scholarly journals Climatic and Oceanographic Controls on Coral Bleaching Conditions in the Maldivian Region

2020 ◽  
Vol 7 ◽  
Author(s):  
Chiara De Falco ◽  
Annalisa Bracco ◽  
Claudia Pasquero
Keyword(s):  
Coral Bleaching ◽  
Relative Magnitude ◽  
Ocean Model ◽  
Sea Surface ◽  
Spatial And Temporal Variability ◽  
Local Cooling ◽  
Recent Warming ◽  
Regional Ocean Model ◽  
Long Term Trend

The frequency of coral bleaching events has been increasing in recent decades due to the temperature rise registered in most regions near the ocean. Their occurrence in the Maldivian Archipelago has been observed in the months following the peak of strong El Niño events. Bleaching has not been uniform, and some reefs have been only marginally impacted. Here, we use satellite observations and a regional ocean model to explore the spatial and temporal variability of sea surface temperatures (SSTs), and quantify the relative magnitude of ENSO-related episodes with respect to the recent warming. In line with other studies, it is confirmed that the long-term trend in SST significantly increases the frequency of stress conditions for the Maldivian corals. It is also found that the interaction between currents and the steep bathymetry is responsible for a local cooling of about 0.2°C in the Archipelago during the warmest season, with respect to the surrounding waters. This cooling largely reduces the frequency of mortality conditions.

scholarly journals Controlling atmospheric forcing parameters of global ocean models: sequential assimilation of sea surface Mercator-Ocean reanalysis data

Ocean Science ◽  
2009 ◽  
Vol 5 (4) ◽  
pp. 403-419 ◽  
Author(s):  
C. Skandrani ◽  
J.-M. Brankart ◽  
N. Ferry ◽  
J. Verron ◽  
P. Brasseur ◽  
...  
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Reanalysis Data ◽  
Ocean Model ◽  
Sea Surface ◽  
Global Ocean ◽  
Atmospheric Forcing ◽  
Ocean Reanalysis ◽  
Ocean Reanalysis Data

Abstract. In the context of stand alone ocean models, the atmospheric forcing is generally computed using atmospheric parameters that are derived from atmospheric reanalysis data and/or satellite products. With such a forcing, the sea surface temperature that is simulated by the ocean model is usually significantly less accurate than the synoptic maps that can be obtained from the satellite observations. This not only penalizes the realism of the ocean long-term simulations, but also the accuracy of the reanalyses or the usefulness of the short-term operational forecasts (which are key GODAE and MERSEA objectives). In order to improve the situation, partly resulting from inaccuracies in the atmospheric forcing parameters, the purpose of this paper is to investigate a way of further adjusting the state of the atmosphere (within appropriate error bars), so that an explicit ocean model can produce a sea surface temperature that better fits the available observations. This is done by performing idealized assimilation experiments in which Mercator-Ocean reanalysis data are considered as a reference simulation describing the true state of the ocean. Synthetic observation datasets for sea surface temperature and salinity are extracted from the reanalysis to be assimilated in a low resolution global ocean model. The results of these experiments show that it is possible to compute piecewise constant parameter corrections, with predefined amplitude limitations, so that long-term free model simulations become much closer to the reanalysis data, with misfit variance typically divided by a factor 3. These results are obtained by applying a Monte Carlo method to simulate the joint parameter/state prior probability distribution. A truncated Gaussian assumption is used to avoid the most extreme and non-physical parameter corrections. The general lesson of our experiments is indeed that a careful specification of the prior information on the parameters and on their associated uncertainties is a key element in the computation of realistic parameter estimates, especially if the system is affected by other potential sources of model errors.

scholarly journals Toward Estimating Climatic Trends in SST. Part I: Methods of Measurement

2006 ◽  
Vol 23 (3) ◽  
pp. 464-475 ◽  
Author(s):  
Elizabeth C. Kent ◽  
Peter K. Taylor
Keyword(s):  
Measurement Method ◽  
Early Period ◽  
Sea Surface ◽  
Data Set ◽  
Climatic Trends ◽  
The Pacific ◽  
The Mean ◽  
Seasonal Signal ◽  
Long Term Trend

Abstract To assess climatic changes in sea surface temperature (SST), changes in the measurement method with time and the effect of these changes on the mean SST must be quantified. Observations from the International Comprehensive Ocean–Atmosphere Data Set (ICOADS) have been analyzed for the period from 1970 to 1997 using both SST measurement metadata contained within the dataset and a World Meteorological Organization (WMO) catalog of observing ships. The WMO metadata were particularly important in identifying engine-intake SSTs during the 1970s, but increased method identification over the entire period. There are strong regional variations in the preferred SST measurement method, with engine-intake SST most common in the Pacific and bucket SST preferred by countries bordering the Atlantic. The number of engine-intake SSTs increases over time and becomes more numerous than buckets by the early 1980s. There are significant differences between SST observations made by different methods. The rounding of reports is more common for engine-intake SST than for either bucket or hull sensor SST, which degrades its quality. Significant time-varying biases exist between SST derived from buckets and from engine intakes. The SST difference has a strong seasonal signal with bucket SST being relatively cold in winter, probably resulting from heat loss from the buckets, and warm in summer, probably resulting from solar warming or the sampling of a shallow warm layer. There is also a long-term trend with engine-intake SST being relatively warm in the early period but with a small annual mean difference between the two methods by 1990.

scholarly journals THE APPLICATION OF CYCLOSTRATIGRAPHY AND ASTROCHRONOLOGY IN THE NEOGENE MARINE DEPOSITS OF EASTERN MEDITERRANEAN: METOCHIA SECTION (GAVDOS ISLAND)

2006 ◽  
Vol 39 (1) ◽  
pp. 17
Author(s):  
A. Antonarakou ◽  
H. Drinia ◽  
F. Pomoni-Papaioannou
Keyword(s):  
Eastern Mediterranean ◽  
Climatic Changes ◽  
Sea Surface ◽  
Time Interval ◽  
Short Term ◽  
Solar Insolation ◽  
Marine Deposits ◽  
Long Term Trend

Significant lithostratigraphical and micropaleontological signatures, of Milankovitchscale climatic changes are recorded in Miocene deep-sea sediments. As a case study, the Metochia Section, in Gavdos Island, which covers the time interval from 9.7 to 6.6 Ma, is used. This study emphasizes the sedimentological and micropaleontological characteristics of the section, attributed to Milankovitch-scale climatic changes. The short-term variations in climate and faunal composition are related to precession- controlled sedimentary cycles and the long-term trend in climate is related to eccentricity and obliquity cycles. Regional changes in sea surface temperature in combination with variations of solar insolation have caused the cyclical astronomical controlled pattern of Globorotalia species.

scholarly journals Controlling atmospheric forcing parameters of global ocean models: sequential assimilation of sea surface Mercator-Ocean reanalysis data

2009 ◽  
Vol 6 (2) ◽  
pp. 1129-1171
Author(s):  
C. Skandrani ◽  
J.-M. Brankart ◽  
N. Ferry ◽  
J. Verron ◽  
P. Brasseur ◽  
...  
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Reanalysis Data ◽  
Ocean Model ◽  
Sea Surface ◽  
Global Ocean ◽  
Atmospheric Forcing ◽  
Ocean Reanalysis ◽  
Ocean Reanalysis Data

Abstract. In the context of stand alone ocean models, the atmospheric forcing is generally computed using atmospheric parameters that are derived from atmospheric reanalysis data and/or satellite products. With such a forcing, the sea surface temperature that is simulated by the ocean model is usually significantly less accurate than the synoptic maps that can be obtained from the satellite observations. This not only penalizes the realism of the ocean long-term simulations, but also the accuracy of the reanalyses or the usefulness of the short-term operational forecasts (which are key GODAE and MERSEA objectives). In order to improve the situation, partly resulting from inaccuracies in the atmospheric forcing parameters, the purpose of this paper is to investigate a way of further adjusting the state of the atmosphere (within appropriate error bars), so that an explicit ocean model can produce a sea surface temperature that better fits the available observations. This is done by performing idealized assimilation experiments in which Mercator-Ocean reanalysis data are considered as a reference simulation describing the true state of the ocean. Synthetic observation datasets for sea surface temperature and salinity are extracted from the reanalysis to be assimilated in a low resolution global ocean model. The results of these experiments show that it is possible to compute piecewise constant parameter corrections, with predefined amplitude limitations, so that long-term free model simulations become much closer to the reanalysis data, with misfit variance typically divided by a factor 3. These results are obtained by applying a Monte Carlo method to simulate the joint parameter/state prior probability distribution. A truncated Gaussian assumption is used to avoid the most extreme and non-physical parameter corrections. The general lesson of our experiments is indeed that a careful specification of the prior information on the parameters and on their associated uncertainties is a key element in the computation of realistic parameter estimates, especially if the system is affected by other potential sources of model errors.

scholarly journals Impact of Assimilating Surface Velocity Observations on the Model Sea Surface Height Using the NCOM-4DVAR*

2016 ◽  
Vol 144 (3) ◽  
pp. 1051-1068 ◽  
Author(s):  
Matthew J. Carrier ◽  
Hans E. Ngodock ◽  
Philip Muscarella ◽  
Scott Smith
Keyword(s):  
Sea Surface Height ◽  
Ocean Model ◽  
Sea Surface ◽  
Surface Velocity ◽  
Velocity Measurements ◽  
Substantial Impact ◽  
Assimilation Experiment ◽  
Regional Ocean Model ◽  
Coastal Ocean Model ◽  
Along Track

Abstract The assimilation of surface velocity observations and their impact on the model sea surface height (SSH) is examined using an operational regional ocean model and its four-dimensional variational data assimilation (4DVAR) analysis component. In this work, drifter-derived surface velocity observations are assimilated into the Navy’s Coastal Ocean Model (NCOM) 4DVAR in weak-constraint mode for a Gulf of Mexico (GoM) experiment during August–September 2012. During this period the model is trained by assimilating surface velocity observations (in a series of 96-h assimilation windows), which is followed by a 30-day forecast through the month of October 2012. A free-run model and a model that assimilates along-track SSH observations are also run as baseline experiments to which the other experiments are compared. It is shown here that the assimilation of surface velocity measurements has a substantial impact on improving the model representation of the forecast SSH on par with the experiment that assimilates along-track SSH observations directly. Finally, an assimilation experiment is done where both along-track SSH and velocity observations are utilized in an attempt to determine if the observation types are redundant or complementary. It is found that the combination of observations provides the best SSH forecast, in terms of the fit to observations, when compared to the previous experiments.

scholarly journals Long-Term Variability and Trends in the Caribbean Sea

2011 ◽  
Vol 2011 ◽  
pp. 1-9 ◽  
Author(s):  
Mark R. Jury
Keyword(s):  
Crop Yields ◽  
Vertical Motion ◽  
Principal Component ◽  
Caribbean Sea ◽  
Ocean Model ◽  
Sea Surface ◽  
Southern Caribbean ◽  
The Caribbean ◽  
Ocean Conditions

Upper ocean conditions in the Caribbean Sea are studied for long-term variability and trends using filtered surface observations and ocean model reanalysis fields. A principal component analysis is made, and trends in the leading mode are extracted. Sea surface temperature shows an accelerating upward trend while air pressure exhibits quasidecadal fluctuations. Sea surface height and subsurface temperature rise linearly while subsurface salinity exhibits fresher upper and saltier lower layers. The amplitude of warming is highest in the southern Caribbean east of 75°W near 150 m and lowest near the surface, indicating little role for a top-down process such as air-sea exchange. The freshening surface layer does not appear connected to river discharge or regional rainfall, so changes in ocean advection and sources are the likely drivers. Westward currents exhibit a reduction of throughflow and an influx from the Windward Passage. The Caribbean Current has slowed ~0.06 m/s in the reanalysis era. Crop yields show little sensitivity to ocean conditions but tend to follow rainfall. Marine catch per capita in the Caribbean follows subsurface currents and vertical motion but is less affected by temperature and salinity.

scholarly journals Impact of prescribed SSTs on climatologies and long-term trends in CCM simulations

2009 ◽  
Vol 9 (1) ◽  
pp. 4489-4524 ◽  
Author(s):  
H. Garny ◽  
M. Dameris ◽  
A. Stenke
Keyword(s):  
Planetary Wave ◽  
Climate Model ◽  
Ocean Model ◽  
Sea Surface ◽  
Recent Past ◽  
The Past ◽  
Ice Coverage ◽  
Long Term Trends ◽  
Over 40 Years

Abstract. Chemistry-Climate Model (CCM) simulations are commonly used to project the past and future development of the dynamics and chemistry of the stratosphere, and in particular the ozone layer. So far, CCMs are usually not interactively coupled to an ocean model, so that sea surface temperatures (SSTs) and sea ice coverage are prescribed in the simulations. While for future integrations SSTs have to be taken from precalculated climate model projections, for CCM experiments resembling the past either modelled or observed SSTs can be used. This study addresses the question to which extent atmospheric climatologies and long-term trends for the recent past simulated in the CCM E39C-A differ when choosing either observed or modelled SSTs. Furthermore, the processes of how the SST signal is communicated to the atmosphere, and in particular to the stratosphere are examined. Two simulations that differ only with respect to the prescribed SSTs and that span years 1960 to 1999 are used. Significant differences in temperature and ozone climatologies between the model simulations are found, but long-term trends over 40 years in annual mean temperature and ozone differ only in the troposphere, where temperatures are directly influenced by the local SST trends. However, differences in trends are found on shorter time scales and the results suggest that these differences in trends are induced by associated SST trends. The SST trends lead to modifications in planetary wave activity and therefore a modulation of the Brewer-Dobson Circulation (BDC). This results in time series of tropical upwelling, as a measure of the strength of the BDC, differing strongly between the simulations. A reverse from negative to positive trends is found in the simulation using observed SSTs while trends are positive throughout the simulation when using modelled SSTs.

scholarly journals Demonstrating the potential of Regional Ocean Model System in simulating the upper ocean characteristic over Arabian Sea: impact of horizontal resolution

2021 ◽  
Author(s):  
Prabha Kushwaha ◽  
Vivek Kumar Pandey
Keyword(s):  
Arabian Sea ◽  
Horizontal Resolution ◽  
Ocean Model ◽  
Model System ◽  
Sea Surface ◽  
Sea Surface Salinity ◽  
Surface Salinity ◽  
Regional Ocean Model System ◽  
Regional Ocean Model ◽  
The Impact

Abstract This study attempted to demonstrate the skill of the regional ocean model system (ROMS) is simulating the hydrographic property of the Arabian Sea (AS). Additionally, the impact of horizontal resolution is investigated. In this regard, ROMS is integrated over AS covering [30˚E-80˚E; 5˚N-30N˚] at two different horizontal resolutions 1/6˚(~ 17km) and 1/4˚(~ 25km) for ten years. The comparison of model results with available observation and reanalysis indicates reasonable resemblances in reproducing the spatial-temporal distribution of surface and subsurface hydrographic property i.e. sea surface temperature (SST), sea surface salinity (SSS), sea surface currents, and subsurface temperature and salinity at both resolutions. The increasing resolution shows minimal improvement, indicating the fact that its not always guaranty to enhance the performance towards increasing resolution for every aspect.

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