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R. G. Pinnick, D. M. Garvey, and L. D. Duncan

Abstract

Measurement of cloud drop size distributions with the Knollenberg model FSSP-100 light-scattering counter can lead to artificial bumps or knees in the distributions at ∼0.6 μm and sometimes 2–4 μm radius if the manufacturer-supplied calibration is used. These artifacts are a consequence of the instrument having multivalued or slowly changing response in these regions of particle size. A modified calibration procedure is given that removes these artifacts so that the true droplet size distribution can be obtained. Measurement of slightly nonspherical particles with refractive indexes characteristic of those of atmospheric aerosols will generally lead to undersizing if the FSSP manufacturer-calibration is used, but likely by not more than a factor 2.

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James B. Duncan Jr., Brian D. Hirth, and John L. Schroeder

Abstract

Remote sensing instruments that scan have the ability to provide high-resolution spatial measurements of atmospheric boundary layer winds across a region. However, the time required to collect the volume of measurements used to produce this spatial representation of atmospheric winds typically limits the extraction of atmospheric turbulence information using traditional temporal analysis techniques. To overcome this constraint, a spatial turbulence intensity (STI) metric was developed to quantify atmospheric turbulence intensity (TI) through analysis of spatial wind field variability. The methods used to determine STI can be applied throughout the measurement domain to transform the spatially distributed velocity fields to analogous measurement maps of STI. This method enables a comprehensive spatial characterization of atmospheric TI. STI efficacy was examined across a range of wind speeds and atmospheric stability regimes using both single- and dual-Doppler measurements. STI demonstrated the ability to capture rapid fluctuations in TI and was able to discern large-scale TI trends consistent with the early evening transition. The ability to spatially depict atmospheric TI could benefit a variety of research disciplines such as the wind energy industry, where an understanding of wind plant complex flow spatiotemporal variability is limited.

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Matthew D. K. Priestley, Duncan Ackerley, Jennifer L. Catto, Kevin I. Hodges, Ruth E. McDonald, and Robert W. Lee

Abstract

The representation of the winter and summer extratropical storm tracks in both hemispheres is evaluated in detail for the available models in phase 6 of the Coupled Model intercomparison Project (CMIP6). The state of the storm tracks from 1979 to 2014 is compared to that in ERA5 using a Lagrangian objective cyclone tracking algorithm. It is found that the main biases present in the previous generation of models (CMIP5) still persist, albeit to a lesser extent. The equatorward bias around the SH is much reduced and there appears to be some improvement in mean biases with the higher-resolution models, such as the zonal tilt of the North Atlantic storm track. Low-resolution models have a tendency to underestimate the frequency of high-intensity cyclones with all models simulating a peak intensity that is too low for cyclones in the SH. Explosively developing cyclones are underestimated across all ocean basins and in both hemispheres. In particular the models struggle to capture the rapid deepening required for these cyclones. For all measures, the CMIP6 models exhibit an overall improvement compared to the previous generation of CMIP5 models. In the NH most improvements can be attributed to increased horizontal resolution, whereas in the SH the impact of resolution is less apparent and any improvements are likely a result of improved model physics.

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