Speaker: Dr.Jezabel Curbelo from Universitat Politècnica de Catalunya

Title: Lagrangian analysis of the smoke plume from the 2019/2020 Australian wildfire event.

Abstract: 

The wildfires of the 2019/2020 bushfire season in Australia created a rising plume which resulted in a record concentration of smoke in the Lower Stratosphere. Following a dynamical system approach in the Lagrangian framework, we focus our study on the time when the cloud reaches a highest concentration of smoke (early January 2020) and the plume disperses into independent transport paths. To better understand the cause of the splitting, the subsequent transport geometry, and the influence of the plume buoyancy on its movement, we characterize the three dimensional atmospheric transport in the region aided by the Finite Time Lyapunov Exponent tool.

Our goal is to identify Lagrangian Coherent Structures (LCS) which simplify the three-dimensional transport description and make possible the characterization of the smoke plume evolution. We provide several examples of the LCS geometries that guide the dynamics around them and control the physical process. It has also allowed us to unveil the qualitatively different dynamical fates and origins of the smoke parcels trajectories depending on the region in which they originated and to identify new transport routes and other mixing patterns in the area. Our numerical modeling results are consistent with the observations of the splitting of the plume into multiple pathways. In the model, we found parcels trajectories with the same behavior as the observed plume, highlighted the contribution of the passive advection of the plume by the wind versus the buoyancy effect of hot smoke, delineated the plume into regions destined to different fates, and showed that the division of the main path was affected by an eddy.