Bachelor Thesis Defense by Lærke Halkjær

Title: Analysis of water-, landspouts and tornadoes in Denmark

This bachelor’s thesis is about a climatological analysis of water-, landspouts and tornadoes in Denmark. Only since 2019 tornadoes have been reported in Denmark. Beforehand it was believed by Danish meteorologists, that the conditions to develop torndaoes would never be possible in Denmark - at the same time there was a tendency to simply call all phenomenons of rotating winds water- and landspouts (non-mesocyclonic tornadoes). The water- and landspouts develop differently than tornadoes. Tornadoes form from a mesocyclone in a upercell, as defined by American meteorologists, whereas the spouts are non-mesocyclonic. The synoptic atmospheric situation is also different.

By making a comprehensive overview of 154 observed water-, landspouts and tornadoes from 1997 to 2022, 39 cases have been selected for further investigation, as there were signs of them deviating from the classic water- and landspouts. Data from accessible observation material from the relevant weather situations have been used for the analysis: Weather charts of the synoptic situations, rawinsondes, radar data, satellite pictures and weather station observations. The 154 observations has been classified as 126 water-/landspouts, six tornadoes, seven ”possible”tornadoes and 14 cases of none of the above. 92 cases has been classified as waterspouts, where 30 out of 34 landspouts were observed in the afternoon due to the seabreeze. The water-/landspouts have a tendency of increasing in number through the years, though this can also be correlated with the number of smart phones.

All 13 tornado cases have only been observed in the afternoon and in the evening. The seven ”possible”tornadoes are not able to be concluded due to missing radar data or uncertainty of the placement and strength of the jet stream at the time of the observation, though the rest of their analysis matches with tornado-related weather. The Danish tornadoes are probably spawned from mini supercells and low precipitation supercells: They are smaller in size and strength than the typical American supercells; some cases do not have a clear hook echo on radar, but still have signs of a mesocyclone. The cases, which has been classified as something different than in their original article, could simply not have been investigated by the meteorologists making a comment on the observations. This shows that meteorologists need to have the right background knowledge of the differences of water-/landspouts and tornadoes, together with modern radar data.

Supervisors: Aksel Walløe Hansen and Sebastian Pelt
Censor: Peter Aakjær