Comparison between European and U.S. Severe Convective Weather Environments in Multiple Reanalyses

Previous studies have identified differences in European and U.S. severe convective storm environments. These findings motivated us to study the atmospheric conditions associated with severe storms using multiple reanalysis datasets, such as ERA-Interim, MERRA and NCEP/NCAR. We investigated the relations between the occurrence of convective storms and a range of atmospheric parameters representing instability, moisture, and shear, which can be derived from multiple reanalysis data. The aim was to increase the understanding of the conditions under which thunderstorms form in both Europe and the United States. Besides thunderstorm occurrence, we focused on severe convective weather environments that produce hazards such as large and very large hail and severe wind gusts.

For Europe, lightning data from the European Cooperation for Lightning Detection (EUCLID) between 2008 and 2016 served as indicator for thunderstorms and data from the European Severe Weather Database (ESWD) as indicator for hazard occurrence. Severe convective weather environments in the United States were analyzed using lightning data from the National Lightning Detection Network (NLDN) and hazard data from the Storm Prediction Center (SPC). The considered time period for NLDN lightning observations is 2010 to 2014.

We investigated favorable environments of thunderstorms and severe convective weather for both regions and we will highlight its differences. On the example of ERA-Interim, we will discuss the spatial distributions and mean annual cycles, as well as the relative frequencies for thunderstorms and severe convective weather in different parameter spaces. Finally, we will present our analysis of trends in the atmospheric parameters for Europe and the United States during the last decades.

For ERA-Interim, for example, the analysis of the probabilities modeled by an additive regressive convective hazard model (AR-CHaMo) suggests a significant positive trend for lightning and hazard occurrences in most of central and eastern Europe, while negative trends were identified for parts of France, Spain and Morocco, and for a region east of the Rocky Mountains in the United States. We will also focus on the differences among multiple reanalyses. For Europe, for example, we identified large differences between atmospheric instability parameters for the different reanalysis datasets.