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Two special seminars

Tidspunkt

02. oktober 2025, 22:00-22:00

Sted

BCCR lecture rom 4020, Jahnebakken 5

Dear all,

 

We are fortunate to have Gokhan Danabasoglu (NCAR) and Jon Robson (NCAS/U. Reading) visiting next week, and they will be giving back-to-back seminars on Friday 2nd October, BCCR seminar room 4020.

 

10:00 - 10:50, High-Resolution Simulations with the Community Earth System Model (CESM), Gokhan Danabasoglu

 

As impacts of climate change are being felt by the society through sea level rise, increased intensity and occurrences of heat waves, droughts, extreme rainfall events, and tropical cyclones (TCs), decision makers and stakeholders need reliable weather and climate information at increasingly finer spatial and temporal scales. There are also numerous science questions regarding representation of and changes in importance of various processes with increased model resolution. It is generally anticipated that with less reliance on uncertain parameterizations and their parameter choices, high-resolution (HR) models will represent various processes and coupled interactions of the Earth system with increased fidelity. To address these needs and challenges, we have made significant advances in HR global Earth system modeling and predictions. Specifically, we have performed an unprecedented set of simulations at a TC-permitting (0.25°) and ocean-eddy-rich (0.1°) horizontal resolution using the Community Earth System Model (CESM-HR). The presentation will introduce these simulations and provide a few highlights from our extensive analysis. While not a panacea to address all model biases, the HR simulations certainly offer promising improvements with reduced biases in comparison with their low-resolution counterparts and advance our understanding of processes. 

 

11:00 - 11:50 Understanding model uncertainty in North Atlantic multi-decadal variability and change,  Jon Robson

 

Changes in the North Atlantic Ocean play an important role in shaping regional weather and climate. Yet climate models differ widely in how they represent both the response to external forcing and internal variability on multi-decadal timescales. These differences contribute to substantial uncertainty in how we might expect the North Atlantic to evolve in the coming decades. In this talk, I will highlight key uncertainties in our understanding of variability and change in the region. Focusing on two central issues—the Atlantic Meridional Overturning Circulation (AMOC) and multi-decadal variability in the tropical North Atlantic—I will discuss some ongoing efforts to untangle the underlying processes and make progress toward reducing uncertainty.

 

 

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1st BCCR AMOC forum

Dear All, We are pleased to announce the 1st BCCR AMOC forum, that will take place on December 10th 2026 in the Bjerknes meeting room 4020. We plan to provide some light snack or meal for lunch/coffee break during this event, within limits of budget and number of participants. Hence, we kindly ask participants to register by Friday December 4th using the link below, so we can plan for this. Link to registration form and tentative program: https://docs.google.com/forms/d/e/1FAIpQLSdlIqpgCVQNbE1D66BiwY2TLB-HTbn2WvBf8g1zEkhXZhMM1Q/viewform?usp=dialog
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BCCR Seminar: Mind the Slope: Why Greenland’s Katabatic Storms Challenge Global Models.

Abstract Katabatic storms in southeastern Greenland are fierce, density-driven downslope wind events that influence both local weather and downstream climate. We assess their representation across three generations of ECMWF global reanalyses (ERA5, ERA-Interim, and ERA40) and a hierarchy of Community Earth System Model version 2 (CESM2) simulations at different horizontal resolutions, using in situ observations and the 2.5-km Copernicus Arctic Regional Reanalysis (CARRA) as benchmarks. The global reanalyses systematically underestimate wind speeds by approximately 30% in ERA5 and 50% in ERA-Interim and ERA40, while failing to capture key storm structures. Similar biases occur in CESM2 simulations at standard 1–2° resolutions. In contrast, variable-resolution CESM2 configurations with local grid refinement to 0.25° and 0.125° better resolve Greenland's topography and substantially improve the representation of storm intensity and structure. Sensitivity experiments further demonstrate that resolving the steep ice-sheet margins is critical for capturing katabatic acceleration. The reanalysis data also reveal that these storms generate fast-moving, high-amplitude ocean wave packets that propagate as far downstream as Scandinavia and the British Isles. Accurately representing these storms in global models and reanalyses is therefore essential for simulating North Atlantic climate variability beyond Greenland's immediate coastal region. Speaker information Marcus Lofverstrom is an associate professor in the Department of Geosciences at the University of Arizona. His research group conducts novel research in the fields of atmospheric dynamics, (paleo-)climatology, and glaciology to understand the evolution of the climate system over multi-millennial time scales. Numerical modeling is an important component of his research program, and the group is utilizing models over a broad range of complexities: from conceptual and linear steady-state models to fully coupled state-of-the-art Earth-system models.