scholarly journals The Role of Ocean Dynamics in the Interaction between the Atlantic Meridional and Equatorial Modes

2012 ◽  
Vol 25 (10) ◽  
pp. 3583-3598 ◽  
Author(s):  
Jieshun Zhu ◽  
Bohua Huang ◽  
Zhaohua Wu
Keyword(s):  
Time Scales ◽  
Time Scale ◽  
Southern Oscillation ◽  
Heat Content ◽  
Transition Process ◽  
Ocean Dynamics ◽  
Global Ocean ◽  
Tropical Atlantic ◽  
Equatorial Atlantic ◽  
Meridional Mode

Abstract This study examines a mechanism of the interaction between the tropical Atlantic meridional and equatorial modes. To derive robust heat content (HC) variability, the ensemble-mean HC anomalies (HCA) of six state-of-the-art global ocean reanalyses for 1979–2007 are analyzed. Compared with previous studies, characteristic oceanic processes are distinguished through their dominant time scales. Using the ensemble empirical mode decomposition (EEMD) method, the HC fields are first decomposed into components with different time scales. The authors’ analysis shows that these components are associated with distinctive ocean dynamics. The high-frequency (first three) components can be characterized as the equatorial modes, whereas the low-frequency (the fifth and sixth) components are featured as the meridional modes. In between, the fourth component on the time scale of 3–4 yr demonstrates “mixed” characteristics of the meridional and equatorial modes because of an active transition from the predominant meridional to zonal structures on this time scale. Physically, this transition process is initiated by the discharge of the off-equatorial HCA, which is first accumulated as a part of the meridional mode, into the equatorial waveguide, which is triggered by the breakdown of the equilibrium between the cross-equatorial HC contrast and the overlying wind forcing, and results in a major heat transport through the equatorial waveguide into the southeastern tropical Atlantic. It is also shown that remote forcing from El Niño–Southern Oscillation (ENSO) exerts important influence on the transition from the equatorial to meridional mode and may partly dictate its time scale of 3–4 yr. Therefore, the authors’ results demonstrate another mechanism of the equatorial Atlantic response to the ENSO forcing.

scholarly journals Tropical Atmosphere–Ocean Interactions in a Conceptual Framework

2009 ◽  
Vol 22 (3) ◽  
pp. 550-567 ◽  
Author(s):  
Malte F. Jansen ◽  
Dietmar Dommenget ◽  
Noel Keenlyside
Keyword(s):  
Indian Ocean ◽  
Conceptual Model ◽  
Southern Oscillation ◽  
Heat Content ◽  
Ocean Model ◽  
Forecast Skill ◽  
Ocean Dynamics ◽  
Intrinsic Variability ◽  
Equatorial Atlantic ◽  
Negative Feedbacks

Abstract Statistical analysis of observations (including atmospheric reanalysis and forced ocean model simulations) is used to address two questions: First, does an analogous mechanism to that of El Niño–Southern Oscillation (ENSO) exist in the equatorial Atlantic or Indian Ocean? Second, does the intrinsic variability in these basins matter for ENSO predictability? These questions are addressed by assessing the existence and strength of the Bjerknes and delayed negative feedbacks in each tropical basin, and by fitting conceptual recharge oscillator models, both with and without interactions among the basins. In the equatorial Atlantic the Bjerknes and delayed negative feedbacks exist, although weaker than in the Pacific. Equatorial Atlantic variability is well described by the recharge oscillator model, with an oscillatory mixed ocean dynamics–sea surface temperature (SST) mode present in boreal spring and summer. The dynamics of the tropical Indian Ocean, however, appear to be quite different: no recharge–discharge mechanism is found. Although a positive Bjerknes-like feedback from July to September is found, the role of heat content seems secondary. Results also show that Indian Ocean interaction with ENSO tends to damp the ENSO oscillation and is responsible for a frequency shift to shorter periods. However, the retrospective forecast skill of the conceptual model is hardly improved by explicitly including Indian Ocean SST. The interaction between ENSO and the equatorial Atlantic variability is weaker. However, a feedback from the Atlantic on ENSO appears to exist, which slightly improves the retrospective forecast skill of the conceptual model.

GFDL’s ESM2 Global Coupled Climate–Carbon Earth System Models. Part I: Physical Formulation and Baseline Simulation Characteristics

2012 ◽  
Vol 25 (19) ◽  
pp. 6646-6665 ◽  
Author(s):  
John P. Dunne ◽  
Jasmin G. John ◽  
Alistair J. Adcroft ◽  
Stephen M. Griffies ◽  
Robert W. Hallberg ◽  
...  
Keyword(s):  
Climate Changes ◽  
Southern Oscillation ◽  
Heat Content ◽  
Ocean Dynamics ◽  
Thermocline Depth ◽  
Earth System ◽  
System Models ◽  
Model Version ◽  
Earth System Models

Abstract The physical climate formulation and simulation characteristics of two new global coupled carbon–climate Earth System Models, ESM2M and ESM2G, are described. These models demonstrate similar climate fidelity as the Geophysical Fluid Dynamics Laboratory’s previous Climate Model version 2.1 (CM2.1) while incorporating explicit and consistent carbon dynamics. The two models differ exclusively in the physical ocean component; ESM2M uses Modular Ocean Model version 4p1 with vertical pressure layers while ESM2G uses Generalized Ocean Layer Dynamics with a bulk mixed layer and interior isopycnal layers. Differences in the ocean mean state include the thermocline depth being relatively deep in ESM2M and relatively shallow in ESM2G compared to observations. The crucial role of ocean dynamics on climate variability is highlighted in El Niño–Southern Oscillation being overly strong in ESM2M and overly weak in ESM2G relative to observations. Thus, while ESM2G might better represent climate changes relating to total heat content variability given its lack of long-term drift, gyre circulation, and ventilation in the North Pacific, tropical Atlantic, and Indian Oceans, and depth structure in the overturning and abyssal flows, ESM2M might better represent climate changes relating to surface circulation given its superior surface temperature, salinity, and height patterns, tropical Pacific circulation and variability, and Southern Ocean dynamics. The overall assessment is that neither model is fundamentally superior to the other, and that both models achieve sufficient fidelity to allow meaningful climate and earth system modeling applications. This affords the ability to assess the role of ocean configuration on earth system interactions in the context of two state-of-the-art coupled carbon–climate models.

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.

scholarly journals Local Coupled Equatorial Variability versus Remote ENSO Forcing in an Intermediate Coupled Model of the Tropical Atlantic

2006 ◽  
Vol 19 (20) ◽  
pp. 5227-5252 ◽  
Author(s):  
Serena Illig ◽  
Boris Dewitte
Keyword(s):  
Mixed Layer ◽  
El Niño ◽  
Time Scale ◽  
El Nino ◽  
Coupled Model ◽  
Tropical Atlantic ◽  
Equatorial Atlantic ◽  
Layer Model ◽  
Intermediate Coupled Model ◽  
Mixed Layer Model

Abstract The relative roles played by the remote El Niño–Southern Oscillation (ENSO) forcing and the local air–sea interactions in the tropical Atlantic are investigated using an intermediate coupled model (ICM) of the tropical Atlantic. The oceanic component of the ICM consists of a six-baroclinic mode ocean model and a simple mixed layer model that has been validated from observations. The atmospheric component is a global atmospheric general circulation model developed at the University of California, Los Angeles (UCLA). In a forced context, the ICM realistically simulates both the sea surface temperature anomaly (SSTA) variability in the equatorial band, and the relaxation of the Atlantic northeast trade winds and the intensification of the equatorial westerlies in boreal spring that usually follows an El Niño event. The results of coupled experiments with or without Pacific ENSO forcing and with or without explicit air–sea interactions in the equatorial Atlantic indicate that the background energy in the equatorial Atlantic is provided by ENSO. However, the time scale of the variability and the magnitude of some peculiar events cannot be explained solely by ENSO remote forcing. It is demonstrated that the peak of SSTA variability in the 1–3-yr band as observed in the equatorial Atlantic is due to the local air–sea interactions and is not a linear response to ENSO. Seasonal phase locking in boreal summer is also the result of the local coupling. The analysis of the intrinsic sustainable modes indicates that the Atlantic El Niño is qualitatively a noise-driven stable system. Such a system can produce coherent interdecadal variability that is not forced by the Pacific or extraequatorial variability. It is shown that when a simple slab mixed layer model is embedded into the system to simulate the northern tropical Atlantic (NTA) SST variability, the warming over NTA following El Niño events have characteristics (location and peak phase) that depend on air–sea interaction in the equatorial Atlantic. In the model, the interaction between the equatorial mode and NTA can produce a dipolelike structure of the SSTA variability that evolves at a decadal time scale. The results herein illustrate the complexity of the tropical Atlantic ocean–atmosphere system, whose predictability jointly depends on ENSO and the connections between the Atlantic modes of variability.

Monitoring the Ocean Heat Content and the Earth Energy imbalance from space altimetry and space gravimetry: the MOHeaCAN product

2021 ◽  
Author(s):  
Marti Florence ◽  
Ablain Michaël ◽  
Fraudeau Robin ◽  
Jugier Rémi ◽  
Meyssignac Benoît ◽  
...  
Keyword(s):  
Time Scales ◽  
Radiant Energy ◽  
Heat Content ◽  
Ocean Heat Content ◽  
Global Ocean ◽  
Argo Data ◽  
Data Set ◽  
Energy Imbalance ◽  
Temporal Sampling ◽  
The Earth

<p>The Earth Energy Imbalance (EEI) is a key indicator to understand climate change. However, measuring this indicator is challenging since it is a globally integrated variable whose variations are small, of the order of several tenth of W.m<sup>-2</sup>, compared to the amount of energy entering and leaving the climate system of ~340 W.m<sup>-2</sup>. Recent studies suggest that the EEI response to anthropogenic GHG and aerosols emissions is 0.5-1 W.m<sup>-2</sup>. It implies that an accuracy of <0.3 W.m<sup>-2</sup> at decadal time scales is necessary to evaluate the long term mean EEI associated with anthropogenic forcing. Ideally an accuracy of <0.1 W.m<sup>-2</sup> at decadal time scales is desirable if we want to monitor future changes in EEI.</p><p>In the frame of the MOHeaCAN project supported by ESA, the EEI indicator is deduced from the global change in Ocean Heat Content (OHC) which is a very good proxy of the EEI since the ocean stores 93% of the excess of heat  gained by the Earth in response to EEI. The OHC is estimated from space altimetry and gravimetry missions (GRACE). This “Altimetry-Gravimetry'' approach is promising because it provides consistent spatial and temporal sampling of the ocean, it samples nearly the entire global ocean, except for polar regions, and it provides estimates of the OHC over the ocean’s entire depth. Consequently, it complements the OHC estimation from the ARGO network. </p><p>The MOHeaCAN product contains monthly time series (between August 2002 and June 2017) of several variables, the main ones being the regional OHC (3°x3° spatial resolution grids), the global OHC and the EEI indicator. Uncertainties are provided for variables at global scale, by propagating errors from sea level measurements (altimetry) and ocean mass content (gravimetry). In order to calculate OHC at regional and global scales, a new estimate of the expansion efficiency of heat at global and regional scales have been performed based on the global ARGO network. </p><p>A scientific validation of the MOHeaCAN product has also been carried out performing thorough comparisons against independent estimates based on ARGO data and on the Clouds and the Earth’s Radiant energy System (CERES) measurements at the top of the atmosphere. The mean EEI derived from MOHeaCAN product is 0.84 W.m<sup>-2</sup> over the whole period within an uncertainty of ±0.12 W.m<sup>-2</sup> (68% confidence level - 0.20 W.m<sup>-2</sup> at the 90% CL). This figure is in agreement (within error bars at the 90% CL) with other EEI indicators based on ARGO data (e.g. OHC-OMI from CMEMS) although the best estimate is slightly higher. Differences from annual to inter-annual scales have also been observed with ARGO and CERES data. Investigations have been conducted to improve our understanding of the benefits and limitations of each data set to measure EEI at different time scales.</p><p><strong>The MOHeaCAN product from “altimetry-gravimetry” is now available</strong> and can be downloaded at https://doi.org/10.24400/527896/a01-2020.003. Feedback from interested users on this product are welcome.</p>

Decadal–Multidecadal Variations of Asian Summer Rainfall from the Little Ice Age to the Present

2019 ◽  
Vol 32 (22) ◽  
pp. 7663-7674 ◽  
Author(s):  
Hui Shi ◽  
Bin Wang ◽  
Jian Liu ◽  
Fei Liu
Keyword(s):  
Time Scales ◽  
Time Scale ◽  
Southern Oscillation ◽  
Summer Rainfall ◽  
Ice Age ◽  
Uniform Structure ◽  
Maritime Continent ◽  
Remarkable Change ◽  
Decadal Time Scale ◽  
Asian Summer

Abstract Features of decadal–multidecadal variations of the Asian summer rainfall are revealed by analysis of the reconstructed Asian summer precipitation (RAP) dataset from 1470 to 2013. Significant low-frequency periodicities of the all-Asian rainfall (AAR) index (AARI) are found on decadal (8–10 yr), quasi-bidecadal (22 yr), and multidecadal (50–54 yr) time scales, as well as centennial time scales. The decadal and multidecadal peaks are mainly from the “monsoon Asia” area and the Maritime Continent, while the 22-yr peak is from the “arid Asia” area. A remarkable change of leading frequency from multidecadal to decadal after AD 1700 is detected across the entire Asian landmass. The leading empirical orthogonal function (EOF) modes on the decadal and multidecadal time scales exhibit a uniform structure similar to that on the interannual time scale, suggesting a cross-time-scale, in-phase variation of the rainfall across continental Asia and the Maritime Continent. Enhanced AAR on a decadal time scale is found associated with the mega-La Niña sea surface temperature (SST) pattern over the Pacific. The AARI–mega-ENSO (El Niño–Southern Oscillation) relationship is persistently significant except from 1820 to around 1900. Enhanced decadal AAR is also found to be associated with extratropical North Atlantic warming. The AARI–AMO (Atlantic multidecadal oscillation) relationship, however, is nonstationary. On the multidecadal time scale, the AAR is significantly related to the AMO. Mechanisms associated with the decadal–multidecadal variability of AAR are also discussed.

Mixed Layer Heat Balance on Intraseasonal Time Scales in the Northwestern Tropical Atlantic Ocean*

2005 ◽  
Vol 18 (20) ◽  
pp. 4168-4184 ◽  
Author(s):  
Gregory R. Foltz ◽  
Michael J. McPhaden
Keyword(s):  
Time Scales ◽  
Mixed Layer ◽  
Heat Balance ◽  
Dominant Role ◽  
Surface Wind ◽  
Local Heat ◽  
Warm Pool ◽  
Surface Mixed Layer ◽  
Tropical Atlantic ◽  
Equatorial Atlantic

Abstract Recent observations have shown evidence of intraseasonal oscillations (with periods of approximately 1–2 months) in the northern and southern tropical Atlantic trade winds. In this paper, the oceanic response to the observed intraseasonal wind variability is addressed through an analysis of the surface mixed layer heat balance, focusing on three locations in the northwestern tropical Atlantic where in situ measurements from moored buoys are available (14.5°N, 51°W; 15°N, 38°W; and 18°N, 34°W). It is found that local heat storage at all three locations is balanced primarily by wind-induced latent heat loss, which is the same mechanism that is believed to play a dominant role on interannual and decadal time scales in the region. It is also found that the intraseasonal wind speed oscillations are linked to changes in surface wind convergence and convection over the western equatorial Atlantic warm pool. These atmospheric circulation anomalies and wind-induced SST anomalies potentially feed back on one another to affect longer time-scale variability in the region.

scholarly journals A Comparison of the Variability and Changes in Global Ocean Heat Content from Multiple Objective Analysis Products During the Argo Period

2021 ◽  
pp. 1-47
Author(s):  
Xinfeng Liang ◽  
Chao Liu ◽  
Rui M. Ponte ◽  
Don P. Chambers
Keyword(s):  
Southern Ocean ◽  
Interannual Variability ◽  
North Atlantic ◽  
Southern Oscillation ◽  
Heat Content ◽  
Global Scale ◽  
Ocean Heat Content ◽  
Objective Analysis ◽  
Global Ocean ◽  
Ocean Measurements

AbstractOcean heat content (OHC) is key to estimating the energy imbalance of the earth system. Over the past two decades, an increasing number of OHC studies were conducted using oceanic objective analysis (OA) products. Here we perform an intercomparison of OHC from eight OA products with a focus on their robust features and significant differences over the Argo period (2005-2019), when the most reliable global scale oceanic measurements are available. For the global ocean, robust warming in the upper 2000 m is confirmed. The 0-300 m layer shows the highest warming rate but is heavily modulated by interannual variability, particularly the El Niño–Southern Oscillation. The 300-700 m and 700-2000 m layers, on the other hand, show unabated warming. Regionally, the Southern Ocean and mid-latitude North Atlantic show a substantial OHC increase, and the subpolar North Atlantic displays an OHC decrease. A few apparent differences in OHC among the examined OA products were identified. In particular, temporal means of a few OA products that incorporated other ocean measurements besides Argo show a global-scale cooling difference, which is likely related to the baseline climatology fields used to generate those products. Large differences also appear in the interannual variability in the Southern Ocean and in the long-term trends in the subpolar North Atlantic. These differences remind us of the possibility of product-dependent conclusions on OHC variations. Caution is therefore warranted when using merely one OA product to conduct OHC studies, particularly in regions and on timescales that display significant differences.

scholarly journals Climate of Brazil's nordeste and tropical atlantic sector: preferred time scales of variability

2014 ◽  
Vol 29 (2) ◽  
pp. 153-160 ◽  
Author(s):  
Dierk Polzin ◽  
Stefan Hastenrath
Keyword(s):  
Time Scales ◽  
Southern Oscillation ◽  
Rainfall Variability ◽  
Tropical Atlantic ◽  
Atlantic Sector ◽  
Short Rainy Season ◽  
Frequency Peak ◽  
Circulation Indices ◽  
Causality Chain

Resuming earlier research, this study explores rainfall variability in Brazil's Nordeste and underlying circulation mechanisms. The semi-arid northern Nordeste has its short rainy season centered around March-April-May, when temperature maximum, low pressure trough and wind confluence reach their southernmost position. Interannual variability can be understood as departures from the average annual cycle. Based on novel long-term datasets, the present study explores the preferred time scales of variability. In Nordeste rainfall and pertinent circulation indices in the tropical Atlantic sector most prominent are frequencies of 13.2, 9.9 and 5.6 years. Frequency peak of 13.1 years appears also in the record of Southern Oscillation, and of 5.6 years in North Atlantic Oscillation, indicative of causality chain.

scholarly journals Analysis of the Atlantic Meridional Mode Using Linear Inverse Modeling: Seasonality and Regional Influences

2012 ◽  
Vol 25 (4) ◽  
pp. 1194-1212 ◽  
Author(s):  
Daniel J. Vimont
Keyword(s):  
High Latitude ◽  
Inverse Modeling ◽  
Southern Oscillation ◽  
Tropical Pacific ◽  
Boreal Summer ◽  
Tropical Atlantic ◽  
Boreal Spring ◽  
Meridional Mode ◽  
Atlantic Meridional Mode ◽  
Sst Anomalies

Abstract Predictability and variability of the tropical Atlantic Meridional Mode (AMM) is investigated using linear inverse modeling (LIM). Analysis of the LIM using an “energy” norm identifies two optimal structures that experience some transient growth, one related to El Niño–Southern Oscillation (ENSO) and the other to the Atlantic multidecadal oscillation (AMO)/AMM patterns. Analysis of the LIM using an AMM-norm identifies an “AMM optimal” with similar structure to the second energy optima (OPT2). Both the AMM-optimal and OPT2 exhibit two bands of SST anomalies in the mid- to high-latitude Atlantic. The AMM-optimal also contains some elements of the first energy optimal (ENSO), indicating that the LIM captures the well-known relationship between ENSO and the AMM. Seasonal correlations of LIM predictions with the observed AMM show enhanced AMM predictability during boreal spring and for long-lead (around 11–15 months) forecasts initialized around September. Regional LIMs were constructed to determine the influence of tropical Pacific and mid- to high-latitude Atlantic SST on the AMM. Analysis of the regional LIMs indicates that the tropical Pacific is responsible for the AMM predictability during boreal spring. Mid- to high-latitude SST anomalies contribute to boreal summer and fall AMM predictability, and are responsible for the enhanced predictability from September initial conditions. Analysis of the empirical normal modes of the full LIM confirms these physical relationships. Results indicate a potentially important role for mid- to high-latitude Atlantic SST anomalies in generating AMM (and tropical Atlantic SST) variations, though it is not clear whether those anomalies provide any societally useful predictive skill.

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