Using physicochemical data to examine giant sea salt particle relationships with stratocumulus clouds

This study uses airborne data from multiple field campaigns off the California coast to determine how well a size distribution parameter and a cloud water chemical measurement can capture the effect of giant sea salt particles on stratocumulus clouds. Near-surface measurements of particle concentration larger than 5 µm and cloud water chloride concentrations are significantly correlated and exhibit expected relationships with other parameters (e.g., surface wind, sub-cloud super-micrometer particle concentrations) that typically coincide with sea salt emissions. Furthermore, the cloud water data on average exhibit a chloride:sodium mass ratio (1.75) close to that of natural sea salt (1.80). Factors influencing the relationship between the two main salt proxies include precipitation rate and the standard deviation of the sub-cloud vertical velocity owing likely to scavenging effects and improved mixing/transport of sea salt to cloud base, respectively. Twelve sets of high and low chloride cloud cases are then compared (at fixed liquid water path and cloud drop number concentration) and show that the average drop spectra exhibit enhanced drop number at sizes exceeding 20 µm, especially above 30 µm. Higher enhancements of chloride in the 12 cases examined coincide with greater enhancements in drop effective radius and rain rate although the latter was less significant owing to other likely interfering factors. The effect of GCCN is greater for more polluted conditions (lower re) and less precipitating clouds with higher LWP, which is consistent with past studies.