Detecting Processes Contributing to Interannual Halosteric and Thermosteric Sea Level Variability

Abstract On interannual time scales, regional sea level variability is largely determined by changes in the steric component. The relation between the thermosteric and halosteric components is studied by separating the components into contributions from the mixed layer and, below the mixed layer, into the part that is related to isopycnal motion and that contributes to the steric sea level and the inactive part related to changes of spiciness. The decomposition provides a simple diagnostic to detect and understand physical mechanisms leading to regional sea level changes. In most areas of the world’s oceans, steric sea level variability is dominated by the contribution from isopycnal motion to the thermosteric sea level while halosteric variability relates more to spiciness. Because of the salinity minimum at middepth, different spatial salinity gradients above and below the minimum lead to opposing contributions and thus to a small contribution from isopycnal motion to the halosteric sea level. In nonpolar regions, both active components oppose each other, rendering the thermosteric variability larger than the steric variability. In the Arctic, the variability of both components is governed by spiciness in the Eurasian Basin and isopycnal motion in the Amerasian Basin.

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Closing the global and regional sea level budgets by combining multi-mission altimetry and GRACE(-FO) data

10.5194/egusphere-egu2020-3507 ◽

2020 ◽

Author(s):

Bernd Uebbing ◽

Christina Lück ◽

Roelof Rietbroek ◽

Kristin Vielberg ◽

Jürgen Kusche

Keyword(s):

Time Series ◽

Sea Level ◽

Sea Level Change ◽

Inversion Method ◽

Data Sets ◽

Sea Level Changes ◽

Steric Sea Level ◽

Level Change ◽

Spatial Coverage ◽

Regional Sea Level

Understanding present day sea level changes and their drivers requires the separation of the total sea level change into individual mass and steric related contributions. Total sea level rise has been observed continuously since 1993 providing a more than 25 year long time series of global and regional sea level variations. However, direct monitoring of ocean mass change has only been done since the start of the Gravity Recovery And Climate Experiment (GRACE) mission in 2002. It ended in 2017 and was succeeded by the follow-on mission (GRACE-FO) in 2018 leaving a gap of about 1 year. In the same time period of GRACE, since the early 2000s, a global array of freely drifting Argo floats samples temperature and salinity profiles of up to 2000m depth which can be converted to steric sea level change.By combining altimetry, GRACE(-FO) and Argo data sets it is possible to derive global and regional sea level budgets. The conventional approach is to analyze at least two of the data sets and derive the residual, or compare with the third one. A more recent approach is the global joint inversion method (Rietbroek et al., 2016) which fits forward-modeled spatial fingerprints to a combination of GRACE gravity data and Jason-1/-2 satellite altimetry data. This enables us, additionally, to separate altimetric sea level change into mass contributions from terrestrial hydrology, the melting of land glaciers and the ice-sheets in Greenland and Antarctica as well as contributions from steric sea level changes due to variations in ocean temperature and salinity. It also allows to include a data weighting scheme in the analysis.Here, we present global and regional sea level budget results from an updated inversion based on multi-mission altimetry (Jason-1/-2/-3, Envisat, Cryosat-2, Sentinel-3, &#8230;) providing better spatial coverage as well as new RL06 GRACE and GRACE-FO data which enables us to extend the time series of individual components of the sea level budget beyond the GRACE era from 2002-04 till 2019-06. The presented sea level budget is closed on global scale with a residual (unexplained) contribution of about 0.1 mm/yr, globally, originating in eddy-active regions. We provide consistent validation of our results against conventionally analyzed altimetry and GRACE data sets where we find agreement on global scales to be better than 0.1 mm/yr but a larger disagreement at regional scales as well as the implications of our results for deriving ocean heat content. We will also provide first results for filling the gap in the sea level budget estimates due to the gap between the GRACE and GRACE-FO missions by additionally incorporating time-variable gravity information from the Swarm mission as well as from Satellite Laser Ranging (SLR) to 5 satellites (Lageos-1/-2, Stella, Starlette, Ajisai).

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Analysis and representation of regional sea-level variability from altimetry and atmospheric-oceanic data

Geophysical Journal International ◽

10.1046/j.1365-246x.2001.00284.x ◽

2001 ◽

Vol 145 (1) ◽

pp. 1-18 ◽

Cited By ~ 34

Author(s):

L. Fenoglio-Marc

Keyword(s):

Sea Level ◽

Sea Level Variability ◽

Regional Sea Level

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Regional sea level changes prediction integrated with singular spectrum analysis and long-short-term memory network

Advances in Space Research ◽

10.1016/j.asr.2021.08.017 ◽

2021 ◽

Author(s):

Jian Zhao ◽

Ruiyang Cai ◽

Weifu Sun

Keyword(s):

Sea Level ◽

Spectrum Analysis ◽

Short Term Memory ◽

Singular Spectrum Analysis ◽

Sea Level Changes ◽

Short Term ◽

Term Memory ◽

Regional Sea Level ◽

Memory Network ◽

Long Short Term Memory

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Atmospheric circulation changes and their impact on extreme sea levels around Australia

Natural Hazards and Earth System Science ◽

10.5194/nhess-19-1067-2019 ◽

2019 ◽

Vol 19 (5) ◽

pp. 1067-1086 ◽

Cited By ~ 4

Author(s):

Frank Colberg ◽

Kathleen L. McInnes ◽

Julian O'Grady ◽

Ron Hoeke

Keyword(s):

Sea Level ◽

Large Scale ◽

Climate Models ◽

Tide Gauge ◽

Austral Summer ◽

Sea Level Changes ◽

Sea Level Variability ◽

Sea Levels ◽

Extreme Sea Levels ◽

Coastal Sea

Abstract. Projections of sea level rise (SLR) will lead to increasing coastal impacts during extreme sea level events globally; however, there is significant uncertainty around short-term coastal sea level variability and the attendant frequency and severity of extreme sea level events. In this study, we investigate drivers of coastal sea level variability (including extremes) around Australia by means of historical conditions as well as future changes under a high greenhouse gas emissions scenario (RCP 8.5). To do this, a multi-decade hindcast simulation is validated against tide gauge data. The role of tide–surge interaction is assessed and found to have negligible effects on storm surge characteristic heights over most of the coastline. For future projections, 20-year-long simulations are carried out over the time periods 1981–1999 and 2081–2099 using atmospheric forcing from four CMIP5 climate models. Changes in extreme sea levels are apparent, but there are large inter-model differences. On the southern mainland coast all models simulated a southward movement of the subtropical ridge which led to a small reduction in sea level extremes in the hydrodynamic simulations. Sea level changes over the Gulf of Carpentaria in the north are largest and positive during austral summer in two out of the four models. In these models, changes to the northwest monsoon appear to be the cause of the sea level response. These simulations highlight a sensitivity of this semi-enclosed gulf to changes in large-scale dynamics in this region and indicate that further assessment of the potential changes to the northwest monsoon in a larger multi-model ensemble should be investigated, together with the northwest monsoon's effect on extreme sea levels.

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