Interaction between the Boreal Spring and Summer Tropical Atlantic Interannual Variability Modes

Mapping Intimacies ◽

10.5194/egusphere-egu2020-7291 ◽

2020 ◽

Author(s):

Marta Martín-Rey ◽

Jose Luis Pelegrí ◽

Emilia Sánchez-Gómez ◽

Christophe Cassou

Keyword(s):

Climate Models ◽

Ocean Dynamics ◽

Tropical Atlantic ◽

Coupled Modes ◽

Boreal Spring ◽

The North ◽

Tropical Atlantic Variability ◽

Coupled Climate Models ◽

Sea Surface Temperature Anomalies

Traditionally, the interannual Tropical Atlantic variability (TAV) is thought to be governed by two air-sea coupled modes denoted as Meridional Mode (MM) and Equatorial Mode (EM), peaking in boreal spring and summer respectively. Several studies have proposed a possible connection between the MM and EM, but without reaching a consensus about its frequency, type and associated mechanisms. Remarkably, recent findings brought to light decadal changes in the structure, intensity and teleconnections of the EM along the observational record. In particular, new overlooked equatorial modes called &#8216;non-canonical EM&#8217; and &#8216;Horse-Shoe mode&#8217; have been reported, which exhibit significant sea surface temperature anomalies in the north tropical Atlantic region. This gives robustness to the connection between the boreal spring and summer interannual modes.Here, using observational and CMIP6 model datasets, we demonstrate the existence of distinct interannual modes in the tropical Atlantic basin along the record. Furthermore, the emergence of these modes is not stationary on time and varies from some decades to the others.&#160; In this study, using observations and coupled climate models we explore the connection between the MM and EM to generate the diverse of tropical Atlantic variability reported in previous works. Moreover, the air-sea mechanisms and ocean dynamics involved in the evolution of these modes and the role of the mean state in the connection between them is assessed.

Download Full-text

Tropical Atlantic Variability: Observations and Modeling

Atmosphere ◽

10.3390/atmos10090502 ◽

2019 ◽

Vol 10 (9) ◽

pp. 502 ◽

Cited By ~ 5

Author(s):

William Cabos ◽

Alba de la Vara ◽

Shunya Koseki

Keyword(s):

Climate Models ◽

Climate Modeling ◽

Low Frequency ◽

Global Ocean ◽

Tropical Atlantic ◽

Atmospheric Models ◽

Tropical Atlantic Variability ◽

Systematic Biases ◽

Frequency Variations

We review the state-of-the-art knowledge of Tropical Atlantic Variability (TAV). A well-developed observing system and sustained effort of the climate modeling community have improved our understanding of TAV. It is dominated by the seasonal cycle, for which some mechanisms have been identified. The interannual TAV presents a marked seasonality with three dominant modes: (i) the Atlantic Zonal Mode (AZM), (ii) the Atlantic Meridional Mode (AMM) and (iii) the variability in the Angola–Benguela Front (ABF). At longer time scales, the AMM is active and low-frequency variations in the strength, periodicity, and spatial structure of the AZM are observed. Also, changes in the mean position of the ABF occur. Climate models still show systematic biases in the simulated TAV. Their causes are model-dependent and relate to drawbacks in the physics of the models and to insufficient resolution of their atmospheric and oceanic components. The identified causes for the biases can have local or remote origin, involving the global ocean and atmospheric circulation. Although there is not a clear consensus regarding the role of model resolution in the representation of the TAV, eddy-resolving ocean models combined with atmospheric models with enhanced horizontal and vertical resolutions simulate smaller biases.

Download Full-text

Links between interannual climate variability and marine ecosystems in the Tropical Atlantic

10.5194/egusphere-egu21-15540 ◽

2021 ◽

Author(s):

Emilia Sanchez ◽

Marta Martin Rey ◽

Roland Seferian ◽

Yeray Santana-Falcon

Keyword(s):

Climate Variability ◽

Climate Models ◽

Coastal Upwelling ◽

Net Primary Production ◽

Surface Wind ◽

Marine Ecosystems ◽

Tropical Atlantic ◽

Coupled Modes ◽

Future Evolution ◽

Interannual Climate Variability

The interannual climate variability in the Tropical Atlantic is mainly controlled by two air-sea coupled modes denoted as Meridional Mode (MM) and Equatorial Mode (EM). The MM, peaking in boreal spring, is characterized by an anomalous Sea Surface Temperature (SST) interhemispheric gradient associated with anomalous surface cross-equatorial winds blowing to the warmer hemisphere.&#160; On the other hand, the positive phase of the EM exhibits an anomalous warming in the equatorial band and along the African coast, related to a weakening of the climatological trade winds. Both interannual modes illustrate significant SST and surface wind changes in the eastern boundary upwelling systems (EBUS) of the tropical Atlantic: the Senegal-Mauritanian and Angola-Benguela. The EBUS are characterized by wind-induced coastal upwelling of deep cold waters rich in nutrients supporting high primary productivity and an abundance of food resources. Hence, the physical or climate characteristics associated with the MM and EM may have a potential effect on marine organisms and ecosystems. The goal of this study is to understand the links between the main modes of tropical Atlantic variability and biogeochemical (BGC) variables such as oxygen, net primary production and ph. These are known to be the main drivers for marine ecosystems. Firstly we study the influence of MM and AM on the EBUS and how these links are represented by the coupled ESM CNRM-ESM2.1 against observations. Second, we use the ESM to investigate the links between the SST anomalies associated to MM and EM and the main BGC stressors mentioned above. For this purpose, a set of numerical experiments performed with CMIP6 climate models are used. This work is supported by the H2020 TRIATLAS project, whose main goal is to understand and evaluate the future evolution of living marine resources in the Atlantic Ocean.

Download Full-text

Checklist of the salps (Tunicata, Thaliacea) from the Western Caribbean Sea with a key for their identification and comments on other North Atlantic salps

Zootaxa ◽

10.11646/zootaxa.3210.1.4 ◽

2012 ◽

Vol 3210 (1) ◽

pp. 50 ◽

Cited By ~ 4

Author(s):

CLARA MARÍA HEREU ◽

EDUARDO SUÁREZ-MORALES

Keyword(s):

North Atlantic ◽

Caribbean Sea ◽

Depth Range ◽

Tropical Atlantic ◽

The North ◽

New Information ◽

Plankton Biomass ◽

Western Caribbean ◽

The Caribbean

In waters of the Northwestern Atlantic pelagic tunicates may contribute significantly to the plankton biomass; however, theregional information on the salp fauna is scarce and limited to restricted sectors. In the Caribbean Sea (CS) and the Gulf ofMexico (GOM) the composition of the salpid fauna is still poorly known and this group remains among the less studiedzooplankton taxa in the Northwestern Tropical Atlantic. A revised checklist of the salp species recorded in the North At-lantic (NA, 0–40° N) is provided herein, including new information from the Western Caribbean. Zooplankton sampleswere collected during two cruises (March 2006, January 2007) within a depth range of 0–941 m. A total of 14 species wererecorded in our samples, including new records for the CS and GOM area (Cyclosalpa bakeri Ritter 1905), for the CS (Cy-closalpa affinis (Chamisso, 1819)), and for the Western Caribbean (Salpa maxima Forskål, 1774). The number of speciesof salps known from the CS and GOM rose to 18. A key for the identification of the species recorded in the region is provided. Studies on the ecological role of salps in several sectors of the NA are scarce and deserve further attention.

Download Full-text

On the Interpretation of the North Atlantic Averaged Sea Surface Temperature

Journal of Climate ◽

10.1175/jcli-d-19-0158.1 ◽

2020 ◽

Vol 33 (14) ◽

pp. 6025-6045

Author(s):

Jing Sun ◽

Mojib Latif ◽

Wonsun Park ◽

Taewook Park

Keyword(s):

Surface Temperature ◽

Sea Surface Temperature ◽

North Atlantic ◽

Climate Models ◽

Ocean Dynamics ◽

Sea Surface ◽

The North ◽

Sst Variability ◽

The North Atlantic ◽

Different Time Scales

AbstractThe North Atlantic (NA) basin-averaged sea surface temperature (NASST) is often used as an index to study climate variability in the NA sector. However, there is still some debate on what drives it. Based on observations and climate models, an analysis of the different influences on the NASST index and its low-pass filtered version, the Atlantic multidecadal oscillation (AMO) index, is provided. In particular, the relationships of the two indices with some of its mechanistic drivers including the Atlantic meridional overturning circulation (AMOC) are investigated. In observations, the NASST index accounts for significant SST variability over the tropical and subpolar NA. The NASST index is shown to lump together SST variability originating from different mechanisms operating on different time scales. The AMO index emphasizes the subpolar SST variability. In the climate models, the SST-anomaly pattern associated with the NASST index is similar. The AMO index, however, only represents pronounced SST variability over the extratropical NA, and this variability is significantly linked to the AMOC. There is a sensitivity of this linkage to the cold NA SST bias observed in many climate models. Models suffering from a large cold bias exhibit a relatively weak linkage between the AMOC and AMO and vice versa. Finally, the basin-averaged SST in its unfiltered form, which has been used to question a strong influence of ocean dynamics on NA SST variability, mixes together multiple types of variability occurring on different time scales and therefore underemphasizes the role of ocean dynamics in the multidecadal variability of NA SSTs.

Download Full-text

Monitoring the Influence of the Mesoscale Ocean Dynamics on Phytoplanktonic Plumes around the Marquesas Islands Using Multi-Satellite Missions

Remote Sensing ◽

10.3390/rs12162520 ◽

2020 ◽

Vol 12 (16) ◽

pp. 2520 ◽

Cited By ~ 1

Author(s):

Angelina Cassianides ◽

Elodie Martinez ◽

Christophe Maes ◽

Xavier Carton ◽

Thomas Gorgues

Keyword(s):

Finite Size ◽

Ocean Dynamics ◽

Dynamic Activity ◽

Marquesas Islands ◽

The North ◽

Run Off ◽

Dynamical Regimes ◽

North And South

The Marquesas islands are a place of strong phytoplanktonic enhancement, whose original mechanisms have not been explained yet. Several mechanisms such as current−bathymetry interactions or island run-off can fertilize waters in the immediate vicinity or downstream of the islands, allowing phytoplankton enhancement. Here, we took the opportunity of an oceanographic cruise carried out at the end of 2018, to combine in situ and satellite observations to investigate two phytoplanktonic blooms occurring north and south of the archipelago. First, Lagrangian diagnostics show that both chlorophyll-a concentrations (Chl) plumes are advected from the islands. Second, the use of Finite-size Lyaponov Exponent and frontogenesis diagnostics reveal how the Chl plumes are shaped by the passage of a mesoscale cyclonic eddy in the south and by a converging front and finer-scale dynamic activity in the north. Our results based on these observations provide clues to the hypothesis of a fertilization from the islands themselves allowing phytoplankton to thrive. They also highlight the role of advection to disperse and shape the Chl plumes in two regions with contrasting dynamical regimes.

Download Full-text

Drivers of biases in the extratropical storm tracks in CMIP6

10.5194/egusphere-egu2020-9745 ◽

2020 ◽

Author(s):

Matthew Priestley ◽

Duncan Ackerley ◽

Jennifer Catto ◽

Kevin Hodges ◽

Ruth McDonald ◽

...

Keyword(s):

Large Scale ◽

Climate Models ◽

Storm Track ◽

Storm Tracks ◽

Extratropical Cyclones ◽

Ocean Coupling ◽

Coupled Climate Models ◽

The Mean ◽

The Impact

Extratropical cyclones are the leading driver of the day-to-day weather variability and wintertime losses for Europe. In the latest generation of coupled climate models, CMIP6, it is hoped that with improved modelling capabilities come improvements in the structure of the storm track and the associated cyclones. Using an objective cyclone identification and tracking algorithm the mean state of the storm tracks in the CMIP6 models is assessed as well as the representation of explosively deepening cyclones. Any developments and improvements since the previous generation of models in CMIP5 are discussed, with focus on the impact of model resolution on storm track representation. Furthermore, large-scale drivers of any biases are investigated, with particular focus on the role of atmosphere-ocean coupling via associated AMIP simulations and also the influence of large-scale dynamical and thermodynamical features.

Download Full-text

An Evaluation of Northern Australian Wet Season Rainfall Bursts in CMIP5 Models

Journal of Climate ◽

10.1175/jcli-d-17-0637.1 ◽

2018 ◽

Vol 31 (19) ◽

pp. 7789-7802 ◽

Cited By ~ 3

Author(s):

Sugata Narsey ◽

Michael J. Reeder ◽

Christian Jakob ◽

Duncan Ackerley

Keyword(s):

Outgoing Longwave Radiation ◽

Climate Models ◽

Longwave Radiation ◽

Cmip5 Models ◽

Madden Julian Oscillation ◽

Wet Season ◽

The North ◽

Coupled Climate Models ◽

The Tropics ◽

The Relationship

The simulation of northern Australian wet season rainfall bursts by coupled climate models is evaluated. Individual models produce vastly different amounts of precipitation over the north of Australia during the wet season, and this is found to be related to the number of bursts they produce. The seasonal cycle of bursts is found to be poor in most of the models evaluated. It is known that northern Australian wet season bursts are often associated with midlatitude Rossby wave packets and their surface signature as they are refracted toward the tropics. The relationship between midlatitude waves and the initiation of wet season bursts is simulated well by the models evaluated. Another well-documented influence on the initiation of northern Australian wet season bursts is the Madden–Julian oscillation (MJO). No model adequately simulated the tropical outgoing longwave radiation temporal–spatial patterns seen in the reanalysis-derived OLR. This result suggests that the connection between the MJO and the initiation of northern Australian wet season bursts in models is poor.

Download Full-text

North Atlantic Ocean Circulation Response to Stochastic Mesoscale Weather Systems

10.5194/egusphere-egu21-1310 ◽

2021 ◽

Author(s):

Shenjie Zhou ◽

Xiaoming Zhai ◽

Ian Renfrew

Keyword(s):

Ocean Circulation ◽

North Atlantic ◽

Climate Models ◽

Meridional Overturning Circulation ◽

Ocean Dynamics ◽

Ensemble Prediction ◽

Subpolar Gyre ◽

Atmospheric Forcing ◽

The North ◽

The North Atlantic

The ocean is forced by the atmosphere on a range of spatial and temporal scales. In ocean and climate models the resolution of the atmospheric forcing sets a limit on the scales that are represented. For typical climate models this means mesoscale (< 400 km) atmospheric forcing is absent. Previous studies have demonstrated that mesoscale forcing significantly affects key ocean circulation systems such as the North Atlantic Subpolar gyre and the Atlantic Meridional Overturning Circulation (AMOC). However, the approach of these studies has either been ad hoc or limited in resolution. Here we present ocean model simulations with and without realistic mesoscale atmospheric forcing that represents scales down to 10 km. We use a novel stochastic parameterization &#8211; based on a cellular automaton algorithm that is common in weather forecasting ensemble prediction systems&#160;&#8211; to represent spatially coherent weather systems over a range of scales, including down to the smallest resolvable by the ocean grid. The parameterization is calibrated spatially and temporally using marine wind observations. The addition of mesoscale atmospheric forcing leads to coherent patterns of change in the sea surface temperature and mixed-layer depth. It also leads to non-negligible changes in the volume transport in the North Atlantic subtropical gyre (STG) and subpolar gyre (SPG) and in the AMOC. A non-systematic basin-scale circulation response to the mesoscale wind perturbation emerges &#8211; an in-phase oscillation in northward heat transport across the gyre boundary, partly driven by the constantly enhanced STG, correspoding to an oscillatory behaviour in SPG and AMOC indices with a typical time scale of 5-year, revealing the importance of ocean dynamics in generating non-local ocean response to the stochastic mesoscale atmospheric forcing. Atmospheric convection-permitting regional climate simulations predict changes in the intensity and frequency of mesoscale weather systems this century, so representing these systems in coupled climate models could bring higher fidelity in future climate projections.

Download Full-text

Climate change in the tropical Atlantic

10.5194/egusphere-egu2020-17853 ◽

2020 ◽

Author(s):

Noel Keenlyside ◽

Lander Crespo ◽

Shunya Koseki ◽

Lea Svendsen ◽

Ingo Richter

Keyword(s):

Climate Change ◽

Climate Models ◽

Coupled Model ◽

Historical Period ◽

Tropical Atlantic ◽

Gulf Of Guinea ◽

Coupled Models ◽

Model Biases ◽

Warming Pattern

The tropical Atlantic SST have warmed by about 1 degree over the historical period, with greatest warming in the east, along the African coast and in the Gulf of Guinea. Experiments performed from the Coupled Model Intercomparison Projects (CMIP) indicate that models fail to reproduce this warming pattern, instead showing a rather uniform warming. Future projections with these models also tend to show rather uniform warming. In constrast. results from anomaly coupled models indicate that model biases impact the ability of climate models to simulate warming patterns in the tropical Atlantic. Here we investigate the role of model biases on climate change in the tropical Atlantic in the CMIP experiments. In addition, we have analyzed impacts of global warming on tropical Atlantic climate variability, and we assess the sensitive of the results are to model biases.

Download Full-text