Search

Ice nucleating particles (INPs) influence the timing and amount of precipitation in mixed-phase clouds by acting as seeds for supercooled liquid droplets to form ice upon. High-resolution, long-term measurements of ice nucleating particles (INPs) have been impeded by complex instrumentation that requires a trained on-site technician to operate or analyze offline. We have significantly updated the well-characterized continuous flow diffusion chamber (CFDC) instrument to run autonomously with minimal in-person handling and easy remote access. This new CFDC, the CFDC-Ice Activation Spectrometer (CFDC-IAS) was deployed for four months (October 2020-January 2021) at the mountain-top Storm Peak Laboratory site in Colorado and provided 5-minute resolution measurements daily at target temperatures of -20, -25, and -30 °C. Concentrations of INPs across all temperatures had a median value of 6 per standard liter (sL-1 ), and a mean of 10 sL -1 with a range of ~0-470 sL-1. The CFDC-IAS was served once a week by a technician who changed out diffusion dryer desiccant and replaced the nitrogen tank as needed, and otherwise was operated remotely for desired changes in the sampling routine. [ABSTRACT FROM AUTHOR]

Glaciogenic cloud seeding has long been practiced as a way to increase water availability in arid regions, such as the interior western United States. Many seeding programs in this region target cold-season orographic clouds with ground-based silver iodide generators. Here, the "seedability" (defined as the fraction of time that conditions are suitable for ground-based seeding) is evaluated in this region from 10 years of hourly output from a regional climate model with a horizontal resolution of 4 km. Seedability criteria are based on temperature, presence of supercooled liquid water, and Froude number, which is computed here as a continuous field relative to the local terrain. The model's supercooled liquid water compares reasonably well to microwave radiometer observations. Seedability peaks at 20%–30% for many mountain ranges in the cold season, with the best locations just upwind of crests, over the highest terrain in Colorado and Wyoming, as well as over ranges in the northwest interior. Mountains farther south are less frequently seedable, because of warmer conditions, but when they are, cloud supercooled liquid water content tends to be relatively high. This analysis is extended into a future climate, anticipated for later this century, with a mean temperature 2.0 K warmer than the historical climate. Seedability generally will be lower in this future warmer climate, especially in the most seedable areas, but, when seedable, clouds tend to contain slightly more supercooled liquid water. Significance Statement: Cloud seeding has long been practiced commercially as a way to increase water availability in arid regions, such as the interior western United States. Many seeding programs in this region target cold-season clouds over mountains with ground-based silver iodide generators. Here, we use 10 years of hourly output from a well-calibrated regional climate model with a horizontal resolution of 4 km to determine how often suitable clouds are present over mountain ranges in the interior western United States. We find that suitable clouds are present 20%–30% of the time over many mountain ranges in the cold season, with the best locations just upwind of crests, especially over ranges in the northwest interior and greater Yellowstone area. Mountains farther south are less frequently seedable, but when they are, the seeding may be relatively more effective in producing extra precipitation—although this study does not attempt to quantify that extra precipitation. In a future climate, anticipated for later this century, seedable clouds become less common in the interior western United States, but cloud seeding may be slightly more effective. [ABSTRACT FROM AUTHOR]