scholarly journals Impact of global ocean model resolution on sea-level variability with emphasis on interannual time scales

Ocean Science ◽  
2010 ◽  
Vol 6 (1) ◽  
pp. 269-284 ◽  
Author(s):  
T. Penduff ◽  
M. Juza ◽  
L. Brodeau ◽  
G. C. Smith ◽  
B. Barnier ◽  
...  
Keyword(s):  
Sea Level ◽  
Large Scale ◽  
Ocean Model ◽  
Coupled Processes ◽  
Global Ocean ◽  
Spatial Correlations ◽  
Temporal Correlations ◽  
Sea Level Anomalies ◽  
Day Range ◽  
Standard Deviations

Abstract. Four global ocean/sea-ice simulations driven by the same realistic 47-year daily atmospheric forcing were performed by the DRAKKAR group at 2°, 1°, &frac12°, and ¼° resolutions. Simulated mean sea-surface heights (MSSH) and sea-level anomalies (SLA) are collocated over the period 1993–2004 onto the AVISO dataset. MSSH fields are compared with an inverse estimate. SLA datasets are filtered and compared over various time and space scales with AVISO regarding three characteristics: SLA standard deviations, spatial correlations between SLA variability maps, and temporal correlations between observed and simulated band-passed filtered local SLA timeseries. Beyond the 2°−1° transition whose benefits are moderate, further increases in resolution and associated changes in subgrid scale parameterizations simultaneously induce (i) strong increases in SLA standard deviations, (ii) strong improvements in the spatial distribution of SLA variability, and (iii) slight decreases in temporal correlations between observed and simulation SLA timeseries. These 3 effects are not only clear on mesoscale (14–180 days) and quasi-annual (5–18 months) fluctuations, but also on the slower (interannual), large-scale variability ultimately involved in ocean-atmosphere coupled processes. Most SLA characteristics are monotonically affected by successive resolution increases, but irregularly and with a strong dependance on frequency and latitude. Benefits of enhanced resolution are greatest in the 1°−½° and ½°−¼° transitions, in the 14–180 day range, and within eddy-active mid- and high-latitude regions. In the real ocean, most eddy-active areas are characterized by a strong SLA variability at all timescales considered here; this localized, broad-banded temporal variability is only captured at ¼° resolution.

scholarly journals Impact of model resolution on sea-level variability characteristics at various space and time scales: insights from four DRAKKAR global simulations and the AVISO altimeter data

2009 ◽  
Vol 6 (2) ◽  
pp. 1513-1545 ◽  
Author(s):  
T. Penduff ◽  
M. Juza ◽  
L. Brodeau ◽  
G. C. Smith ◽  
B. Barnier ◽  
...  
Keyword(s):  
Sea Level ◽  
Large Scale ◽  
Coupled Processes ◽  
Global Ocean ◽  
Altimeter Data ◽  
Spatial Correlations ◽  
Temporal Correlations ◽  
Sea Level Anomalies ◽  
Day Range ◽  
Standard Deviations

Abstract. Four global ocean/sea-ice simulations driven by the same realistic 46-year daily atmospheric forcing were performed within the DRAKKAR project at 2°, 1°, ½° and ¼° resolutions. Model sea-level anomalies are collocated over the period 1993–2004 onto the AVISO SLA dataset. These five collocated SLA datasets are then filtered and quantitatively compared over various time and space scales regarding three characteristics: SLA standard deviations, spatial correlations between SLA variability maps, and temporal correlations between observed and simulated band-passed filtered local SLA timeseries. Beyond the 2°–1° transition whose benefits are quite moderate, further increases in resolution and associated changes in subgrid scale parameterizations simultaneously induce (i) strong increases in SLA standard deviations, (ii) strong improvements in the spatial distribution of SLA variability, and (iii) slight decreases in temporal correlations between observed and simulation SLA timeseries. These 3 effects are not only clear on mesoscale (14–180 days) and quasi-annual (5–18 months) fluctuations, but also on the slower (interannual), large-scale variability ultimately involved in ocean-atmosphere coupled processes. Most SLA characteristics are monotonically affected by successive resolution increases, but irregularly and with a strong dependance on frequency and latitude. Benefits of enhanced resolution are maximum in the ½°–¼° transition, in the 14–180 day range, and within eddy-active mid- and high-latitude regions. They are particularly clear in the Southern Ocean where mesoscale eddies probably sustain a substantial intrinsic interannual variability.

scholarly journals Ocean Model Diagnosis of Interannual Coevolving SST Variability in the South Indian and South Atlantic Oceans

2005 ◽  
Vol 18 (15) ◽  
pp. 2864-2882 ◽  
Author(s):  
J. C. Hermes ◽  
C. J. C. Reason
Keyword(s):  
Atmospheric Circulation ◽  
Southern Hemisphere ◽  
Large Scale ◽  
Ocean Model ◽  
South Atlantic ◽  
Heat Fluxes ◽  
Global Ocean ◽  
The South ◽  
Sst Variability ◽  
South Indian

Abstract A global ocean model (ORCA2) forced with 50 yr of NCEP–NCAR reanalysis winds and heat fluxes has been used to investigate the evolution and forcing of interannual dipolelike sea surface temperature (SST) variability in the South Indian and South Atlantic Oceans. Although such patterns may also exist at times in only one of these basins and not the other, only events where there are coherent signals in both basins during the austral summer have been chosen for study in this paper. A positive (negative) event occurs when there is a significant warm (cool) SST anomaly evident in the southwest of both the South Indian and South Atlantic Oceans and a cool (warm) anomaly in the eastern subtropics. The large-scale forcing of these events appears to consist of a coherent modulation of the wavenumber-3 or -4 pattern in the Southern Hemisphere atmospheric circulation such that the semipermanent subtropical anticyclone in each basin is shifted from its summer mean position and its strength is modulated. A relationship to the Antarctic Oscillation is also apparent, and seems to strengthen after the mid-1970s. The modulated subtropical anticyclones lead to changes in the tropical easterlies and midlatitude westerlies in the South Atlantic and South Indian Oceans that result in anomalies in latent heat fluxes, upwelling, and Ekman heat transports, all of which contribute to the SST variability. In addition, there are significant modulations to the strong Rossby wave signals in the South Indian Ocean. The results of this study confirm the ability of the ORCA2 model to represent these dipole patterns and indicate connections between large-scale modulations of the Southern Hemisphere midlatitude atmospheric circulation and coevolving SST variability in the South Atlantic and South Indian Oceans.

scholarly journals Data-Driven Interpolation of Sea Level Anomalies Using Analog Data Assimilation

2019 ◽  
Vol 11 (7) ◽  
pp. 858 ◽  
Author(s):  
Redouane Lguensat ◽  
Phi Huynh Viet ◽  
Miao Sun ◽  
Ge Chen ◽  
Tian Fenglin ◽  
...  
Keyword(s):  
Data Assimilation ◽  
Sea Level ◽  
Large Scale ◽  
Empirical Orthogonal Functions ◽  
Data Driven ◽  
Optimal Interpolation ◽  
Observation System ◽  
Orthogonal Functions ◽  
Sea Level Anomalies ◽  
Recent Developments

From the recent developments of data-driven methods as a means to better exploit large-scale observation, simulation and reanalysis datasets for solving inverse problems, this study addresses the improvement of the reconstruction of higher-resolution Sea Level Anomaly (SLA) fields using analog strategies. This reconstruction is stated as an analog data assimilation issue, where the analog models rely on patch-based and Empirical Orthogonal Functions (EOF)-based representations to circumvent the curse of dimensionality. We implement an Observation System Simulation Experiment (OSSE) in the South China Sea. The reported results show the relevance of the proposed framework with a significant gain in terms of Root Mean Square Error (RMSE) for scales below 100 km. We further discuss the usefulness of the proposed analog model as a means to exploit high-resolution model simulations for the processing and analysis of current and future satellite-derived altimetric data with regard to conventional interpolation schemes, especially optimal interpolation.

scholarly journals El Niño Effects and Upwelling off South Australia

2007 ◽  
Vol 37 (10) ◽  
pp. 2458-2477 ◽  
Author(s):  
John F. Middleton ◽  
Craig Arthur ◽  
Paul Van Ruth ◽  
Tim M. Ward ◽  
Julie L. McClean ◽  
...  
Keyword(s):  
Sea Level ◽  
Wind Stress ◽  
El Niño ◽  
El Nino ◽  
South Australia ◽  
Ocean Model ◽  
Global Ocean ◽  
Shelf Edge ◽  
The West ◽  
Enso Events

Abstract To determine the possible importance of ENSO events along the coast of South Australia, an exploratory analysis is made of meteorological and oceanographic data and output from a global ocean model. Long time series of coastal sea level and wind stress are used to show that while upwelling favorable winds have been more persistent since 1982, ENSO events (i) are largely driven by signals from the west Pacific Ocean shelf/slope waveguide and not local meteorological conditions, (ii) can account for 10-cm changes in sea level, and (iii) together with wind stress, explain 62% of the variance of annual-averaged sea level. Thus, both local winds and remote forcing from the west Pacific are likely important to the low-frequency shelf edge circulation. Evidence also suggests that, since 1983, wintertime downwelling during the onset of an El Niño is reduced and the following summertime upwelling is enhanced. In situ data show that during the 1998 and 2003 El Niño events anomalously cold (10.5°–11.5°C) water is found at depths of 60–120 m and is more than two standard deviations cooler than the mean. A regression showed that averaged sea level can provide a statistically significant proxy for these subsurface temperature changes and indicates a 2.2°C decrease in temperature for the 10-cm decrease in sea level that was driven by the 1998 El Niño event. Limited current- meter observations, long sea level records, and output from a global ocean model were also examined and provide support for the hypothesis that El Niño events substantially reduce wintertime (but not summertime) shelf-edge currents. Further research to confirm this asymmetric response and its cause is required.

scholarly journals The GPU version of LASG/IAP Climate System Ocean Model version 3 (LICOM3) under the heterogeneous-compute interface for portability (HIP) framework and its large-scale application

2021 ◽  
Vol 14 (5) ◽  
pp. 2781-2799
Author(s):  
Pengfei Wang ◽  
Jinrong Jiang ◽  
Pengfei Lin ◽  
Mengrong Ding ◽  
Junlin Wei ◽  
...  
Keyword(s):  
General Circulation ◽  
Large Scale ◽  
Vertical Direction ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Ocean Model ◽  
Climate System ◽  
Global Ocean ◽  
Processing Unit ◽  
Model Version

Abstract. A high-resolution (1/20∘) global ocean general circulation model with graphics processing unit (GPU) code implementations is developed based on the LASG/IAP Climate System Ocean Model version 3 (LICOM3) under a heterogeneous-compute interface for portability (HIP) framework. The dynamic core and physics package of LICOM3 are both ported to the GPU, and three-dimensional parallelization (also partitioned in the vertical direction) is applied. The HIP version of LICOM3 (LICOM3-HIP) is 42 times faster than the same number of CPU cores when 384 AMD GPUs and CPU cores are used. LICOM3-HIP has excellent scalability; it can still obtain a speedup of more than 4 on 9216 GPUs compared to 384 GPUs. In this phase, we successfully performed a test of 1/20∘ LICOM3-HIP using 6550 nodes and 26 200 GPUs, and on a large scale, the model's speed was increased to approximately 2.72 simulated years per day (SYPD). By putting almost all the computation processes inside GPUs, the time cost of data transfer between CPUs and GPUs was reduced, resulting in high performance. Simultaneously, a 14-year spin-up integration following phase 2 of the Ocean Model Intercomparison Project (OMIP-2) protocol of surface forcing was performed, and preliminary results were evaluated. We found that the model results had little difference from the CPU version. Further comparison with observations and lower-resolution LICOM3 results suggests that the 1/20∘ LICOM3-HIP can reproduce the observations and produce many smaller-scale activities, such as submesoscale eddies and frontal-scale structures.

scholarly journals An Interhemispheric Tropical Sea Level Seesaw due to El Niño Taimasa

2014 ◽  
Vol 27 (3) ◽  
pp. 1070-1081 ◽  
Author(s):  
Matthew J. Widlansky ◽  
Axel Timmermann ◽  
Shayne McGregor ◽  
Malte F. Stuecker ◽  
Wenju Cai
Keyword(s):  
Sea Level ◽  
El Niño ◽  
Pacific Islands ◽  
El Nino ◽  
Ocean Model ◽  
Trade Winds ◽  
Sea Levels ◽  
Sea Level Anomalies ◽  
El Niño Events ◽  
El Nino Events

Abstract During strong El Niño events, sea level drops around some tropical western Pacific islands by up to 20–30 cm. Such events (referred to as taimasa in Samoa) expose shallow reefs, thereby causing severe damage to associated coral ecosystems and contributing to the formation of microatolls. During the termination of strong El Niño events, a southward movement of weak trade winds and the development of an anomalous anticyclone in the Philippine Sea are shown to force an interhemispheric sea level seesaw in the tropical Pacific that enhances and prolongs extreme low sea levels in the southwestern Pacific. Spectral features, in addition to wind-forced linear shallow water ocean model experiments, identify a nonlinear interaction between El Niño and the annual cycle as the main cause of these sea level anomalies.

scholarly journals Impact of the Indonesian Throughflow on Agulhas leakage

Ocean Science ◽  
2013 ◽  
Vol 9 (5) ◽  
pp. 773-785 ◽  
Author(s):  
D. Le Bars ◽  
H. A. Dijkstra ◽  
W. P. M. De Ruijter
Keyword(s):  
Large Scale ◽  
Ocean Model ◽  
Global Ocean ◽  
Momentum Balance ◽  
Indonesian Throughflow ◽  
Current Transport ◽  
Flat Bottom ◽  
Agulhas Current ◽  
The Pacific ◽  
Wide Range

Abstract. Using ocean models of different complexity we show that opening the Indonesian Passage between the Pacific and the Indian oceans increases the input of Indian Ocean water into the South Atlantic via the Agulhas leakage. In a strongly eddying global ocean model this response results from an increased Agulhas Current transport and a constant proportion of Agulhas retroflection south of Africa. The leakage increases through an increased frequency of ring shedding events. In an idealized two-layer and flat-bottom eddy resolving model, the proportion of the Agulhas Current transport that retroflects is (for a wide range of wind stress forcing) not affected by an opening of the Indonesian Passage. Using a comparison with a linear model and previous work on the retroflection problem, the result is explained as a balance between two mechanisms: decrease retroflection due to large-scale momentum balance and increase due to local barotropic/baroclinic instabilities.

scholarly journals Two Modes of Gulf Stream Variability Revealed in the Last Two Decades of Satellite Altimeter Data

2014 ◽  
Vol 44 (1) ◽  
pp. 149-163 ◽  
Author(s):  
M. Dolores Pérez-Hernández ◽  
Terrence M. Joyce
Keyword(s):  
Sea Level ◽  
Gulf Stream ◽  
Large Scale ◽  
Altimeter Data ◽  
Point Index ◽  
Modes Of Variability ◽  
Simple Index ◽  
Sea Level Anomalies ◽  
Time Scale Separation ◽  
Low Pass

Abstract Monthly mapped sea level anomalies (MSLAs) of the NW Atlantic in the region immediately downstream of the Gulf Stream (GS) separation point reveal a leading mode in which the path shifts approximately 100 km meridionally about a nominal latitude of 39°N, producing coherent sea level anomaly (SLA) variability from 72° to 50°W. This mode can be captured by use of a simple 16-point index based on SLA data taken along the maximum of the observed variability in the region 33°–46°N and 45°–75°W. The GS shifts between 2010 and 2012 are the largest of the last decade and equal to the largest of the entire record. The second group of EOF modes of variability describes GS meanders, which propagate mainly westward interrupted by brief periods of eastward or stationary meanders. These meanders have wavelengths of approximately 400 km and can be seen in standard EOFs by spatial phase shifting of a standing meander pattern in the SLA data. The spectral properties of these modes indicate strong variability at interannual and longer periods for the first mode and periods of a few to several months for the meanders. While the former is quite similar to a previous use of the altimeter for GS path, the simple index is a useful measure of the large-scale shifts in the GS path that is quickly estimated and updated without changes in previous estimates. The time-scale separation allows a low-pass filtered 16-point index to be reflective of large-scale, coherent shifts in the GS path.

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