Energy Export from the Tropical Pacific via the Atmosphere - a Lagrangian Perspective

The El Niño-Southern Oscillation (ENSO) is linked with energy exchange between the ocean, atmosphere and space. It has a global impact on weather, agriculture and the economic system. In association with ENSO, we analyse the atmospheric energy export from the Tropical Pacific with the particle dispersion model FLEXPART using meteorological input data from the ERA5 reanalysis. In this Lagrangian model, the atmosphere was filled homogeneously with five million particles, which were traced forward in time and represent the global atmospheric mass transport. From this Lagrangian reanalysis dataset covering the years 1979-2017, air masses residing within the Nino3.4 + Nino3 region and below 1 km are selected and followed 30 days forward in time. We found that some of these relatively warm air masses are transported to the Atlantic Ocean where they are mainly located at upper layers. Furthermore, we found strong correlations between the mass transport and the Nino3.4 Index, thus more air is exported to the Atlantic Ocean during El Niño conditions. This transported air further releases energy, as shown by a negative energy divergence. Even over the Sahel zone there is a significant signal, which indicates a direct atmospheric connection between West Africa and the Tropical Pacific. Based on our findings, the transported air might support drier surface conditions during El Niño in that region. In summary, the Lagrangian technique provides new insights into how energy is exported from the Tropical Pacific via the atmosphere and clarifies the relevance of atmospheric transport associated with ENSO.