PhD Defence Lasse Husbjerg

Principal supervisor:

• Senior Researcher Olivier Chanrion, DTU Space

Co-supervisors

• Senior Researcher Martin Stendel, Danish Meteorological Institute
• Professor Eigil Kaas, Niels Bohr Institute

Examiners

• Senior Scientist Anders Henry Nielsen, DTU Physics
• Professor Sebastian Celestin, LPC2E, University of Orleans, France
• Professor Yoav Yair, Reichman University (IDC Herzliya) Israel

Chairperson at defence

• Senior Researcher Martin Andreas Bødker Enghoff

Summary

Observations of thunderstorms from space by Andreas Mogensen in 2015 showed that the tops of thunderclouds are far more active than previously known. The profuse activity of blue discharges at
the tops of thunderclouds have led to questions regarding their effect on the chemical composition of the upper atmosphere.

This thesis focused on these blue discharges using observations from the Danish led instrument: The Atmosphere-Space Interactions Monitor (ASIM). The distinctly blue signature of blue discharges as
seen in the ASIM photometers indicates that they have a lower temperature than lightning. They occur at relatively high altitude when the top of the thundercloud reach the tropopause and impact the chemistry related to green house gases. They are far more frequent than thought before and little is yet known about the importance of their chemical impact on the atmosphere.

This work has shown that these blue discharges, also known as Blue Corona Discharges (BCDs), are related to more severe weather than lightning is and that their production is likely to increase in a warming climate, at a rate of about 7% per degree Kelvin in global average temperature.

The work also showed that geographically the BCD events are likely to increase mainly in central Africa, but increases are also expected in the higher latitudes such as Australia, North America and
Europe.