Climate Modelling Group
School of Earth and Ocean Sciences

Climate Research Network

Collaborative Research Agreement at the University of Victoria

on Behalf of the Canadian Institute for Climate Studies and Environment Canada

(CICS—Arctic Ocean; and subcomponent of CICS- Variability)

Progress Report:

October 1, 2000

This progress report is available on the world wide web at:

http://climate.uvic.ca/projects/CCC-Arctic-Progress3.html

1: Principal Investigator

Andrew Weaver

2: Co-Investigators

Ed Carmack, Greg Flato, Lawrence Mysak

3: Institution

School of Earth & Ocean Sciences, University of Victoria

PO Box 3055, Victoria, BC, V8W 3P6

4: Research Progress

This progress report will discuss research conducted during the second year of financial support from the MSC/CICS Arctic Node of the Canadian Climate Research Network. The McGill component of this project will be reported on in a separate progress report.

Substantial leverage of the CICS grant occurred during the last fiscal year. In particular, Flato and Weaver received $100 000 over two years to support a new research associate (Oleg Saenko) to assist in the implementation of the Bitz et al (2000) dynamic/thermodynamic sea ice model into the CCCma coupled model. In addition, A. Weaver and M. Holland at NCAR received a $100 000 US per year (for two years) grant from the International Arctic Research Center in Fairbanks Alaska. This grant will allow for the participation of M. Holland in the collaborative research conducted in the CICS Arctic Node.

The progress report below is broken up into a number of sections detailing progress towards different objectives. Those projects which were completed and reported on in the April 2000 progress report will not discussed.

4.1 Sea ice model sensitivity analyses

Sea ice cover is an important factor in the climate system due to feedback mechanisms associated with its influence on the surface albedo and ice-ocean-atmosphere exchange. However, sea ice models in GCMs typically used relatively crude physics. Single column and basin scale ice models have attempted to assess the importance of different physical parameterizations, however, this has often been done in uncoupled systems which means that various coupled feedback mechanisms are missing.

We examined the sensitivity of climate change simulations in the UVic coupled model to different sea ice physics. In particular, we addressed the influences of ice dynamics and a sub-gridscale ice thickness distribution on the simulation of present-day climate conditions and the climate response to increasing atmospheric CO2 levels. Additionally, we examined the influence of the albedo feedback mechanism in climate change experiments.

As in several previous studies, we found that the sea-ice parameterizations have a significant influence on present-day climate simulations, modifying both the annual mean ice-ocean-atmosphere conditions and the seasonal variation of these properties. For example, in models with motionless sea ice (i.e., thermodynamic-only models) the ice volume increases significantly and undergoes a smaller seasonal cycle. Resolving the ice thickness distribution also increases the ice thickness, but acts to enhance the seasonal cycle. Additionally, the ocean circulation is modified due to different ice/ocean buoyancy fluxes, leading to different Antarctic Bottom Water formation rates.

The presence of ice dynamics and the sub-gridscale ice thickness distribution also influence the response of the system to climate perturbations. Under increased atmospheric CO2 forcing, simulating ice dynamics and the ice thickness distribution enhances the ice area response. However, the ice volume response is diminished when ice dynamics in included and is enhanced when the ice thickness distribution is resolved. The ocean response to global warming is also modified due to the changes in ice physics and the thermohaline circulation is less sensitive to climate change scenarios in models that resolve ice dynamics and the ice thickness distribution.

Additional simulations were performed to quantify the influence of the albedo feedback mechanism on climate change simulations. In increasing CO2 simulations, which neglected the influence of a changing surface albedo, amplified warming was still present (although reduced) at high latitudes due to the poleward retreat of the ice cover and larger ocean-atmosphere heat exchange. In these simulations, the albedo feedback has a considerable influence on the climate response to global warming, accounting for 17% of the global air temperature increase, 37% of the Northern Hemisphere ice area decrease and 31% of the Northern Hemisphere ice volume decrease.

The results of this study have been submitted for publication Holland et al (2000).

4.2: Projections of climate change onto modes of atmospheric variability

D. Stone, A Ph.D. student, has made substantial progress towards the completion of several of the goals of this project. One of the goals of this project was to verify the hypothesis that the Arctic Oscillation (AO) and other dominant patterns of variability remain important in climates with higher greenhouse gas concentrations. Another goal of this project was to determine if climate change induced by increased greenhouse gas concentrations projects onto the natural modes of climate variability.

Two possible interpretations of forced climate change view it as projecting, either linearly or nonlinearly, onto the dominant modes of variability of the climate system. An evaluation of these two interpretations was performed using sea level pressure (SLP) and surface air temperature (SAT) fields obtained from integrations of the Geophysical Fluid Dynamics Laboratory coupled general circulation model forced with varying concentrations of greenhouse gases.

The dominant modes of SLP both represent much of the total variability and remain important in warmer climates. With SAT, however, the dominant modes are often related to variations in the sea ice edge and so do not remain important since the ice retreats as the climate warms; those unrelated to sea ice remain dominant in the warmer climates, but represent smaller fractions of the total variability.

The change in SLP projects partially onto the AO-like mode in the Northern Hemisphere. In the Southern Hemisphere the change projects negligibly onto the dominant modes between equilibrium climates, but almost entirely onto the AAO-like mode in the transient integration. This difference between the transient and equilibrium responses arises from the substantial retreat of Antarctic sea ice and subsequent ocean warming. Unlike SLP, the changes in SAT do not project substantially onto any of the dominant patterns of variability. Changes appear to project strongly onto the ENSO-like mode, but in fact ~90% of this projection relates to the mean global warming associated with the mode, while only ~10% relates to the actual pattern.

In all cases examined the projection of climate change overwhelmingly manifests itself as a linear trend in the mode, with no important alteration of its behaviour. These results also demonstrate that recent observational studies supporting the nonlinear projection interpretation may instead be indicative of a linear projection of climate change onto the dominant modes.

This research has been published in Stone et al. (2000).

4.3 Fresh water fluxes through the Canadian Arctic Archipelago

As part of his PhD, Gilles Arfeuille participated in an Arctic cruise which completed 184 science stations in the western part of the Canadian Arctic Archipelago from the 23rd of August to the 25th of October 1999. During these sciences stations CTD/Rosette casts were conducted to infer the fresh water flux through the Canadian Arctic Archipelago, especially in its western part (i.e. Amundsen Gulf, Prince of Wales Strait, Dolphin and Union Strait, Coronation Gulf, Dease Strait, Queen Maud Gulf, Simpson Strait, Chantrey Inlet, Rae Strait, James Ross Strait, Peel Sound, and Bellot Strait), which has not been studied in detail in previous years. Using 1995, 1997 and this 1999 data, the fresh water flux by sea ice transport and buoyancy boundary currents will be inferred. The fresh water import into the North Atlantic via Baffin Bay is estimated to be 20% of the sea-ice export through Fram Strait. The dO18 data from the water samples taken during the science cruise will reveal the origin of the fresh water forming the buoyancy boundary currents observed during the cruise using the CTD data (i.e. sea-ice melting or river runoff origin).

The post-cruise calibrations and the salinity measurements from the salinity samples have been calculated, and the data has been filtered. Initial results, which are promising, reveal the relative importance of fresh water input from rivers and sea-ice melting in the Archipelago and the transport of this fresh water via buoyancy boundary currents. One of the interesting results is the high variability of these buoyancy boundary currents. To infer more on the variability of the latter Gilles recently spent a two week period undertaking repeated transverse sections out of Cambridge Bay. He is currently writing up his initial analyses for publication.

Julie Bacle, a new PhD student working with E. Carmack has also recently joined this project (Sept. 1, 2000). She is currently undertaking course work and recently came back from a cruise in the region.

4.4 Towards the implementation of a new sea ice model in the CCCma coupled model

A description of, and the results from, a number of sensitivity analyses conducted using the sea ice model, to be included in the CCCma coupled model, has been accepted for publication (Bitz et al. 2000). Linda Waterman (a new PhD student) and Mike Eby (a Research Associate), both funded off CICS Arctic grants, are undertaking further sensitivity analyses using this model. Linda will is focusing on a modelling-based study of the heat and freshwater flux balance of the Arctic Ocean. The vertical resolution of the UVic ocean model will be increased and a parameterization for local turbulent mixing, which has been found better suited to high latitude work, will be incorporated and tested. In related work, the physics of the ocean-sea ice interface will be reviewed and improved. It is also hoped to better resolve significant Arctic Ocean exchange points, including the Canadian Archipelago and Bering Strait, to estimate their impact on the flux balance.

The primary objective of this work was to provide a new, ‘state-of-the-art’ sea ice component for use in the CCCma global climate model. This will include the Hunke and Dukowicz (1997) ice dynamics model and the Bitz and Lipscombe (1999) multi-category thermodynamic model. In order to allow efficient testing of the new sea-ice and related ocean parameterizations, this ice model has been coupled to a global ocean model (a version of the GFDL MOM code).

A series of global ice-ocean model experiments were conducted to investigate the sensitivity of ocean temperature and salinity distributions and circulation patterns to the parameterization of under-ice mixing — specifically the disposition of brine rejected during ice formation.

In a second set of experiments, the global ice-ocean model was forced in one case by ‘observed’ atmospheric data (NCEP reanalysis) and in another case by the observed forcing plus the changes projected by the CCCma global coupled model at the middle of the 21st century. These experiments provide an estimate of the sensitivity of the new sea-ice component to the forcing changes expected under greenhouse-gas-induced climate warming.

Results from these two sets of ice-ocean model experiments have been analyzed and a manuscript will be submitted next month.

Introduction of the new sea-ice component into the CCCma global coupled model has proceeded in a systematic manner. The latest version of the CCCma global model, CGCM2 (Flato and Boer, 2000), uses a rather idealized sea-ice dynamics scheme (the ‘cavitating fluid’ model of Flato and Hibler, 1992). This has been replaced by the Hunke and Dukowicz ‘elastic-viscous-plastic’ model, and multi-year test runs of the global model were conducted. In these test runs, the thermodynamic component remained unchanged. Work is currently underway to replace the thermodynamic component, although, because of the complexity of coupling between ice and atmospheric surface energy exchanges, this is a substantial technical challenge.

In preparation for replacing the thermodynamic component, stand-alone single-column versions of both the original (‘0-layer’) and new Bitz/Lipscomb thermodynamic models have been constructed. These will allow rapid and efficient parameter studies aimed at optimizing the parameter values to be used in the global model implementation. These single-column model versions are also being used in the WCRP ACSYS/CLIC thermodynamic ice model intercomparison project (http://www.cccma.bc.ec.gc.ca/acsys/simip2). This will allow us to benefit directly from the coordinated evaluation of sea-ice thermodynamic models being conducted by this international project.

References:

Bitz, C.M. and W.H. Lipscomb, An energy-conserving thermodynamic model of sea ice. J. Geophys. Res., 104, 15,669-15,677, 1999.

Hunke, E.C. and J.K. Dukowicz, An elastic-viscous-plastic model for sea ice dynamics. J. Phys. Oceanogr., 27, 1849-1867, 1997.

4.7 Analysis of sea-ice variability in the CCCma global coupled model.

A master's student, Jaqueline Dumas, arrived this fall to begin work on a project related to Arctic climate processes. She has begun her course work and has started reading papers related to potential project topics. She will begin her thesis project in early 2001

Although not funded by the CRN, G. Flato's activities related to Arctic research are complementary to and augment those funded through the node and so are outlined briefly here:

• In his role as Chair of the WCRP ACSYS/CLIC NEG, G. Flato has begun organization of the Sea Ice Model Intercomparison Project, Phase 2 (SIMIP2). This will provide a coordinated international comparison of sea-ice thermodynamic models and parameterisations. Two meetings have been held, and initial model simulations have been conducted by Dr. O. Saenko at U.Vic. More details are available at: http://www.cccma.bc.ec.gc.ca/acsys/simip2/

• An Atmospheric Model Intercomparison Project (AMIP) subproject has been initiated through collaboration between J. Fyfe (CCCma), C. Bitz (U. Washington) and G. Flato to investigate Arctic atmospheric circulation errors in GCMs and their role in modelled ice thickness patterns. A manuscript describing this work is in preparation.

• G. Flato has begun work on an invited chapter in a book entitled "Mass balance of the cryosphere: observations and modelling of contemporary and future changes", to be published by Cambridge University Press.

Year 2000 Publications for Weaver and Flato. Those numbers in bold indicated publications supported by the CICS Arctic/Variability Projects.

Weaver:

1. Holland, M.M., A.J. Brasket and A.J. Weaver, 2000: The impact of rising atmospheric CO2 on low frequency North Atlantic climate variability. Geophysical Research Letters, 27, 1519—1522.

2. Weaver, A.J., P.B. Duffy, M. Eby and E.C. Wiebe, 2000: Evaluation of ocean and climate models using present-day observations and forcing. Atmosphere-Ocean, 38, 271—301.

3. Stone, D.A., A.J. Weaver and F.W. Zwiers, 2000: Trends in Canadian precipitation intensity. Atmosphere-Ocean, 38, 321—347.

4. Flato, G.M., G.J. Boer, W.G. Lee, N.A. McFarlane, D. Ramsden, M.C. Reader and A.J. Weaver, 2000: The Canadian Centre for Climate Modelling and Analysis global coupled model and its climate. Climate Dynamics, 16, 451—467.

5. Rutter, N.W., A.J. Weaver, D. Rokosh, A.F. Fanning and D.G. Wright, 2000: Data-model comparison of the Younger Dryas event. Canadian Journal of Earth Sciences, 37, 811—830.

6. Weaver, A.J., and F.W. Zwiers, 2000: Uncertainty in climate change Nature, 407, 571-572..

7. Duffy, P.B., M. Eby and A.J. Weaver, 2000: Climate model simulations of effects of increased atmospheric CO2 and loss of sea ice on ocean salinity and tracer uptake. Journal of Climate, in press.

8. Holland, M.M., C.M. Bitz, M. Eby and A.J. Weaver, 2000: The role of ice ocean interactions in the variability of the North Atlantic thermohaline circulation. Journal of Climate, in press.

9. Yoshimori, M., A.J. Weaver, S.J. Marshall and G.K.C. Clarke, 2000: Glacial termination: Sensitivity to orbital and CO2 forcing in a coupled climate system model. Climate Dynamics, in press.

10. Bitz, C.M., M.M. Holland, A.J. Weaver and M. Eby, 2000: Simulating the ice-thickness distribution in a coupled climate model. Journal of Geophysical Research, in press.

11. Stone, D.A., A.J. Weaver and R.J. Stouffer, 2000: Projection of climate change onto modes of atmospheric variability. J. Climate., submitted.

12. McLaughlin, F. E. Carmack, R. Macdonald, A.J. Weaver and J. Smith, 2000: The Canada Basin 1989-1995: Upstream events and far-field effects of the Barents Sea branch. Journal of Geophysical Research., submitted.

13. Weaver, A.J. and H. Raptis, 2000: Gender differences in introductory atmospheric and oceanic science exams: Multiple choice versus constructed response questions. Journal of Science Education and Technology, submitted.

14. Schmittner, A. and A.J. Weaver, 2000: Dependence of multiple climate states on ocean mixing parameters. Geophysical Research Letters, submitted.

15. Holland, M.M., C.M. Bitz and A.J. Weaver, 2000: The influence of sea ice physics on simulations of climate change. Journal of Geophysical Research, submitted.

16. Hillaire-Marcel, C., A. de Vernal, G. Bilodeau and A.J. Weaver, 2000: Thermohaline structure and instabilities of the Labrador Sea during the present and last interglacials. Nature, submitted.

Flato:

1. Monahan, A.H., J.C. Fyfe and G.M. Flato. 2000: A regime view of northern hemisphere atmospheric variability and change under global warming.Geophys. Res. Lett. 27, 1139-1142.

2. Weaver, R.L.S., K. Steffen, J. Heinrichs, J. Maslanik, and G.M. Flato. 2000: Data assimilation in sea ice monitoring. in press, Annals of Glaciology.

3. Davey, M.K., M. Huddleston, K.R. Sperber, P. Braconnot, F. Bryan, D. Chen, R.A. Colman, C. Cooper, U. Cubasch, P. Delecluse, D. DeWitt, L. Fairhead, G. Flato and 24 others, 2000: STOIC: A study of coupled model climatology and variability in tropical ocean regions. Climate Dynamics, submitted.

4. Gregory, J.M., J.A. Church, G.J. Boer, K.W. Dixon, G.M. Flato and 4 others, 2000: Comparison of results from several AOGCMs for global and regional sea-level change 1900-2100. Climate Dynamics, submitted.

5. Schramm, J.L. G.M. Flato and J.C. Curry. 2000: Towards the modelling of enhanced basal melting in ridge keels. in press, J. Geophys. Res.

6. Kreyscher, M., M. Harder, P. Lemke and G.M. Flato. 2000: Results of the Sea Ice Model Intercomparison Project: Evaluatoin of sea-ice rheology schemes for use in climate simulations. J. Geophys. Res., 105, (C5), 11299 - 11320.

7. Goyette, S., N.A. McFarlane, and G.M. Flato. 2000: Application of the Canadian Regional Climate Model to the Laurentian Great Lakes region: Implementation of a lake model. in press, Atmosphere-Ocean.

8. Covey, C., A. Abe-Ouchi, G.J. Boer, B.A. Boville, U. Cubasch, L. Fairhead, G.M. Flato, plus 16 others. 2000: The seasonal cycle in coupled ocean-atmosphere general circulation models. Climate Dynamics, 16:775-787.

9. Flato, G.M., G.J. Boer, W.G. Lee, N.A. McFarlane, D. Ramsden, M.C. Reader, and A.J. Weaver. 2000: The Canadian Centre for Climate Modeling and Analysis Global Coupled Model and its Climate. Climate Dynamics, 16:451-467.

10. Boer, G.J., G.M. Flato, M.C. Reader, and D. Ramsden. 2000: A transient climate change simulation with greenhouse gas and aerosol forcing: experimental design and comparison with the intrumental record from the 20th century. Climate Dynamics, 16:405-425

11. Boer, G.J., G.M. Flato, and D. Ramsden. 2000: A transient climate change simulation with greenhouse gas and aerosol forcing: projected climate change in the 21st century. Climate Dynamics, 16:427-450.

12. Flato, G.M. and G.J. Boer, 2000: Warming asymmetry in climate change simulations. Geophys. Res. Lett., in press.


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