Giga-LES of Hector the Convector and Its Two Tallest Updrafts up to the Stratosphere

Abstract

he dynamics of Hector the Convector, which overshot into the stratosphere on 30 November 2005 over the Tiwi Islands, Australia, is investigated using a giga-large-eddy simulation with a 100-m cubic mesh. Individual updrafts, defined as 3D objects with vertical velocity above 10 m s?1 are identified. Among the 20 000 updrafts formed during the most intense phase, only a dozen were more than 4 km tall. The two tallest updrafts accounted for more than 90% of the total vertical mass flux through the tropical tropopause layer. Their locations were determined by low-level convergence lines first created by the sea breeze in the morning, then enhanced by cold pools due to cumulus congestus. They finally reinforced each other as they moved inland and intersected. The two tallest updrafts that overshot the tropopause were contrasted with those occurring 1 h earlier and later. They presented larger widths (up to 8 km), greater buoyancy (up to 0.1 m s?2), stronger vertical velocities (up to 50 m s?1), and larger hydrometeor contents (more than 10 g kg?1). They kept their core weakly diluted on their way to the stratosphere with an entrainment rate as low as 0.08 km?1. Both the low-level convergence lines intensified by cold pools and the reduced mixing in the troposphere were found to be the determinant for the transition from deep to very deep convection.