Impact of Cloud Microphysics on the Development of Trailing Stratiform Precipitation in a Simulated Squall Line: Comparison of One- and Two-Moment Schemes

Abstract

A new two-moment cloud microphysics scheme predicting the mixing ratios and number concentrations of five species (i.e., cloud droplets, cloud ice, snow, rain, and graupel) has been implemented into the Weather Research and Forecasting model (WRF). This scheme is used to investigate the formation and evolution of trailing stratiform precipitation in an idealized two-dimensional squall line. Results are compared to those using a one-moment version of the scheme that predicts only the mixing ratios of the species, and diagnoses the number concentrations from the specified size distribution intercept parameter and predicted mixing ratio. The overall structure of the storm is similar using either the one-or two-moment schemes, although there are notable differences. The two-moment (2-M) scheme produces a widespread region of trailing stratiform precipitation within several hours of the storm formation. In contrast, there is negligible trailing stratiform precipitation using the one-moment (1-M) scheme. The primary reason for this difference are reduced rain evaporation rates in 2-M compared to 1-M in the trailing stratiform region, leading directly to greater rain mixing ratios and surface rainfall rates. Second, increased rain evaporation rates in 2-M compared to 1-M in the convective region at midlevels result in weaker convective updraft cells and increased midlevel detrainment and flux of positively buoyant air from the convective into the stratiform region. This flux is in turn associated with a stronger mesoscale updraft in the stratiform region and enhanced ice growth rates. The reduced (increased) rates of rain evaporation in the stratiform (convective) regions in 2-M are associated with differences in the predicted rain size distribution intercept parameter (which was specified as a constant in 1-M) between the two regions. This variability is consistent with surface disdrometer measurements in previous studies that show a rapid decrease of the rain intercept parameter during the transition from convective to stratiform rainfall.

Evaluation of cloud microphysics schemes in simulations of a winter storm using radar and radiometer measurements

“…[8] The four microphysical schemes investigated in this paper include the Goddard bulk single-moment scheme [hereinafter GSFC, Tao and Simpson, 1993;Tao et al, 2003;Lang et al, 2007], the WRF single-moment 6-class scheme [hereinafter WSM6, [Hong and Lim, 2006], the Thompson scheme [hereinafter THOM, Thompson et al, 2008], and the Morrison double-moment scheme [hereinafter MORR, Morrison et al, 2005;Morrison et al, 2009]. Each scheme assumes six categories of water species: water vapor, cloud water, cloud ice, snow, graupel, and rain.…”

High‐resolution simulation over central Europe: assimilation experiments during COPS IOP 9c

“…The physics subset for this study contains the Morrison two-moment scheme for cloud microphysics which includes prognostic variables for the mass of water species (cloud water, cloud ice, rainwater, snow and graupel) and for their number concentrations (Morrison et al, 2009). This is suitable for higher-resolution applications and realistically represents microphysical processes .…”

“…Currently the focuses are set on planetary boundary-layer (PBL) schemes (e.g. Hong et al, 2006;Hong, 2007), new two-moment cloud microphysics schemes predicting not only hydrometeor quantities but also their number concentrations (Thompson et al, 2008;Morrison et al, 2009;Lim and Hong, 2010) and land-surface models (LSMs; e.g. Ek et al, 2003).…”

Suppression of Arctic Air Formation with Climate Warming: Investigation with a Two-Dimensional Cloud-Resolving Model

“…From a Lagrangian standpoint, clouds form as warm and moist air masses are advected and cooled over the Arctic Ocean in both summer, leading to ice melt and fog (Tjernstrom et al 2015), and winter, leading to bottom-heavy warming and weakening of surface inversions (Woods and Caballero 2016). A key finding from recent field studies in the Arctic is bimodality of the Arctic winter boundary layer: the coupled system of boundary layer and surface prefer to reside in either a ''radiatively clear'' state or an ''opaquely cloudy'' state (Stramler et al 2011;Morrison et al 2012). The radiatively clear state is characterized by clear skies or optically thin ice cloud, a colder surface and stronger surface inversion, and net surface radiative cooling of ;40 W m 22 , whereas the opaquely cloudy state is characterized by presence of cloud liquid, a warmer surface under a weaker elevated inversion, and near-zero surface net radiation.…”