An Airborne Profiling Radar Study of the Impact of Glaciogenic Cloud Seeding on Snowfall from Winter Orographic Clouds

Abstract

Data from an airborne vertically pointing millimeter-wave Doppler radar are used to study the cloud microphysical effect of glaciogenic seeding of cold-season orographic clouds. Fixed flight tracks were flown downstream of ground-based silver iodide (AgI) generators in the Medicine Bow Mountains of Wyoming. Composite data from seven flights, each with a no-seeding period followed by a seeding period, indicate that radar reflectivity was higher near the ground during the seeding periods. Several physical considerations argue in favor of the hypothesis that the increase in near-surface reflectivity is attributed to AgI seeding. While the increase in near-surface reflectivity and thus snowfall rate are statistically significant, caution is warranted in view of the large natural variability of weather conditions and the small size of the dataset.

Implementation of a Silver Iodide Cloud-Seeding Parameterization in WRF. Part II: 3D Simulations of Actual Seeding Events and Sensitivity Tests

“…The average ice crystal number concentration of the seeded clouds Figures 4bl-4b4 show the LWP'' of the control simwas found to range between 25 and 100 L~' for the ulations (color shaded) and regions of Agi number ground-based seeding cases and-150 L"'for the airborne-concentration of greater than lO^'m"'^ at 3000 m MSL seeding case (not shown). These simulated ice concentrations were in good agreement with previous studies (Deshler et al 1990;Meyers et al 1995;Reisin et al ^n ¡s the supercooled LWP since the temperatures at the LCL 1996; Geerts et al 2010).…”

Boundary Layer Turbulence and Orographic Precipitation Growth in Cold Clouds: Evidence from Profiling Airborne Radar Data

“…Matrosov (2007) computed Z-S relationships for this radar frequency based on Mie scattering theory, assuming different ice size distributions, shapes, and densities. His relationship S 5 0.11Z 1.25 (S in mm h 21 , Z in mm 6 m 23 ) appears to apply for the storms analyzed herein (Geerts et al 2010).…”

“…2g). The frontal snowband was rather deep, and clouds became shallower following cold-frontal passage (Geerts et al 2010).…”

Governing Experimental Responses

“…This programme had a major observational component Geerts et al, 2010), a numerical modeling component Xue et al, 2013a and2013b) and a randomized cloud seeding experiment that started in 2006 and will be completed in 2014. Although the statistical results from the randomized experiment is not yet available because the experiment is still ongoing, Geerts et al (2010) provided, for the first time, experimental evidence using vertically pointing airborne radar data that ground-based silver iodide seeding can increase reflectivity in the PBL in orographic snow, producing storms over complex terrain. further the science in this field and to support the work of the Expert Team.…”