scholarly journals The sensitivity of a global ocean model to wind forcing: A test using sea level and wind observations from satellites and operational wind analysis

1997 ◽  
Vol 24 (14) ◽  
pp. 1783-1786 ◽  
Author(s):  
Lee-Lueng Fu ◽  
Yi Chao
Keyword(s):  
Sea Level ◽  
Ocean Model ◽  
Wind Forcing ◽  
Global Ocean ◽  
Wind Analysis

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 Data assimilation in a reduced gravity ocean model using ERS-l scatterometer and TOPEX altimeter data

MAUSAM ◽  
2021 ◽  
Vol 48 (4) ◽  
pp. 669-678
Author(s):  
RAJ KUMAR ◽  
SUJIT BASU ◽  
B. S. GOHIL ◽  
P. C. PANDEY
Keyword(s):  
Sea Level ◽  
Wind Stress ◽  
Western Indian Ocean ◽  
Ocean Model ◽  
Wind Forcing ◽  
Altimeter Data ◽  
Reduced Gravity ◽  
The North ◽  
Model Equations ◽  
Adjoint Approach

 This paper discusses import of ERS-1 scatterometer winds and assimilation of sea level variability data derived from TOPEX altimeter on the ocean model using adjoint approach. The model developed for the purpose is linear reduced gravity model for the north-western Indian ocean. Experiments have been done with forcing provided using ERS-l satellite scatterometer and analysed wind forcing provided by Florida State University (FSU). Impact on the model has been studied using the analysed wind stress as well as with ERS-l scatterometer-derived wind stress fields. The cost function has been defined as difference between the model derived sea level and altimeter observations. This misfit between model and observations has been minimised with the model equations as constraints. Assimilation has been done for 30 days using scatterometer wind forcing. It has been observed that assimilated sea level with scatterometer-derived wind forcing gives much better results in comparison to unassimilated sea level.    

scholarly journals The Global Ocean Mass Budget in 1993–2003 Estimated from Sea Level Change

2007 ◽  
Vol 37 (2) ◽  
pp. 203-213 ◽  
Author(s):  
Manfred Wenzel ◽  
Jens Schröter
Keyword(s):  
Atlantic Ocean ◽  
Sea Level ◽  
Ocean Circulation ◽  
General Circulation ◽  
Circulation Model ◽  
Ocean Model ◽  
Global Ocean ◽  
Mass Budget ◽  
Ocean Mass ◽  
The Pacific

Abstract The mass budget of the ocean in the period 1993–2003 is studied with a general circulation model. The model has a free surface and conserves mass rather than volume; that is, freshwater is exchanged with the atmosphere via precipitation and evaporation and inflow from land is taken into account. The mass is redistributed by the ocean circulation. Furthermore, the ocean’s volume changes by steric expansion with changing temperature and salinity. To estimate the mass changes, the ocean model is constrained by sea level measurements from the Ocean Topography Experiment (TOPEX)/Poseidon mission as well as by hydrographic data. The modeled ocean mass change within the years 2002–03 compares favorably to measurements from the Gravity Recovery and Climate Experiment (GRACE), and the evolution of the global mean sea level for the period 1993–2003 with annual and interannual variations can be reproduced to a 0.15-cm rms difference. Its trend has been measured as 3.37 mm yr−1 while the constrained model gives 3.34 mm yr−1 considering only the area covered by measurements (3.25 mm yr−1 for the total ocean). A steric rise of 2.50 mm yr−1 is estimated in this period, as is a gain in the ocean mass that is equivalent to an eustatic rise of 0.74 mm yr−1. The amplitude and phase (day of maximum value since 1 January) of the superimposed eustatic annual cycle are also estimated to be 4.6 mm and 278°, respectively. The corresponding values for the semiannual cycle are 0.42 mm and 120°. The trends in the eustatic sea level are not equally distributed. In the Atlantic Ocean (80°S–67°N) the eustatic sea level rises by 1.8 mm yr−1 and in the Indian Ocean (80°S–30°N) it rises by 1.4 mm yr−1, but it falls by −0.20 mm yr−1 in the Pacific Ocean (80°S–67°N). The latter is mainly caused by a loss of mass through transport divergence in the Pacific sector of the Antarctic Circumpolar Current (−0.42 Sv; Sv ≡ 109 kg s−1) that is not balanced by the net surface water supply. The consequence of this uneven eustatic rise is a shift of the oceanic center of mass toward the Atlantic Ocean and to the north.

scholarly journals Formulation of a new explicit tidal scheme in ocean general circulation model

2022 ◽  
Author(s):  
Jiangbo Jin ◽  
Run Guo ◽  
Minghua Zhang ◽  
Guangqing Zhou ◽  
Qingcun Zeng
Keyword(s):  
Sea Level ◽  
General Circulation ◽  
Thermohaline Circulation ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Ocean Model ◽  
Tidal Mixing ◽  
Global Ocean ◽  
The North ◽  
Tidal Constituents

Abstract. Tides play an important role in ocean energy transfer and mixing, and provide major energy for maintaining thermohaline circulation. This study proposes a new explicit tidal scheme and assesses its performance in a global ocean model. Instead of using empirical specifications of tidal amplitudes and frequencies, the new scheme directly uses the positions of the Moon and Sun in a global ocean model to incorporate tides. Compared with the traditional method that has specified tidal constituents, the new scheme can better simulate the diurnal and spatial characteristics of the tidal potential of spring and neap tides as well as the spatial patterns and magnitudes of major tidal constituents (K1 and M2). It significantly reduces the total errors of eight tidal constituents (with the exception of N2 and Q1) in the traditional explicit tidal scheme. Relative to the control simulation without tides, both the new and traditional tidal schemes can lead to better dynamic sea level (DSL) simulation in the North Atlantic, reducing significant negative biases in this region. The new tidal scheme also shows smaller positive bias than the traditional scheme in the Southern Ocean. The new scheme is suited to calculate regional distributions of sea level height in addition to tidal mixing.

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.

Reproduction and projection of sea level around Korean Peninsula using regional climate ocean model with dynamical downscaling method

2020 ◽  
Author(s):  
Kwang-Young Jeong ◽  
Eunil Lee ◽  
Do-Seong Byun ◽  
Gwang-Ho Seo ◽  
Hwa-Young Lee ◽  
...  
Keyword(s):  
Climate Change ◽  
Sea Level Rise ◽  
Sea Level ◽  
Korean Peninsula ◽  
Climate Change Scenario ◽  
Climate Models ◽  
Regional Climate ◽  
Ocean Model ◽  
Global Ocean ◽  
Change Scenario

<p>Recently, the rate of sea level rise in accelerating with time, and many studies have reported that sea level will increase rapidly in the near future. Also, various global ocean climate models are used to predict sea level rise due to global warming. However, most global ocean climate models have low resolutions, so it is hard to explain detailed the ocean phenomena such as sea level and currents around Korean Peninsula. This study aims to past 30-year reproduce and future 100-year predict for rising trend of sea level using Regional Climate Ocean Model (RCOM) with ROMS according to IPCC climate change scenario (RCP 4.5).</p><p>The RCOM with high resolution of 1/20° horizontally and 40 layers vertically has been established for reproduction and long term forecast of sea-level rise in the Northwest Pacific, including marginal seas around Korea. Dynamic downscaling processes using result of the global climate models were applied to the open boundary conditions of our RCOM. To prepare the optimal boundary data for RCOM, the CMIP5 climate model was evaluated to select 4 climate models: IPSL-CM5A-LR, and -MR, NorESM1-M, MPI-ESM-LR.</p><p>Based on the RCOM results of 4 experiments, the rate of sea level rise for IPCC climate change scenario (RCP4.5) around Korean peninsula were 2.52, 2.21, 3.11, 3.36 mm/yr for the last 30 years (1976~2005), and 5.17, 4.99, 5.62, 5.42 mm/yr for the next 100 years (2006~2100), respectively. Ensemble mean value of next 100 years for 4 model results was 5.30 mm/yr. The sea level rise of 4 models for RCP 4.5 were 48, 48, 58, 48 cm for next 100 years, respectively, and ensemble mean value of 4 models was 50 cm during 2006~2100.</p><p>Future studies will focus on predicting the next 100 years of sea level change based on IPCC climate change scenario (RCP2.6, 8.5).</p><p> </p>

scholarly journals On the Role of Westerly Wind Anomalies in the Development of the 1982–1983 El Niño

2021 ◽  
Author(s):  
David J. Webb
Keyword(s):  
Sea Level ◽  
El Niño ◽  
Initial Conditions ◽  
El Nino ◽  
Ocean Model ◽  
Global Ocean ◽  
Westerly Wind ◽  
The North ◽  
North Equatorial Counter Current ◽  
Counter Current

Abstract. A recent study of two strong El Niños highlighted the potential importance of a region of low sea level that developed in the western equatorial Pacific prior to the El Niños of 1982–1983 and 1997–1998. Here the cause of the low sea level in 1982 is investigated using a series of runs of a global ocean model with different wind fields and initial conditions. The results indicate that the low sea level was due to the increased wind shear that developed just north of the Equator during 1982. This generated Ekman divergence at the latitudes of the North Equatorial Trough, raising the underlying density surfaces and increasing the depth of the trough. This also increased the strength of the North Equatorial Counter Current which lies on the southern slope of the trough. The anomalous westerly winds associated with Madden Julian Oscillations are often held responsible for triggering El Niños through the generation of westerly wind bursts and the resulting equatorial Kelvin waves in the ocean. However if Webb (2018) is correct, the present results imply that a different physical process was involved in which Ekman divergence due to the same winds, increased the heat transported by the North Equatorial Counter Current early in the year and ultimately caused the strong 1982–1983 El Niño.

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