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132 results on '"Bitz, C. M."'

12. Model Forecast Skill and Sensitivity to Initial Conditions in the Seasonal Sea Ice Outlook

Author

Blanchard-Wrigglesworth, E, Cullather, R. I, Wang, W, Zhang, J, and Bitz, C. M

Subjects
Meteorology And Climatology
Abstract

We explore the skill of predictions of September Arctic sea ice extent from dynamical models participating in the Sea Ice Outlook (SIO). Forecasts submitted in August, at roughly 2 month lead times, are skillful. However, skill is lower in forecasts submitted to SIO, which began in 2008, than in hindcasts (retrospective forecasts) of the last few decades. The multimodel mean SIO predictions offer slightly higher skill than the single-model SIO predictions, but neither beats a damped persistence forecast at longer than 2 month lead times. The models are largely unsuccessful at predicting each other, indicating a large difference in model physics and/or initial conditions. Motivated by this, we perform an initial condition sensitivity experiment with four SIO models, applying a fixed −1 m perturbation to the initial sea ice thickness. The significant range of the response among the models suggests that different model physics make a significant contribution to forecast uncertainty.

Published
2015
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20. Climate Modelling at the University of Victoria

Author

Wiebe, E. C., Bitz, C. M., Dravnieks, O., Eby, M., Fanning, A. F., Holland, M. M., Poussart, P. F., Stone, D. A., Yoshimori, M., Weaver, A. J., Pollard, Andrew, editor, Mewhort, Douglas J. K., editor, and Weaver, Donald F., editor

Published
2000
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25. Multi-model seasonal forecast of Arctic sea-ice: forecast uncertainty at pan-Arctic and regional scales

Author

Blanchard-Wrigglesworth, E., primary, Barthélemy, A., additional, Chevallier, M., additional, Cullather, R., additional, Fučkar, N., additional, Massonnet, F., additional, Posey, P., additional, Wang, W., additional, Zhang, J., additional, Ardilouze, C., additional, Bitz, C. M., additional, Vernieres, G., additional, Wallcraft, A., additional, and Wang, M., additional

Published
2016
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28. Antarctic Climate Response to Stratospheric Ozone Depletion in a Fine Resolution Ocean Climate Model

Author

Bitz, C. M. and Polvani, Lorenzo M.

Subjects
Meteorology, Atmosphere, Climatic changes
Abstract

We investigate the impact of stratospheric ozone depletion on Antarctic climate, paying particular attention to the question of whether eddy parameterizations in the ocean fundamentally alter the results. This is accomplished by contrasting two versions of the Community Climate System Model (version 3.5), one at 0.1° ocean and sea ice resolution and the other at 1° with parameterized ocean eddies. At both resolutions, pairs of integrations are performed: one with high (1960) and one with low (2000) ozone levels. We find that the effect of ozone depletion is to warm the surface and the ocean to a depth of 1000 m and to significantly reduce the sea ice extent. While the ocean warming is somewhat weaker when the eddies are resolved, the total loss of sea ice area is roughly the same in the fine and coarse resolution cases.

Published
2012
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29. The reversibility of sea ice loss in a state-of-the-art climate model

Author

Armour, K. C., Eisenman, I., Blanchard-Wrigglesworth, E., McCusker, K. E., and Bitz, C. M.

Abstract

Rapid Arctic sea ice retreat has fueled speculation about the possibility of threshold (or ‘tipping point’) behavior and irreversible loss of the sea ice cover. We test sea ice reversibility within a state-of-the-art atmosphere–ocean global climate model by increasing atmospheric carbon dioxide until the Arctic Ocean becomes ice-free throughout the year and subsequently decreasing it until the initial ice cover returns. Evidence for irreversibility in the form of hysteresis outside the envelope of natural variability is explored for the loss of summer and winter ice in both hemispheres. We find no evidence of irreversibility or multiple ice-cover states over the full range of simulated sea ice conditions between the modern climate and that with an annually ice-free Arctic Ocean. Summer sea ice area recovers as hemispheric temperature cools along a trajectory that is indistinguishable from the trajectory of summer sea ice loss, while the recovery of winter ice area appears to be slowed due to the long response times of the ocean near the modern winter ice edge. The results are discussed in the context of previous studies that assess the plausibility of sea ice tipping points by other methods. The findings serve as evidence against the existence of threshold behavior in the summer or winter ice cover in either hemisphere.

Published
2011

32. Summer landfast sea ice desalination at Point Barrow : Model and Observations

Author

Vancoppenolle, M., Bitz, C. M., Fichefet, T., Institut d'Astronomie et de Géophysique Georges Lemaître (UCL-ASTR), and Université Catholique de Louvain = Catholic University of Louvain (UCL)

Subjects
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, ComputingMilieux_MISCELLANEOUS
Abstract

International audience; no abstract

Published
2007

33. Climate Modelling at the University of Victoria

Author

Wiebe, E. C., primary, Bitz, C. M., additional, Dravnieks, O., additional, Eby, M., additional, Fanning, A. F., additional, Holland, M. M., additional, Poussart, P. F., additional, Stone, D. A., additional, Yoshimori, M., additional, and Weaver, A. J., additional

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45. CORRIGENDUM

Author

Bitz, C. M., primary, Gent, P. R., additional, Woodgate, R. A., additional, Holland, M. M., additional, and Lindsay, R., additional

Published
2007
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48. Offsetting effects of aerosols on Arctic and global climate in the late 20th century.

Author

Q. Yang, Bitz, C. M., and Doherty, S. J.

Abstract

We examine the impacts of atmospheric aerosols on Arctic and global climate using a series of 20th century transient simulations from Community Climate System Model version 4 (CCSM4). We focus on the response of surface air temperature to the direct radiative forcing driven by changes in sulfate and black carbon (BC) concentrations from 1975 to 2005 and we also examine the response to sulfate, BC, and organic carbon aerosols varying at once. The direct forcing from sulfate dominates the aerosol climate effect. Globally averaged, all three aerosols produce a cooling trend of 0.015 Kdecade-1 during the period 1975-2005. In the Arctic, surface air temperature has large spatial variations in response to changes in aerosol concentrations. Over the European Arctic, aerosols induce about 0.6 K decade-1 warming which is about 1.8 K warming over the 30 yr period. This warming is triggered mainly by the reduction in sulfate and BC emissions over Europe since the 1970s and is reinforced by sea ice loss and a strengthening in atmospheric northward heat transport. Over the Siberian and North American Arctic, surface air temperature is likely influenced primarily by changes in aerosol emissions from Asia. An increase in sulfate emissions over Asia induces a large cooling while an increase in BC over Asia causes a significant warming. [ABSTRACT FROM AUTHOR]

Published
2013
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