Browsing by Author "Van den Broek, Daan"

Supercells are thunderstorms characterized by a persistently rotating updraft, which is separated from, and in quasi-steady state with the downdraft. The structure of a supercell allows for long-lived thunderstorms, capable of producing severe weather such as significant hail (hail with a diameter >5 cm) and tornadoes. Despite their relative rarity, supercells are responsible for a disproportionate share of thunderstorm related hazards and damage. Although uncommon at high latitudes, supercells do occur in Finland, where documented cases have led to severe weather events and substantial damage. The goal of this study is to improve our understanding on the meteorological environment in which supercells in Finland occur. Specifically, we aim to discriminate between the meteorological environment of supercell thunderstorms and ordinary thunderstorms in Finland. This is done by examining how kinematic and thermodynamical parameters from proximity soundings between both groups differ. Additionally, we inspect the difference in meteorological environments of significant hail-producing supercells (acronym HAIL) and tornado-producing supercells (acronym TOR) environments. The results indicate that bulk wind shear in various levels, as well as effective bulk wind shear (the bulk wind shear over the unstable layer), are strong discriminators between supercell and ordinary thunderstorm environments in Finland. Composite parameters such as the Energy Helicity Index (EHI) and Supercell Composite Parameter (SCP) also show some utility in distinguishing supercell and ordinary thunderstorm environments. Equilibrium Level (EL) and low-level Convective Available Potential Energy (CAPE) stand out as significant discriminators between significant hail-producing and tornado-producing supercell environments, while Lifting Condensation Level (LCL) and low-level humidity appear to show critical threshold values that may help distinguishing significant hail-producing supercell and tornado-producing supercell environments. Interestingly, the ratio of low-level CAPE to CAPE discriminates very strongly between significant hail-producing supercell and tornado-producing supercell environments. Composite parameters and Storm Relative Helicity (SRH) exhibit very limited utility in differentiating between significant hail and tornado-producing supercell environments in Finland.