A Climatology of Coupled Tracks of Extratropical Cyclones and Mesoscale Convective Systems

Abstract

Weather in the midlatitudes is dominated by extratropical cyclones (ETCs) with horizontal length scales of roughly 1,000 km and mesoscale convective systems (MCSs), with horizontal length scales of roughly 100 km. This study investigates the multi‐scale interactions of these storms by comparing databases of Lagrangian tracks for both storm types and locating points which are co‐located in space and time to identify “coupled” systems. We find that these coupled tracks occur at the southward edge of the regions with the most ETC points and on the northward edge of the MCS points. The coupled points also show a strong seasonal cycle. However, during all seasons the coupled points tend to be concentrated over warm ocean waters in the Kuroshio, Gulf Stream, and over central North America. We also show that ETC systems which contain MCSs deepen faster than systems without an MCS. Most of the coupled points occur at the initial coupling time for both systems, indicating that the ETCs and MCSs are forming at very similar times. Additionally, intensification tends to happen after the time of first coupling. To investigate the dynamics behind this, we interpolate ERA5 data around the time of initial coupling and find that the coupled systems are occurring in regions of particularly strong initial frontal conditions, which is followed by a strong intensification of the ETC. These results suggest that understanding the distribution of strong fronts is key to understanding the coupling between the different storm types.