The global population of mesoscale convective complexes

A global set of 714 mesoscale convective complexes is compiled and some of the common properties of the convective systems are identified and examined from a global perspective. The data set includes date of occurrence, time of first storms, initiation, maximum extent, termination, duration, cold-cloud shield areas, and tracks from initiation to termination. It is found that the typical convective complex is nocturnal, generates a cold-cloud shield area of approximately 350000 km(2), and persists for about 10 h. The largest systems and most persistent systems tend to occur near the summer solstices. For the globe, about 400 systems occur each year, primarily over land areas. Most systems develop in favoured zones, although some activity occurs over every continent (except Antarctica) and all major oceans. The concentration of activity into favoured zones indicates that there must be special dynamic and/or thermodynamic conditions necessary for convection to organize into convective complexes. Activity is strongly tied to the solar day, and shifts from 35 degrees S in early January to about 50 degrees N during the boreal summer and back to 35 degrees S by December Within the northern hemisphere there is a pronounced poleward migration as the jet stream shifts northward. Relatively little migration occurs in the ocean-dominated southern hemisphere where the subtropical jet remains quasi-stationary over the convective-complex regions. The nocturnal life cycles, copious rainfall, large cloud shields, and great frequency of mesoscale convective complexes suggest that they may be significant contributors to the global hydrologic cycle and earth-system energy budget.