Particle-Based Tracking of Cold Pool Gust Fronts.

Olga Henneberg,Bettina Meyer,Jan O Haerter

doi:10.1029/2019ms001910

Olga Henneberg, Bettina Meyer + Show 1 more

Open Access

https://doi.org/10.1029/2019ms001910

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Abstract

The gust fronts of convective cold pools (CPs) are increasingly recognized as loci of enhanced triggering for subsequent convective cells. It has so far been difficult to track these gust fronts in high‐resolution data, such as large eddy simulations (LES)—rendering mechanistic analysis of CP interaction incomplete. Here, a simple tracking method is defined, tested, and applied, which uses horizontal advection and a condition on horizontal divergence, to emit tracers at the perimeter of surface precipitation patches. Tracers are then reliably transported to the gust front, yielding closed bands marking the CP boundary. The method thereby allows analysis of the dynamics also along the gust front, which allows to identify point‐like loci of pronounced updrafts. The tracking works well for a single idealized CP and reliably tracks a population of CPs in a midlatitude diurnal cycle. As the method uniquely links CPs and their tracers to a specific parent precipitation cell, it may be useful for the analysis of interactions in evolving CP populations.

Highlights

Precipitation from cumulus clouds can form cold and dry downbursts by the evaporative cooling of precipitation (Doswell, 2001)
The area of cold pools (CPs) identified by temperature-based methods tends to reduce during later stages of the CP lifetime (Feng et al, 2015). This retreating feature stands in contradiction to the dynamics of CP gust fronts, which often continue to spread by inertia, even if the temperature anomaly is reduced (Fournier & Haerter, 2019; Grant & van den Heever, 2018)
This study introduced a simple method to track CP gust fronts in the network formed by the narrow near-surface convergence bands in high-resolution simulation output

Summary

Introduction

Precipitation from cumulus clouds can form cold and dry downbursts by the evaporative cooling of precipitation (Doswell, 2001). The area of CPs identified by temperature-based methods tends to reduce during later stages of the CP lifetime (Feng et al, 2015) This retreating feature stands in contradiction to the dynamics of CP gust fronts, which often continue to spread by inertia, even if the temperature anomaly is reduced (Fournier & Haerter, 2019; Grant & van den Heever, 2018). We refer to the region of the convergence peak as the CP edge As this dynamically defined CP edge will always lie ahead (or on top) of the thermodynamic boundary, this method has the advantage that both types of convective triggering occur within the identified CP area. We close with an outlook on possible applications (section 5)

LES Data

Methodology

Application of Particle-Based CP Tracking

Conclusion and Outlook