Large-scale controls on intensity-duration characteristics of heatwaves in an idealised model

Abel Shibu , Joy Merwin Monteiro

The relationship between the large-scale structure of the atmospheric circulation and the mean intensity and duration of heatwaves is studied in an idealised climate model. Using the tight relationship between near-surface temperature and lower tropospheric dry static energy (DSE) in the model, we study the energetics of the lower troposphere during heatwaves in the model. This analysis leads to a quantitative framework to partition intensity and duration of heatwaves to different components of advection and identify the main contributors. We observe that while contribution of the meridional advection of DSE explains the difference between high and low intensity heatwaves in a given location, it does not explain variation of mean intensity across latitudes. In a similar manner, we find that while the contribution of meridional advection is important in explaining the difference between high and low duration heatwaves in a given location, it does not explain variation of mean duration across latitudes. We find that the zonal advection of DSE plays an important role in explaining variation of mean intensity and duration of heatwaves across latitudes. By linking these advective terms to the variation of the lower-tropospheric circulation across latitudes, we present an explanation of how the general circulation of the atmosphere - particularly the location of the storm track - controls the mean intensity and duration of heatwaves in our model.