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Summer school in Norway zooms in on the climate dynamics of the seasonal cycle

By Katherine Hutchinson, PhD Student*, SAEON Egagasini Node
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Twenty-five advanced PhD candidates and early career post-docs from 10 different countries and 19 universities met at Rondane National Park in Norway for a two-week adventure in science and learning.

I was lucky to be one of the chosen few - only one in five applicants were selected. I learnt a huge amount, formed valuable contacts, and made great friends.

Core lectures

The first week of the school kicked off with “core lectures” on the fundamentals of seasonal variability of the ocean, land and atmosphere. We started by focusing on the seasonal cycle of temperature and how this varies from ocean to land and Northern to Southern Hemisphere. I learnt about the global asymmetry in response, as in the Southern Hemisphere we are essentially “ocean dominated”, versus the Northern Hemisphere where there are more land masses. These lectures specifically focused on the role of ocean and atmospheric transport in redistributing this heat differential on seasonal timescales.

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The Climate Dynamics of the Seasonal Cycle Summer School was held in Rondane National Park, Norway. The photo shows the Rondvassbu cabin where the students stayed and where the classes took place. (Photo courtesy of Iselin Medhaug)

We covered fascinating topics such as the El Niňo Southern Oscillation and how there is a coupling of this variability with the seasonal cycle in cross equatorial winds. Another fascinating lecture was from an oceanographer at Woods Hole, which addressed the seasonal processes of the subtropical, subpolar, and polar oceans.

I heard the word “bicoherence” for the first time and realised that so many processes are linked to the seasonal cycle. It is, after all, the most basic form of variability in temperature of the Earth’s system. So many studies start off by removing the seasonality; we started off by looking only at this annual variability.

Every lecture was summarised by students and the summaries presented the next morning before the new day of lessons began. I found this to be incredibly useful as my peers often found the same concepts confusing as I did and explained them in the summary sessions in a way that was clearer to me than in the lectures.

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The summer school was attended by 25 advanced PhD candidates and early career post-docs from 10 different countries and 19 universities. (Photo courtesy of Iselin Medhaug)

Energy balance model

One of the lectures I summarised was on the energy balance model. This model describes the energy at the Earth’s surface as the sum of the incoming short wave solar radiation, incoming long wave radiation re-emitted from the atmosphere, minus the long wave radiation from Earth’s surface.

We started off with a zero-dimensional model and then built it up by including variations in incoming solar radiation with latitude and time. For the final step of the model, we included the seasonal cycle.

We set up the energy balance equations for the surface and the atmosphere, which contained different heat capacities of the atmosphere, ocean and land. Comparing typical values, we saw that the heat capacity of the ocean is an order of magnitude larger than that of the atmosphere, and two orders of magnitude larger than that of the land. These differences in ability to store heat result in some interesting patterns of the seasonal variability in temperature at different latitudes.

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SAEON student Katherine Hutchinson (centre) presents a summary to the group on the second day. (Photo courtesy of Iselin Medhaug)

The second week of lectures looked at topics of interest. I especially enjoyed looking at what we can learn from long-term responses of the annual cycle, and Milankovitch forcing as perturbations of the annual cycle. We investigated the use of many different seasonal proxies, from ocean sediments to ice cores, to tree rings - we even did our own tree ring core!

Group projects

During the second week of the school, we divided up into groups and came up with group projects. My group decided to investigate the response of CMIP 5 models (Coupled Model Intercomparison Experiment version 5) to a drying out effect of some places on Earth with climate change.

The hypothesis is that as the Earth warms, most areas will become drier due to an increase in evaporation and a consequential decrease in soil moisture. Wet areas have a smaller variance in their summertime surface temperature than dry areas, as some of the incoming radiation is used for evaporation and not heating.

The idea is that as many areas shift towards a drier regime, their summertime surface temperature variance will increase. However, many CMIP 5 models are currently biased high in their temperature variance and so may not be able to capture this change. We investigated this and found that in fact all models, biased high and low in temperature variance compared to observations, will increase in their temperature variance in the future - indicating skill in capturing the drying out of the planet with climate change.

I learnt much about terrestrial processes and the role of advection of signals from the ocean onto land and the associated feedbacks.

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The students enjoy the fresh mountain air during a hike. (Photo courtesy of Iselin Medhaug)

Student lectures

Every evening we had student lectures and I presented my PhD results to the 24 other students and eight lecturers. My lecture got a very positive response and much discussion was generated about the seasonal variability of western boundary currents - why are most of them strongest in their respective hemisphere’s summers?

We certainly did have a great debate and I loved hearing everyone’s different theories and opinions. Throughout the duration of the school, students were encouraged to debate and argue with the lecturers and so there was never a lack of vibrant discussion and inspiring ideas.

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Katherine (in red jacket) says she learnt a huge amount during the summer school, formed valuable contacts and made great friends. (Photo courtesy of Iselin Medhaug)

The ACDC summer school reignited my passion for science and opened my eyes and mind to ocean-atmospheric coupling and feedbacks. I feel motivated to throw myself into the last few months of my PhD and have been reminded of just how cool science is!

* Katherine is a Professional Development Programme (PDP) student with Dr Juliet Hermes at SAEON’s Egagasini Node, working as part of the ASCA team. The Professional Development Programme of the Department of Science and Technology and the National Research Foundation aims to accelerate the development of scientists and research professionals in key research areas.

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