Technical specifications SSM/IS – DMSP: Operating frequency and corresponding spatial resolution (along track*cross track / meters): 19.35 GHz H/V 73*47, 22.235 GHz V 73*47, 37.00 GHz H/V 41*31 From 50.3 to 60.72 GHz (13 bands) 17.6*27.3 91.665 GHz H/V 14*13 150 GHz 14*13 183.311 GHz (2 bands) 14*13
Data and method Sea ice concentration: Matching different passive microwave record at geophysical product level Sea ice extent: Area with ≥15% ice concentration (Atmospheric interference, low ice concentration, thin ice thickness) How sea ice extent is defined? Why?
Trend of ice extent in three periods: 1979-1996, 1979-2006, 1979-2010
Conclusion and further discussion Northern hemisphere ice extent variability showed a declining trend. Trend is mostly pronounced in Arctic Ocean, and in summer. Trend of declining rapidly increased during last decade. What trend does northern hemisphere sea ice extent variation have? When and where the trend is strongest? What change does such trend have in recent years?
Discussion to The changing Arctic sea ice cover by Perovich D. (2011) Oceanography 24(3):162-173
Monthly northern hemisphere sea ice extent by passive microwave
September ice extent abnormal -12.8%/decade Standard deviation=1.6%
Ice age First year ice survived through next September minimum is counted as multiyear ice. Observation: Active microwave remote sensing and ice parcels tracking. Difference: Multiyear ice tend to be thicker and more resilient to environmental forcing. How multiyear ice defined? How to observe ice age? What is the most important different between first and multi year ice?
Sea ice age derived from drift tracking of ice floes, March
Ice thickness Related to ice age, proxy. Field observation: with submersed upward looking sonar onboard nuclear submarine Remote sensing: satellite altimetry Lacking continuous pan Arctic sea ice thickness record Is there continuous sea ice thickness data record in Arctic?
Explanation to 2007 extreme event Preconditioning: loss of multiyear ice, decreasing of ice thickness Advection of ocean heat through Bering Strait Trans-Arctic drift to Fram Strait, and warm air inflow from Pacific by wind forcing Ice-Albedo feedback What is ice albedo feedback? Decrease in cloudiness – more impact on open water- warmer water-more bottom and lateral melting
Linear trend of total solar heat input directly into the ocean, percent/year
Air and water temperature dynamics by buoy deployed at Beaufort Sea, Aug 2006 - Sep 2007
Conclusion from two presented papers Ice extent: Declining trend - mostly due to recent extreme summer minimum extent Ice age and thickness: Declining - due to climate change - contributing to preconditioning Extreme low summer minimum extent: - triggered by environmental forcing - triggers ice-albedo feedback - further enhancing preconditioning What contribute most to the accelerating declining trend of Arctic sea ice extent, statistically? What is the relationship between the declining ice age/thickness and ice extnet? What role does ice-albedo feedback played in the process of sea ice declining?