Thesis defence: never-seen-before phenomenon discovered in near-Earth space using the Vlasiator model

The researcher Yann Pfau-Kempf from the Finnish Meteorological Institute has participated in the development of the world's most accurate near-Earth space model Vlasiator. Pfau-Kempf has investigated in his thesis the physical results obtained with Vlasiator. The last article in the thesis introduces a phenomenon never observed before, where the processes in the Earth's magnetosphere influence the upstream solar wind properties. The phenomenon was first identified in Vlasiator simulations and then confirmed with ground-based and spacecraft observations.

"The unprecedented quality of the Vlasiator plasma model was vital in obtaining these new pioneering results. Vlasiator shows that in space physics everything affects everything and local-scale phenomena cannot be studied separately from their global context. The new results pave the way towards explanations to long-standing open problems and exciting scientific discoveries", says Yann Pfau-Kempf. "The research shows that Vlasiator matches excellently both established theories and observational data from spacecraft, which gives strong confidence in the Vlasiator results", Yann Pfau-Kempf adds.

The Vlasiator results are also verified and validated by comparing to previously published data.A key aspect of Yann Pfau-Kempf's thesis work resides in adapting and optimising the algorithms to make them run efficiently on top-tier supercomputers, which are required to simulate large systems. Simulations were run on some of Europe's largest supercomputers, harnessing the computing power of tens of thousands of processors in parallel. "This thesis sums up my model development work, but it will also hopefully be a reference for future generations of Vlasiator developers and users. The code has now reached maturity and promises an avalanche of great space science in the months and years to come", says Yann Pfau-Kempf.

Vlasiator is a completely new model type

Vlasiator was developed from scratch by Research professor Minna Palmroth's group at the Finnish Meteorological Institute, which received funding from the European Research Council and the Academy of Finland since 2008. Vlasiator is currently the most accurate model of near-Earth space at large scales. The model preserves nevertheless detailed plasma physical properties. The model describes the plasma pervading space, which is a very tenuous medium made of electrons and ions and is threaded by magnetic fields.

Historically, modelling the magnetosphere, that is the space volume around Earth where our planet's magnetic field controls plasma dynamics, was done with two types of models. The simplest do not include a lot of physical detail whereas the more complex models offer a better description of plasma physics, but are marred by noise. Unlike these two model types, Vlasiator applies a very clean and detailed model, which was however until recently deemed too computationally heavy to be used to described the magnetosphere at large scales.

The young French-German researcher Yann Pfau-Kempf got a triple bachelor's degree from the Universities of Luxembourg (Luxembourg), Saarland (Germany) and Nancy (France) in 2010 before he came to Finland. He is one of the youngest researchers from the Finnish Meteorological Institute to defend his thesis in space physics ever. Yann Pfau-Kempf's thesis "Vlasiator – From local to global magnetospheric hybrid-Vlasov simulations" will be publicly examined on December 1st, 2016 at 12 at the University of Helsinki in Auditorium E204 in Physicum on Kumpula campus, street address Gustaf Hällströmin katu 2. The Opponent is Dr Benoit Lavraud from the Institut de Recherche en Astrophysique et Planétologie, Toulouse, France. The Custos is Professor Hannu Koskinen from the University of Helsinki Department of physics.

Further information:

Researcher Yann Pfau-Kempf, phone +358 50 4147 241, yann.kempf@fmi.fihttp://vlasiator.fmi.fi

The doctoral thesis is published in the Finnish Meteorological Institute Contributions series and is available at http://urn.fi/URN:ISBN:978-952-336-001-3.