Mechanisms for convection triggering by cold pools

TL;DR

This paper investigates how cold pools trigger deep convection by mechanically lifting air parcels and thermodynamically reducing inhibition, using a Lagrangian tracking method in a radiative-convective simulation.

Contribution

It introduces a Lagrangian tracking method to distinguish and quantify mechanical and thermodynamic forcing in cold pool-induced convection.

Findings

Mechanical forcing lifts parcels from the surface.

Thermodynamic forcing reduces inhibition before reaching free convection.

Both forcings contribute at different ascent stages.

Abstract

Cold pools are fundamental ingredients of deep convection. They contribute to organizing the sub-cloud layer and are considered key elements in triggering convective cells. It was long known that this could happen mechanically, through lifting by the cold pools' fronts. More recently, it has been suggested that convection could also be triggered thermodynamically, by accumulation of moisture around the edges of cold pools. A method based on Lagrangian tracking is here proposed to disentangle the signatures of both forcings and quantify their importance in a given environment. Results from a simulation of radiative-convective equilibrium over the ocean show that parcels reach their level of free convection through a combination of both forcings, each being dominant at different stages of the ascent. Mechanical forcing is an important player in lifting parcels from the surface, whereas thermodynamic forcing reduces the inhibition encountered by parcels before they reach their level of free convection.