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Research Experience Placements: Tor Sorensen

What are you studying?
I’m now starting the final year of the BSc Geophysics at University College London.

Tell us a bit about the project you have been working on this summer?
Fog is a phenomenon frequently observed by researchers in polar regions, including at the Summit Station in the middle of the Greenland Ice Sheet, sometimes leading to fogbows (figure 1) and spectacular ice halos (figure 2). While fog is expected to be of significance for the regions, many questions remain unanswered: When does it occur? How is it formed? How does it interact with aerosols? And how does it affect the climate of the polar regions?

There are several reasons why little is still known about the potentially important fog, but one essential reason is our instrument’s inability to detect it; it’s too close to the surface for the ground based remote sensing instruments to detect and it’s too close to the surface and has too similar temperature for the satellite-borne remote sensing instruments to detect. Only in-situ measurements with instruments as spectrometers (Cox et al., 2019) and optical particle counters (Guy et al., 2021, under review) have so far been successful in systematically detecting fog, however the data is sparse, has significant uncertainties and potential bias. Exploiting any unused source of data about polar fog can therefore significantly increase our knowledge of its role in the cold climate.

During my summer research project, I have developed a machine learning algorithm to detect fogbows and ice halos on pictures from the Total Sky Imager (figure 3), an instrument operating for more than 10 years. With an efficient method of analysing the about 2 million pictures from the instrument, I’ve created the most comprehensive timeseries of the Greenlandic fog events at Summit so far. Frequency, duration and other fundamental knowledge about the fog events can then be quantified from this, providing a better general understanding of the fog that can hopefully be useful in the future studies of the polar clouds. You can see all the code and results on my GitHub-page:

Christopher J. Cox et al., Supercooled liquid fogs over the central Greenland Ice Sheet, 2019.
Heather Guy et al., Controls on surface aerosol number concentrations and aerosol-limited cloud regimes over the central Greenland Ice Sheet, 2021 (under review)

What new skills have you learned while doing this internship?
This summer internship has been a crash course in machine learning, in which I had no previous experience. My supervisors had great insights in the climate and atmospheric processes of the Greenland Ice Sheet but essentially no experience within machine learning, why the learning was very much on my own hands. Over the whole process I’ve also learned much about the difficulties of arctic research and the importance of getting the most use out of the sparse data available.

How have you found working with your research team?
’m very grateful for the unexpected amount of freedom I had over the internship. Essentially, I was allowed to and did shape the project as I wanted. The project my supervisors initially hired me for was very different from what I ended up doing, and when I after the first week realised that their project would only result in a limited outcome, we decided to take a chance and pursue the somewhat uncertain project I ended up doing. I felt like an integrated part of the research group and as an equal colleague, making the experience very enjoyable.

What has been the highlight of the internship for you?
The highlight of the internship was definitely the last day where I for the first time presented the results for my supervisors! It wasn’t before a few hours before the meeting that the data analysis was done, and I found out that the results actually looked good. I was very uncertain whether my method would work and there was a good chance that the results would have been completely useless or that I wouldn’t be done in time, so seeing the results a few hours before the end of my last working day was such a relief. Now I just hope that my finding will be used in future research!

How has doing this internship changed your plans or thoughts about your future career?
I was already considering a career in polar research and this experience has certainly confirmed my thoughts about the career path. The project has revived my dreams about doing arctic field work and opened my eyes for the amazing nature of the extreme and harsh polar environments, and I hope one day to work with my supervisors Ryan R. Neely and Heather Guy again – maybe on a field expedition on Greenland?

Follow Tor on Twitter @torbsorensen