scholarly journals Refining the sea surface identification approach for determining freeboards in the ICESat-2 sea ice products

2021 ◽  
Vol 15 (2) ◽  
pp. 821-833
Author(s):  
Ron Kwok ◽  
Alek A. Petty ◽  
Marco Bagnardi ◽  
Nathan T. Kurtz ◽  
Glenn F. Cunningham ◽  
...  
Keyword(s):  
Sea Ice ◽  
Sea Surface Height ◽  
Sea Surface ◽  
The Arctic ◽  
Surface Reflectance ◽  
Data Product ◽  
Sea Surface Heights ◽  
Identification Approach ◽  
Southern Oceans

Abstract. In Release 001 and 002 of the ICESat-2 sea ice products, candidate height segments used to estimate the reference sea surface height for freeboard calculations included two surface types: specular and smooth dark leads. We found that the uncorrected photon rates, used as proxies of surface reflectance, are attenuated due to clouds resulting in the potential misclassification of sea ice as dark leads, biasing the reference sea surface height relative to those derived from the more reliable specular returns. This results in higher reference sea surface heights and lower estimated ice freeboards. The resolution of available cloud flags from the ICESat-2 atmosphere data product is too coarse to provide useful filtering at the lead segment scale. In Release 003, we have modified the surface-reference-finding algorithm so that only specular leads are used. The consequence of this change can be seen in the composites of mean freeboard of the Arctic and Southern oceans. Broadly, coverages have decreased by ∼10–20 % because there are fewer leads (by excluding the dark leads), and the composite means have increased by 0–4 cm because of the use of more consistent specular leads.

scholarly journals Refining the sea surface identification approach for determining freeboards in the ICESat-2 sea ice products

2020 ◽  
Author(s):  
Ron Kwok ◽  
Alek A. Petty ◽  
Marco Bagnardi ◽  
Nathan T. Kurtz ◽  
Glenn F. Cunningham ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Sea Surface Height ◽  
Sea Surface ◽  
The Arctic ◽  
Surface Reflectance ◽  
Data Product ◽  
Sea Surface Heights ◽  
Identification Approach

Abstract. In Release 1 and 2 of the ICESat-2 sea ice products, candidate height segments used to estimate the reference sea surface height for freeboard calculations included two surface types: specular and smooth dark leads. We found that the uncorrected photon rates, used as proxies of surface reflectance, are attenuated due to clouds resulting in the potential misclassification of sea ice as dark leads, biasing the reference sea surface height relative to those derived from the more reliable specular returns. This results in higher reference sea surface heights and lowering estimated ice freeboards. Resolution of available cloud flags from the ICESat-2 atmosphere data product are too coarse to provide useful filtering at the lead segment scale. In Release 3, we have modified the surface reference finding algorithm so that only specular leads are used. The consequence of this change can be seen in the freeboard composites of the Arctic and Southern Ocean. Broadly, coverages have decreased by ~10–20 % because there are fewer leads (by excluding the dark leads), and the composite means have increased by 0–4 cm because of the use of more consistent specular leads.

scholarly journals Mechanisms of the time-varying sea surface height and heat content trends in the eastern Nordic Seas

2019 ◽  
Author(s):  
Sara Broomé ◽  
Léon Chafik ◽  
Johan Nilsson
Keyword(s):  
North Atlantic ◽  
Decadal Variability ◽  
North Atlantic Ocean ◽  
Heat Budget ◽  
Heat Content ◽  
Sea Surface Height ◽  
Sea Surface ◽  
The Arctic ◽  
Nordic Seas ◽  
Sea Surface Heights

Abstract. The Nordic Seas is the main ocean conveyor of heat between the North Atlantic Ocean and the Arctic Ocean. Although the decadal variability of the Subpolar North Atlantic has been given significant attention lately, especially regarding the cooling trend since mid-2000s, less is known about the potential connection downstream in the northern basins. Using sea surface heights from satellite altimetry over the past 25 years (1993–2017), we find significant variability on multiyear-to-decadal time scales in the Nordic Seas. In particular, the regional trends in sea surface height show signs of a slowdown since mid-2000s as compared to the rapid increase in the preceding decade since early 1990s. This change is most prominent in the Atlantic origin waters in the eastern Nordic Seas and is closely linked, as estimated from hydrography, to heat content. Furthermore, we formulate a simple heat budget for the eastern Nordic Seas to discuss the relative importance of local and remote sources of variability; advection of temperature anomalies in the Atlantic inflow is found to be the main mechanism. A conceptual model of ocean heat convergence, with only upstream temperature measurements at the inflow to the Nordic Seas as input, is able to reproduce key aspects of the decadal variability of the Nordic Seas' heat content. Based on these results, we argue that there is a strong connection with the upstream Subpolar North Atlantic. However, although the shift in trends in the mid-2000s is coincident in the Nordic Seas and the Subpolar North Atlantic, the eastern Nordic Seas has not seen a reversal of trends but instead maintain elevated sea surface heights and heat content in the recent decade considered here.

scholarly journals Mechanisms of decadal changes in sea surface height and heat content in the eastern Nordic Seas

Ocean Science ◽  
2020 ◽  
Vol 16 (3) ◽  
pp. 715-728
Author(s):  
Sara Broomé ◽  
Léon Chafik ◽  
Johan Nilsson
Keyword(s):  
North Atlantic ◽  
Decadal Variability ◽  
North Atlantic Ocean ◽  
Heat Budget ◽  
Heat Content ◽  
Sea Surface Height ◽  
Sea Surface ◽  
The Arctic ◽  
Nordic Seas ◽  
Sea Surface Heights

Abstract. The Nordic Seas constitute the main ocean conveyor of heat between the North Atlantic Ocean and the Arctic Ocean. Although the decadal variability in the subpolar North Atlantic has been given significant attention lately, especially regarding the cooling trend since the mid-2000s, less is known about the potential connection downstream in the northern basins. Using sea surface heights from satellite altimetry over the past 25 years (1993–2017), we find significant variability on multiyear to decadal timescales in the Nordic Seas. In particular, the regional trends in sea surface height show signs of a weakening since the mid-2000s, as compared to the rapid increase in the preceding decade since the early 1990s. This change is most prominent in the Atlantic origin waters in the eastern Nordic Seas and is closely linked, as estimated from hydrography, to heat content. Furthermore, we formulate a simple heat budget for the eastern Nordic Seas to discuss the relative importance of local and remote sources of variability; advection of temperature anomalies in the Atlantic inflow is found to be the main mechanism. A conceptual model of ocean heat convergence, with only upstream temperature measurements at the inflow to the Nordic Seas as input, is able to reproduce key aspects of the decadal variability in the heat content of the Nordic Seas. Based on these results, we argue that there is a strong connection with the upstream subpolar North Atlantic. However, although the shift in trends in the mid-2000s is coincident in the Nordic Seas and the subpolar North Atlantic, the eastern Nordic Seas have not seen a reversal of trends but instead maintain elevated sea surface heights and heat content in the recent decade considered here.

scholarly journals Lasting impact of winds on Arctic sea ice through the ocean's memory

2021 ◽  
Author(s):  
Qiang Wang ◽  
Sergey Danilov ◽  
Longjiang Mu ◽  
Dmitry Sidorenko ◽  
Claudia Wekerle
Keyword(s):  
Sea Ice ◽  
Numerical Simulations ◽  
Spatial Patterns ◽  
Sea Surface Height ◽  
Arctic Sea Ice ◽  
Sea Surface ◽  
The Arctic ◽  
Geostrophic Currents ◽  
Arctic Sea ◽  
The Impact

Abstract. In this paper we studied the impact of winds on Arctic sea ice through the ocean’s memory by using numerical simulations. We found that the changes in ocean freshwater content induced by wind perturbations can significantly affect the Arctic sea ice drift, thickness, concentration and deformation rates regionally even years after the wind perturbations. Changes in the Arctic liquid freshwater content cause changes in the sea surface height and surface geostrophic currents, which further enforce a lasting and strong impact on sea ice. Both the changes in sea surface height gradient force (due to changes in sea surface height) and ice-ocean stress (due to changes in surface geostrophic currents) are found to be important in determining the overall ocean effects. The revealed ocean effects are mainly associated with changes in sea ice dynamics, not thermodynamics. Depending on the preceding atmospheric mode driving the ocean, the ocean’s memory of the wind forcing can lead to changes in Arctic sea ice characteristics with very different spatial patterns. We identified these spatial patterns associated with Arctic Oscillation, Arctic Dipole Anomaly and Beaufort High modes through dedicated numerical simulations. The dynamical impact of the ocean has strong seasonal variations, stronger in summer and weaker in winter and spring. It implies that declining trends of Arctic sea ice will very possibly allow a stronger ocean impact on the sea ice in a warming climate.

Sea surface height anomaly of the ice-covered oceans from ICESat-2 and CryoSat-2

2021 ◽  
Author(s):  
Marco Bagnardi ◽  
Nathan Kurtz ◽  
Alek Petty ◽  
Ron Kwok
Keyword(s):  
Sea Ice ◽  
European Space Agency ◽  
Sea Surface Height ◽  
Sea Surface ◽  
The Arctic ◽  
Height Anomaly ◽  
Polar Regions ◽  
Waveform Data ◽  
Polar Oceans ◽  
Sea Surface Height Anomaly

<p>Rapid changes in Earth’s sea ice and land ice have caused significant disruption to the polar oceans in terms of fresh water storage, ocean circulation, and the overall energy balance. While we can routinely monitor, from space, the ocean surface at lower latitudes, measurements of sea surface in the ice-covered oceans remains challenging due to sampling deficiencies and the need to discriminate returns between sea ice and ocean.</p><p>The European Space Agency’s (ESA) CryoSat-2 satellite has been acquiring unfocussed synthetic aperture radar altimetry data over the polar regions since 2010, providing a key breakthrough in our ability to routintely monitor the ice-covered oceans. Since October 2018, NASA’s Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2) and its onboard Advanced Topographic Laser Altimeter (ATLAS) have provided new measurements of sea ice and sea surface elevations over similar polar regions. With over two years of overlapping data, we now have the opportunity to compare coincident sea surface height retrievals from the two missions and assess potential elevation differences over two entire freeze-melt cycles across both polar oceans .</p><p>Also, as of August 2020, CryoSat-2’s orbit has been modified as part of the <em>CRYO2ICE</em> campaign, such that every 19 orbits (20 orbits for ICESat-2) the two satellites align for hundreds of kilometers over the Arctic Ocean, acquiring data along coincident ground tracks with a time difference of approximately three hours.</p><p>In this work, we compare sea surface height anomaly (SSHA) retrievals from CryoSat-2 (Level 1b and Level 2 data) and  ICESat-2 (Level 3a data, ATL10). We apply a recently updated waveform fitting method to the CryoSat-2 waveform data (Level 1b) to determine the retracking corrections,  based on <em>Kurtz et al.</em> (2014). We apply the same mean sea surface adjustment used for ICESat-2 to CryoSat-2 data, and we apply similar geophysical and atmospheric corrections to both datasets.</p><p>While we find an overall good agreement between the two datasets, some discrepancies between CryoSat-2 and ICESat-2 SSHA estimates remain. In this work we explore the potential causes of these discrepancies, related to both lead finding/distribution, and range biases.</p><p> </p>

Long-lasting impacts of winds on Arctic sea ice through the ocean’s memory

2021 ◽  
Author(s):  
Qiang Wang ◽  
Sergey Danilov ◽  
Longjiang Mu ◽  
Dmitry Sidorenko ◽  
Claudia Wekerle
Keyword(s):  
Sea Ice ◽  
Spatial Patterns ◽  
Sea Surface Height ◽  
Arctic Sea Ice ◽  
Sea Surface ◽  
The Arctic ◽  
Gradient Force ◽  
Ice Drift ◽  
Arctic Sea ◽  
Sea Ice Drift

<p>This modelling study reveals that the changes in the ocean state induced by wind perturbations can significantly influence the Arctic sea ice drift, thickness, concentration and deformation rates even after the wind perturbations have been eliminated for years. Wind perturbations can change the Arctic Ocean liquid freshwater content locally or basin-wide, thus changing the sea surface height and ocean surface geostrophic current accordingly. Such changes in the ocean can last for many years, which enforces long-lasting and strong imprint on sea ice. Both the changes in sea surface height gradient force (due to changes in sea surface height) and ocean-ice stress (due to changes in ocean geostrophic velocity) are found to be important in determining the overall impacts on sea ice. Depending on the preceding atmospheric mode driving the ocean, the ocean’s memory of wind forcing can lead to changes in Arctic sea ice characteristics with very different spatial patterns. We identified these spatial patterns associated with Arctic Oscillation, Arctic Dipole Anomaly and Beaufort High modes through dedicated numerical simulations in this study. Our results suggest the importance of initial ocean state in sea ice prediction on subseasonal to decadal time scales.</p>

scholarly journals Lasting impact of winds on Arctic sea ice through the ocean's memory

2021 ◽  
Vol 15 (10) ◽  
pp. 4703-4725
Author(s):  
Qiang Wang ◽  
Sergey Danilov ◽  
Longjiang Mu ◽  
Dmitry Sidorenko ◽  
Claudia Wekerle
Keyword(s):  
Sea Ice ◽  
Numerical Simulations ◽  
Spatial Patterns ◽  
Sea Surface Height ◽  
Arctic Sea Ice ◽  
Sea Surface ◽  
The Arctic ◽  
Geostrophic Currents ◽  
Arctic Sea ◽  
The Impact

Abstract. In this paper we studied the impact of winds on Arctic sea ice through the ocean's memory by using numerical simulations. We found that the changes in halosteric height induced by wind perturbations can significantly affect the Arctic sea ice drift, thickness, concentration and deformation rates regionally even years after the wind perturbations. Changes in the Arctic liquid freshwater content and thus in halosteric height can cause changes in the sea surface height and surface geostrophic currents, which further enforce a lasting and strong impact on sea ice. The changes in both sea surface height gradient force (due to changes in sea surface height) and ice–ocean stress (due to changes in surface geostrophic currents) are found to be important in determining the overall ocean effects. The revealed ocean effects are mainly associated with changes in sea ice dynamics, not thermodynamics. Depending on the preceding atmospheric mode driving the ocean, the ocean's memory of the wind forcing can lead to changes in Arctic sea ice characteristics with very different spatial patterns. We obtained these spatial patterns associated with Arctic Oscillation, Arctic Dipole Anomaly and Beaufort High modes through dedicated numerical simulations. The dynamical impact of the ocean has strong seasonal variations, stronger in summer and weaker in winter and spring. This implies that declining trends of Arctic sea ice will very possibly allow a stronger ocean impact on the sea ice in a warming climate.

scholarly journals Record high Pacific Arctic seawater temperatures and delayed sea ice advance in response to episodic atmospheric blocking

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Tsubasa Kodaira ◽  
Takuji Waseda ◽  
Takehiko Nose ◽  
Jun Inoue
Keyword(s):  
Sea Ice ◽  
Arctic Region ◽  
Arctic Sea Ice ◽  
Sea Surface ◽  
The Arctic ◽  
Atmospheric Blocking ◽  
Sea Ice Extent ◽  
The Pacific ◽  
Arctic Sea ◽  
Highly Correlated

AbstractArctic sea ice is rapidly decreasing during the recent period of global warming. One of the significant factors of the Arctic sea ice loss is oceanic heat transport from lower latitudes. For months of sea ice formation, the variations in the sea surface temperature over the Pacific Arctic region were highly correlated with the Pacific Decadal Oscillation (PDO). However, the seasonal sea surface temperatures recorded their highest values in autumn 2018 when the PDO index was neutral. It is shown that the anomalous warm seawater was a rapid ocean response to the southerly winds associated with episodic atmospheric blocking over the Bering Sea in September 2018. This warm seawater was directly observed by the R/V Mirai Arctic Expedition in November 2018 to significantly delay the southward sea ice advance. If the atmospheric blocking forms during the PDO positive phase in the future, the annual maximum Arctic sea ice extent could be dramatically reduced.

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