Investigation of the vertical structure of the lower atmosphere during heat wave conditions

Research on heat waves and extreme events in general is highly motivated by their impacts on human life and the economy. Therefore, the focus is on near surface variables and less research has been done on the state of the lower atmosphere as a whole. In a study of the mega heat waves of 2003 in France and 2010 in Russia, Miralles et al. (2014) investigate which factors have to come together to enable such extremes. One interesting finding is the gradual increase in planetary boundary layer height during those events. Also, their simulations display a correlation between mean potential temperature in the lower atmosphere and the boundary layer height. For these reasons, we believe that a systematic analysis of the planetary boundary layer during heat waves may provide valuable insights into their formation and persistence. We investigate whether these features are common traits of European heat waves in general. To this end, we apply a classification and regression scheme to vertical profiles taken from COSMO-REA6 data for the summers of 2014 to 2018. The reanalysis data is also used to identify heat waves, such that a comparison of boundary layers during normal and extreme conditions is possible. We analyse the distributions of planetary boundary layer heights for every grid point to check for regional differences. For validation, we make a comparison to radio soundings taken from the DWD Open Data service. The results of our work could possibly be used to improve the discriminability of different severity levels of heat waves or to formulate a heat wave measure that is not based solely on surface variables.