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Tagging moisture sources with Eulerian and Lagrangian tracers: Application to an intense atmospheric river event.
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1  Non-Linear Physics Group, University of Santiago de Compostela, Spain.


One Eulerian and two Lagrangian tracers’ tools are evaluated for studies on atmospheric moisture sources and pathways. The first method has been recently implemented online into the Weather Research and Forecasting (WRF) mesoscale model (Insua-Costa and Míguez-Macho, 2017), while the Lagrangian methods are described here. 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 follows exactly the stream lines of the flow (Stohl and James, 2004). On the other hand, the initial moisture volume can be thought to depend on time as the flow is advected due to thermodynamic processes (for example, pressure, and temperature changes). In this case, the drag on the tracer volume must be taken into account. Equations have been implemented and moisture convection (Forster et al., 2007) was taken into account for both Lagrangian models.

We apply these methods to evaluate the intense atmospheric river (AR; i.e., a narrow plume of strong water vapor flux) that devastated the Pacific North Western America with flooding rains and intense winds in early November 2006 (Neiman et al., 2008). We note that the usual Lagrangian method underestimate moisture availability on the continent while the active tracers (both Eulerian and Lagrangian) achieve better results.


Forster, C., Stohl, A. and Seibert, P. J. Applied Meteo. and Climatology. 46, 403 (2007).

Insua-Costa, D. and Míguez-Macho, G. Eath Syst. Dyn. (2017).

Neiman, P.J. et al. Monthly Wea. Rev. 136, 4398 (2008).

Stohl, A. and James, P. J. Hidrometeor. 5, 656 (2004).

Keywords: moisture sources, lagrangian framework, eulerian framework, atmospheric rivers, WRF, tracers.
Comments on this paper
Raquel Nieto
interesting work
This is a very interesting proceeding, and it will a really good paper on comparig methodologies of atmospheric moisture tracking.

A pair of questions or comments:

There are some typos along the text.

Figure 1: the arrows need to be larger to make then look beter. And in the caption is missing the explanation about black contours.

This sentence: "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 [28, 29, 10, 26]". 28 and 29 references are about detection of moisture sources in terms of climatology, and 10 determines sinks of moisture for moisture with an oceanic origin. Only [26] detects anomalous sources of moisture for extreme events related to ARs.

The sentence about the Lagrangian approaches overestimates e and p needs a reference.

How the WRF model infer in the Eulerian tagging results?

In my point of view the Eulerian tagging predefines the source of moisture for a region, a previous calculation of the main source of moisture for the region of interest would define better the area for starting the trajectories to follow.

This is a nomenclature question: inertial and Lagrangian methods are both lagrangian models, so it could be better rename them.

Did the authors compare these results with the common used FLEXPART model?

It is a good work. Congratulations!