Idealized Simulations of a Squall Line from the MC3E Field Campaign Applying Three Bin Microphysics Schemes: Dynamic and Thermodynamic Structure

Abstract

The squall-line event on 20 May 2011, during the Midlatitude Continental Convective Clouds (MC3E) field campaign has been simulated by three bin (spectral) microphysics schemes coupled into the Weather Research and Forecasting (WRF) Model. Semi-idealized three-dimensional simulations driven by temperature and moisture profiles acquired by a radiosonde released in the preconvection environment at 1200 UTC in Morris, Oklahoma, show that each scheme produced a squall line with features broadly consistent with the observed storm characteristics. However, substantial differences in the details of the simulated dynamic and thermodynamic structure are evident. These differences are attributed to different algorithms and numerical representations of microphysical processes, assumptions of the hydrometeor processes and properties, especially ice particle mass, density, and terminal velocity relationships with size, and the resulting interactions between the microphysics, cold pool, and dynamics. This study shows that different bin microphysics schemes, designed to be conceptually more realistic and thus arguably more accurate than bulk microphysics schemes, still simulate a wide spread of microphysical, thermodynamic, and dynamic characteristics of a squall line, qualitatively similar to the spread of squall-line characteristics using various bulk schemes. Future work may focus on improving the representation of ice particle properties in bin schemes to reduce this uncertainty and using the similar assumptions for all schemes to isolate the impact of physics from numerics.

Simulating a Mesoscale Convective System Using WRF With a New Spectral Bin Microphysics: 1: Hail vs Graupel

“…The simulated MCSs in all versions have geometric similarity with the observed system, realistic Ze at different altitudes, and realistic area ratios between convective and stratiform regions. Analysis of the MCE structures simulated by FSBM‐1 (e.g., Xue et al, ) shows that the differences between results of the FSBM‐2 versions are smaller than those between FSBM‐2 and FSBM‐1. Nevertheless, there were noticeable and, at times, substantial differences between H43, H33, G33, and H43‐noR. It is important to take into account the existence of large hail particles in the convective updrafts.…”

“…The second size distribution describes high‐density particles (e.g., graupel) with a typical density of 0.4 g/cm 3 . FSBM‐1 has been used in various configurations for simulations of tropical cyclones (Khain et al, ), isolated convective storms (Lynn & Khain, ), rain events (Lynn et al, ; Noppel et al, ), and the MC3E case (Xue et al, ). After 2009 several modified versions of FSBM‐1 have been developed and widely used for simulations of different cloud‐related phenomenon and their sensitivity to aerosols (Khain & Pinsky, ).…”

“…The cross sections in all the simulations (Figure 7) clearly show two separate areas of enhanced Ze: the first area is the leading convective line and the second area is within the stratiform part of the DCS, about 100-150 km behind the convective area. The formation of the area of enhanced Ze within the stratiform region was simulated by Xue et al (2017) using different bin-microphysics schemes. This area likely forms by aggregation of ice particles detrained from the convective region.…”

“…MCSs have been simulated using different microphysical schemes coupled to various CRMs (e.g., Fan et al, , , ; Fierro et al, , ; Han et al, ; Li et al, , ; Marinescu et al, ; Milbrandt & Morrison, ; Liu et al, ; Morrison et al, , ; Tao et al, , , ; Xue et al, ; Zhang & Gao, ). A typical problem of CRM squall‐line simulations is the underestimation of the stratiform area and corresponding stratiform rain, as well as overestimation of the vertical velocity and radar reflectivity in the convective area (Baldauf et al, ; Fan et al, ; Fan, Han, et al, ; Han et al, ; Lebo et al, ; Morrison et al, ; Varble et al, , ).…”

“…In most CRMs that use either bulk‐microphysical parameterization or FSBM‐1 schemes, high‐density hydrometeors are typically represented by graupel (Khain et al, ; Lynn et al, ; Xue et al, ). In FSBM‐1, the maximum graupel diameter is 0.88 cm with a graupel density of 0.4 g/cm 3 .…”