scholarly journals Seasonality in the relationship between equatorial-mean heat content and interannual eastern equatorial Atlantic sea surface temperature variability

2022 ◽  
Author(s):  
Kyle J. Turner ◽  
Natalie J. Burls ◽  
Anna von Brandis ◽  
Joke Lübbecke ◽  
Martin Claus
Keyword(s):  
Heat Content ◽  
Sea Surface ◽  
Warm Water ◽  
Boreal Summer ◽  
Water Volume ◽  
Boreal Winter ◽  
Equatorial Atlantic ◽  
Warm Water Volume ◽  
The Relationship ◽  
Sst Anomalies

AbstractInterannual sea surface temperature (SST) variations in the tropical Atlantic Ocean lead to anomalous atmospheric circulation and precipitation patterns with important ecological and socioeconomic consequences for the semiarid regions of sub-Saharan Africa and northeast Brazil. This interannual SST variability is characterized by three modes: an Atlantic meridional mode featuring an anomalous cross-equatorial SST gradient that peaks in boreal spring; an Atlantic zonal mode (Atlantic Niño mode) with SST anomalies in the eastern equatorial Atlantic cold tongue region that peaks in boreal summer; and a second zonal mode of variability with eastern equatorial SST anomalies peaking in boreal winter. Here we investigate the extent to which there is any seasonality in the relationship between equatorial warm water recharge and the development of eastern equatorial Atlantic SST anomalies. Seasonally stratified cross-correlation analysis between eastern equatorial Atlantic SST anomalies and equatorial heat content anomalies (evaluated using warm water volume and sea surface height) indicate that while equatorial heat content changes do occasionally play a role in the development of boreal summer Atlantic zonal mode events, they contribute more consistently to Atlantic Niño II, boreal winter events. Event and composite analysis of ocean adjustment with a shallow water model suggest that the warm water volume anomalies originate mainly from the off-equatorial northwestern Atlantic, in agreement with previous studies linking them to anomalous wind stress curl associated with the Atlantic meridional mode.

scholarly journals Atlantic Niño/Niña Prediction Skills in NMME Models

Atmosphere ◽  
2021 ◽  
Vol 12 (7) ◽  
pp. 803
Author(s):  
Ran Wang ◽  
Lin Chen ◽  
Tim Li ◽  
Jing-Jia Luo
Keyword(s):  
Sea Surface ◽  
Prediction Skill ◽  
Boreal Summer ◽  
Boreal Winter ◽  
Equatorial Atlantic ◽  
Multimodel Ensemble ◽  
Spring Predictability Barrier ◽  
Anomaly Correlation Coefficient ◽  
Earth’S Climate ◽  
Atlantic Niño

The Atlantic Niño/Niña, one of the dominant interannual variability in the equatorial Atlantic, exerts prominent influence on the Earth’s climate, but its prediction skill shown previously was unsatisfactory and limited to two to three months. By diagnosing the recently released North American Multimodel Ensemble (NMME) models, we find that the Atlantic Niño/Niña prediction skills are improved, with the multi-model ensemble (MME) reaching five months. The prediction skills are season-dependent. Specifically, they show a marked dip in boreal spring, suggesting that the Atlantic Niño/Niña prediction suffers a “spring predictability barrier” like ENSO. The prediction skill is higher for Atlantic Niña than for Atlantic Niño, and better in the developing phase than in the decaying phase. The amplitude bias of the Atlantic Niño/Niña is primarily attributed to the amplitude bias in the annual cycle of the equatorial sea surface temperature (SST). The anomaly correlation coefficient scores of the Atlantic Niño/Niña, to a large extent, depend on the prediction skill of the Niño3.4 index in the preceding boreal winter, implying that the precedent ENSO may greatly affect the development of Atlantic Niño/Niña in the following boreal summer.

Estimating the Diapycnal Transport Contribution to Warm Water Volume Variations in the Tropical Pacific Ocean

2010 ◽  
Vol 23 (2) ◽  
pp. 221-237 ◽  
Author(s):  
Jaclyn N. Brown ◽  
Alexey V. Fedorov
Keyword(s):  
Pacific Ocean ◽  
Wind Stress ◽  
Southern Oscillation ◽  
Heat Content ◽  
Rate Of Change ◽  
Warm Water ◽  
Water Volume ◽  
Wind Stress Curl ◽  
Central Pacific ◽  
Warm Water Volume

Abstract Variations in the warm water volume (WWV) of the equatorial Pacific Ocean are considered a key element of the dynamics of the El Niño–Southern Oscillation (ENSO) phenomenon. WWV, a proxy for the upper-ocean heat content, is usually defined as the volume of water with temperatures greater than 20°C. It has been suggested that the observed variations in WWV are controlled by interplay among meridional, zonal, and vertical transports (with vertical transports typically calculated as the residual of temporal changes in WWV and the horizontal transport divergence). Here, the output from a high-resolution ocean model is used to calculate the zonal and meridional transports and conduct a comprehensive analysis of the mass balance above the 25 kg m−3 σθ surface (approximating the 20°C isotherm). In contrast to some earlier studies, the authors found that on ENSO time scales variations in the diapycnal transport across the 25 kg m−3 isopycnal are small in the eastern Pacific and negligible in the western and central Pacific. In previous observational studies, the horizontal transports were estimated using Ekman and geostrophic dynamics; errors in these approximations were unavoidably folded into the estimates of the diapycnal transport. Here, the accuracy of such estimates is assessed by recalculating mass budgets using the model output at a spatial resolution similar to that of the observations. The authors show that errors in lateral transports can be of the same order of magnitude as the diapycnal transport itself. Further, the rate of change of WWV correlates well with wind stress curl (a driver of meridional transport). This relationship is explored using an extended version of the Sverdrup balance, and it is shown that the two are correlated because they both have the ENSO signal and not because changes in WWV are solely attributable to the wind stress curl.

Ocean Response to Wind Variations, Warm Water Volume, and Simple Models of ENSO in the Low-Frequency Approximation

2010 ◽  
Vol 23 (14) ◽  
pp. 3855-3873 ◽  
Author(s):  
Alexey V. Fedorov
Keyword(s):  
Low Frequency ◽  
Equatorial Pacific ◽  
Warm Water ◽  
Water Volume ◽  
Thermocline Depth ◽  
Phase Lag ◽  
Eastern Equatorial Pacific ◽  
The Pacific ◽  
Warm Water Volume ◽  
Frequency Approximation

Abstract Physical processes that control ENSO are relatively fast. For instance, it takes only several months for a Kelvin wave to cross the Pacific basin (Tk ≈ 2 months), while Rossby waves travel the same distance in about half a year. Compared to such short time scales, the typical periodicity of El Niño is much longer (T ≈ 2–7 yr). Thus, ENSO is fundamentally a low-frequency phenomenon in the context of these faster processes. Here, the author takes advantage of this fact and uses the smallness of the ratio ɛk = Tk/T to expand solutions of the ocean shallow-water equations into power series (the actual parameter of expansion also includes the oceanic damping rate). Using such an expansion, referred to here as the low-frequency approximation, the author relates thermocline depth anomalies to temperature variations in the eastern equatorial Pacific via an explicit integral operator. This allows a simplified formulation of ENSO dynamics based on an integro-differential equation. Within this formulation, the author shows how the interplay between wind stress curl and oceanic damping rates affects 1) the amplitude and periodicity of El Niño and 2) the phase lag between variations in the equatorial warm water volume and SST in the eastern Pacific. A simple analytical expression is derived for the phase lag. Further, applying the low-frequency approximation to the observed variations in SST, the author computes thermocline depth anomalies in the western and eastern equatorial Pacific to show a good agreement with the observed variations in warm water volume. Ultimately, this approach provides a rigorous framework for deriving other simple models of ENSO (the delayed and recharge oscillators), highlights the limitations of such models, and can be easily used for decadal climate variability in the Pacific.

scholarly journals On the Relationship between Regional Ocean Heat Content and Sea Surface Height

2017 ◽  
Vol 30 (22) ◽  
pp. 9195-9211 ◽  
Author(s):  
John T. Fasullo ◽  
Peter R. Gent
Keyword(s):  
Time Scales ◽  
Low Frequency ◽  
Heat Content ◽  
Sea Surface Height ◽  
Ocean Heat Content ◽  
Ocean Dynamics ◽  
Sea Surface ◽  
Altimeter Data ◽  
Model Control ◽  
The Relationship

Abstract An accurate diagnosis of ocean heat content (OHC) is essential for interpreting climate variability and change, as evidenced for example by the broad range of hypotheses that exists for explaining the recent hiatus in global mean surface warming. Potential insights are explored here by examining relationships between OHC and sea surface height (SSH) in observations and two recently available large ensembles of climate model simulations from the mid-twentieth century to 2100. It is found that in decadal-length observations and a model control simulation with constant forcing, strong ties between OHC and SSH exist, with little temporal or spatial complexity. Agreement is particularly strong on monthly to interannual time scales. In contrast, in forced transient warming simulations, important dependencies in the relationship exist as a function of region and time scale. Near Antarctica, low-frequency SSH variability is driven mainly by changes in the circumpolar current associated with intensified surface winds, leading to correlations between OHC and SSH that are weak and sometimes negative. In subtropical regions, and near other coastal boundaries, negative correlations are also evident on long time scales and are associated with the accumulated effects of changes in the water cycle and ocean dynamics that underlie complexity in the OHC relationship to SSH. Low-frequency variability in observations is found to exhibit similar negative correlations. Combined with altimeter data, these results provide evidence that SSH increases in the Indian and western Pacific Oceans during the hiatus are suggestive of substantial OHC increases. Methods for developing the applicability of altimetry as a constraint on OHC more generally are also discussed.

The Importance of Central Pacific Meridional Heat Advection to the Development of ENSO

2021 ◽  
pp. 1-59
Author(s):  
Caihong Wen ◽  
Arun Kumar ◽  
Michelle L’ Heureux ◽  
Yan Xue ◽  
Emily Becker
Keyword(s):  
Water Volume ◽  
Primary Role ◽  
Equatorial Pacific Ocean ◽  
Central Pacific ◽  
Enso Prediction ◽  
Enso Events ◽  
Ocean Reanalyses ◽  
Equatorial Thermocline ◽  
Warm Water Volume ◽  
The Relationship

AbstractThe relationship between the Warm Water Volume (WWV) ENSO precursor and ENSO SST weakened substantially after ~2000, coinciding with a degradation in dynamical model ENSO prediction skill. It is important to understand the drivers of the equatorial thermocline temperature variations and their linkage to ENSO onsets. In this study, a set of ocean reanalyses is employed to assess factors responsible for the variation of the equatorial Pacific Ocean thermocline during 1982-2019. Off-equatorial thermocline temperature anomalies carried equatorward by the mean meridional currents associated with Pacific Tropical Cells are shown to play an important role in modulating the central equatorial thermocline variations, which is rarely discussed in the literature. Further, ENSO events are delineated into two groups based on precursor mechanisms: the western equatorial type (WEP) ENSO, when the central equatorial thermocline is mainly influenced by the zonal propagation of anomalies from the western Pacific, and the off-equatorial central Pacific (OCP) ENSO, when off-equatorial central thermocline anomalies play the primary role. WWV is found to precede all WEP ENSO by 6-9 months, while the correlation is substantially lower for OCP ENSO events. In contrast, the central tropical Pacific (CTP) precursor, which includes off-equatorial thermocline signals, has a very robust lead correlation with the OCP ENSO. Most OCP ENSO events are found to follow the same ENSO conditions, and the number of OCP ENSO increases substantially since the 21st century. These results highlight the importance of monitoring off-equatorial subsurface preconditions for ENSO prediction and to understand multi-year ENSO.

The Impacts of Inter–El Niño Variability on the Tropical Atlantic and Northeast Brazil Climate

2011 ◽  
Vol 24 (13) ◽  
pp. 3402-3422 ◽  
Author(s):  
Regina R. Rodrigues ◽  
Reindert J. Haarsma ◽  
Edmo J. D. Campos ◽  
Tércio Ambrizzi
Keyword(s):  
El Niño ◽  
El Nino ◽  
South Atlantic ◽  
Ocean Dynamics ◽  
Boreal Winter ◽  
Cold Tongue ◽  
Equatorial Atlantic ◽  
Boreal Spring ◽  
Benguela Upwelling ◽  
Sst Anomalies

Abstract In this study, observations and numerical simulations are used to investigate how different El Niño events affect the development of SST anomalies in the Atlantic and how this relates to the Brazilian northeast (NE) precipitation. The results show that different types of El Niño have different impacts on the SST anomalies of the equatorial and tropical South Atlantic but a similar SST response in the tropical North Atlantic. Strong and long (weak and short) El Niños with the main heating source located in the eastern (central) Pacific generate cold (warm) anomalies in the cold tongue and Benguela upwelling regions during boreal winter and spring. When the SST anomalies in the eastern equatorial and tropical South Atlantic are cold (warm), the meridional SST gradient across the equator is positive (negative) and the ITCZ is not allowed (allowed) to move southward during the boreal spring; as a consequence, the precipitation is below (above) the average over the NE. Thus, strong and long (weak and short) El Niños are followed by dry (wet) conditions in the NE. During strong and long El Niños, changes in the Walker circulation over the Atlantic and in the Pacific–South Atlantic (PSA) wave train cause easterly wind anomalies in the western equatorial Atlantic, which in turn activate the Bjerknes mechanism, establishing the cold tongue in boreal spring and summer. These easterly anomalies are also responsible for the Benguela upwelling. During short and weak El Niños, westerly wind anomalies are present in the western equatorial Atlantic accompanied by warm anomalies in the eastern equatorial and tropical South Atlantic; a positive phase of the South Atlantic dipole develops during boreal winter. The simulations highlight the importance of ocean dynamics in establishing the correct slope of the equatorial thermocline and SST anomalies, which in turn determine the correct rainfall response over the NE.

Interannual Tropical Pacific Sea Surface Temperatures and Their Relation to Preceding Sea Level Pressures in the NCAR CCSM2

2006 ◽  
Vol 19 (6) ◽  
pp. 998-1012 ◽  
Author(s):  
Bruce T. Anderson ◽  
Eric Maloney
Keyword(s):  
Sea Level ◽  
Tropical Pacific ◽  
Equatorial Pacific ◽  
Sea Surface ◽  
Boreal Winter ◽  
Atmospheric Variability ◽  
Climate System Model ◽  
Sst Variability ◽  
Ocean Atmosphere ◽  
Sst Anomalies

Abstract This paper describes aspects of tropical interannual ocean/atmosphere variability in the NCAR Community Climate System Model Version 2.0 (CCSM2). The CCSM2 tropical Pacific Ocean/atmosphere system exhibits much stronger biennial variability than is observed. However, a canonical correlation analysis technique decomposes the simulated boreal winter tropical Pacific sea surface temperature (SST) variability into two modes, both of which are related to atmospheric variability during the preceding boreal winter. The first mode of ocean/atmosphere variability is related to the strong biennial oscillation in which La Niña–related sea level pressure (SLP) conditions precede El Niño–like SST conditions the following winter. The second mode of variability indicates that boreal winter tropical Pacific SST anomalies can also be initiated by SLP anomalies over the subtropical central and eastern North Pacific 12 months earlier. The evolution of both modes is characterized by recharge/discharge within the equatorial subsurface temperature field. For the first mode of variability, this recharge/discharge produces a lag between the basin-average equatorial Pacific isotherm depth anomalies and the isotherm–slope anomalies, equatorial SSTs, and wind stress fields. Significant anomalies are present up to a year before the boreal winter SLP variations and two years prior to the boreal winter ENSO-like events. For the second canonical factor pattern, the recharge/discharge mechanism is induced concurrent with the boreal winter SLP pattern approximately one year prior to the ENSO-like events, when isotherms initially deepen and change their slope across the basin. A rapid deepening of the isotherms in the eastern equatorial Pacific and a warming of the overlying SST anomalies then occurs during the subsequent 12 months.

scholarly journals One plausible reason for the change in ENSO characteristics in the 2000s

2013 ◽  
Vol 10 (4) ◽  
pp. 951-984
Author(s):  
V. N. Stepanov
Keyword(s):  
Southern Ocean ◽  
Equatorial Pacific ◽  
Warm Water ◽  
Water Volume ◽  
Atmospheric Conditions ◽  
Enso Events ◽  
Wind Variability ◽  
Western Equatorial Pacific ◽  
Warm Water Volume ◽  
The Tropics

Abstract. It is well known that El Niño Southern Oscillation (ENSO) causes floods, droughts and the collapse of fisheries, therefore forecasting of ENSO is an important task in climate researches. Variations in the equatorial warm water volume of the tropical Pacific and wind variability in the western equatorial Pacific has been considered to be a good ENSO predictor. However, in the 2000s, the interrelationship between these two characteristics and ENSO onsets became weak. This article attempts to find some plausible explanation for this. The results presented here demonstrate a possible link between the variability of atmospheric conditions over the Southern Ocean and their impact on the ocean circulation leading to the amplifying/triggering of ENSO events. It is shown that the variability of the atmospheric conditions upstream of Drake Passage can strongly influence ENSO events. The interrelationship between ENSO and variability in the equatorial warm water volume of the equatorial Pacific, together with wind variability in the western equatorial Pacific has recently weakened. It can be explained by the fact that the process occurred in the Southern Ocean recently became a major contributor amplifying ENSO events (in comparison with the processes of interaction between the atmosphere and the ocean in the tropics of the Pacific). Likely it is due to a warmer ocean state observed from the end of the 1990s that led to smaller atmospheric variability in the tropics and insignificant their changes in the Southern Ocean.

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