Investigating Cold Pool Dynamics with a Lagrangian Perspective

Cold pools are fundamental ingredients of deep convection. They contribute to organizing the sub-cloud layer and they are considered key elements in triggering new convective cells. Lagrangian particle dispersion models are powerful tools in the study of such systems. The main advantage of these models, besides the large amount of information they provide, is that they allow a direct contact with concepts that are at the basis of many parameterizations, like plumes or parcels, which also make techniques like Lagrangian tracking particularly suited to inform convective parameterizations.

As a first example of the application of such methods, we will show how Lagrangian tracking can be used to study the mechanisms through which cold pools trigger new convective cells in a case in radiative-convective equilibrium with no large-scale organization. Our results show that Lagrangian particles reach their level of free convection only through a cooperation between gust front lifting and thermodynamic forcing, rather than only because of the latter factor, as previously believed.

Then, we will discuss how Lagrangian methods can also be used to investigate the dynamics of precipitation-driven downdrafts that give rise to cold pools. Results in the same case as above show that most downdrafts originate within 1.5 km from the surface and that they are driven mostly by condensate loading, rather than rain evaporation.

Finally, we will apply Lagrangian tracking to investigate the moisture-rich areas at the edges of expanding cold pools and that are also considered as important players in the thermodynamic forcing. We will present results regarding the structure of these areas and we will assess the relative role played by surface fluxes and rain evaporation in generating them.