Evaluation of the aerosol indirect effect in marine stratocumulus clouds : droplet number, size, liquid water path, and radiative impact

Data from nine stratocumulus clouds in the northeastern Pacific Ocean were analyzed to determine the effect of aerosol particles on cloud microphysical and radiative properties. Seven nighttime and two daytime cases were included. The number concentration of below-cloud aerosol particles (> 0.10 μm diameter) was highly correlated with cloud droplet number concentration. Droplet number concentrations were typically about 75% of particle number concentration in the range of particle concentrations studied (< 400 cm¯³). Particle number was anticorrelated with droplet size and with liquid water content in drizzle-sized drops. Radiative impact also depends upon cloud liquid water content and geometric thickness. Although most variability in these macroscopic properties of the clouds could be attributed to variability in the large-scale environment, a weak anticorrelation between particle concentration and cloud geometric thickness was observed. Because of these variations, no correlation between calculated cloud optical thickness or albedo and particle concentration was detectable for the data set as a whole. For regions with comparable liquid water contents in an individual cloud, higher particle concentrations did correspond to increased cloud optical thickness. These results verify that higher particle concentrations do directly affect the microphysics of stratiform clouds. However, the constant liquid water path assumption usually invoked in the Twomey aerosol indirect effect may not be valid

Examining the generalizability of research findings from archival data

This initiative examined systematically the extent to which a large set of archival research findings generalizes across contexts. We repeated the key analyses for 29 original strategic management effects in the same context (direct reproduction) as well as in 52 novel time periods and geographies; 45% of the reproductions returned results matching the original reports together with 55% of tests in different spans of years and 40% of tests in novel geographies. Some original findings were associated with multiple new tests. Reproducibility was the best predictor of generalizability—for the findings that proved directly reproducible, 84% emerged in other available time periods and 57% emerged in other geographies. Overall, only limited empirical evidence emerged for context sensitivity. In a forecasting survey, independent scientists were able to anticipate which effects would find support in tests in new samples

Sea-spray regulates sulfate cloud droplet activation over oceans

Sulfate aerosols are typically the dominant source of cloud condensation nuclei (CCN) over remote oceans and their abundance is thought to be the dominating factor in determining oceanic cloud brightness. Their activation into cloud droplets depends on dynamics (i.e. vertical updrafts) and competition with other potential CCN sources for the condensing water. We present new experimental results from the remote Southern Ocean illustrating that, for a given updraft, the peak supersaturation reached in cloud, and consequently the number of droplets activated on sulfate nuclei, is strongly but inversely proportional to the concentration of sea-salt activated despite a 10-fold lower abundance. Greater sea-spray nuclei availability mostly suppresses sulfate aerosol activation leading to an overall decrease in cloud droplet concentrations; however, for high vertical updrafts and low sulfate aerosol availability, increased sea-spray can augment cloud droplet concentrations. This newly identified effect where sea-salt nuclei indirectly controls sulfate nuclei activation into cloud droplets could potentially lead to changes in the albedo of marine boundary layer clouds by as much as 30%.The research leading to these results has received funding from SFI under MaREI; the European Union’s Seventh Framework Programme (FP7/2007–2013) project BACCHUS under grant agreement n_603445; Spanish Ministry of Economy and Competitiveness (MINECO) as part of the PEGASO (Ref.: CTM2012-37615) and BIONUC (Ref: CGL2013-49020-R) projects. The Antarctic cruise that led to this study was organised by R. Simo and M. Dall’Osto from the Institut de Ciéncies del Mar (CSIC), Barcelona, Catalonia, Spain.peer-reviewe

The Chilean Coastal Orographic Precipitation Experiment: Observing the influence of microphysical rain regimes on coastal orographic precipitation

The Chilean Coastal Orographic Precipitation Experiment (CCOPE) was conducted during the australwinter of 2015 (May–August) in the Nahuelbuta Mountains (peak elevation 1.3 km MSL) of southern Chile(388S). CCOPE used soundings, two profiling Micro Rain Radars, a Parsivel disdrometer, and a rain gaugenetwork to characterize warm and ice-initiated rain regimes and explore their consequences for orographicprecipitation. Thirty-three percent of foothill rainfall fell during warm rain periods, while 50% of rainfall fellduring ice-initiated periods. Warm rain drop size distributions were characterized by many more and relativelysmaller drops than ice-initiated drop size distributions. Both the portion and properties of warm and ice-initiated rainfall compare favorably with observations of coastal mountain rainfall at a similar latitude inCalifornia. Orographic enhancement is consistently strong for rain of both types, suggesting that seeding fromice aloft is not a requisite for large orographic enhancement. While the data suggest that orographic en-hancement may be greater during warm rain regimes, the difference in orographic enhancement betweenregimes is not significant. Sounding launches indicate that differences in orographic enhancement are not easilyexplainable by differences in low-level moisture flux or nondimensional mountain height between the regimes