 10∘ latitude in both hemispheres and also relevant in the very east of the tropical domain. Buoyancy-flux-forced anomalies are correlated with variations driven by wind stress changes, but their effect on the prevailing anomalies and the importance of heat and freshwater fluxes vary locally. In the eastern tropical basin, interannual sea level variability is amplified by anomalous heat fluxes, while the importance of freshwater fluxes is small, and neither has any impact on decadal timescales. In the western tropical Pacific, the variability on interannual and decadal timescales is dampened by both heat and freshwater fluxes. The mechanism involves westward-propagating Rossby waves that are triggered during El Niño–Southern Oscillation (ENSO) events by anomalous buoyancy fluxes in the central tropical Pacific and counteract the prevailing sea level anomalies once they reach the western part of the basin.

scholarly journals Reducing Climatology Bias in an Ocean–Atmosphere CGCM with Improved Coupling Physics

2005 ◽  
Vol 18 (13) ◽  
pp. 2344-2360 ◽  
Author(s):  
Jing-Jia Luo ◽  
Sebastien Masson ◽  
Erich Roeckner ◽  
Gurvan Madec ◽  
Toshio Yamagata
Keyword(s):  
Wind Stress ◽  
Surface Current ◽  
Ocean Surface ◽  
Tropical Pacific ◽  
Equatorial Pacific ◽  
Eastern Pacific ◽  
Cold Tongue ◽  
Easterly Wind ◽  
Ocean Atmosphere ◽  
The Tropical Pacific

Abstract The cold tongue in the tropical Pacific extends too far west in most current ocean–atmosphere coupled GCMs (CGCMs). This bias also exists in the relatively high-resolution SINTEX-F CGCM despite its remarkable performance of simulating ENSO variations. In terms of the importance of air–sea interactions to the climatology formation in the tropical Pacific, several sensitivity experiments with improved coupling physics have been performed in order to reduce the cold-tongue bias in CGCMs. By allowing for momentum transfer of the ocean surface current to the atmosphere [full coupled simulation (FCPL)] or merely reducing the wind stress by taking the surface current into account in the bulk formula [semicoupled simulation (semi-CPL)], the warm-pool/cold-tongue structure in the equatorial Pacific is simulated better than that of the control simulation (CTL) in which the movement of the ocean surface is ignored for wind stress calculation. The reduced surface zonal current and vertical entrainment owing to the reduced easterly wind stress tend to produce a warmer sea surface temperature (SST) in the western equatorial Pacific. Consequently, the dry bias there is much reduced. The warming tendency of the SST in the eastern Pacific, however, is largely suppressed by isopycnal diffusion and meridional advection of colder SST from south of the equator due to enhanced coastal upwelling near Peru. The ENSO signal in the western Pacific and its global teleconnection in the North Pacific are simulated more realistically. The approach as adopted in the FCPL run is able to generate a correct zonal SST slope and efficiently reduce the cold-tongue bias in the equatorial Pacific. The surface easterly wind itself in the FCPL run is weakened, reducing the easterly wind stress further. This is related with a weakened zonal Walker cell in the atmospheric boundary layer over the eastern Pacific and a new global angular momentum balance of the atmosphere associated with reduced westerly wind stress over the southern oceans.

scholarly journals Contribution of buoyancy fluxes to tropical Pacific sea level variability

2021 ◽  
Author(s):  
Patrick Wagner ◽  
Markus Scheinert ◽  
Claus W. Böning
Keyword(s):  
Sea Level ◽  
Fresh Water ◽  
Wind Stress ◽  
Tropical Pacific ◽  
Water Fluxes ◽  
Sea Level Variability ◽  
Steric Sea Level ◽  
Enso Events ◽  
Stress Changes ◽  
The Tropical Pacific

Abstract. Regional anomalies of steric sea level are either due to redistribution of heat and freshwater anomalies or due to ocean-atmosphere buoyancy fluxes. Interannual to decadal variability in sea level across the tropical Pacific is mainly due to steric variations driven by wind stress anomalies. The importance of air--sea buoyancy fluxes is less clear. We use a global, eddy permitting ocean model and a series of sensitivity experiments with quasi-climatological momentum and buoyancy fluxes to identify the contribution of buoyancy fluxes for interannual to decadal sea level variability in the tropical Pacific. We find their contribution on interannual timescales to be strongest in the central tropical Pacific at around 10° latitude in both hemispheres and also relevant in the very east of the tropical domain. Buoyancy flux forced anomalies are in phase with variations driven by wind stress changes but their effect on the prevailing anomalies and the importance of heat and fresh water fluxes vary locally. In the eastern tropical basin interannual sea level variability is amplified by anomalous heat fluxes, while the importance of fresh water fluxes is small and neither has any impact on decadal timescales. In the western tropical Pacific the variability on interannual and decadal timescales is dampened by both, heat and freshwater fluxes. The mechanism involves westward propagating Rossby waves that are triggered during ENSO events by anomalous buoyancy fluxes in the central tropical Pacific and counteract the prevailing sea level anomalies once they reach the western part of the basin.

Simulating ENSO SSTAs from TAO/TRITON Winds: The Impacts of 20 Years of Buoy Observations in the Pacific Waveguide and Comparison with Reanalysis Products

2017 ◽  
Vol 30 (3) ◽  
pp. 1041-1059 ◽  
Author(s):  
Andrew M. Chiodi ◽  
D. E. Harrison
Keyword(s):  
Wind Stress ◽  
Southern Oscillation ◽  
Surface Wind ◽  
Major Elements ◽  
Ocean Model ◽  
Tropical Pacific ◽  
Wind Fields ◽  
Enso Events ◽  
The Pacific ◽  
The Impact

Abstract The fundamental importance of near-equatorial zonal wind stress in the evolution of the tropical Pacific Ocean’s seasonal cycle and El Niño–Southern Oscillation (ENSO) events is well known. It has been two decades since the TAO/TRITON buoy array was deployed, in part to provide accurate surface wind observations across the Pacific waveguide. It is timely to revisit the impact of TAO/TRITON winds on our ability to simulate and thereby understand the evolution of sea surface temperature (SST) in this region. This work shows that forced ocean model simulations of SST anomalies (SSTAs) during the periods with a reasonably high buoy data return rate can reproduce the major elements of SSTA variability during ENSO events using a wind stress field computed from TAO/TRITON observations only. This demonstrates that the buoy array usefully fulfills its waveguide-wind-measurement purpose. Comparison of several reanalysis wind fields commonly used in recent ENSO studies with the TAO/TRITON observations reveals substantial biases in the reanalyses that cause substantial errors in the variability and trends of the reanalysis-forced SST simulations. In particular, the negative trend in ERA-Interim is much larger and the NCEP–NCAR Reanalysis-1 and NCEP–DOE Reanalysis-2 variability much less than seen in the TAO/TRITON wind observations. There are also mean biases. Thus, even with the TAO/TRITON observations available for assimilation into these wind products, there remain oceanically important differences. The reanalyses would be much more useful for ENSO and tropical Pacific climate change study if they would more effectively assimilate the TAO/TRITON observations.

scholarly journals Global Air–Sea CO2 Flux in 22 CMIP5 Models: Multiyear Mean and Interannual Variability*

2016 ◽  
Vol 29 (7) ◽  
pp. 2407-2431 ◽  
Author(s):  
Fang Dong ◽  
Yangchun Li ◽  
Bin Wang ◽  
Wenyu Huang ◽  
Yanyan Shi ◽  
...  
Keyword(s):  
Interannual Variability ◽  
Dissolved Inorganic Carbon ◽  
Southern Oscillation ◽  
Dominant Role ◽  
Co2 Flux ◽  
Tropical Pacific ◽  
Cmip5 Models ◽  
Period Range ◽  
Enso Events ◽  
The Tropical Pacific

Abstract To assess the capability of the latest Earth system models (ESMs) in representing historical global air–sea CO2 flux, 22 models from phase 5 of the Coupled Model Intercomparision Project (CMIP5) are analyzed, with a focus on the spatial distribution of multiyear mean and interannual variability. Results show that the global distribution of air–sea CO2 flux is reasonable in most of the models and that the main differences between models and observationally based results exist in regions with strong vertical movement. The annual mean flux in the 18-member multimodel ensemble (MME; four models were excluded because of their poor performances) mean during 1996–2004 is 1.95 Pg C yr−1 (1 Pg = 1015 g; positive values mean into the ocean), and all but one model describe the rapid increasing trend of air–sea CO2 flux observed during 1960–2000. The first mode of the global air–sea CO2 flux variability during 1870–2000 in six of the models represents the El Niño–Southern Oscillation (ENSO) mode. The remaining 12 models fail to represent this important character for the following reasons: in five models, the tropical Pacific does not play a dominant role in the interannual variability of global air–sea CO2 flux because of stronger interannual variability in the Southern Ocean; two models poorly represent the interannual fluctuation of dissolved inorganic carbon (DIC) in the surface ocean of the tropical Pacific; and four models have shorter periods of the air–sea CO2 flux, which are out of the period range of ENSO events.

scholarly journals Impact of westerly wind burst on El Niño-sourthern oscillation

2020 ◽  
Author(s):  
◽  
Mohammad Alam
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Coupled Model ◽  
Vital Role ◽  
Tropical Pacific ◽  
Westerly Wind ◽  
Central Pacific ◽  
Enso Events ◽  
The Tropical Pacific

Westerly wind bursts (WWBs), usually occurring in the tropical Pacific region, play a vital role in El Niño–Southern Oscillation (ENSO). In this study, we use a hybrid coupled model (HCM) for the tropical Pacific Ocean-atmosphere system to investigate WWBs impact on ENSO. To achieve this goal, two experiments are performed: (a) first, the standard version of the HCM is integrated for years without prescribed WWBs events; and (b) second, the WWBs are added into the HCM (HCM-WWBs). Results show that HCM-WWBs can generate not only more realistic climatology of sea surface temperature (SST) in both spatial structure and temporal amplitudes, but also better ENSO features, than the HCM. In particular, the HCM-WWBs can capture the central Pacific (CP) ENSO events, which is absent in original HCM. Furthermore, the possible physical mechanisms responsible for these improvements by WWBs are discussed.

scholarly journals Tropical Pacific Climate and Its Response to Global Warming in the Kiel Climate Model

2009 ◽  
Vol 22 (1) ◽  
pp. 71-92 ◽  
Author(s):  
W. Park ◽  
N. Keenlyside ◽  
M. Latif ◽  
A. Ströh ◽  
R. Redler ◽  
...  
Keyword(s):  
Global Warming ◽  
Climate Model ◽  
Southern Oscillation ◽  
Global Climate ◽  
Global Climate Model ◽  
Co2 Concentration ◽  
Tropical Pacific ◽  
Equatorial Pacific ◽  
Cold Bias ◽  
The Tropical Pacific

Abstract A new, non-flux-corrected, global climate model is introduced, the Kiel Climate Model (KCM), which will be used to study internal climate variability from interannual to millennial time scales and climate predictability of the first and second kind. The version described here is a coarse-resolution version that will be employed in extended-range integrations of several millennia. KCM’s performance in the tropical Pacific with respect to mean state, annual cycle, and El Niño–Southern Oscillation (ENSO) is described. Additionally, the tropical Pacific response to global warming is studied. Overall, climate drift in a multicentury control integration is small. However, KCM exhibits an equatorial cold bias at the surface of the order 1°C, while strong warm biases of several degrees are simulated in the eastern tropical Pacific on both sides off the equator, with maxima near the coasts. The annual and semiannual cycles are realistically simulated in the eastern and western equatorial Pacific, respectively. ENSO performance compares favorably to observations with respect to both amplitude and period. An ensemble of eight greenhouse warming simulations was performed, in which the CO2 concentration was increased by 1% yr−1 until doubling was reached, and stabilized thereafter. Warming of equatorial Pacific sea surface temperature (SST) is, to first order, zonally symmetric and leads to a sharpening of the thermocline. ENSO variability increases because of global warming: during the 30-yr period after CO2 doubling, the ensemble mean standard deviation of Niño-3 SST anomalies is increased by 26% relative to the control, and power in the ENSO band is almost doubled. The increased variability is due to both a strengthened (22%) thermocline feedback and an enhanced (52%) atmospheric sensitivity to SST; both are associated with changes in the basic state. Although variability increases in the mean, there is a large spread among ensemble members and hence a finite probability that in the “model world” no change in ENSO would be observed.

scholarly journals A Pacific Centennial Oscillation Predicted by Coupled GCMs*

2012 ◽  
Vol 25 (17) ◽  
pp. 5943-5961 ◽  
Author(s):  
Kristopher B. Karnauskas ◽  
Jason E. Smerdon ◽  
Richard Seager ◽  
Jesús Fidel González-Rouco
Keyword(s):  
Time Scale ◽  
General Circulation ◽  
Southern Oscillation ◽  
Heat Content ◽  
General Circulation Models ◽  
Wave Pattern ◽  
Tropical Pacific ◽  
Equatorial Pacific ◽  
Centennial Time Scale ◽  
The Tropical Pacific

Abstract Internal climate variability at the centennial time scale is investigated using long control integrations from three state-of-the-art global coupled general circulation models. In the absence of external forcing, all three models produce centennial variability in the mean zonal sea surface temperature (SST) and sea level pressure (SLP) gradients in the equatorial Pacific with counterparts in the extratropics. The centennial pattern in the tropical Pacific is dissimilar to that of the interannual El Niño–Southern Oscillation (ENSO), in that the most prominent expression in temperature is found beneath the surface of the western Pacific warm pool. Some global repercussions nevertheless are analogous, such as a hemispherically symmetric atmospheric wave pattern of alternating highs and lows. Centennial variability in western equatorial Pacific SST is a result of the strong asymmetry of interannual ocean heat content anomalies, while the eastern equatorial Pacific exhibits a lagged, Bjerknes-like response to temperature and convection in the west. The extratropical counterpart is shown to be a flux-driven response to the hemispherically symmetric circulation anomalies emanating from the tropical Pacific. Significant centennial-length trends in the zonal SST and SLP gradients rivaling those estimated from observations and model simulations forced with increasing CO2 appear to be inherent features of the internal climate dynamics simulated by all three models. Unforced variability and trends on the centennial time scale therefore need to be addressed in estimated uncertainties, beyond more traditional signal-to-noise estimates that do not account for natural variability on the centennial time scale.

scholarly journals Intraseasonal Atmospheric Variability in the Extratropics and Its Relation to the Onset of Tropical Pacific Sea Surface Temperature Anomalies

2007 ◽  
Vol 20 (5) ◽  
pp. 926-936 ◽  
Author(s):  
Bruce T. Anderson
Keyword(s):  
Wind Stress ◽  
Surface Pressure ◽  
North Pacific ◽  
Southern Oscillation ◽  
Tropical Pacific ◽  
Sea Surface ◽  
Stress Fields ◽  
Boreal Winter ◽  
Enso Events ◽  
Central North Pacific

Abstract Previous research has shown that seasonal-mean boreal winter variations in the subtropical/extratropical sea level pressure and wind stress fields over the central North Pacific are significantly related to the state of the El Niño–Southern Oscillation (ENSO) 12–15 months later. Results presented in this note indicate that boreal winter ENSO events are also preceded by increased intraseasonal variance in the antecedent boreal winter atmospheric circulation patterns over the extratropical central North Pacific as well. Low (high) surface pressure anomalies associated with intraseasonal variability in this region are related to intraseasonal wind stress anomalies that represent a weakening (strengthening) of the trade winds over both the north and south subtropical/tropical Pacific. There is also a concurrent increase (decrease) in the central and eastern subtropical North Pacific sea surface temperatures that projects onto the seasonal-mean SST anomalies that precede mature ENSO events by 9–12 months. Overall these results suggest that similar to seasonal-mean subtropical surface pressure and wind stress fields, enhanced transient variability in the midlatitudes can subsequently induce changes in the atmospheric and oceanic structure of the tropical Pacific that may serve as a precursor to ENSO variability.

Successive Modulation of ENSO to the Future Greenhouse Warming

2008 ◽  
Vol 21 (1) ◽  
pp. 3-21 ◽  
Author(s):  
Soon-Il An ◽  
Jong-Seong Kug ◽  
Yoo-Geun Ham ◽  
In-Sik Kang
Keyword(s):  
General Circulation ◽  
Southern Oscillation ◽  
General Circulation Models ◽  
Tropical Pacific ◽  
Greenhouse Warming ◽  
Delayed Response ◽  
Subsurface Temperature ◽  
Climate System Model ◽  
The Mean ◽  
The Tropical Pacific

Abstract The multidecadal modulation of the El Niño–Southern Oscillation (ENSO) due to greenhouse warming has been analyzed herein by means of diagnostics of Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) coupled general circulation models (CGCMs) and the eigenanalysis of a simplified version of an intermediate ENSO model. The response of the global-mean troposphere temperature to increasing greenhouse gases is more likely linear, while the amplitude and period of ENSO fluctuates in a multidecadal time scale. The climate system model outputs suggest that the multidecadal modulation of ENSO is related to the delayed response of the subsurface temperature in the tropical Pacific compared to the response time of the sea surface temperature (SST), which would lead a modulation of the vertical temperature gradient. Furthermore, an eigenanalysis considering only two parameters, the changes in the zonal contrast of the mean background SST and the changes in the vertical contrast between the mean surface and subsurface temperatures in the tropical Pacific, exhibits a good agreement with the CGCM outputs in terms of the multidecadal modulations of the ENSO amplitude and period. In particular, the change in the vertical contrast, that is, change in difference between the subsurface temperature and SST, turns out to be more influential on the ENSO modulation than changes in the mean SST itself.

Sign in / Sign up

Export Citation Format

Share Document