Variability of Arctic sea ice Nikolay Vladimirovich Koldunov 79 Berichte zur Erdsystemforschung 2010 Reports on Earth System Science 79 Berichte zur Erdsystemforschung 2010 Variability of Arctic sea ice Nikolay Vladimirovich Koldunov aus Sankt Petersburg, Russland Hamburg 2010 79 Reports on Earth System Science 2010 ISSN 1614-1199 Nikolay Vladimirovich Koldunov Max-Planck-Institut für Meteorologie Bundesstrasse 53 20146 Hamburg Germany Als Dissertation angenommen vom Department Geowissenschaften der Universität Hamburg auf Grund der Gutachten von Prof. Dr. Detlef Stammer und Prof. Dr. Jochem Marotzke Hamburg, den 23. April 2010 Prof. Dr. Jürgen Oßenbrügge Leiter des Departments für Geowissenschaften ISSN 1614-1199 Variability of Arctic sea ice Nikolay Vladimirovich Koldunov Hamburg 2010 Cover picture Upper panel: Mean sea ice concentration analyzed from the GSFC satellite data over the period 1980-1999 for (left) March and (right) September. Lower panel: Standard deviation of monthly mean sea ice concentrations analyzed from the GSFC satellite data over the period 1980-1999 for (left) March and (right) September. Rectangles indicate geographic locations for which time series of sea ice concentrations are shown in Fig. 2.9 i Contents Dedication xi Acknowledgement xiii Abstract 1 1 Introduction 3 1.1 Goals of the thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 1.2 Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2 Present-day Arctic Sea Ice Variability in the Coupled ECHAM5/MPI-OM Model 9 2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.2 Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2.2.1 MPI-OM model . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2.2.2 Satellite observations . . . . . . . . . . . . . . . . . . . . . . . 13 2.2.3 In situ data . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 2.3 Sea ice concentration and thickness . . . . . . . . . . . . . . . . . . . 17 2.3.1 Seasonal distribution of sea ice concentration . . . . . . . . . 17 2.3.2 Seasonal sea ice thickness . . . . . . . . . . . . . . . . . . . . 21 2.3.3 Interannual variations of sea ice concentration . . . . . . . . . 24 2.4 Sea ice transports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 2.5 Forcing fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 2.5.1 Atmospheric forcing . . . . . . . . . . . . . . . . . . . . . . . 30 2.5.2 Ocean forcing . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 2.6 Discussion and Conclusion . . . . . . . . . . . . . . . . . . . . . . . . 37 3 Adjoint-based sensitivities of the Arctic sea ice 41 3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 3.2 Present knowlege . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 3.3 Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 3.3.1 MITgcm model setup . . . . . . . . . . . . . . . . . . . . . . 47 3.3.2 Adjoint calculation of sensitivities . . . . . . . . . . . . . . . 49 3.3.3 Experimental design . . . . . . . . . . . . . . . . . . . . . . . 50 3.4 Comparison of satellite and simulated SIC . . . . . . . . . . . . . . . 52 ii Contents 3.5 Spatial variability of mean adjoint sensitivities . . . . . . . . . . . . 58 3.6 Adjoint sensitivities during the three time periods: 1980-1989, 1990- 1999, and 2000-2007 . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 3.7 Time evolution of sensitivities in different regions . . . . . . . . . . . 86 3.8 Five-year run . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 3.9 Discussion and conclusions . . . . . . . . . . . . . . . . . . . . . . . . 98 4 Conclusions and outlook 105 4.1 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 4.2 Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 Bibliography 111 iii List of Figures 1.1 Arctic Ocean including geographical place names. The Amerasian Basin,mentioned inthetext, includestheregion fromtheLomonosov RidgetowardsthePacificOcean. TheEurasianBasinincludesregions from the Lomonosov Ridge towards the Atlantic Ocean. Based on a map produced by the International Bathymetric Chart of the Arctic Ocean (IBCAO), Jakobsson et al. (2008). . . . . . . . . . . . . . . . 4 2.1 Upper panel: Mean sea ice concentration analyzed from the GSFC satellite data over the period 1980-1999 for (left) March and (right) September. Lowerpanel: Standarddeviationofmonthlymeanseaice concentrations analyzed fromthe GSFC satellite data over the period 1980-1999for(left)Marchand(right)September. Rectanglesindicate geographiclocationsforwhichtimeseriesofseaiceconcentrations are shown in Fig. 2.9 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 2.2 Upper panel: March mean sea ice concentrations (1980-1999) simu- lated by (left) the ECHAM run and (right) the FNCEP run. Lower panel: Differences in March mean (1980-1999) sea ice concentrations of (left) ECHAM minus GSFC and (right) FNCEP minus GSFC. . 18 2.3 Upperpanel: Septembermeanseaiceconcentrations(1980-1999)sim- ulated by (left) the ECHAM run and (right) the FNCEP run. Lower panel: Differences in September mean (1980-1999) sea ice concentra- tions of (left) ECHAM minus GSFC and (right) FNCEP minus GSFC. 19 2 6 2.4 Top panel: September Arctic Sea ice extent (in km 10 ) as observed over the last 30 years (through 2008; green curve) and as simulated by the MPI-OM ECHAM run (red curve) and the FNCEP run (blue curve). Theperiodusedinthisanalysismarkedbyrectangle. Bottom panel: DistributionofNorthernHemisphereseaiceconcentration(bin width 0.1 frac., beginning at 0.01 frac.) for September (1980-1999), as simulated by the two model runs and as observed by satellites. . 20 2.5 Left: ClimatologicalAprilmeanthicknessofobservedseaice,adapted from Romanov (1995). Right column: mean April sea ice thickness for (top) ECHAM and (bottom) FNCEP. . . . . . . . . . . . . . . . 21 2.6 Left: Climatological August-September mean thickness of observed sea ice, adapted from Romanov (1995). Right column: mean August- September sea ice thickness for (top) ECHAM and (bottom) FNCEP. 22 iv List of Figures 2.7 Distribution of sea ice thickness (bin width 0.5 m, beginning at 0.01 m) as simulated by the ECHAM and FNCEP model runs. . . . . . 24 2.8 Standard deviation of monthly mean sea ice concentrations for September (1980-1999) (left) in the ECHAM run and (right) in the FNCEP run. Rectangles indicate geographic locations for which time series of sea ice concentrations are shown in Fig. 2.9. . . . . . . . . 25 2.9 Time series of mean September sea ice concentrations from different areas for the period 1980-1999. Shown are GSFC observations (green curve),theECHAMrun(redcurve)andtheFNCEPrun(bluecurve). Shown in the top, center and bottom panels are time series from positions 1 through 3 in Figs. 2.1 and 2.8, respectively. . . . . . . . 26 2.10 Ice motion vectors for March (left column) and October (right col- umn) for (upper panel) Pathfinder project data, (middle panel) the ECHAM run, and (lower panel) the FNCEP run. For Pathfinder data, every fifth vector is shown, for ECHAM and FNCEP runs, ev- ery second vector is shown. Color-coded is the speed of each vector −1 (in cm s ). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 2.11 Distribution of seaice velocities fromtheentire NorthernHemisphere for March (upper panel) and September (lower panel). Percentage values of the y-axis correspond to histogram bins along the x-axis −1 −1 with a bin width of 0.01 m s beginning at 0.001 m s . Shown are Pathfinder data, the ECHAM run and the FNCEP run as green, red and blue curves, respectively. Note the different vertical scale on graphs.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 2.12 Seaicevolume transportthroughtheFram Straitas simulated by the ECHAM and FNCEP model runs and analyzed by previous studies. 29 2.13 Climatological monthly mean surface air temperature (color coded in ◦ C) and sea level pressure (contours as hPa) fields for (left) March and (right) September. Shown are results for (upper row) ECHAM and (lower row) the NCEP-RA1 reanalysis. . . . . . . . . . . . . . . 31 2.14 Toprow: Shownascontoursaredifferencesbetweentheclimatological monthly mean (left) March and (right) September ECHAM - NCEP- RA1 SLP (contour interval is 1 hPa). Superimposed as vector field aretherespectiveclimatological monthlymeandifferencefieldsforice motions,withonlyeverysecondvectorplottedandspeedscolorcoded −1 in cm s . Bottom row: Shown as contour lines are differences in climatological (left) March and (right) September ECHAM - NCEP- RA1 SAT fields. Superimposed as color are respective ECHAM - GSFC SIC difference fields. . . . . . . . . . . . . . . . . . . . . . . . 32 2.15 Upper row: Vertical profiles of September ocean; top:temperature, middle:salinity and bottom:density from PHC climatolofy and model runs (1980-1999). Green -PHC, red - ECHAM run, blue - FNCEP run. Parameters are averaged over the area showed at the middle panel. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35