scholarly journals Decadal sea-level variability in the Australasian Mediterranean Sea

Ocean Science ◽  
2021 ◽  
Vol 17 (5) ◽  
pp. 1473-1487
Author(s):  
Patrick Wagner ◽  
Claus W. Böning
Keyword(s):  
Mediterranean Sea ◽  
Interannual Variability ◽  
Sea Level ◽  
Wind Stress ◽  
Southern Oscillation ◽  
Horizontal Resolution ◽  
Intrinsic Variability ◽  
Sea Level Variability ◽  
The Pacific ◽  
Regional Sea Level

Abstract. Strong regional sea-level trends, mainly related to basin-wide wind stress anomalies, have been observed in the western tropical Pacific over the last 3 decades. Analyses of regional sea level in the densely populated regions of the neighbouring Australasian Mediterranean Sea (AMS; also called tropical Asian seas) are hindered by its complex topography and respective studies are sparse. We used a series of global eddy-permitting ocean models, including a high-resolution configuration that resolves the AMS with 120∘ horizontal resolution, forced by a comprehensive atmospheric forcing product over 1958–2016 to characterize the patterns and magnitude of decadal sea-level variability in the AMS. The nature of this variability is elucidated further by sensitivity experiments with interannual variability restricted to either the momentum or buoyancy fluxes, building on an experiment employing a repeated-year forcing without interannual variability in all forcing components. Our results suggest that decadal fluctuations of the El Niño–Southern Oscillation (ENSO) account for over 80 % of the variability in all deep basins of the region, except for the central South China Sea (SCS). Changes related to the Pacific Decadal Oscillation (PDO) are most pronounced in the shallow Arafura and Timor seas and in the central SCS. On average, buoyancy fluxes account for less than 10 % of decadal SSH variability, but this ratio is highly variable over time and can reach values of up to 50 %. In particular, our results suggest that buoyancy flux forcing amplifies the dominant wind-stress-driven anomalies related to ENSO cycles. Intrinsic variability is mostly negligible except in the SCS, where it accounts for 25 % of the total decadal SSH variability.

The role of oceanic internal instabilities on the Great Whirl interannual variability 

2021 ◽  
Author(s):  
Kwatra Sadhvi ◽  
Iyyappan Suresh ◽  
Takeshi Izumo ◽  
Jérôme Vialard ◽  
Matthieu Lengaigne ◽  
...  
Keyword(s):  
Interannual Variability ◽  
Sea Level ◽  
Wind Stress ◽  
General Circulation ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Offshore Wind ◽  
Intrinsic Variability ◽  
Wind Stress Curl ◽  
Sea Level Anomalies

<p>The Great Whirl (GW) is a quasi-permanent anticyclonic eddy that appears every summer monsoon in the western Arabian Sea off the horn of Africa. It generally forms in June, peaks in July-August, and dissipates afterward. While the annual cycle of the GW has been previously described, its year-to-year variability has been less explored. Satellite observations reveal that the leading mode of summer interannual sea-level variability in this region is associated with a typically ~100-km northward or southward shift of the GW. This shift is associated with coherent sea surface temperature and surface chlorophyll signals, with warmer SST and reduced marine primary productivity in regions with positive sea level anomalies and vice versa. Eddy-permitting (~25 km) and eddy-resolving (~10 km) ocean general circulation model simulations reproduce the observed pattern reasonably well, even in the absence of interannual variations in the surface forcing. This implies that the GW interannual variability partly arises from oceanic internal instabilities. Ensemble oceanic simulations further reveal that this stochastic oceanic intrinsic variability and the deterministic response to wind forcing each contribute to ~50% of the total GW interannual variability in July-August. The deterministic part appears to be related to the oceanic response  to Somalia alongshore wind stress and offshore wind-stress curl variations during the monsoon onset projecting onto the GW structure, and getting amplified by oceanic instabilities. After August, the stochastic component dominates the GW variability.</p>

scholarly journals Contribution of buoyancy fluxes to tropical Pacific sea level variability

Ocean Science ◽  
2021 ◽  
Vol 17 (4) ◽  
pp. 1103-1113
Author(s):  
Patrick Wagner ◽  
Markus Scheinert ◽  
Claus W. Böning
Keyword(s):  
Sea Level ◽  
Wind Stress ◽  
Southern Oscillation ◽  
Tropical Pacific ◽  
Sea Level Variability ◽  
Steric Sea Level ◽  
Enso Events ◽  
Freshwater Fluxes ◽  
Stress Changes ◽  
The Tropical Pacific

Abstract. Regional anomalies of steric sea level are either due to redistribution of heat and freshwater anomalies or due to ocean–atmosphere buoyancy fluxes. Interannual to decadal variability in sea level across the tropical Pacific is mainly due to steric variations driven by wind stress anomalies. The importance of air–sea buoyancy fluxes is less clear. We use a global, eddy-permitting ocean model and a series of sensitivity experiments with quasi-climatological momentum and buoyancy fluxes to identify the contribution of buoyancy fluxes for interannual to decadal sea level variability in the tropical Pacific. We find their contribution on interannual timescales to be strongest in the central tropical Pacific at around a 10∘ latitude in both hemispheres and also relevant in the very east of the tropical domain. Buoyancy-flux-forced anomalies are correlated with variations driven by wind stress changes, but their effect on the prevailing anomalies and the importance of heat and freshwater fluxes vary locally. In the eastern tropical basin, interannual sea level variability is amplified by anomalous heat fluxes, while the importance of freshwater fluxes is small, and neither has any impact on decadal timescales. In the western tropical Pacific, the variability on interannual and decadal timescales is dampened by both heat and freshwater fluxes. The mechanism involves westward-propagating Rossby waves that are triggered during El Niño–Southern Oscillation (ENSO) events by anomalous buoyancy fluxes in the central tropical Pacific and counteract the prevailing sea level anomalies once they reach the western part of the basin.

Contributions of Wind Forcing and Surface Heating to Interannual Sea Level Variations in the Atlantic Ocean

2006 ◽  
Vol 36 (9) ◽  
pp. 1739-1750 ◽  
Author(s):  
Cécile Cabanes ◽  
Thierry Huck ◽  
Alain Colin de Verdière
Keyword(s):  
Atlantic Ocean ◽  
Sea Level ◽  
Wind Stress ◽  
Large Scale ◽  
Sea Surface Height ◽  
Sea Surface ◽  
Altimeter Data ◽  
Local Response ◽  
Sea Level Variability ◽  
Sea Level Variations

Abstract Interannual sea surface height variations in the Atlantic Ocean are examined from 10 years of high-precision altimeter data in light of simple mechanisms that describe the ocean response to atmospheric forcing: 1) local steric changes due to surface buoyancy forcing and a local response to wind stress via Ekman pumping and 2) baroclinic and barotropic oceanic adjustment via propagating Rossby waves and quasi-steady Sverdrup balance, respectively. The relevance of these simple mechanisms in explaining interannual sea level variability in the whole Atlantic Ocean is investigated. It is shown that, in various regions, a large part of the interannual sea level variability is related to local response to heat flux changes (more than 50% in the eastern North Atlantic). Except in a few places, a local response to wind stress forcing is less successful in explaining sea surface height observations. In this case, it is necessary to consider large-scale oceanic adjustments: the first baroclinic mode forced by wind stress explains about 70% of interannual sea level variations in the latitude band 18°–20°N. A quasi-steady barotropic Sverdrup response is observed between 40° and 50°N.

Intraseasonal-to-Interannual Variability of South Indian Ocean Sea Level and Thermocline: Remote versus Local Forcing

2012 ◽  
Vol 42 (4) ◽  
pp. 602-627 ◽  
Author(s):  
Laurie L. Trenary ◽  
Weiqing Han
Keyword(s):  
Indian Ocean ◽  
Interannual Variability ◽  
Sea Level ◽  
Time Scales ◽  
Ekman Pumping ◽  
Remote Forcing ◽  
South Indian ◽  
The Pacific ◽  
The Indian Ocean ◽  
Thermocline Variability

Abstract The relative importance of local versus remote forcing on intraseasonal-to-interannual sea level and thermocline variability of the tropical south Indian Ocean (SIO) is systematically examined by performing a suite of controlled experiments using an ocean general circulation model and a linear ocean model. Particular emphasis is placed on the thermocline ridge of the Indian Ocean (TRIO; 5°–12°S, 50°–80°E). On interannual and seasonal time scales, sea level and thermocline variability within the TRIO region is primarily forced by winds over the Indian Ocean. Interannual variability is largely caused by westward propagating Rossby waves forced by Ekman pumping velocities east of the region. Seasonally, thermocline variability over the TRIO region is induced by a combination of local Ekman pumping and Rossby waves generated by winds from the east. Adjustment of the tropical SIO at both time scales generally follows linear theory and is captured by the first two baroclinic modes. Remote forcing from the Pacific via the oceanic bridge has significant influence on seasonal and interannual thermocline variability in the east basin of the SIO and weak impact on the TRIO region. On intraseasonal time scales, strong sea level and thermocline variability is found in the southeast tropical Indian Ocean, and it primarily arises from oceanic instabilities. In the TRIO region, intraseasonal sea level is relatively weak and results from Indian Ocean wind forcing. Forcing over the Pacific is the major cause for interannual variability of the Indonesian Throughflow (ITF) transport, whereas forcing over the Indian Ocean plays a larger role in determining seasonal and intraseasonal ITF variability.

Mediterranean Sea-Level Variability and Trends

2012 ◽  
pp. 257-299 ◽  
Author(s):  
Damià Gomis ◽  
Mikis Tsimplis ◽  
Marta Marcos ◽  
Luciana Fenoglio-Marc ◽  
Begoña Pérez ◽  
...  
Keyword(s):  
Mediterranean Sea ◽  
Sea Level ◽  
Sea Level Variability

Positive Regional Sea Level Anomalies in Southern Brazil Due to Changes in Austral Atmospheric Circulation

2021 ◽  
Author(s):  
Venisse Schossler ◽  
Francisco Aquino ◽  
Jefferson Simões ◽  
Pedro Reis ◽  
Denilson Viana
Keyword(s):  
Sea Level ◽  
Wind Stress ◽  
Southern Annular Mode ◽  
Altimeter Data ◽  
Western Boundary ◽  
Positive Trend ◽  
Boundary Current ◽  
Wind Stress Curl ◽  
Sea Level Anomalies ◽  
Regional Sea Level

Abstract Pressure gradients and winds play an important role in Southern Hemisphere (SH) sea levels, which are currently associated with the positive trend of the Southern Annular Mode (SAM). This study investigated regional sea level anomalies (SLAs) in the southern coast Brazil using altimeter data (1993–2019), post-processed by the X-TRACK (CTOH/LEGOS). We observed a negative SLA from 1993 to 2009 and a positive SLA from 2010 to 2019, with upward trends throughout the evaluation period. We analyzed wind stress curl, pressure, and wind fields at sea level (FNMOC and ERA 5, respectively) in addition to sea surface temperature and height anomalies (SSTA/SSHA-OISST) in the South Atlantic Ocean (SAO) for 1993–2009 and 2010–2019. In relation to the first period, the second shows the enhancement in Hadley and Walker cells and trade winds, in addition to greater SSTA and SSHA in SAO. The SAO subtropical gyre and zonal winds at 45°S contribute to the intensification of the western boundary current. A greater pressure gradient between the SAO surface and the southeast of South America is noteworthy. Regionally, the positive SAM brings an increase in sea level to the study area, caused by greater wind stress and variability in heat flows.

Interannual Modality of Upper-Ocean Temperature: 4D Structure Revealed by Argo Data

2015 ◽  
Vol 28 (9) ◽  
pp. 3441-3452 ◽  
Author(s):  
Ge Chen ◽  
Hanou Chen
Keyword(s):  
Interannual Variability ◽  
Southern Oscillation ◽  
Hadley Circulation ◽  
Walker Circulation ◽  
Upper Ocean ◽  
Kelvin Wave ◽  
Argo Data ◽  
Sea Temperature ◽  
Equatorial Undercurrent ◽  
The Pacific

Abstract Using the newly available decade-long Argo data for the period 2004–13, a detailed study is carried out on deriving four-dimensional (4D) modality of sea temperature in the upper ocean with emphasis on its interannual variability in terms of amplitude, phase, and periodicity. Three principal modes with central periodicities at 19.2, 33.8, and 50.3 months have been identified, and their relationship with El Niño–Southern Oscillation (ENSO) is investigated, yielding a number of useful results and conclusions: 1) A striking tick-shaped pipe-like feature of interannual variability maxima, which is named the “Niño pipe” in this paper, has been revealed within the 10°S–10°N upper Pacific Ocean. 2) The pipe core extends downward from ~50 m at 130°E to ~250 m near the date line before tilting upward to the sea surface at about 275°E, coinciding nicely with the pathway of the Pacific equatorial undercurrent (EUC). 3) The double-peak zonal modality pattern of the Niño pipe in the upper Pacific is echoed in the subsurface Atlantic and Indian Oceans through Walker circulation, while its single-peak meridional modality pattern is mirrored in the subsurface North and South Pacific through Hadley circulation. 4) A coherent three-peak modal structure implies a strong coupling between sea level variability at the surface and sea temperature variability around the thermocline. Accumulating evidence suggests that Rossby/Kelvin wave dynamics in tandem with EUC-based thermocline dynamics are the main mechanisms of the three-mode Niño pipe in ENSO cycles.

Sign in / Sign up

Export Citation Format

Share Document