Anatomy of atmospheric rivers: the internal signature of extreme events

Atmospheric rivers are transient filaments of high integrated water vapour transport (IVT), spanning across oceanic basins, that can be associated with heavy precipitation. Possible feedbacks between convection at the mesoscale and moisture transport could modulate impacts at the leading end of atmospheric rivers, but while the link with synoptic-scale dynamics and more specifically with extratropical cyclones has been the object of numerous studies, finer scale phenomena remain less investigated, apart from case-studies in specific regions such as the Californian coast.

This work aims at characterizing convection within atmospheric rivers and its interactions with moisture fluxes. We investigate the extent to which the conceptual scheme for the structure of atmospheric rivers is valid, and whether it should be refined.

A Lagrangian perspective on atmospheric rivers is key in order to study their internal structure from tail to head, from genesis to termination. We therefore use the tARget database of ERA5 atmospheric rivers (Guan and Waliser, 2024), detected globally on the basis of a relative regional threshold for high-IVT structures. We point out that it catches high-IVT objects that differ from the classical picture of atmospheric rivers and that could be separately classified through the description of their structure. We then develop an algorithm that detects the internal features of atmospheric rivers. We show that there can be multiple moisture transport axes, with varying connections to a cold front. Moreover, atmospheric rivers associated with extreme precipitation or IVT exhibit specific internal structures in terms of overturning circulations and tilted updrafts. 

This work underlines the need to consider the diversity of atmospheric rivers to better understand their impacts.