Abstract
The aerosols that influence the initiation and amount of precipitation are cloud condensation nuclei (CCN), giant CCN, and ice nuclei. Aerosols are ever-present, their properties are variable, and their abundance is dynamic. Therefore, the extent of their impact on the outcome of meteorological contexts that are favorable for rain are difficult to specify. Rainfall can generate aerosols. Those of biological origin that are generated after rainfall can accumulate in a persistent manner over several weeks. Based on a recently developed index of rainfall feedback that focuses on persistent feedback effects and that represents the a priori sensitivity of rainfall to aerosols— of biological origin in particular—we mapped the intensity and patterns of rainfall feedback at 1,250 sites in the western United States where 100-year daily rainfall data were available and where drought is critically severe. This map reveals trends in feedback related to orographic context, geographical location, and season, among other trends. We describe an open-access tool (http://w3.avignon.inra.fr/rainfallfeedback/index.html) for mapping rainfall feedback on a planetary scale to provide a framework for future research to generate hypotheses and to establish rationale to choose field sites for experimentation. This will contribute to the long-term goal of developing a robust understanding of specific and contextual aerosol effects on rainfall applicable to forecasting and to land-use management.
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A supplement to this article is available online (10.1175/BAMS-D-15-00293.2)
