Liisi Jakobson is the first to characterise low-level jets in the central Arctic Ocean in her PhD thesis

Kairi Janson | 21.06.2018

On June 19 2018, Junior Research Fellow at the observatory’s Group of Remote Sensing of Atmosphere Liisi Jakobson defended her PhD thesis on the mutual effects of wind speed, air temperature and sea ice concentration in the Arctic and their teleconnections with climate variability in the eastern Baltic Sea region. Among other things, low-level jets and their generation mechanisms in the central Arctic Ocean were characterised for the very first time.

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The summary of Jakobson’s thesis can be read below.

First ever central Arctic data

The Arctic region is the key area of climate change. Over the past half century, the Arctic region has warmed at about twice the global rate. Atmospheric reanalyses are widely applied in the Arctic research. Due to the Tara expedition, the team had a rare opportunity to use unique data collected during the expedition. It was not included into data assimilations and had a good vertical resolution.

The first ranked was the ERA-Interim model. Near-surface parameters were best captured by NCEP-CFSR. NCEP-CFSR was used to investigate the Arctic key element, sea ice, and near-surface wind speed interaction. Based on data, a clearly negative correlation between sea ice concentration and wind speed at 10 m in all time scales from synoptic to inter-annual exists. During winter, spring and autumn the decreasing sea ice generates less stable stratification, which leads to stronger near-surface winds.

One of the biggest problems in the investigations in the Arctic region is the spatial irregularity of data. There are quite few observational data from central Arctic and these are commonly assimilated to reanalyses.  In the thesis, observational data were used to characterise, for the first time, low-level jets and their generation mechanisms in the central Arctic. The results are important to better the models of this region.

Teleconnections with the eastern Baltic Sea region

Unprecedented warming in the Arctic and its possible feedbacks open up different climatological and ecological circumstances and may influence other regions of the World. Potential Arctic teleconnections with Europe are less clear than with North America and Asia. There have been no previous studies on how the Arctic region may influence on climate variability in the eastern Baltic Sea region.

Strong teleconnections are present between different climate variables at the eastern Baltic Sea testing point and the Arctic. Temperature and wind speed at the 1000 hPa level in the eastern Baltic Sea region have in all seasons strong teleconnections with the sea ice concentration in some regions of the Arctic Ocean. The strongest teleconnections appeared in the Greenland sector. Further research is needed to understand the physical mechanisms of the teleconnections.

By defending her thesis, Jakobson received the degree of Doctor philosophiae in physical geography at the University of Tartu. Her supervisors were University of Tartu Professor Jaak Jaagus and  and Senior Research Fellow at Tartu Observatory Erko Jakobson.

The full text of the thesis can be read in DSpace.