Extreme events can have a major impact on society and ecosystems and pose a significant challenge to scientists. The occurrence of extremes in two or more meteorological parameters, so called compound events, add an additional level of complexity, especially when considering also the ongoing warming of the Earth’s climate. We focus on extratropical cyclones and present a new method for identifying compound wind and precipitation extremes, and present climatologies of these.

To investigate cyclones that trigger extreme wind and precipitation a cyclone detection and tracking algorithm is applied, which is designed to estimate the radius of each cyclone. This scale metric is used to identify the area that is influenced by a low-pressure system. The high-resolution reanalysis dataset ERA5 is used as input for the tracking, and has been found especially valuable for analysing extreme events. Tracking synoptic systems provides a quasi-Lagrangian perspective of such extreme events, which is in contrast to the often used Eularian approach when investigating compound events.

To be considered as an extreme event the seasonal 99^th percentile has to be exceeded at several ‘grid points’ within the impacting area, defined by the radius. Only extratropical cyclones that fulfil that criterion both in precipitation and 10-meter wind gust are considered as compound extreme event.

We will show that the peak occurrence of the cyclones that exceed this criterion for wind are slightly displaced from those that exceed the required precipitation threshold. The results show also that the precipitation criterion is more often exceeded than the one for wind. Several of the compound events are located over the open water following the storm track, but there are also interesting occurrences over land, e.g., in the southern part of mainland Australia and in Tasmania. The compound extreme events will be further investigated according to their atmospheric conditions.