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Interests

 

My research is focused on climate dynamics, including climate variability and climate change, sea ice, the hydrological cycle, and ocean circulation. The ultimate goal of my research is to develop a better understanding of the processes that shape Earth's climate, with a particular focus on how the surface, spanning the ocean, cryosphere and land system, shapes and is shaped by the atmosphere. I use a range of tools and techniques including comprehensive climate models like model intercomparison projects or large ensembles, targeted experiments in climate models of various complexity, conceptual models that provide simplified representations of underlying physical processes, and advanced statistical methods. The field of climate dynamics is inherently interdisciplinary, as the atmosphere, ocean, cryosphere, and land surface are intimately coupled, and affect Earth’s climate on timescales ranging from seasons to millennia. I enjoy working and collaborating on research questions that are at the intersection of these components.

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Climate variability and climate change

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The spatial pattern of climate change is set by interactions between poleward energy transport, radiative forcing, radiative feedbacks, and ocean heat uptake. I am interested in the relative importance of each and how energy balance models or simple energetic frameworks can be used to infer processes that influence polar-amplified warming, shifts in tropical rainfall, or land-sea contrasts. This research uses simple methods and idealized models to identify how various components contribute to the patterns of climate change. I am also interested in estimating the forced and internal patterns of climate change using advanced statistical methods. Recent and ongoing work examines: the influence of continental land configurations on the climate response; mechanisms for long-term surface temperature trends; and mechanisms for abrupt sea ice changes and warming in the polar regions. I am also currently developing an idealized model of the ocean-atmosphere system to explore: how coupling impacts the ocean's global overturning circulation; mechanisms of ocean heat uptake; and controls on the transient climate response.

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Relevant publications

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  • Bonan, D.B., K.C. Armour, G.H. Roe, N. Siler, and N. Feldl (2018): Sources of uncertainty in the meridional pattern of climate change.​ Geophysical Research Letters, 45 (17), 9131-9140. doi: 10.1029/2018GL079429

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  • Wilson, E.A., D.B. Bonan, A.F. Thompson, N. Armstrong, and S.C. Riser (2023): Mechanisms for abrupt summertime circumpolar surface warming in the Southern Ocean. Journal of Climate, 36 (20), 7025-7039. doi: 10.1175/JCLI-D-22-0501.1

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  • Dong, Y., L.M. Polvani, and D.B. Bonan (submitted): Recent multi-decadal Southern Ocean surface cooling unlikely caused by Southern Annular Mode trends. Geophysical Research Letters. 

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  • Bonan, D.B., A.F. Thompson, T. Schneider, and L. Zanna (in preparation): A conceptual model of the coupled ocean-atmosphere system. Journal of Advances in Modeling Earth Systems.

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  • Bonan, D.B., M.M. Laguë, and W.R. Boos (in preparation): Effects of continental land distribution on the climate response to greenhouse-gas forcing. Journal of Climate.

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Sea ice​

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Sea ice is a fundamental component of the climate system and it is rapidly changing. Both Arctic and Antarctic sea ice have undergone striking changes over the past few decades and are projected to continue to change throughout the next century. One of the goals of my research is to identify processes that control the short- and long- term evolution of sea ice and explain how the sea ice cover in both hemispheres interacts with the atmosphere and ocean. My work uses state-of-the-art climate models, observations, idealized models, and advanced statistical methods. I am also broadly interested in the predictability of sea ice and improving the representation of sea ice in climate models. Recent and ongoing work examines: constraints on Arctic sea ice loss, sources of low-frequency sea ice variability, and drivers of very rapid ice loss events.

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Relevant publications

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  • Bonan, D.B., M. Bushuk, and M. Winton (2019): A spring barrier for regional predictions of summer Arctic sea ice. Geophysical Research Letters, 46 (11), 5937-5947. doi: 10.1029/2019GL082947
     

  • Bushuk, M., M. Winton, D.B. Bonan, E. Blanchard-Wrigglesworth, and T. Delworth (2020): A mechanism for the Arctic sea ice spring predictability barrier. Geophysical Research Letters, 47 (13), e2020GL088335. doi: 10.1029/2020GL088335

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  • Bonan, D.B., F. Lehner, and M.M. Holland (2021): Partitioning uncertainty in projections of Arctic sea ice. Environmental Research Letters, 16 (4), 044002. doi: 10.1088/1748-9326/ABE0EC

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  • Bonan, D.B., T. Schneider, I. Eisenman, and R.C.J. Wills (2021): Constraining the date of a seasonally ice-free Arctic using a simple model. Geophysical Research Letters, 48 (18), e2021GL094309. doi: 10.1029/2020GL094309

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  • Dörr, J., D.B. Bonan, M. Årthun, L. Svendsen, and R.C.J Wills (2023): Forced and internal components of observed Arctic sea-ice changes. The Cryosphere, 17 (9), 4133-4153. doi: 10.5194/TC-17-4133-2023

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  • ​Bonan, D.B., J. Dörr, R.C.J. Wills, A.F. Thompson, and M. Årthun (submitted): Sources of low-frequency variability in observed Antarctic sea ice. The Cryosphere.

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Hydrological cycle​

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The hydrological cycle is a crucial component of the climate system, affecting the formation of water masses in the ocean and the amount of runoff or availability of water over the land, which can impact soil moisture availability, drought, flooding, and wildfires. Large-scale features of the hydrological cycle like the Intertropical Convergence Zone and extratropical storm tracks are strongly influenced by atmospheric circulations like the Hadley cells and transient eddies. I am interested in the processes that shape the large-scale patterns of precipitation and evaporation, including how energetic frameworks can be used to constrain features of the atmospheric circulation. Recent and ongoing work examines: the response of the hydrological cycle to global warming in an energy balance model; the contributions to regional precipitation change under warming; the influence of climate feedbacks on regional hydrological change; and the dynamic and thermodynamic components of regional hydrological changes.

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Relevant publications

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  • Bonan, D.B., N. Siler, G.H. Roe, and K.C. Armour (2023): Energetic constraints on the pattern of changes to the hydrological cycle under global warming. Journal of Climate, 36 (10), 3499-3522. doi: 10.1175/JCLI-D-22-0337.1
     

  • Bonan, D.B., N. Feldl, M.D. Zelinka, and L.C. Hahn (2023): Contributions to regional precipitation change and its polar-amplified pattern under warming. Environmental Research: Climate, 2 (3), 035010. doi: 10.1088/2752-5295/ACE27A

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  • Siler, N., D.B. Bonan, and A. Donohoe (2023): Diagnosing mechanisms of hydrologic change under global warming in the CESM1 Large Ensemble. Journal of Climate, 36 (xx), xxxx-xxxx, doi: 10.1175/JCLI-D-23-0086.1

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  • Bonan, D.B., N. Feldl, N. Siler, J.E. Kay, K.C. Armour, I. Eisenman, and G.H. Roe (submitted): The influence of climate feedbacks on regional hydrological changes under global warming. ​​Geophysical Research Letters.

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  • Bonan, D.B., and T. Schneider (in preparation): Controls on the transient and equilibrium global hydrological sensitivity under greenhouse-gas forcing. Journal of Climate.

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  • Bonan, D.B., T. Schneider, and J. Zhu (in preparation): Global precipitation over a wide range of climates simulated with comprehensive GCMs. Geophysical Research Letters.

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Ocean circulation

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The ocean's global overturning circulation regulates Earth's climate by transporting heat between hemispheres, influencing the rate of ocean heat uptake,  ventilating the interior of the ocean, and sequestering carbon. Sparse observations necessitates the use of idealized, conceptual models that help to reveal primary controls on the ocean's overturning circulation. Such models, in conjunction with state-of-the-art climate models, have been fundamental in our understanding of the ocean’s deep stratification and meridional overturning circulation. Recent and ongoing work examines: how the ocean's global overturning circulation responds to warming on centennial-to-millennial timescales; the influence of ocean-atmosphere coupling on the ocean's global overturning circulation; and the role of low-latitude surface forcing in transitions of the oceans's global overturning circulation in past climates.

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Relevant publications

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  • Bonan, D.B., A.F. Thompson, E.R. Newsom, S. Sun, and M. Rugenstein (2022): Transient and equilibrium responses of the Atlantic overturning circulation to warming in coupled climate models: the role of temperature and salinity. Journal of Climate, 35 (15), 5173-5193. doi: 10.1175/JCLI-D-21-0912.1

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  • Nayak, M., D.B. Bonan, E.R. Newsom, and A.F. Thompson (in preparation): Surface constraints on the strength of the Atlantic overturning circulation in coupled climate models. Geophysical Research Letters. ​​​​​

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  • Bonan, D.B., A.F. Thompson, T. Schneider, L. Zanna, K.C. Armour, and S. Sun (in preparation): Constraints on weakening of the Atlantic meridional overturning circulation over the 21st century.

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  • Bonan, D.B., A.F. Thompson, T. Schneider, and L. Zanna (in preparation): Transient and equilibrium responses of the ocean's overturning circulation to climate change: insights from a conceptual model. ​Journal of Physical Oceanography.

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