Significant Contribution of Mesoscale Overturning to Tropical Mass and Energy Transport Revealed by the ERA5 Reanalysis

Differential solar heating drives a global multiscale atmospheric overturning that has remained elusive due to the lack of accurate estimates of vertical motions at/below the mesoscale (<1,000 km). Here we compare the atmospheric overturning in the newest-generation (ERA5) and the previous-generation (ERA-Interim) reanalyses from the European Centre for Medium-Range Weather Forecasts based on isentropic averaging that identifies the contribution of different scales. The two reanalyses feature large-scale overturning of similar magnitude. However, ERA5 reveals a mesoscale overturning that is 74% of the large-scale overturning over the tropics, while the former in ERA-Interim is much weaker (42%). Comparison with observed outgoing longwave radiation suggests that the magnitude and seasonal migrations of the deep mesoscale overturning in the upper troposphere over the tropics are better captured by ERA5 than ERA-Interim. Hence, in the tropics, mesoscale overturning may play a comparable role to large-scale overturning in vertical mass and energy transport.