Alexandra Jahn

Fellow

  • Assistant Professor, Department for Atmospheric and Oceanic Sciences, CU-Boulder
  • Fellow at INSTAAR

Departments

Education

  • PhD: McGill University, 2010
  • Dipl: Free University of Berlin, 2004
  • Exchange student: University of Washington in Seattle, 2001

Contact Information

(Office) 303 735-3352
http://instaar.colorado.edu/people/alexandra-jahn/

Specialty

Climate modeling, polar climate, paleoclimate, cryosphere, oceanography, modeling of isotopes.

Research Interests

Climate modeling; Arctic Ocean and sea ice variability; Arctic freshwater dynamics; paleoclimate modeling; climate model evaluation, isoptope modeling

Awards

  • Advanced Study Program Postdoctoral Fellowship, National Center for Atmospheric Research, 2012
  • Christine Mirzayan National Academies Policy Fellowship, National Academy of Sciences, 2010
  • PhD Fellowship, German National Academic Foundation, 2006
  • Outstanding student scholarship, German National Academic Foundation, 2001
  • Fulbright Travel Award, The Fulbright Program, 2001
  • Exchange Fellowship, Free University of Berlin and University of Washington, 2001

Research

Research Statement

Climate models are a powerful tool to understand dynamics in the climate system: they offer the unique advantage of providing a self-consistent dataset that can be used to study mechanisms, perform sensitivity studies, and test hypotheses. While model studies have provided critical insights on climate system functioning, it is important to remember that they are approximations of the real world. Connecting model results with observational data is therefore essential, and much of my research is motivated by the desire to improve model-data comparisons, for example through model developments that make model variables more comparable to observed data.

I am particularly interested in the climate of the polar regions, particularly the Arctic Ocean. Beside its breathtaking beauty, the Arctic Ocean is also the region where we see the largest climate changes occurring. Given that observational data in the Arctic is very limited, model studies are a great tool to better understand Arctic climate processes and their global impacts. In order to better predict future changes in the Arctic, for example when certain regions of the Arctic Ocean will become consistently accessible to commercial shipping during the summer, it is crucial to improve our understanding of the observed changes, as well as the shortcomings of the current generation of climate models. One of my main research foci is to understand the role of natural variability versus forced trends in the Arctic ocean and sea ice system during the 20th and 21st century. In this work, my main focus is on the Arctic sea ice and oceanic freshwater dynamics.

In addition to the present day changes, polar regions also played a key role in the past: Glaciations were initiated in the high northern latitudes, and Dansgaard-Oeschger and Heinrich events, which are among the most rapid climate change events on record, also originated in the high northern latitudes. We know about these past changes from paleo records (e.g., from ice cores and ocean sediment cores). Model simulations are uniquely suited to test hypotheses based on paleo records and to examine the physical mechanisms that led to these large climate shifts, as they provide consistent datasets and allow for sensitivity studies. My paleo-research is currently focussed on the climate at the Last Glacial Maximum (21 ka BP), during the deglaciation (21 ka BP to ~11 ka BP), and the climate of the Holocene (11 ka BP to the present), with the main focus on changes in the ocean circulation during these times.

Postdocs interesting in working with me on research questions focused on modeling Arctic sea ice and ocean dynamics, climate and especially ocean circulation changes during the past 21 ka, modeling isotopes and geotracers, and other related research areas are welcome to contact me.

Active Research

Research Labs and Groups

Publications

FeaturedPublications

Alexandra Jahn,Kay, J. E.,Holland, M. M.,Hall, D. M, 2016: How predictable is the timing of a summer ice-free Arctic?. Geophysical Research Letters, 43(17): 9113-9120. DOI: 10.1002/2016GL070067

Sanderson, B. M.,Xu, Y.,Tebaldi, C.,Wehner, M.,O'Neill, B.,Alexandra Jahn,Pendergrass, A. G.,Lehner, F.,Strand, W. G.,Lin, L.,Knutti, R.,Lamarque, J. F, 2017: Community Climate Simulations to assess avoided impacts in 1.5 °C and 2 °C futures . Earth System Dynamics, preprint. DOI: 10.5194/esd-2017-42

Zhu, J.,Liu, Z.,Brady, E.,Otto-Bliesner, B.,Zhang, J.,Noone, D.,Tomas, R.,Nusbaumer, J.,Wong, T.,Alexandra Jahn,Tabor, C, 2017: Reduced ENSO variability at the LGM revealed by an isotope-enabled Earth system model. Geophysical Research Letters, 44(13): 6984-6992. DOI: 10.1002/2017GL073406

Otto-Bliesner, B. L.,Alexandra Jahn,Feng, R.,Brady, E. C.,Hu, A.,Löfverström, M, 2017: Amplified North Atlantic warming in the late Pliocene by changes in Arctic gateways. Geophysical Research Letters, 44(2): 957-964. DOI: 10.1002/2016GL071805

Wang, Q.,Ilicak, M.,Gerdes, R., Drange, H., Aksenov, Y., Bailey, D. A., Bentsen, M., Biastoch, A., Bozec, A., Boening, C.,Cassou, C., Chassignet, E., Coward, A. C., Curry, B., Danabasoglu, G., Danilov, S, Fernandez, E., Fogli, P. G., Fujii, Y.,Griffies, S. M., Iovino, D.,Alexandra Jahn,Jung, T., Large, W. G., Lee, C., Lique, C., Lu, J., Masina, S., Nurser, A. J. G.,Rabe, B., Roth, C., Salas y Melia, D., Samuels, B. L., Spence, P., Tsujino, H., Valcke, S., Voldoire, A., Wang, X.,Yeager, S. G, 2016: An assessment of the Arctic Ocean in a suite of interannual CORE-II simulations. Part I: Sea ice and solid freshwater. Ocean Modelling, 99: 110-132. DOI: 10.1016/j.ocemod.2015.12.008

Wang, Q.,Ilicak, M.,Gerdes, R., Drange, H., Aksenov, Y., Bailey, D. A., Bentsen, M., Biastoch, A., Bozec, A., Boening, C.,Cassou, C., Chassignet, E., Coward, A. C., Curry, B., Danabasoglu, G., Danilov, S, Fernandez, E., Fogli, P. G., Fujii, Y.,Griffies, S. M., Iovino, D.,Alexandra Jahn,Jung, T., Large, W. G., Lee, C., Lique, C., Lu, J., Masina, S.,Nurser, A. J. G., Rabe, B., Roth, C., Salas y Melia, D., Samuels, B. L., Spence, P.,Tsujino, H., Valcke, S., Voldoire, A., Wang, X.,Yeager, S. G, 2016: An assessment of the Arctic Ocean in a suite of interannual CORE-II simulations. Part II: Liquid freshwater. Ocean Modelling, 99: 86-109. DOI: 10.1016/j.ocemod.2015.12.009

Ilicak, M.,Drange, H.,Wang, Q.,Gerdes, R.,Aksenov, Y.,Bailey, D.,Bentsen, M.,Biastoch, A.,Bozec, A.,Boening, C.,Cassou, C.,Chassignet, E.,Coward, A. C.,Curry, B.,Danabasoglu, G.,Danilov, S.,Fernandez, E.,Fogli, P. G.,Fujii, Y.,Griffies, S. M.,Iovino, D.,Alexandra Jahn,Jung, T.,Large, W. G.,Lee, C.,Lique, C.,Lu, J.,Masina, S.,Nurser, A. J. G.,Roth, C.,Salas y Melia, D.,Samuels, B. L.,Spence, P.,Tsujino, H.,Valcke, S.,Voldoire, A.,Wang, X.,Yeager, S. G, 2016: An assessment of the Arctic Ocean in a suite of interannual CORE-II simulations. Part III: Hydrography and fluxes. Ocean Modelling, 100: 141-161. DOI: 10.1016/j.ocemod.2016.02.004

Notz, D.,Alexandra Jahn,Holland, M. M.,Hunke, E.,Massonnet, F. ,Stroeve, S.,Tremblay, B.,Vancoppenolle, M, 2016: The CMIP6 Sea-Ice Model Intercomparison Project (SIMIP): Understanding sea ice through climate-model simulations. Geoscientific Model Development, 9: 3427-3446. DOI: 10.5194/gmd-9-3427-2016

Otto-Bliesner, B. L.,Brady, E. C.,Fasullo, J.,Alexandra Jahn,Landrum, L.,Stevenson, S.,Rosenbloom, N.,Mai, A.,Strand, G, 2016: Climate variability and change since 850 C.E.: An ensemble approach with the Community Earth System Model (CESM). Bulletin of the American Meteorological Society, 97(5): 735-754. DOI: 10.1175/BAMS-D-14-00233.1

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Academics

Outreach