Abstract. Two Lagrangian tracer tools are evaluated for studies on atmospheric
moisture sources and pathways. In these methods, a moisture volume is
assigned to each particle, which is then advected by the wind flow. Usual
Lagrangian methods consider this volume to remain constant and the particle
to follow flow path lines exactly. In a different approach, the initial
moisture volume can be considered to depend on time as it is advected by the
flow due to thermodynamic processes. In this case, the tracer volume drag
must be taken into account. Equations have been implemented and moisture
convection was taken into account for both Lagrangian and inertial models. We
apply these methods to evaluate the intense atmospheric rivers that
devastated (i) the Pacific Northwest region of the US and (ii) the western
Iberian Peninsula with flooding rains and intense winds in early
November 2006 and 20 May 1994, respectively. We note that the usual
Lagrangian method underestimates moisture availability in the continent, while
active tracers achieve more realistic results.