Relation between mean sea level, current and wind stress on the east coast of Australia

1975 ◽  
Vol 26 (3) ◽  
pp. 389 ◽  
Author(s):  
BV Hamon ◽  
JS Godfrey ◽  
MA Greig
Keyword(s):  
Sea Level ◽  
Wind Stress ◽  
Average Rate ◽  
Clear Correlation ◽  
Similar Data ◽  
Shelf Edge ◽  
Longshore Current ◽  
Mean Sea Level ◽  
Level Difference ◽  
Sea Level Difference

Five-day mean sea level differences between Evans Head (29� 07'S.) and Coffs Harbour 30� 19'S.), and between Coffs Harbour and Crowdy Head (31� 50'S.) were regressed on estimates of longshore current acceleration, mean longshore current and longshore wind stress, with the following results: (i) A relation was found between sea level difference from Coffs Harbour to Crowdy Head, and current acceleration. There was no similar relation for the section Evans Head to Coffs Harbour, and no reason could be found for the difference in behaviour between the two sections. (ii) A weakly defined relation was found, in both sections of the coast, between sea level difference and the square of the mean longshore current (a friction effect). (iii) An apparent relation was found, again in both sections of the coast, between sea level difference and longshore wind stress. This relation was more marked than expected from theory. The longshore currents were obtained from ships' drift, and covered a period of 2 years. The current data show a southward drift of current pattern, at an average rate of 9 km day-1. They also show a clear correlation between currents at the shelf edge (approximately 19 km offshore) and currents nearer shore (approximately 6.5 km offshore). It was found that the nearer-shore currents lagged the shelf-edge currents by between 7 and 10 days. Time and space correlations of the shelf-edge currents confirm earlier estimates from similar data. A frequency spectrum of the shelf-edge currents showed a broad maximum in the period range 50-170 days.

Atlantic to Mediterranean Sea Level Difference Driven by Winds near Gibraltar Strait

2007 ◽  
Vol 37 (2) ◽  
pp. 359-376 ◽  
Author(s):  
Dimitris Menemenlis ◽  
Ichiro Fukumori ◽  
Tong Lee
Keyword(s):  
Mediterranean Sea ◽  
Sea Level ◽  
Wind Stress ◽  
Coastal Current ◽  
Alboran Sea ◽  
Mean Sea Level ◽  
Level Difference ◽  
Gibraltar Strait ◽  
Sea Level Difference ◽  
Alborán Sea

Abstract Observations and numerical simulations show that winds near Gibraltar Strait cause an Atlantic Ocean to Mediterranean Sea sea level difference of 20 cm peak to peak with a 3-cm standard deviation for periods of days to years. Theoretical arguments and numerical experiments establish that this wind-driven sea level difference is caused in part by storm surges due to alongshore winds near the North African coastline on the Atlantic side of Gibraltar. The fraction of the Moroccan coastal current offshore of the 284-m isobath is deflected across Gibraltar Strait, west of Camarinal Sill, resulting in a geostrophic surface pressure gradient that contributes to a sea level difference at the stationary limit. The sea level difference is also caused in part by the along-strait wind setup, with a contribution proportional to the along-strait wind stress and to the length of Gibraltar Strait and adjoining regions and inversely proportional to its depth. In the 20–360-day band, average transfer coefficients between the Atlantic–Alboran sea level difference and surface wind stress at 36°N, 6.5°W, estimated from barometrically corrected Ocean Topography Experiment (TOPEX)/Poseidon data and NCEP–NCAR reanalysis data, are 0.10 ± 0.04 m Pa−1 with 1 ± 5-day lag and 0.19 ± 0.08 m Pa−1 with 5 ± 4-day lag for the zonal and meridional wind stresses, respectively. This transfer function is consistent with equivalent estimates derived from a 1992–2003 high-resolution barotropic simulation forced by the NCEP–NCAR wind stress. The barotropic simulation explains 29% of the observed Atlantic–Alboran sea level difference in the 20–360-day band. In turn, the Alboran and Mediterranean mean sea level time series are highly correlated, ρ = 0.7 in the observations and ρ = 0.8 in the barotropic simulation, hence providing a pathway for winds near Gibraltar Strait to affect the mean sea level of the entire Mediterranean.

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 On the relation between Meridional Overturning Circulation and sea-level gradients in the Atlantic

2012 ◽  
Vol 3 (1) ◽  
pp. 325-356 ◽  
Author(s):  
H. Kienert ◽  
S. Rahmstorf
Keyword(s):  
Sea Level ◽  
Co2 Concentration ◽  
Meridional Overturning Circulation ◽  
Overturning Circulation ◽  
Simultaneous Application ◽  
Level Difference ◽  
Ocean Winds ◽  
Meridional Overturning ◽  
The Individual ◽  
Sea Level Difference

Abstract. On the basis of model simulations, we examine what information on changes in the strength of the Atlantic Meridional Overturning Circulation (AMOC) can be extracted from associated changes in sea surface height (SSH), specifically from a broad Atlantic north-south gradient as has been suggested previously in the literature. Since a relation between AMOC and SSH changes can only be used as an AMOC diagnostic if it is valid independently of the specific forcing, we consider three different forcing types: increase of CO2 concentration, freshwater fluxes to the northern convection sites and the modification of Southern Ocean winds. We concentrate on a timescale of 100 yr. We find approximately linear and numerically similar relations between a sea-level difference within the Atlantic and the AMOC for freshwater as well as wind forcing. However, the relation is more complex in response to atmospheric CO2 increase, which precludes this sea-level difference as an AMOC diagnostic under climate change. Finally, we show qualitatively to what extent changes in SSH and AMOC strength that are caused by simultaneous application of different forcings correspond to the sum of the changes due to the individual forcings, a potential prerequisite for more complex SSH-based AMOC diagnostics.

scholarly journals DYNAMIC OF SEA LEVEL ANOMALY OF INDONESIAN WATERS

2015 ◽  
Vol 7 (1) ◽  
Author(s):  
Bisman Nababan ◽  
Sri Hadianti ◽  
Nyoman M.N. Natih
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Southern Oscillation ◽  
Average Rate ◽  
Seasonal Pattern ◽  
Sea Level Anomaly ◽  
Mean Sea Level ◽  
Enso Events ◽  
The Pacific ◽  
Global Sea Level

A trend in sea level rise as a result of global warming could be a threat to small islands and coastal areas in Indonesia. The objective of this study was to determine the trend and variability of mean sea level anomaly (MSLA) in Indonesian waters during the 20 years of observation. The data used in this study were monthly MSLA data obtained from the AVISO website (ftp://ftp.aviso.oceanobs.com). Supporting data were the Southern Oscillation Index (SOI) (http://www.gom.gov.au/climate/enso), Dipole Indian Mode (DIM) index (http://gcmd.nasa.gov/records/GCMD_Indian_Ocean_Dipole.html), and the Pacific Decadal Oscillation (PDO) index (http://research.jisao.washington.edu/pdo/). Eigth stations of Indonesian waters were selected to study the variability of MSLA. In general, MSLA variabilities of Indonesian waters had a seasonal pattern, positively correlated with the SOI index, and negatively correlated with DIM and PDO indexes. The partial correlation of DIM was more dominant in west of Sumatra (r=-0.52) and south of Java (r=-0.44), PDO was more dominant in the northern waters of Papua (r=-0.37) and Makassar Strait (r=-0.33), and SOI was more dominant in northern Papua (r=0.52) and less toward the west of Indonesian waters. Overall, the MSLA variability of Indonesian waters can be explained by the variabilities of SOI, DIM, and PDO indexes with the lowest value in Natuna waters by 12% (R2=0.12) and the highest value in the northern waters of Papua by 54% (R2=0.54). Interannual variabilities were observed during ENSO events (SOI<-10) along with the maximum value of DIM index resulted in the lowest value of MSLA. Meanwhile, the highest value of MSLA was found during La Nina events (SOI>10) in conjunction with a minimum value of DIM and PDO indexes. The average rate of sea level rise in Indonesian waters was 5.84 mm/yr, almost two times higher than the average rate of global sea level rise (3.2 mm/yr). Keywords: mean sea level, anomaly, SOI, DIM, PDO, interannual, ENSO

scholarly journals Global sea-level budget 1993–present

2018 ◽  
Vol 10 (3) ◽  
pp. 1551-1590 ◽  
Author(s):  
Keyword(s):  
Sea Level ◽  
Average Rate ◽  
Deep Ocean ◽  
Grand Challenge ◽  
Mean Sea Level ◽  
Climate Research ◽  
Global Mean Sea Level ◽  
Land Water ◽  
Global Mean ◽  
Individual Mass

Abstract. Global mean sea level is an integral of changes occurring in the climate system in response to unforced climate variability as well as natural and anthropogenic forcing factors. Its temporal evolution allows changes (e.g., acceleration) to be detected in one or more components. Study of the sea-level budget provides constraints on missing or poorly known contributions, such as the unsurveyed deep ocean or the still uncertain land water component. In the context of the World Climate Research Programme Grand Challenge entitled Regional Sea Level and Coastal Impacts, an international effort involving the sea-level community worldwide has been recently initiated with the objective of assessing the various datasets used to estimate components of the sea-level budget during the altimetry era (1993 to present). These datasets are based on the combination of a broad range of space-based and in situ observations, model estimates, and algorithms. Evaluating their quality, quantifying uncertainties and identifying sources of discrepancies between component estimates is extremely useful for various applications in climate research. This effort involves several tens of scientists from about 50 research teams/institutions worldwide (www.wcrp-climate.org/grand-challenges/gc-sea-level, last access: 22 August 2018). The results presented in this paper are a synthesis of the first assessment performed during 2017–2018. We present estimates of the altimetry-based global mean sea level (average rate of 3.1 ± 0.3 mm yr−1 and acceleration of 0.1 mm yr−2 over 1993–present), as well as of the different components of the sea-level budget (http://doi.org/10.17882/54854, last access: 22 August 2018). We further examine closure of the sea-level budget, comparing the observed global mean sea level with the sum of components. Ocean thermal expansion, glaciers, Greenland and Antarctica contribute 42 %, 21 %, 15 % and 8 % to the global mean sea level over the 1993–present period. We also study the sea-level budget over 2005–present, using GRACE-based ocean mass estimates instead of the sum of individual mass components. Our results demonstrate that the global mean sea level can be closed to within 0.3 mm yr−1 (1σ). Substantial uncertainty remains for the land water storage component, as shown when examining individual mass contributions to sea level.

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