Doctoral dissertation: The circulation of the Norwegian Sea - An investigation from space and ocean

Nansen Center scientist Roshin Pappukutty Raj has defended his doctoral degree at Geophysical Institute, University of Bergen on studies of the circulation of the Norwegian Sea using observations from space and in the ocean.

The doctoral study addresses the circulation of the Norwegian Sea, which is known for its influence on the local climate in the northwestern Europe. The in the dissertation “The circulation of the Norwegian Sea - An investigation from space and ocean” the ocean circulation is studied using a suite of different satellite, hydrographic, numerical ocean model, surface drifter and re-analysis datasets. The findings of the thesis are presented in the form of four submitted scientific papers. The first paper “The two-branch structure of the Norwegian Atlantic Current-transport variability and coMean Dynamic Topography (MDT) derived from the GOCE gradiometer data (release 3) and altimetry (from 1993-2009) with a spatial resolution of about 80 km. The colour bar is in units of meter. The structures of the North Pacific are not investigated in this paper. Note that the GOCE data (release 4) available since March 2013 is more accurate due to more than doubling in the amount of data (Johannessen, Raj et al, in press – Survey in Geophysics).Mean Dynamic Topography (MDT) derived from the GOCE gradiometer data (release 3) and altimetry (from 1993-2009) with a spatial resolution of about 80 km. The colour bar is in units of meter. The structures of the North Pacific are not investigated in this paper. Note that the GOCE data (release 4) available since March 2013 is more accurate due to more than doubling in the amount of data (Johannessen, Raj et al, in press – Survey in Geophysics).nnecting flows” focuses on the circulation of the Norwegian Sea, its seasonal and inter-annual variability, connecting flows between the two branches of the Norwegian Atlantic Current, the relationship between the surface flows and the Atlantic Water beneath, and the volume transports at six key locations. The second paper “Processes influencing the dense water formation in the Lofoten Basin” zooms into the Lofoten Basin, and addresses the processes influencing the spatial and temporal evolution of dense water formation in the basin and its link to the overflow waters exiting at the Faroe Shetland Channel. The third paper “The Lofoten vortex of the Nordic Seas” zooms further into the western Lofoten Basin and presents a comprehensive study focusing on a most anomalous anticyclonic vortex of the Nordic Seas. In a step towards more precise satellite measurements, the fourth paper “Towards improved estimation of the dynamic topography and ocean circulation in the high latitude and Arctic Ocean” shows estimates of a new mean dynamic topography (MDT) for the North Atlantic and the Arctic from Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite gravity anomaly data. Employing the newly estimated data, the circulation of the Norwegian Sea region is revisited (the illustration figure is from this paper).

The successful dissertation took place on 10. January 2014 and the opponents were Professor Johan Nilsson, Stockholms University and scientist Hjálmar Hátún, Faroe Marine Research Institute. Professor Tor Gammelsrød, Geophysical Institute, University of Bergen was also a member of the evaluation committee.

Dr. Roshin Raj took his Master degree in 2006 at Cochin University of Science and Technology (CUSAT) in Kerala, India, where he was introduced to and started working at the Nansen Environmental Research Centre – INDIA (NERCI). In August 2008 he started as a Ph.D. fellow at Geophysical Institute and in October 2011 he started working as a junior scientist at the Nansen Center. Dr. Roshin Raj is the 45th PhD candidate defending the Doctoral Degree with affiliation to the Nansen Center. He will continue his work as a scientist at the Nansen Center.