Aerosol-Cloud-Precipitation Interactions During STORMVEX

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Description

One of the motivating aspects of StormVEx was to collect in situ microphysical measurements of cloud and snow properties at Storm Peak Laboratory (SPL) while instruments below the lab collected typical remote-sensing measurements. The Scanning W-band Cloud Radar (SWACR) routinely pointed directly at the lab so that we have coincident radar reflectivity measurements and in situ microphysics. One of our objectives has been to analyze this coincident data to determine the microphysical properties of the snow such as mass-dimensional relationships. Such relationships are typically assumed and tend to cause very large uncertainties in microphysical retrievals. To this end we have created a record of mixed-phase microphysics from the raw 2-D imagery and cloud probe data by fitting the PSDs with bimodal (cloud and precipitation) gamma functions. Additionally, the cloud probe data were reprocessed using OASIS software. In general, the average 1-D and 2-D particle size distributions overlap quite well. The largest discrepancy appears to be for the small crystals (75-200 µm), and is described. To interpret the radar data in terms of the microphysics, we have developed a T-Matrix radar-scattering application that gives co- and cross-polar backscatter cross sections for the geometry of the radar-lab set up. These two adaptations allow us to characterize the microphysical properties of the snow using an optimal estimation retrieval algorithm. The results of this analysis are described. The second aim of this study is to test for a statistically significant connection between New Particle Formation (NPF) and growth to Cloud Condensation Nuclei (CCN). Previous work at SPL has shown a frequent occurrence of NPF events, documented seasonality, and demonstrated an association with elevated Sulfur Dioxide (Hallar et al., 2011 and 2016). During the StormVEx field campaign, NPF was observed on 29 of the 173 measurement days (17% of the time) at SPL. The growth rates at SPL were 7.6 +/- 5.4 nm/hr. NPF was more frequent at Christy Peak (lower elevation site) during StormVEx. In fact, NPF was observed 75 of the 159 measurement days (47%). These events had a grown rate of 5.7 +/- 4.5 nm/hr. SPL was frequently in cloud during the StormVEx field campaign, which limited NPF days. A correlation was investigated between days with NPF and enhanced CCN concentrations. Statistical analysis was conducted on these data sets to determine significance.