The use of vertical gradients of radar reflectivity factor and radial velocity to diagnose dynamical and microphysical structures in extratropical cyclones: results from IMPACTS

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Abstract The Investigation of Microphysics and Precipitation for Atlantic Coast-Threatening Snowstorms field campaign comprised three deployments in January and February of 2020, 2022, and 2023. Throughout these deployments, the NASA Earth Resources-2 (ER-2) aircraft conducted 26 research flights, equipped with three vertically pointing radars. These radars sampled the vertical structure of extratropical cyclone clouds at four distinct radar wavelengths, enabling a finer scale analysis of reflectivity and radial velocity structures within extratropical cyclones with a vertical sampling resolution of 26.5 m. In this analysis, we introduce a novel technique utilizing vertical gradients in radial velocity and reflectivity, which proved effective in identifying turbulence, waves, and layers of ascent over 132.5 m layers for all flight legs conducted during the campaign. The spatial scale of 132.5 m was chosen to capture fine-scale variations associated with small-scale turbulent eddies and shear zones in frontal regions. The gradient analysis aided in detecting small scale changes in reflectivity and radial velocity that might have gone unnoticed otherwise. Moreover, the corresponding gradients in reflectivity suggest potential interactions of falling ice crystals with turbulence, waves, and shear layers, possibly influencing the microphysical characteristics and the vertical spatial distribution of falling snow. The observed vertical gradients in radial velocity often exhibited linear, layered patterns, but in some instances displayed wave-like appearances, sloped patterns along frontal boundaries, or magnitude fluctuations. This paper focuses on presenting and detailing the vertical gradient technique to examine winter storms. Future work will involve a comprehensive analysis of these gradients in relation to dual-frequency radar measurements and in situ microphysical characteristics.