Our group uses climate models to understand polar ocean and sea ice dynamics and paleo ocean changes. In our work, we aim to improve model-data comparisons by adding additional tracers and functions to climate models that allow a more direct comparison with observations, as well as quantify the projection uncertaity introduced by internal variability.
Current opening for a Postdoctoral Researcher: https://jobs.colorado.edu/jobs/JobDetail/?jobId=14226
Assessing the Simulated Arctic Freshwater System in CMIP5 Models, the CESM Large Ensemble, and Forced Simulations
In this NSF-funded project, we are working on assessing the Arctic freshwater budget simulated by climate models, the influence of internal variability on the simulated Arctic freshwater budget, and the Arctic freshwater dynamics. We are collaborating with Marika Holland (NCAR) and Bruno Tremblay (Columbia University & McGill University), as well as with Peter Schlosser and Robert Newton from the Arctic Switchyward project at Lamont Doherty.
C-iTRACE: Isotope-enabled paleo ocean modeling for the deglacial
In this NSF-funded project, we are using recenty developed carbon, water, neodynium, and Pa/Th isotopes within the CESM ocean model to assess the simulated deglacial climate evolution against proxy records and isotope observations. Collaborators include Zhengyu Liu (The Ohio State University) and Bette Otto-Blienser (NCAR).
Understanding Arctic melt season changes through modeling
In this project, we are working on better understanding the melt season changes in the Arctic Ocean. The first part of this project was focused on assessing the impact of definition choices and internal variability on melt season charcteristics. This work is under review at Cryosphere Discussions (Ahlert and Jahn, 2018). The next step is to develop a passive microwave sea ice emulator for melt onset for the use in earth system models, to better compare sea ice simulatons of melt onset from earth system models with satellite retrievals, to ultimatly improve the sea ice simulations. On the sea ice simulator, we are collaborating with Dirk Notz and Clara Burgard from the Max Plank Institute of Meoerology in Hamburg. We are also working on comparing melt season characteristics in CMIP models, in collaboration with M. Wang (UW).
Predictability studies of Arctic sea ice: Sea ice in the CESM Large Ensemble
Using the 40 member large ensemble from the CESM, we are assessing how predictabile aspects of the decline of the Arctic sea ice cover is, given the large internal variability in the climate system. Examples of this work are published in Jahn et al. (2016) and Jahn (2018), focussing on the predictability and probability of an summer ice-free Arctic Ocean.
Climate of the past 2000 years: past2k CESM simulation
In this project, we have performed a transient CESM model simulation for the last 2000 years, called past2k. In the anlysis, we have focussed on the assessment of the drivers of the asymetric cooling rates of the Atlantic and Pacific Arctic. We are collaborating with Y. Zhong (University of Wisconsin Madison), G. Miller (INSTAAR) and A. Geirsdottir (Univ. of Iceland) on this projects. Results are under review at GRL (Zhong et al. 2018). Please contact A. Jahn for access to the model results. Forcing data for this simulation is published as Zhong et al. (2018), at https://doi.org/10.5281/zenodo.1304427
Paleoceanographic Impacts of the Onset of Arctic-Baffin Bay Throughflow
In this NSF-funded project, we will use modeling and multi-proxy analyses of sediment cores from northern Baffin Bay to discover the timing and climatic consequences of the opening of the western gateway for Arctic freshwater to the Labrador Sea. For this project, we will perform mid-Holocene model simulations with the CESM to assess the impacts of the opening of the western freshwater route of the Arctic-Atlantic throughflow on the freshwater outflow to the North Atlantic, the watermass structure in Baffin Bay, and the formation of the North Water Polynia. Collaborators include A. Jennings, T. Marchitto, L. Woelder and J. T. Andrews (all INSTAAR).