An energetic view of the relation between the Mediterranean storm track and the North Atlantic Oscillation

The time tendency equation of eddy kinetic energy (EKE) includes some important forcing terms such as baroclinic conversion (BCC), barotropic conversion (BTC) and energy flux. This article compares the ensemble mean distribution of these forcing terms, as well as the baroclinic generation (BCG) term, in critical positive and critical negative months of the North Atlantic Oscillation (NAO), focusing on the Mediterranean and Middle East regions. Results show that all the computed terms attain larger values and all the extrema are stronger in the positive phase. The energy‐flux vectors point to energy transfer from the west of the Atlantic and north of Europe to the Mediterranean region, with the transfer being weaker in the positive phase. There is energy‐flux divergence over the central region of the Mediterranean Sea, which is more extensive in the positive phase relative to the negative phase. The energy‐flux divergence leads to a radiation source in this region. The direction of the energy‐flux vectors then indicates that the energy radiated from the central Mediterranean region is transferred southeastward, leading to an energy‐flux convergence over the Red Sea and the northeast of Africa. This convergence is stronger and more extensive in the positive phase, which may be responsible for the observed larger value of the upper‐level eddy kinetic energy in the positive phase. The patterns of the BCG and BCC, together with the energy‐flux convergence, suggest that while the Mediterranean storm track is affected by the North Atlantic storm track more strongly in the negative phase it acts as an independent centre of action by radiating energy southeastward in the positive phase. Copyright © 2011 Royal Meteorological Society