Atmospheric forcing of the Eastern Mediterranean Transient by midlatitude cyclones

2012 ◽  
Vol 39 (3) ◽  
pp. n/a-n/a ◽  
Author(s):  
Joy Romanski ◽  
Anastasia Romanou ◽  
Michael Bauer ◽  
George Tselioudis
Keyword(s):  
Eastern Mediterranean ◽  
Atmospheric Forcing ◽  
Midlatitude Cyclones

scholarly journals Investigation of the Inherent Variability of the Mediterranean Sea Under Contrasting Extreme Climatic Conditions

2021 ◽  
Vol 8 ◽  
Author(s):  
Angeliki Sampatakaki ◽  
Vassilis Zervakis ◽  
Ioannis Mamoutos ◽  
Elina Tragou ◽  
Alexandra Gogou ◽  
...  
Keyword(s):  
Mediterranean Sea ◽  
Thermohaline Circulation ◽  
Eastern Mediterranean ◽  
Internal Variability ◽  
Climatic Conditions ◽  
Spatiotemporal Variability ◽  
Atmospheric Forcing ◽  
Buoyancy Forcing ◽  
Deep Layers ◽  
The Mediterranean

The internal variability of the thermohaline circulation of the Mediterranean Sea is examined under contrasting extreme thermal and mass atmospheric forcing conditions. Three millennium-long numerical simulation experiments were performed under: (a) the current climatology, (b) a strong buoyancy forcing (SBF) scenario due to cold and dry conditions resembling the Younger Dryas event, and (c) a weak buoyancy forcing (WBF) scenario due to S1a sapropel deposition-like conditions (warm and wet). To isolate the inherent variability of the system, independent of interannual atmospheric forcing variability, the latter was defined as a perpetual year pertinent to each experiment. Self-diagnosed heat and salt fluxes, consistent to sea-surface characteristics of the above periods, forced three millenium-long, relaxation-free numerical experiments. These simulations were preceded by initial spin-up periods. The inherent spatiotemporal variability of the Mediterranean Sea was analyzed using the empirical orthogonal function (EOF) and spectral analysis on the simulated density fields. Our results revealed that the Mediterranean Sea exhibits high sensitivity to climatic conditions, allowing its circulation to change from anti-estuarine (for the SBF scenario, leading to a buoyancy loss to the atmosphere) to estuarine (for the WBF scenario, corresponding to a buoyancy gain from the atmosphere). In all three experiments, the interannual and decennial variabilities dominate in upper layers, and the decennial variability dominates in the Gibraltar and Sicily Straits. Under current climatic conditions the first two EOF modes express only 60% of the density variability in the deep layers. This contribution exceeds 90% under more extreme conditions. Moreover, the first EOF modes correspond to a basin-wide in-phase variability of the deep layers under the reference and WBF conditions. During SBF conditions the first modes reveal a vertical buoyancy exchange between upper and deeper layers. The second EOF mode of deep waters under both extreme scenarios showed that the western and eastern basins exchange buoyancy in decennial (for the cold/dry) and interdecennial (for the warm/humid) timescales. The residence time of the Eastern Mediterranean deep water was diagnosed to be centennial, semicentennial, and intercentennial for the cases of current period, SBF, and WBF, respectively.

scholarly journals Drivers of the decadal variability of the North Ionian Gyre upper layer circulation during 1910–2010: a regional modelling study

2021 ◽  
Author(s):  
Feifei Liu ◽  
Uwe Mikolajewicz ◽  
Katharina D. Six
Keyword(s):  
Ocean Circulation ◽  
Adriatic Sea ◽  
Decadal Variability ◽  
Eastern Mediterranean ◽  
Circulation Model ◽  
Atmospheric Forcing ◽  
Sensitivity Experiment ◽  
Data Set ◽  
The North ◽  
Upper Layer Circulation

AbstractA long simulation over the period 1901–2010 with an eddy-permitting ocean circulation model is used to study the variability of the upper layer circulation in the North Ionian Gyre (NIG) in the Eastern Mediterranean Sea (EMed). The model is driven by the atmospheric forcing from the twentieth century reanalysis data set ERA-20C, ensuring a consistent performance of the model over the entire simulation period. The main modes of variability known in the EMed, in particular the decadal reversals of the NIG upper layer circulation observed since the late 1980s are well reproduced. We find that the simulated NIG upper layer circulation prior to the observational period is characterized by long-lasting cyclonic phases with weak variability during years 1910–1940 and 1960–1985, while in the in-between period (1940–1960) quasi-decadal NIG circulation reversals occur with similar characteristics to those observed in the recent decades. Our simulation indicates that the NIG upper layer circulation is rather prone to the cyclonic mode with occasional kicks to the anticyclonic mode. The coherent variability of the NIG upper layer circulation mode and of the Adriatic Deep Water (AdDW) outflow implies that atmospheric forcing triggering strong AdDW formation is required to kick the NIG into an anticyclonic circulation 1–2 years later. A sensitivity experiment mimicking a cold winter event over the Adriatic Sea supports this hypothesis. Our simulation shows that it is the multi-decadal variability of the salinity in the Adriatic Sea that leads to periods where low salinity prevents strong AdDW formation events. This explains the absence of quasi-decadal NIG reversals during 1910–1940 and 1960–1985.

EM-MHeatWaves: Eastern Mediterranean marine heatwaves - Ocean responses to atmospheric forcing and impacts on marine ecosystems

2021 ◽  
Author(s):  
Elena Xoplaki ◽  
Elina Tragou ◽  
Alexandra Gogou ◽  
Vassilis Zervakis ◽  
Drosos Koutsoubas ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
Coastal Upwelling ◽  
Current Knowledge ◽  
Eastern Mediterranean ◽  
Marine Ecosystem ◽  
Statistical Characteristics ◽  
The Black Sea ◽  
Oceanic Circulation ◽  
Atmospheric Forcing ◽  
Marine Research

<p>Even before the introduction of the term “Marine Heat Wave” (MHW) and its statistical definition in global-scale studies, the scientific community had studied and recorded potentially harmful impacts of persistent conditions of warm surface layers and highly stratified water columns on the marine ecosystem. The main triggers for MHWs are yet not well understood and the current knowledge is mainly based on mass mortalities linked to temperature anomalies. EM-MHeatWaves is an interdisciplinary, collaborative, DAAD/IKYDA funded research project that investigates the atmospheric forcing, oceanic circulation and ecosystem response of MHWs in the Eastern Mediterranean Sea over the past 35 years. Two universities (Justus-Liebig-University Giessen, University of the Aegean) and one research center (Hellenic Centre for Marine Research) re-examine the definition of MHWs with emphasis on the Eastern Mediterranean by applying a holistic approach that includes reverse-engineering using model data and reanalysis covering the period 1985 to 2014. We focus on the Eastern Mediterranean because of the high sensitivity of the basin’s ecosystem to atmospheric and marine warming events, the invasion of tropical alien (Lessepsian) species, the characteristic oceanic circulation with the Eastern Mediterranean Transient events, the exchange with the Black Sea through the Turkish Strait System as well as the coastal upwelling areas. In order to study the spatiotemporal characteristics of Eastern Mediterranean MHWs we work towards a better understanding of the oceanographic processes as well as of the compounding character of the atmospheric contribution. Based on the response of marine biogeochemical cycles (depletion of subsurface oxygen levels, observed changes in the mixed layer and chlorophyll maxima depths, nutrient stoichiometries, carbon uptake and sequestration rates) and their impacts on ecosystems (i.e. shifts in planktonic and benthic community regimes, mass mortality events, disease outbreaks, etc.), triggered by the rise of ocean temperatures, we study the statistical characteristics of the oceanic temperatures and assess the corresponding ocean circulation, the synchronous and lagged contribution of the large scale atmospheric circulation. We further study the signature of these extreme Mediterranean MHW events in future projections from model runs with respect to duration, severity and spatial extent and compare them to reanalysis.    <br>EM-MHeatWaves aims at strengthening the partnership between the German and Greek institutions by conducting joint research at a high scientific level.</p>

scholarly journals A nested circulation model for the North Aegean Sea

Ocean Science ◽  
2007 ◽  
Vol 3 (1) ◽  
pp. 1-16 ◽  
Author(s):  
V. Kourafalou ◽  
K. Tsiaras
Keyword(s):  
High Resolution ◽  
Eastern Mediterranean ◽  
Circulation Model ◽  
Aegean Sea ◽  
Scale Model ◽  
Atmospheric Forcing ◽  
The North ◽  
Basin Scale ◽  
North Aegean ◽  
North Aegean Sea

Abstract. A multi-nested approach has been employed for numerical simulations in the northern part of the Aegean Sea in the framework of the MFSTEP (Mediterranean Forecast System: Toward Environmental Predictions) project. The high resolution (~1.6 km) hydrodynamic model of the North Aegean Sea (NAS) has been nested within a coarser model of the Eastern Mediterranean (resolution ~3.6 km) which is also nested within a basin scale model for the Mediterranean Sea (resolution of ~7 km). The high resolution of the NAS model allows the representation of topographic details that have never been reproduced in modelling studies of the region. Such details can enhance the simulation of coastal features, but can also influence basin-scale processes, such as the pathways of waters of Black Sea origin inflowing at the Dardanelles Straits and bifurcating through island passages. We employ comparisons of the North Aegean and Eastern Mediterranean models in terms of computed flow fields and distribution of hydrodynamic properties, to evaluate the nesting procedure, the initialization requirements and the ability of a nested model to perform reliable short term simulations that employ high resolution atmospheric forcing, when initialized from a coarser OGCM. We show that the topographic details of the high resolution, nested NAS model affect the distribution of the Dardanelles plume and the evolution of coastal currents, while the imposed high frequency, high resolution atmospheric forcing allows for the formation of an overall energetic flow field after a few days of spin-up period. Increased resolution and smaller coastal depth in the NAS simulations influence the flow through island passages and straits. A longer initialization procedure results in the establishment of stronger currents and better-developed buoyant plumes.

scholarly journals A nested circulation model for the North Aegean Sea

2006 ◽  
Vol 3 (3) ◽  
pp. 343-372 ◽  
Author(s):  
V. H. Kourafalou ◽  
K. P. Tsiaras
Keyword(s):  
High Resolution ◽  
Eastern Mediterranean ◽  
Circulation Model ◽  
Aegean Sea ◽  
Scale Model ◽  
Atmospheric Forcing ◽  
The North ◽  
Basin Scale ◽  
North Aegean ◽  
North Aegean Sea

Abstract. A multi-nested approach has been employed for numerical simulations in the northern part of the Aegean Sea in the framework of the MFSTEP (Mediterranean Forecast System: Toward Environmental Predictions) project. The high resolution (~1.6 km) hydrodynamic model of the North Aegean Sea (NAS) has been nested within a coarser model of the Eastern Mediterranean (resolution ~3.6 km) which is also nested within a basin scale model for the Mediterranean Sea (resolution of ~7 km). The high resolution of the NAS model allows the representation of topographic details that have never been reproduced in modelling studies of the region. Such details can enhance the simulation of coastal features, but can also influence basin-scale processes, such as the pathways of waters of Black Sea origin inflowing at the Dardanelles Straits and bifurcating through island passages. We employ comparisons of the North Aegean and Eastern Mediterranean models in terms of computed flow fields and distribution of hydrodynamic properties, to evaluate the nesting procedure, the initialization requirements and the ability of a nested model to perform reliable short term simulations that employ high resolution atmospheric forcing, when initialized from a longer running coarser OGCM. We show that the topographic details of the high resolution, nested NAS model mostly affect the distribution of the Dardanelles plume, while the imposed high frequency, high resolution atmospheric forcing allows for the formation of an overall energetic flow field after a few days of spin-up period. A longer initialization procedure is suggested for the establishment of stronger currents and better developed buoyant plumes.

scholarly journals Long-Term Changes, Inter-Annual, and Monthly Variability of Sea Level at the Coasts of the Spanish Mediterranean and the Gulf of Cádiz

Geosciences ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 350
Author(s):  
Manuel Vargas-Yáñez ◽  
Elena Tel ◽  
Francina Moya ◽  
Enrique Ballesteros ◽  
Mari Carmen García-Martínez
Keyword(s):  
Sea Level ◽  
Linear Models ◽  
Numerical Models ◽  
Eastern Mediterranean ◽  
Tide Gauges ◽  
Atmospheric Forcing ◽  
Contributing Factors ◽  
Sea Level Variability ◽  
Coastal Sea

One of the effects of climate change is the rise of sea level, which poses an important threat to coastal areas. Therefore, the protection and management of coastal ecosystems as well as human infrastructures and constructions require an accurate knowledge of those changes occurring at a local scale. In this study, long time series of sea level from tide gauges distributed along the southern (Atlantic) and eastern (Mediterranean) Spanish coasts were analyzed. Linear trends were calculated for two periods, from early 1940s to 2018 and from 1990 to 2018. Values for the former period ranged between 0.68 and 1.22 mm/year. These trends experienced a significant increase for the second period, when they ranged between 1.5 and 4.6 mm/year. Previous research analyzed the effect of atmospheric forcing in the Mediterranean Sea by means of 2D numerical models, and the steric contribution was directly evaluated by the integration of density along the water column. In this study, the effect of atmospheric forcing and the thermosteric and halosteric contributions on coastal sea level were empirically determined by means of statistical linear models that established which factors affected sea level at each location and what the numerical response of the observed sea level was to the contributing factors. Atmospheric pressure and the west–east component of the wind hada significant contribution to the sea level variability at most of the tide gauges. The thermosteric and halosteric components of sea level also contributed to the sea level variability at all the tide gauges, with the only exception of Alicante. Atmospheric forcing and the steric components of sea level experienced long-term trends. The combination of such trends, with the response of sea level to these factors, allowed us to estimate their contribution to the observed sea level trends. The part of these trends not explained by the atmospheric variables and the steric contributions was attributed to mass addition. Trends associated with mass addition ranged between 0.6 and 1.2 mm/year for the period 1948–2018 and between 1.0 and 4.5 mm/year for the period 1990–2018.

scholarly journals The response of Mediterranean thermohaline circulation to climate change: a minimal model

2009 ◽  
Vol 5 (4) ◽  
pp. 713-720 ◽  
Author(s):  
P. Th. Meijer ◽  
H. A. Dijkstra
Keyword(s):  
Minimal Model ◽  
General Circulation ◽  
Large Scale ◽  
Thermohaline Circulation ◽  
Eastern Mediterranean ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Ocean Model ◽  
Atmospheric Forcing ◽  
Overturning Circulation

Abstract. Physics-based understanding of the effects of paleoclimate and paleogeography on the thermohaline circulation of the Mediterranean Sea requires an ocean model capable of long integrations and involving a minimum of assumptions about the atmospheric forcing. Here we examine the sensitivity of the deep circulation in the eastern Mediterranean basin to changes in atmospheric forcing, considered a key factor in the deposition of organic-rich sediments (sapropels). To this extent we explore the setup of an ocean general circulation model (MOMA) with realistic (present-day) bathymetry and highly idealized forcing. The model proves able to qualitatively capture some important features of the large-scale overturning circulation, in particular for the eastern basin. The response to (i) a reduction in the imposed meridional temperature gradient, or (ii) a reduction in net evaporation, proves to be non-linear and, under certain conditions, of transient nature. Consistent with previous model studies, but now based on a minimum of assumptions, we find that a reduction in net evaporation (such as due to an increase in freshwater input) may halt the deep overturning circulation. The ability to perform long model integrations allows us to add the insight that, in order to have the conditions favourable for sapropel formation persist, we must also assume that the vertical mixing of water properties was reduced. The "minimal" model here presented opens the way to experiments in which one truly follows the basin circulation into, or out of, the period of sapropel formation and where forcing conditions are continously adjusted to the precession cycle.

scholarly journals The response of Mediterranean thermohaline circulation to climate change: a minimal model

2009 ◽  
Vol 5 (3) ◽  
pp. 1731-1749 ◽  
Author(s):  
P. Th. Meijer ◽  
H. A. Dijkstra
Keyword(s):  
Minimal Model ◽  
General Circulation ◽  
Large Scale ◽  
Thermohaline Circulation ◽  
Eastern Mediterranean ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Ocean Model ◽  
Atmospheric Forcing ◽  
Overturning Circulation

Abstract. Physics-based understanding of the effects of paleoclimate and paleogeography on the thermohaline circulation of the Mediterranean Sea requires an ocean model capable of long integrations and involving a minimum of assumptions about the atmospheric forcing. Here we examine the sensitivity of the deep circulation in the eastern Mediterranean basin to changes in atmospheric forcing, considered a key factor in the deposition of organic-rich sediments (sapropels). To this extent we explore the setup of an ocean general circulation model (MOMA) with realistic (present-day) bathymetry and highly idealized forcing. The model proves able to qualitatively capture some important features of the large-scale overturning circulation, in particular for the eastern basin. The response to (i) a reduction in the imposed meridional temperature gradient, or (ii) a reduction in net evaporation, proves to be non-linear and, under certain conditions, of transient nature. Consistent with previous model studies, but now based on a minimum of assumptions, we find that a reduction in net evaporation (such as due to an increase in freshwater input) may halt the deep overturning circulation. The ability to perform long model integrations allows us to add the insight that, in order to have the conditions favourable for sapropel formation persist, we must also assume that the vertical mixing of water properties was reduced. The "minimal" model here presented opens the way to experiments in which one truly follows the basin circulation into, or out of, the period of sapropel formation and where forcing conditions are continuously adjusted to the precession cycle.

Sign in / Sign up

Export Citation Format

Share Document