Abstract
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.
Highlights
Extreme precipitation and flooding in many areas of the world, on the US and European west coasts, are often related to the presence of atmospheric rivers (ARs) (Dettinger et al, 2011; Ralph and Dettinger, 2011; Lavers and Villarini, 2013; Eiras-Barca et al, 2016; Waliser and Guan, 2017)
Inertial tracers accelerate due to external forces acting on the particle and their motion in nonuniform incompressible flows can be modeled by the momentum equation (Zapryanov and Tabakova, 1999; Michaelides, 2003; Takemura and Magnaudet, 2004; PérezMuñuzuri, 2015; Pérez-Muñuzuri and Garaboa-Paz, 2016), dvi = Dui + 2 dt Dt
The AR is well defined for the inertial model, while the pure Lagrangian one seems to quickly lose the tagged moisture from the tropics
Summary
Extreme precipitation and flooding in many areas of the world, on the US and European west coasts, are often related to the presence of atmospheric rivers (ARs) (Dettinger et al, 2011; Ralph and Dettinger, 2011; Lavers and Villarini, 2013; Eiras-Barca et al, 2016; Waliser and Guan, 2017). Lagrangian models have been widely used in climatic studies of atmospheric water vapor sources and in the diagnosis of the origin of moisture in extreme precipitation events (Stohl and James, 2004, 2005; Gimeno et al, 2010; Ramos et al, 2016). These models, widely used, cannot correctly describe evaporation (e) and precipitation (p), in addition to neglecting liquid water and ice, which results in an overestimation of both e and p. Generally known as water vapor tracers (WVTs), are based on coupling a moisture tagging technique with a global or regional meteorological model (Singh et al, 2016; Insua-Costa and Miguez-Macho, 2018; Eiras-Barca et al, 2017). Two Lagrangian models will be considered depending on whether inertial forces on tracers are considered or not
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