A three dimensional Lagrangian analysis of the smoke plume from the 2019/2020 Australian wildfire event

Abstract

During the 2019/2020 bushfire season in Australia a rising plume, which had record concentration of smoke in the lower Stratosphere, was generated by the intense wildfires in southeast Australia. In this paper, we use the atmospheric wind reanalysis model ERA5 to characterize the three dimensional atmospheric transport in the region following a dynamical system approach in the Lagrangian framework. Aided by the Finite Time Lyapunov Exponent tool (FTLE) we identify Lagrangian Coherent Structures which simplify the three-dimensional transport description and make possible the characterization of the smoke plume evolution. Different reduced FTLE formulations are compared to study the impact of the vertical velocity and the vertical shear on the movement of the plume. Several examples of the LCS geometries are described and we show the presence of 3D lobe dynamics at play. Also, we unveil the qualitatively different dynamical fates of the smoke parcels trajectories depending on the region in which they originated. Transport paths obtained with the inclusion of the buoyancy effects are compared with those obtained considering only the reanalysis velocity.