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Session Chair: Rachel Tilling Session Chair: Eero Rinne
4:10pm - 4:30pm
Invited - Keynote: Understanding Inter-annual Variability, and Long Term Trends, in Polar Sea Ice using Satellite Laser and Radar Altimetry: Current Achievements and Future Prospects
4:30pm - 4:50pm
Monthly Variability of Sea Ice Thickness from CryoSat-2
Jet Propulsion Laboratory, California Institute of Technology, United States of America
Monthly changes in CryoSat-2 sea ice thickness can be separated into changes due to dynamics and ice growth using estimates of ice deformation calculated from large-scale ice drift. Over a region of persistent convergence north of the coasts of Greenland and the Canadian Arctic Archipelago, divergence and shear explain up to 69% monthly thickness variability in CryoSat-2 thickness estimates. The estimated area-averaged growth of 0.12±0.03 m/month compares with measurements from ice mass balance buoys of about 0.14 m/month. It can be see in the mechanical redistribution process that areas covered by ice < 3 m are reduced, while areas of thicker ice (>3 m) increased. Ice convergence near the Arctic coasts of Greenland and the Canadian Arctic Archipelago (CAA) is a source of some of the thickest ice in the Arctic and alters the response of the ice cover to atmospheric and oceanic forcing at different time and space scales. The thicker, more deformed ice adds to the variability and challenges the predictability of the ice cover in during summer melt. The signature of ice convergence on the behavior of the summer ice cover is discussed.
4:50pm - 5:10pm
Drop of Arctic Sea-Ice Growth in Winter 2015/16 Observed with Merged CryoSat-2/SMOS Data Record
Robert Ricker1,2, Stefan Hendricks1, Fanny Girard-Ardhuin2, Lars Kaleschke3, Camille Lique1, Xiangshan Tian-Kunze3, Marcel Nicolaus1, Jennifer King4, Christian Haas1, Stephan Paul1
1IFREMER, France; 2AWI, Germany; 3University of Hamburg, Germany; 4Norwegian Polar Institute, Norway
A new record low in Arctic sea-ice maximum winter extent has been observed in 2016, associated with an anomalous warm winter. The high winter temperatures lead to reduced thermodynamic ice growth associated with a thinner first-year sea-ice cover in spring. This can also have consequences for the melt season, since, in addition to the summer conditions, it is crucial how thick and resistant the ice cover is in spring, at the end of the freezing period. Previous studies have shown that preconditioning through a thinned ice cover substantially contributed to the ice extent record minimum in September 2012. Sea-ice thickness on global scale is derived from different satellite sensors using independent retrieval methods. Due to the sensor and orbit characteristics, such satellite retrievals differ in spatial and temporal resolution as well as in the sensitivity to certain sea-ice types and thickness ranges. Satellite altimeters, such as ICESat or CryoSat-2, sense the height of the ice or snow surface above the sea level, and can be converted into sea-ice thickness assuming hydrostatic balance. However, relative uncertainties associated with this method are largest over thin ice regimes, where surface elevations are small. Another retrieval strategy is realized by the evaluation of surface emissivity in L-band, obtained from the Soil Moisture and Ocean Salinity (SMOS) satellite, which is restricted to the thin first-year sea-ice thickness range, where relative uncertainties are smaller than those of altimetry-based retrievals. In addition, the SMOS retrieval provides complete coverage in conjunction with a better temporal resolution over sea ice in lower latitudes. Here, we use the first joint data fusion of CryoSat-2 and SMOS ice thickness retrievals to investigate how the Arctic-wide anomalous warm winter in 2016 has affected the thermodynamic ice growth and the sea-ice thickness in spring. We evaluate ice thickness and volume anomalies in 2016 with respect to previous years, also considering the role of ice dynamics.
5:10pm - 5:30pm
Towards Climate Data Records of Arctic and Antarctic Sea Ice Thickness from CryoSat-2 and Envisat Radar Altimetry
Stefan Hendricks1, Eero Rinne2, Stephan Paul1, Robert Ricker1, Henriette Skourup3, Stefan Kern4, Stein Sandven5
1Alfred Wegener Institute, Germany; 2Finish Meteorological Institute, Finland; 3Danish Technical University, Denmark; 4Universität Hamburg, Germany; 5Nansen Environmental and Remote Sensing Center, Norway
The CryoSat-2 mission has demonstrated the value of radar altimetry to assess the interannual variability and short-term trends of Arctic sea ice over the existing observational record of 7 winter seasons. CryoSat-2 is a particularly successful mission for sea ice mass balance assessment due to its novel radar altimeter concept and orbit configuration, but radar altimetry data is available since 1993 from the ERS-1/2 and Envisat missions. Combining these datasets promises a decadal climate data record of sea ice thickness, but inter-mission biases must be taken into account due to the evolution of radar altimeters and the impact of changing sea ice conditions on retrieval algorithm parameterizations. Particular challenges are the classification of surface types and freeboard retrieval based on radar waveforms because of the significantly varying footprint sizes of the instruments involved. However, consistent decadal time series from radar altimetry has the prospect for cross-calibration of sea ice thickness estimates from CryoSat-2 and ICESat and for investigation of decadal trends of sea ice thickness.
The ESA Climate Change Initiative on Sea Ice aims to extent the list of data records for Essential Climate Variables (ECV’s) with a consistent time series of sea ice thickness from available radar altimeter data. We will report first results and uncertainty estimates for sea ice thickness retrieval in the Arctic and Antarctic Oceans from CryoSat-2 and Envisat and the planned release cycle of the sea ice thickness climate data record.