Observed Microphysical Evolution of a Seeded Cloud during SNOWIE

The 2017 SNOWIE field campaign yielded a comprehensive observational dataset to better understand microphysical cloud and precipitation processes within wintertime orographic clouds in the presence of glaciogenic cloud seeding. Analyses of observations from SNOWIE continue to improve understandings of natural orographic cloud processes while significantly advancing research on the impact of cloud seeding. For instance, French et al. (2018; PNAS) described the initiation, growth, and fallout of ice crystals due to glaciogenic seeding, Friedrich et al. (2021; JAMC) established a connection between seeding and the microphysical properties of clouds, and Friedrich et al. (2020; PNAS) quantified seeding impacts on precipitation at the surface in three SNOWIE cases. Analyses from all of these studies were used to inform and validate the modeling study of Xue et al. (2022; JAMC).

In this study, we analyze another case from SNOWIE, IOP1 that occurred on January 8, 2017. Similar to three other cases (IOPs 5, 6, and 9) reported in the literature (Tessendorf et al 2019; BAMS) IOP1 shows clear evidence of ice production resulting from airborne cloud seeding. But unlike those cases, IOP1 contained widespread natural precipitation.

The IOP followed an overrunning snow band associated with a fast-moving jet streak. Observations from the University of Wyoming King Air research aircraft recorded natural cloud conditions with near cloud top temperatures between −11°C and −16 °C at flight levels from 3900 and 4800 m MSL. Maximum cloud droplet concentrations were only 35 cm^-3. Significant drizzle, in isolated pockets, was observed with drizzle mass content up to 1.0 g m^-3 collocated with ice crystal concentrations of no more than 0.3 L^-1 (Majewski and French 2020; ACP). Other regions that contained higher ice concentrations were associated with regions of light snow. Data from a ground-based X-band radar and an airborne W-band radars allow us to describe natural precipitation development and pockets of enhanced echo intensity associated with glaciogenic seeding. Detailed in situ measurements reveal the microphysical evolution of both the natural and seeded cloud. We utilize methodologies established in previous SNOWIE cases to compare microphysical characteristics of seeded and natural cloud, which will be used to constrain and validate future numerical simulations.