Representation of Northwest African upwelling in CMIP5 models

2020 ◽  
Author(s):  
Antonio Castaño-Tierno ◽  
Belén Rodríguez-Fonseca ◽  
Elsa Mohino ◽  
Teresa Losada
Keyword(s):  
Coastal Upwelling ◽  
Sea Surface ◽  
Cmip5 Models ◽  
Pressure Gradients ◽  
Ekman Pumping ◽  
North West ◽  
The North ◽  
Northwest Africa ◽  
Leading Mode ◽  
Pressure Changes

<p>The Northwest Africa (NWA) upwelling region is located along the Senegalese and Mauritanian coast, between 10°N and 25°N and in a very narrow longitudinal band. In this region, most of the upwelled waters are due to alongshore surface winds through Ekman pumping.</p><p>The rapid increase in the upper ocean upwelling in this region along the 20th century and the contradictions found about future projections put forward the need for a better understanding of model’s ability to simulate Ekman induced upwelling processes.</p><p>In this work we assess intermodel variability to better understand the causes of different responses and spread among a set of CMIIP5 models.  </p><p>Results suggest that the seasonal cycle of NWA upwelling is qualitatively well simulated by CMIP5 models, although models tend to show strong biases for the permanent upwelling latitudes (north of 20°N) and the seasonal upwelling area (around 15°N in boreal spring). The maximum vertical temperature gradient shown by CMIP5 models is higher than that of SODA reanalysis and prevents cold waters from deeper layers to reach the surface, thus making coastal upwelling less effective in affecting sea surface temperatures.</p><p>Most of the intermodel variance is explained by the two first EOF modes of intermodel variability. The first mode shows a latitudinal structure, with a maximum in the permanent upwelling season, while. the second one is more seasonal. Both modes are very related to changes in the North-West Africa land-sea surface pressure gradient. In the case of the leading mode, incoming solar radiation differences between the North African desert and the ocean are the cause of the pressure gradients. For the second mode pressure changes in the Atlantic Ocean are driven by ITCZ shifts in response to interhemispheric differential warming.</p>

Seasonal to interannual variations of wind forcing in the Peruvian upwelling system

2020 ◽  
Author(s):  
Sadegh Yari ◽  
Volker Mohrholz
Keyword(s):  
Wind Stress ◽  
Coastal Upwelling ◽  
Temporal Variations ◽  
Wind Forcing ◽  
Enso Cycle ◽  
Spatial And Temporal Variability ◽  
Ekman Pumping ◽  
North West ◽  
Upwelling System ◽  
Peruvian Coast

<p>The Humboldt (Peruvian) Upwelling System (HUS) is the most productive among the main Eastern Boundary Upwelling Systems (EBUS), namely California, North West Africa, Benguela and itself. In spite of comparable upwelling intensity its fisheries production exceeds that of the other upwelling systems considerably (Chavez and Messie 2009). Wind is the major driving force of the coastal and curl driven upwelling, that controlls the nutrient supply from the deep water pool to the euphotic surface layer. Strength, spatial and temporal variability of the wind forcing are subjected to seasonal and interannual changes. The core of this study is describe the wind driven upwelling cells in the Peruvian coastal area in detail using long-term data which is not well understood. A better understanding of the state and dynamics of HUS seems essential for fututre regional climate predictions. ASCAT wind stress data for the period of 11 years (2008-2018) is analyzed to assess the spatio-temporal variations of the wind stress field, coastal upwelling and Ekman pumping along the Peruvian coast. The meridional component of wind stress off the peruvian coast, which is the main driver of offshore transport, has been marginally inensified over the entire priod. However, a high level of interannual variability is evident. The El-Niño years show anomalously high wind stress and associated Ekman transoprt. Our results indicate that the southern sector is more influenced by ENSO cycle than the northern sector. Additionally, a strong seasonality in the wind stress is observed. During the austral summer (December-February) the wind stress show the minimum value while the high values are observed in July-September.</p>

scholarly journals Application of interval approach to pattern recognition for identification of preceeding baric structures that determine extreme thermal modes in the South-Kuril area in summer

2021 ◽  
Vol 201 (2) ◽  
pp. 470-483
Author(s):  
T. A. Shatilina ◽  
G. Sh. Tsitsiashvili ◽  
T. V. Radchenkova
Keyword(s):  
East Asia ◽  
Sea Surface ◽  
Okhotsk Sea ◽  
The South ◽  
West Pacific ◽  
North West ◽  
The North ◽  
Interval Approach ◽  
Warm Summer ◽  
Extreme Cold

Patterns of atmosphere baric fields preceeded to development of extreme thermal modes in the South-Kuril area in summer are identified using the interval approach to their recogni tion. The best recognition rates are noted for the field of AT 500 hPa over the region of East Asia in February, March, May, and June. Extreme cold summer conditions in the South-Kuril area in summer were preceeded by development of AT 500 hPa trough and baric depression at the sea surface over East Asia in these winter and spring months. Warm summer conditions in the South-Kuril area were preceeded by opposite patterns, as AT 500 hPa ridge over the North-West Pacific and high pressure over the Okhotsk Sea, with positive anomalies of H500 height over the North-West Pacific and Kuril Islands.

scholarly journals Temporal and spatial characteristics of sea surface height variability in the North Atlantic Ocean

Ocean Science ◽  
2006 ◽  
Vol 2 (2) ◽  
pp. 147-159 ◽  
Author(s):  
D. Cromwell
Keyword(s):  
North Atlantic ◽  
Sea Surface Height ◽  
Sea Surface ◽  
Altimeter Data ◽  
Atlantic Basin ◽  
North Atlantic Basin ◽  
The North ◽  
Second Mode ◽  
Leading Mode ◽  
The North Atlantic

Abstract. We investigate the spatial and temporal variability of sea surface height (SSH) in the North Atlantic basin using satellite altimeter data from October 1992–January 2004. Our primary aim is to provide a detailed description of such variability, including that associated with propagating signals. We also investigate possible correlations between SSH variability and atmospheric pressure changes as represented by climate indices. We first investigate interannual SSH variations by deriving the complex empirical orthogonal functions (CEOFs) of altimeter data lowpass-filtered at 18 months. We determine the spatial structure of the leading four modes (both in amplitude and phase) and also the associated principal component (PC) time series. Using wavelet analysis we derive the time-varying spectral density of the PCs, revealing when particular modes were strongest between 1992–2004. The spatial pattern of the leading CEOF, comprising 30% of the total variability, displays a 5-year periodicity in phase; signal propagation is particularly marked in the Labrador Sea. The second mode, with a dominant 3-year signal, has strong variability in the eastern basin. Secondly, we focus on the Azores subtropical frontal zone. The leading mode (35%) is strong in the south and east of this region with strong variations at 3- and 5-year periods. The second mode (21%) has a near-zonal band of low variance between  22°–27° N, sandwiched between two regions of high variance. Thirdly, we lowpass filter the altimeter data at a cutoff of 30 days, instead of 18 months, in order to retain signals associated with propagating baroclinic Rossby waves and/or eddies. The leading mode is the annual steric signal, around 46% of the SSH variability. The third and fourth CEOFs,  11% of the remaining variability, are associated with westward propagation which is particularly dominant in a "waveband" between 32°–36° N. For all three cases considered above, no significant cross-correlation is found between the North Atlantic Oscillation index and the amplitude of the leading four PCs of interannual SSH variability. The only exception is an anti-correlation found over the North Atlantic basin between the NAO and the 4th PC. In the subtropical front, the East Atlantic Pattern index is anti-correlated with the leading PC for SSH variations lowpass filtered at 30 days. Further investigation of forcing mechanisms is suggested using hindcasts from ocean general circulation models.

scholarly journals Appearance of the common paper nautilus Argonauta argo related to the increase of the sea surface temperature in the north-eastern Atlantic

2002 ◽  
Vol 82 (5) ◽  
pp. 855-858 ◽  
Author(s):  
A. Guerra ◽  
A.F. González ◽  
F. Rocha
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
First Record ◽  
Mature Female ◽  
Sea Surface ◽  
North West ◽  
The North ◽  
North Eastern ◽  
The Common ◽  
The Relationship

The relationship between the increase of the sea surface temperature observed off the Galician coast and the appearance of a tropical poikilotherm species Argonauta argo in these coasts is discussed. This is the first record of Argonautaargo in the north-west Iberian Peninsula. A female of this species was captured alive near the surface at dusk on 22 December 2000 in the Ria de Aldán (42°15′N–08°48′W). The specimen, a mature female of 70 mm mantle length and 96 mm shell diameter, died 36 hours after introduction in the tank.

North Australian Sea Surface Temperatures and the El Niño–Southern Oscillation in the CMIP5 Models

2012 ◽  
Vol 25 (18) ◽  
pp. 6375-6382 ◽  
Author(s):  
Jennifer L. Catto ◽  
Neville Nicholls ◽  
Christian Jakob
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
La Niña ◽  
Sea Surface ◽  
Cmip5 Models ◽  
Sea Surface Temperatures ◽  
The North ◽  
La Nina ◽  
Surface Temperatures

Abstract Aspects of the climate of Australia are linked to interannual variability of the sea surface temperatures (SSTs) to the north of the country. SST anomalies in this region have been shown to exhibit strong, seasonally varying links to ENSO and tropical Pacific SSTs. Previously, the models participating in phase 3 of the Coupled Model Intercomparison Project (CMIP3) have been evaluated and found to vary in their abilities to represent both the seasonal cycle of correlations between the Niño-3.4 and north Australian SSTs and the evolution of SSTs during composite El Niño and La Niña events. In this study, the new suite of models participating in the CMIP5 is evaluated using the same method. In the multimodel mean, the representation of the links is slightly improved, but generally the models do not capture the strength of the negative correlations during the second half of the year. The models also still struggle to capture the SST evolution in the north Australian region during El Niño and La Niña events.

scholarly journals Temporal and spatial characteristics of sea surface height variability in the North Atlantic Ocean

2006 ◽  
Vol 3 (3) ◽  
pp. 609-636 ◽  
Author(s):  
D. Cromwell
Keyword(s):  
North Atlantic ◽  
Principal Components ◽  
Sea Surface Height ◽  
Sea Surface ◽  
Frontal Region ◽  
Altimeter Data ◽  
The North ◽  
Second Mode ◽  
Leading Mode ◽  
The North Atlantic

Abstract. We investigate the spatial and temporal variability of sea surface height (SSH) in the North Atlantic basin using altimeter data from October 1992–January 2004. Our primary aim is to provide a fuller description of such variability, particularly that associated with propagating signals. We also investigate possible correlations between SSH variability and climate indices. We first investigate interannual SSH variations by deriving the complex empirical orthogonal functions (CEOFs) of altimeter data lowpass-filtered at 18 months. We determine the spatial structure of the leading four modes (both in amplitude and phase) and also the associated principal components (PCs). Using wavelet analysis we derive the time-varying spectral density of the PCs revealing when particular modes are strongest between 1992–2004. The spatial pattern of the leading CEOF, comprising 30% of the total variability, has a 5-year period. Signal propagation with a 5-year period is also observed in the Labrador Sea. The second mode, with a dominant 3-year signal, has strong variability in the eastern basin. We next focus on the Azores subtropical frontal region. The leading mode (35%) is strong in the south and east of this region. The second mode (21%) has a near-zonal band of low variance between ~22°–27° N sandwiched between two regions of high variance. We then lowpass filter the altimeter data at a cutoff of 30 days, instead of 18 months, in order to retain signals associated with propagating baroclinic Rossby waves. The leading mode is the annual steric signal, around 46% of the SSH variability. The third and fourth CEOFs, 11% of the remaining variability, are associated with westward propagation which is particularly dominant in a ''waveband'' between 32°–36° N. No significant cross-correlation is found between the North Atlantic Oscillation index and the amplitude of the leading two principal components of interannual SSH variability. The East Atlantic Pattern index, however, is correlated with the principal components of the two leading modes of SSH variability, particularly with PC2 in the Azores subtropical frontal region. Further investigation of forcing mechanisms is suggested using hindcasts from ocean general circulation models.

scholarly journals Can wave coupling improve operational regional ocean forecasts for the North-West European Shelf?

2018 ◽  
Author(s):  
Huw W. Lewis ◽  
Juan Manuel Castillo Sanchez ◽  
John Siddorn ◽  
Robert R. King ◽  
Marina Tonani ◽  
...  
Keyword(s):  
Mixed Layer ◽  
Sea Surface ◽  
Ocean Wave ◽  
Prediction System ◽  
Wave Coupling ◽  
North West ◽  
The North ◽  
European Shelf ◽  
Ocean Prediction ◽  
The Impact

Abstract. Operational ocean forecasts are typically produced by modelling systems run using a forced mode approach. The evolution of the ocean state is not directly influenced by surface waves, and the ocean dynamics are driven by an external source of meteorological data which is independent of the ocean state. Model coupling provides one approach to increase the extent to which ocean forecast systems can represent the interactions and feedbacks between ocean, waves and the atmosphere seen in nature. This paper demonstrates the impact of improving how the effect of waves on the momentum exchange across the ocean-atmosphere interface is represented through ocean-wave coupling on the performance of an operational regional ocean prediction system. This study focuses on the eddy-resolving (1.5 km resolution) Atlantic Margin Model (AMM15) ocean model configuration for the North-West European Shelf (NWS) region. A series of two-year duration forecast trials of the Copernicus Marine Environment Monitoring Service (CMEMS) North-West Shelf regional ocean prediction system are analysed. The impact of including ocean-wave feedbacks via dynamic coupling on the simulated ocean is discussed. The main interactions included are the modification of surface stress by wave growth and dissipation, Stokes–Coriolis forcing and wave height dependent ocean surface roughness. Given the relevance to operational forecasting, trials with and without ocean data assimilation are considered. Summary forecast metrics demonstrate that the ocean-wave coupled system is a viable evolution for future operational implementation. When results are considered in more depth, wave coupling was found to result in an annual cycle of relatively warmer winter and cooler summer sea surface temperatures for seasonally stratified regions of the NWS. This is driven by enhanced mixing due to waves, and a deepening of the ocean mixed layer during summer. The impact of wave coupling is shown to be reduced within the mixed layer with assimilation of ocean observations. Evaluation of salinity and ocean currents against profile measurements in the German Bight demonstrates improved simulation with wave coupling relative to control simulations. Further, evidence is provided of improvement to simulation of extremes of sea surface height anomalies relative to coastal tide gauges.

Drift of large tabular icebergs in response to atmospheric surface pressure gradients, an observational study

2010 ◽  
Vol 22 (2) ◽  
pp. 199-208 ◽  
Author(s):  
Ian D. Turnbull
Keyword(s):  
Surface Pressure ◽  
Ocean Current ◽  
Pressure Gradients ◽  
Limited Region ◽  
North West ◽  
The North ◽  
Global Positioning ◽  
Parking Lot ◽  
Pressure Anomaly ◽  
Pressure Regime

AbstractWhile ocean current and winds certainly play a major role in guiding the trajectories of free-floating icebergs, the direct effect of atmospheric surface pressure gradients can also have an important influence on the trajectories of large icebergs whose horizontal dimensions are sufficiently great to span synoptic systems. This effect is examined as a way of understanding why icebergs B15A, B15J, B15K, and C16 became “trapped” in a limited region immediately north of Ross Island for a period of several years, without being grounded. This limited region is otherwise flushed annually by summer surface winds and currents; thus the delay of the northward drift of the large icebergs (particularly B15A and B15J) defied expectation. The best explanation for this unexpected iceberg behaviour is that the large volcanic massifs on Ross Island create a quasi-permanent surface pressure anomaly patterned as a dipole, with high pressure in the area upwind of the island (an area appropriately called Windless Bight), and low pressure in the downwind area of the iceberg parking lot. The surface pressure regime experienced by two icebergs B15A and B15K is estimated using Automatic Weather Station observations and Global Positioning System receivers deployed on their surfaces to explain why they remained trapped. Breakdown of the atmospheric pressure gradients allowed them to eventually escape from the region to the north-west.

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