Size dependence in chord characteristics from simulated and observed continental shallow cumulus

Abstract

Abstract. In this study we compare long-term Doppler and Raman lidar observations against a full month of large eddy simulations of continental shallow cumulus clouds. The goal is to evaluate if the simulations can reproduce the mean observed vertical velocity and moisture structure of cumulus clouds and their associated subcloud circulations, as well as to establish if these properties depend on the size of the cloud. We propose methods to compare continuous chords of cloud detected from Doppler and Raman lidars with equivalent chords derived from 1D and 3D model output. While the individual chords are highly variable, composites of thousands of observed and millions of simulated chords contain a clear signal. We find that the simulations underestimate cloud size and fraction but successfully reproduce the observed structure of vertical velocity and moisture perturbations. There is a clear scaling of vertical velocity and moisture anomalies below the chords with chord size, but the moisture anomalies are only 1 %–2 % higher than the horizontal mean values. The differences between the observations and simulations are smaller than the difference in sampling the modeled chords in time or space. The shape of the vertical velocity and moisture anomalies from cloud chords sampled spatially from 3D model snapshots is almost perfectly symmetric. In contrast, the chords sampled temporally from the lidar observations and 1D model output have a marked asymmetry, with stronger updrafts and higher moisture anomalies occurring earlier on.

Generalized eddy-diffusivity mass-flux (GEM) formulation for the parameterization of atmospheric convection and turbulence

“…Therefore, we must consider the asymptotic behavior w ′ (z, r → ∞) = 0 in order to obtain a complete parameterization in which the subgrid fluxes containing the convective radial velocity are not neglected. This asymptotic behavior can be also observed from recent measurements and numerical simulations (Mallaun et al, 2019;Griewank et al, 2020;Gu et al, 2021;Savre, 2021).…”

“…Moreover, in this work, we derive the expressions for the subgrid fluxes for generic radial profiles and we discuss the situation in which every convective plume is characterised by an updraft located in the center and a subsidising shell around the updraft area, as it follows from the recent observational and numerical evidence (Mallaun et al, 2019;Griewank et al, 2020;Nair et al, 2020;Gu et al, 2021;Savre, 2021;Denby et al, 2022). We show that for such a profile of the convective vertical velocity we can obtain the subgrid fluxes without requiring that the fractional area occupied by the convection in a given grid box be very small.…”

Using aircraft measurements to characterize subgrid-scale variability of aerosol properties near the Atmospheric Radiation Measurement Southern Great Plains site

“…At a minimum, it represents a transect across the grid cell; therefore, we assume that the spatial variability along that line is consistent with the variability within the entire cell. This is analogous to cloud chord sampling (e.g., Barron et al, 2020;Griewank et al, 2020). However, there were some flights that had a grid pattern near the Central Facility (Fig.…”

Generalized eddy‐diffusivity mass‐flux formulation for the parametrization of atmospheric convection and turbulence

“…Moreover, in this work, we derive the expressions for the subgrid fluxes for generic radial profiles and we discuss the situation in which every convective plume is characterized by an updraft located in the center and a subsiding shell around the updraft area, as it follows from the recent observational and numerical evidence (Denby et al, 2022; Griewank et al, 2020; Gu et al, 2021; Mallaun et al, 2019; Nair et al, 2020; Savre, 2021). We show that for such a profile of the convective vertical velocity we can obtain the subgrid fluxes without requiring that the fractional area occupied by the convection in a given grid box be very small.…”