Diagnosing Convective Dependencies on Near-Storm Environments Using Ensemble Sensitivity Analyses

• Published in: Monthly weather review 2019-02, Vol.147 (2), p.495-517
• Main Authors: Kerr, Christopher A., Stensrud, David J., Wang, Xuguang
• Format: Article
• Language: English
• Subjects: Boundary conditions; Computer simulation; Convection; Data assimilation; Evolution; Helicity; Inflow; Initial conditions; Kalman filters; Localization; Mathematical models; Mesoscale convective systems; Perturbations; Physics; Radar; Sensitivity analysis; Storms; Supercells; Thunderstorms; Tornadoes; Vertical wind shear; Weather forecasting; Wind; Wind shear
• ISSN: 0027-0644; 1520-0493
• DOI: 10.1175/MWR-D-18-0140.1

Convection intensity and longevity is highly dependent on the surrounding environment. Ensemble sensitivity analysis (ESA), which quantitatively and qualitatively interprets impacts of initial conditions on forecasts, is applied to very short-term (1–2 h) convective-scale forecasts for three cases during the Mesoscale Predictability Experiment (MPEX) in 2013. The ESA technique reveals several dependencies of individual convective storm evolution on their nearby environments. The three MPEX cases are simulated using a previously verified 36-member convection-allowing model (Δx = 3 km) ensemble created via the Weather Research and Forecasting (WRF) Model. Radar and other conventional observations are assimilated using an ensemble adjustment Kalman filter. The three cases include a mesoscale convective system (MCS) and both nontornadic and tornadic supercells. Of the many ESAs applied in this study, one of the most notable is the positive sensitivity of supercell updraft helicity to increases in both storm inflow region deep and shallow vertical wind shear. This result suggests that larger values of vertical wind shear within the storm inflow yield higher values of storm updraft helicity. Results further show that the supercell storms quickly enhance the environmental vertical wind shear within the storm inflow region. Application of ESA shows that these storm-induced perturbations then affect further storm evolution, suggesting the presence of storm–environment feedback cycles where perturbations affect future mesocyclone strength. Overall, ESA can provide insight into convection dependencies on the near-storm environment.