Seasonal variability and future changes of physical characteristics of MCS-like precipitation objects in a Europe-wide convection permitting model simulation

Abstract:

Mesoscale convective system (MCS)-like precipitation objects have been tracked in Met Office Europe-wide convection permitting model (CPM) simulations. The Europe-wide CPM simulations include an ERA-Interim driven hindcast, a present-climate simulation and a future-climate simulation under the RCP8.5 scenario toward the end of 21^st century. The tracking algorithm is originally developed to track radar precipitation over the UK (project DYMECS) but has since been applied to continental-scale CPM simulations (for Africa and Europe). We focus on MCS-like objects, which we define as tracks with a maximum area above 1000 km**2 and maximum intensity above 20 mm/h after the CPM data is regridded to 12km. We have analysed various diagnostics of the tracked objects including maximum and mean precipitation intensity, the frequency of such objects, and the lifetime/movement speed/area of these objects, which are all important to extreme precipitation. We look at the changes and variability of the diagnostics between different seasons and between the present and future climate simulation. We find a large future percentage increase in the frequency of MCSs which overshadows the smaller percentage increase in MCS precipitation intensity. A clear correlation between movement speed and lifetime or area is also found; this correlation is found in the seasonal cycle (summer MCSs are smaller, shorter-lived, and move slower than autumn MCSs) as well as in the future changes (future MCSs are smaller, shorter-lived, and move slower than present-day MCSs). MCS changes are also examined regionally across Europe, showing that future increases of MCSs are particularly high for Northern Europe whilst such MCSs are historically concentrated around the Mediterranean Sea.