måndag 16 april 2012

Arctic mini Workshop

Last week we had a full day at our department focusing on Arctic atmospheric research. 3 guest speakers were invited as well as people from the Swedish Meteorological and Hydrological Institute (SMHI). We all have an interest in knowing more about the climate system in the Arctic and especially about the recent warming.

The first talk was by Jennifer Kay from the National Center for Atmospheric Research (NCAR), USA. She gave a really nice presentation. I really liked her summary on what is causing the warming the Arctic and what might be causing the Arctic Amplification, because there is a difference!

Already in the 1980's, the early models showed an increased surface warming in the Arctic, when the global climate changed. For example, the paper by Manabe & Stouffer (1980) where they first popularized the phrase “polar amplification”.

Kay also talked about her paper with Gettelman (2009), where they tried to investigate the cloud response to a change in the sea ice cover in the Arctic. Since I am a cloud person, this of course made me interested :) Using satellite data, they found out that the change was not so significant in the summer, but more in the autumn. However, the satellite data is somewhat restricted and have problems detecting the low clouds. From the observations I'm studying, we can see that there is a lot of low clouds during the Arctic summer, at least during 40 days in 2008.

Kay did a summary of the different processes and feedbacks that are both causing and not causing the Arctic Amplification:

Processes contributing to Arctic Amplification:
  • surface albedo feedback
  • Planck feedback
  • lapse rate feedback
  • ocean heat transport

Processes NOT contributing to Arctic Amplification:
  • greenhouse gas forcing
  • water vapor feedback
Note! These processes are still causing surface warming in the Arctic, but not the Amplification. Then there are some features and processes that are still debated:
  • Clouds
  • Atmospheric heat transport
and the question is, which one is the most important one?

This subject is very complicated and as Kay continued her presentation, showing results from different climate models, trying to rule out different parameters I realized that is difficult to distinguish between these processes, because everything is connected. For example, looking at clouds the shortwave radiation (SW) feedback might not be guilty to the amplification, while the longwave feedback is more important. Also, how do you see the difference between what is causing the warming and what is causing the amplification?

The following 2 presentations were more concentrated on specific topics, Gudrun Magnusdottir from University of California at Irvine talked about the atmospheric circulation patterns and the interaction with the sea ice. They had a very interesting approach, using a mathematical method from the economics to test different hypotheses.

The last presentation was Torben Koenigk from SMHI, talking about the Arctic climate and climate change in a relatively new climate model, EC-Earth. He showed some results looking at the turbulent fluxes over the Arctic Ocean and also how the sea ice will change in the future. According to this model, we will still have sea ice in winter time, but the atmosphere will be different, with less stable stratification since the warming will be strongest at the surface (lapse rate feedback). He also showed some results on how the clouds will change with less sea ice, but again the results are dependent on satellite data. The model seems to good a fairly good job, but the are still improvements to be done.

A lot of the uncertainties in clouds in climate models goes back to the humidity transportation. Where it is, what temperature it is and how it interacts with the radiation. In the afternoon discussion, we had some ideas about improving the models and there is always the issue about the resolution. Most people talk about the horizontal resolution, but it might also be interesting to increase the vertical resolution. This, of course, depend on what you wanna study. However, is not trivial since there might be problems with the time resolution and how to keep the model stable.

All the participants in the workshop had a 3-minute presentation in the afternoon about their research and it was interesting to see what everyone was doing. My presentation was over very fast :) The following discussion was also good and it might lead to some new projects in the future. Expect for discussing model improvements, we also talked more about specific physical processes and methods how to analyze the different feedbacks, especially in the Arctic Region. Overall, it was a really nice workshop and I hope we will be able to do something similar again, here at the department.