A wavelet‐based analysis of convective organization in ICON large‐eddy simulations

• Published in: Quarterly journal of the Royal Meteorological Society Vol. 144; no. 717; pp. 2812 - 2829
• Main Authors: Brune, Sebastian, Kapp, Florian, Friederichs, Petra
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01-10-2018; Wiley Subscription Services, Inc
• Subjects: Anisotropy; Convection; convective organization; ICON‐LEM; Mesoscale convective systems; Organizations; Rain; Rainfall simulators; Spectra; Squall lines; Squalls; Supercells; wavelet transform; wavelet‐based organization index; Wind shear
• ISSN: 0035-9009; 1477-870X
• DOI: 10.1002/qj.3409

Wavelet spectra of rain rates are used to characterize convective organization in high‐resolution simulations (horizontal grid spacing 156 m) with the large‐eddy model ICON‐LEM over Germany. Scattered convection takes place on scales between 1.2 and 4.8 km, while organized structures like supercells or mesoscale convective systems act on scales above 4.8 km. Organization of convection within squall lines is visible in the spectra as spectral energy is increased in certain directions. We further investigate the dynamical properties that relate to convective organization, and highlight the role of parameters such as CAPE and wind shear.
Preferred spatial scale, average convective rain rate and anisotropy as inferred from the wavelet spectra are important characteristics to quantify convective organization. They are used to introduce a wavelet‐based organization index (WOI). Compared with other indices for convective organization, WOI does not require the definition of objects. Using the WOI we are able to distinguish organized from non‐organized convection.
(a) Elevation and model area in ICON‐LEM. Black framed area indicates the power of two 512 × 512 field for the wavelet decomposition. (b) Model level height (black dots, left axis) and layer thickness (grey dots, right axis) for every vertical level (bottom axis).