Speaker:  Professor Raffaele Ferrari from MIT

Prof. Ferrari will lead the discussion on the paper by Gertler and O’Gorman titled “Changing available energy for extratropical cyclones and associated convection in Northern Hemisphere summer."

Here is a brief summary of the paper adapted from the abstract:

The circulation of the Northern Hemisphere extratropical troposphere has changed over recent decades, with marked decreases in extratropical cyclone activity and eddy kinetic energy (EKE) in summer and increases in the fraction of precipitation that is convective in all seasons. Changes to mean available potential energy (MAPE), which is the energetic reservoir from which extratropical cyclones draw are studied, and the authors calculate trends in MAPE for the Northern extratropics in summer over the years 1979–2017, decomposing MAPE into convective and nonconvective components. Nonconvective MAPE decreased over this period, consistent with decreases in EKE and extratropical cyclone activity, but convective MAPE increased, implying an increase in the energy available to convection. These results connect changes in the atmospheric mean state with changes in both large-scale and convective circulations, and they suggest that extratropical cyclones can weaken even as their associated convection becomes more energetic.[Paper]