Seasonality of intermediate waters hydrography west of the Iberian Peninsula from an 8 yr semiannual time series of an oceanographic section

Abstract. Seasonality of hydrographical properties at depth in the western Iberian margin (eastern North Atlantic) is analysed from a 2003–2010 time series of a semiannual oceanographic section extending ∼200 nm off Cape Finisterre (43° N). All water masses down to the permanent thermocline (2000 dbar) show a consistent seasonal signature in their thermohaline properties and there is a notable asymmetry between the slope region and the outer ocean (in the surroundings of the Galicia Bank). There is overall cooling and freshening of eastern North Atlantic central waters in summertime, which is larger and deeper-reaching on the slope. In summertime, Mediterranean Water (MW) gets tightly attached against the slope and is uplifted, reinforcing its thermohaline signature and diminishing its presence at the outer ocean. In wintertime the situation reverses, MW seems to detach from the slope and spreads out to the open ocean, even being observed a secondary branch around the Galicia Bank. Thermohaline seasonality at depth shows values up to 0.4 °C and 0.08 in salinity at the lower MW, of the order of 20% of the overall interannual variability observed during the whole period. Decomposition of thermohaline changes at isobaric levels to changes along isoneutral surfaces and changes due to vertical displacements help analyse the physical processes behind the observed seasonality in terms of (1) the large-scale seasonality of the subtropical gyre in response to the seasonal migration of the subtropical high pressure system and subsequent anomalies in Ekman transport and wind stress curl, (2) the continental slope dynamics, characterized by summer upwelling, winter development of the Iberian Poleward Current and Mediterranean water spreading, and (3) the possible influence of seasonal changes of water mass properties at their formation sources.

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Seasonality of intermediate waters hydrography west of the Iberian Peninsula from a 8-yr semiannual timeseries of an oceanographic section

Ocean Science Discussions ◽

10.5194/osd-9-3393-2012 ◽

2012 ◽

Vol 9 (6) ◽

pp. 3393-3430 ◽

Cited By ~ 1

Author(s):

E. Prieto ◽

C. González-Pola ◽

A. Lavín ◽

R. F. Sánchez ◽

M. Ruiz-Villarreal

Keyword(s):

North Atlantic ◽

Large Scale ◽

Seasonal Migration ◽

Ekman Transport ◽

Wind Stress Curl ◽

Pressure System ◽

Mass Properties ◽

Vertical Displacements ◽

Eastern North Atlantic ◽

Mediterranean Water

Abstract. Seasonality of hydrographical properties at depth in the western Iberian margin (Eastern North Atlantic) is analysed from a 2003–2010 timeseries of a semi-annual oceanographic section extending ~ 200 nm off Cape Finisterre (43° N). All waters masses down to the whole extent of the permanent thermocline (2000 dbar) show a consistent seasonal signature in their termohaline properties and there is a notable asymmetry between the slope region and the outer ocean (in the surroundings of the Galicia Bank). There is overall cooling and freshening of East North Atlantic Central Waters in summertime, which is larger and deeper-reaching on the slope. In summertime, Mediterranean Water gets tightly attached against the slope and is uplifted, reinforcing its thermohaline signature and diminishing its presence at the outer ocean. In wintertime the situation reverses, MW seems to detach from the slope and spreads out to the open ocean, even developing a secondary branch around the Galicia Bank. Thermohaline seasonality at depth shows values up to 0.4 °C and 0.08 in salinity at the lower MW, of the order of 20 % of the overall interannual variability observed during the whole period. Decomposition of thermohaline changes at isobaric levels to changes along isoneutral surfaces and changes due to vertical displacements helps to analyse the physical processes behind the observed seasonality in terms of (1) the large-scale seasonality of the subtropical gyre in response to the seasonal migration of the subtropical high pressure system and subsequent anomalies in Ekman transport and wind stress curl, (2) the continental slope dynamics, characterized by summer upwelling, winter development of the Iberian Poleward Current and Mediterranean Water spreading and (3) the possible influence of seasonal changes of water mass properties at their formation sources.

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Seasonal Predictability of Wintertime mid-latitude Cyclonic Activity over the North Atlantic and Europe

10.5194/egusphere-egu21-11134 ◽

2021 ◽

Author(s):

Alvise Aranyossy ◽

Sebastian Brune ◽

Lara Hellmich ◽

Johanna Baehr

Keyword(s):

North Atlantic ◽

Large Scale ◽

Jet Stream ◽

Cyclonic Activity ◽

Max Planck ◽

Pressure System ◽

Wind Speeds ◽

Average Lifespan ◽

The North ◽

The North Atlantic

<p>We analyse the connections between the wintertime North Atlantic Oscillation (NAO), the eddy-driven jet stream with the mid-latitude cyclonic activity over the North Atlantic and Europe. We investigate, through the comparison against ECMWF ERA5 and hindcast simulations from the Max Planck Institute Earth System Model (MPI-ESM), the potential for enhancement of the seasonal prediction skill of the Eddy Kinetic Energy (EKE) by accounting for the connections between large-scale climate and the regional cyclonic activity. Our analysis focuses on the wintertime months (December-March) in the 1979-2019 period, with seasonal predictions initialized every November 1st. We calculate EKE from wind speeds at 250 hPa, which we use as a proxy for cyclonic activity. The zonal and meridional wind speeds are bandpass filtered with a cut-off at 3-10 days to fit with the average lifespan of mid-latitude cyclones.&#160;</p><p>Preliminary results suggest that in ERA5, major positive anomalies in EKE, both in quantity and duration, are correlated with a northern position of the jet stream and a positive phase of the NAO. Apparently, a deepened Icelandic low-pressure system offers favourable conditions for mid-latitude cyclones in terms of growth and average lifespan. In contrast, negative anomalies in EKE over the North Atlantic and Central Europe are associated with a more equatorward jet stream, these are also linked to a negative phase of the NAO.&#160; Thus, in ERA5, the eddy-driven jet stream and the NAO play a significant role in the spatial and temporal distribution of wintertime mid-latitude cyclonic activity over the North Atlantic and Europe. We extend this connection to the MPI-ESM hindcast simulations and present an analysis of their predictive skill of EKE for wintertime months.</p>

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Contrasting characteristics of open- and closed- cellular stratocumulus cloud in the Eastern North Atlantic

10.5194/acp-2021-63 ◽

2021 ◽

Author(s):

Michael P. Jensen ◽

Virendra P. Ghate ◽

Dié Wang ◽

Diana K. Apoznanski ◽

Mary J. Bartholomew ◽

...

Keyword(s):

Boundary Layer ◽

North Atlantic ◽

Large Scale ◽

Marine Boundary Layer ◽

Open Cell ◽

Cold Air ◽

Closed Cell ◽

Boundary Layer Cloud ◽

Eastern North Atlantic ◽

Layer Cloud

Abstract. Extensive regions of marine boundary layer cloud impact the radiative balance through their significant shortwave albedo while having little impact on outgoing longwave radiation. Despite this importance, these cloud systems remain poorly represented in large-scale models due to difficulty in representing the processes that drive their lifecycle and coverage. In particular, the mesoscale organization, and cellular structure of marine boundary clouds has important implications for the subsequent cloud feedbacks. In this study, we use long-term (2013–2018) observations from the Atmospheric Radiation Measurement (ARM) Facility's Eastern North Atlantic (ENA) site on Graciosa Island, Azores, Portugal to identify cloud cases with open- or closed-cellular organization. More than 500 hours of each organization type are identified. The ARM observations are combined with reanalysis and satellite products to quantify the cloud, precipitation, aerosol, thermodynamic and large-scale synoptic characteristics associated with these cloud types. Our analysis shows that both cloud organization populations occur during similar sea surface temperature conditions, but the open-cell cases are distinguished by stronger cold-air advection and large-scale subsidence compared to the closed-cell cases, consistent with their formation during cold-air outbreaks. We also find that the open-cell cases were associated with deeper boundary layers, stronger low-level winds, and higher-rain rates compared to their closed-cell counterparts. Finally, raindrops with diameters larger than one millimeter were routinely recorded at the surface during both populations, with a higher number of large drops during the open-cellular cases. The similarities and differences noted herein provide important insights into the environmental and cloud characteristics during varying marine boundary layer cloud mesoscale organization and will be useful for the evaluation of model simulations for ENA marine clouds.

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Contrasting characteristics of open- and closed-cellular stratocumulus cloud in the eastern North Atlantic

Atmospheric Chemistry and Physics ◽

10.5194/acp-21-14557-2021 ◽

2021 ◽

Vol 21 (19) ◽

pp. 14557-14571

Author(s):

Michael P. Jensen ◽

Virendra P. Ghate ◽

Dié Wang ◽

Diana K. Apoznanski ◽

Mary J. Bartholomew ◽

...

Keyword(s):

Boundary Layer ◽

North Atlantic ◽

Large Scale ◽

Marine Boundary Layer ◽

Open Cell ◽

Cold Air ◽

Closed Cell ◽

Boundary Layer Cloud ◽

Eastern North Atlantic ◽

Layer Cloud

Abstract. Extensive regions of marine boundary layer cloud impact the radiative balance through their significant shortwave albedo while having little impact on outgoing longwave radiation. Despite this importance, these cloud systems remain poorly represented in large-scale models due to difficulty in representing the processes that drive their life cycle and coverage. In particular, the mesoscale organization and cellular structure of marine boundary clouds have important implications for the subsequent cloud feedbacks. In this study, we use long-term (2013–2018) observations from the Atmospheric Radiation Measurement (ARM) Facility's Eastern North Atlantic (ENA) site on Graciosa Island, Azores, Portugal, to identify cloud cases with open- or closed-cellular organization. More than 500 h of each organization type are identified. The ARM observations are combined with reanalysis and satellite products to quantify the cloud, precipitation, aerosol, thermodynamic, and large-scale synoptic characteristics associated with these cloud types. Our analysis shows that both cloud organization populations occur during similar sea surface temperature conditions, but the open-cell cases are distinguished by stronger cold-air advection and large-scale subsidence compared to the closed-cell cases, consistent with their formation during cold-air outbreaks. We also find that the open-cell cases were associated with deeper boundary layers, stronger low-level winds, and higher rain rates compared to their closed-cell counterparts. Finally, raindrops with diameters larger than 1 mm were routinely recorded at the surface during both populations, with a higher number of large drops during the open-cellular cases. The similarities and differences noted herein provide important insights into the environmental and cloud characteristics during varying marine boundary layer cloud mesoscale organization and will be useful for the evaluation of model simulations for ENA marine clouds.

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A model of Fe speciation and biogeochemistry at the Tropical Eastern North Atlantic Time-Series Observatory site

Biogeosciences ◽

10.5194/bg-6-2041-2009 ◽

2009 ◽

Vol 6 (10) ◽

pp. 2041-2061 ◽

Cited By ~ 32

Author(s):

Y. Ye ◽

C. Völker ◽

D. A. Wolf-Gladrow

Keyword(s):

Time Series ◽

Vertical Distribution ◽

North Atlantic ◽

Decay Time ◽

Particle Aggregation ◽

Dust Particles ◽

Dimensional Model ◽

One Dimensional ◽

Fe Speciation ◽

Eastern North Atlantic

Abstract. A one-dimensional model of Fe speciation and biogeochemistry, coupled with the General Ocean Turbulence Model (GOTM) and a NPZD-type ecosystem model, is applied for the Tropical Eastern North Atlantic Time-Series Observatory (TENATSO) site. Among diverse processes affecting Fe speciation, this study is focusing on investigating the role of dust particles in removing dissolved iron (DFe) by a more complex description of particle aggregation and sinking, and explaining the abundance of organic Fe-binding ligands by modelling their origin and fate. The vertical distribution of different particle classes in the model shows high sensitivity to changing aggregation rates. Using the aggregation rates from the sensitivity study in this work, modelled particle fluxes are close to observations, with dust particles dominating near the surface and aggregates deeper in the water column. POC export at 1000 m is a little higher than regional sediment trap measurements, suggesting further improvement of modelling particle aggregation, sinking or remineralisation. Modelled strong ligands have a high abundance near the surface and decline rapidly below the deep chlorophyll maximum, showing qualitative similarity to observations. Without production of strong ligands, phytoplankton concentration falls to 0 within the first 2 years in the model integration, caused by strong Fe-limitation. A nudging of total weak ligands towards a constant value is required for reproducing the observed nutrient-like profiles, assuming a decay time of 7 years for weak ligands. This indicates that weak ligands have a longer decay time and therefore cannot be modelled adequately in a one-dimensional model. The modelled DFe profile is strongly influenced by particle concentration and vertical distribution, because the most important removal of DFe in deeper waters is colloid formation and aggregation. Redissolution of particulate iron is required to reproduce an observed DFe profile at TENATSO site. Assuming colloidal iron is mainly composed of inorganic colloids, the modelled colloidal to soluble iron ratio is lower that observations, indicating the importance of organic colloids.

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Dynamic wavelet correlation analysis for multivariate climate time series

Scientific Reports ◽

10.1038/s41598-020-77767-8 ◽

2020 ◽

Vol 10 (1) ◽

Author(s):

Josué M. Polanco-Martínez ◽

Javier Fernández-Macho ◽

Martín Medina-Elizalde

Keyword(s):

Time Series ◽

Tropical Cyclone ◽

North Atlantic ◽

Large Scale ◽

Southern Oscillation ◽

Atlantic Multidecadal Oscillation ◽

Last Millennium ◽

Climate Data ◽

The North ◽

Climate Time Series

AbstractThe wavelet local multiple correlation (WLMC) is introduced for the first time in the study of climate dynamics inferred from multivariate climate time series. To exemplify the use of WLMC with real climate data, we analyse Last Millennium (LM) relationships among several large-scale reconstructed climate variables characterizing North Atlantic: i.e. sea surface temperatures (SST) from the tropical cyclone main developmental region (MDR), the El Niño-Southern Oscillation (ENSO), the North Atlantic Multidecadal Oscillation (AMO), and tropical cyclone counts (TC). We examine the former three large-scale variables because they are known to influence North Atlantic tropical cyclone activity and because their underlying drivers are still under investigation. WLMC results obtained for these multivariate climate time series suggest that: (1) MDRSST and AMO show the highest correlation with each other and with respect to the TC record over the last millennium, and: (2) MDRSST is the dominant climate variable that explains TC temporal variability. WLMC results confirm that this method is able to capture the most fundamental information contained in multivariate climate time series and is suitable to investigate correlation among climate time series in a multivariate context.

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The Empirical Forcing Function as a tool for the diagnosis of large-scale atmospheric anomalies

Annales Geophysicae ◽

10.5194/angeo-28-75-2010 ◽

2010 ◽

Vol 28 (1) ◽

pp. 75-87

Author(s):

C. Andrade ◽

J. A. Santos ◽

J. G. Pinto ◽

J. Corte-Real ◽

S. Leite

Keyword(s):

Atmospheric Circulation ◽

North Atlantic ◽

Potential Vorticity ◽

Radiative Forcing ◽

Large Scale ◽

Atmospheric Flow ◽

Material Derivative ◽

The North ◽

Forcing Function ◽

Eastern North Atlantic

Abstract. The time-mean quasi-geostrophic potential vorticity equation of the atmospheric flow on isobaric surfaces can explicitly include an atmospheric (internal) forcing term of the stationary-eddy flow. In fact, neglecting some non-linear terms in this equation, this forcing can be mathematically expressed as a single function, called Empirical Forcing Function (EFF), which is equal to the material derivative of the time-mean potential vorticity. Furthermore, the EFF can be decomposed as a sum of seven components, each one representing a forcing mechanism of different nature. These mechanisms include diabatic components associated with the radiative forcing, latent heat release and frictional dissipation, and components related to transient eddy transports of heat and momentum. All these factors quantify the role of the transient eddies in forcing the atmospheric circulation. In order to assess the relevance of the EFF in diagnosing large-scale anomalies in the atmospheric circulation, the relationship between the EFF and the occurrence of strong North Atlantic ridges over the Eastern North Atlantic is analyzed, which are often precursors of severe droughts over Western Iberia. For such events, the EFF pattern depicts a clear dipolar structure over the North Atlantic; cyclonic (anticyclonic) forcing of potential vorticity is found upstream (downstream) of the anomalously strong ridges. Results also show that the most significant components are related to the diabatic processes. Lastly, these results highlight the relevance of the EFF in diagnosing large-scale anomalies, also providing some insight into their interaction with different physical mechanisms.

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