Evaluating the meteorological conditions associated with dusty atmospheric rivers

Abstract:

Trans-Pacific dust has been shown to influence the micro-physical characteristics of atmospheric rivers that make landfall along the U.S. west coast. Atmospheric Rivers (AR) reaching North America provide valuable water resources, but also can produce damaging floods. While substantial research has been devoted to understanding the structure and meteorological drivers of ARs, far less is known about the conditions that lead to the presence of dust within and around these storms. Here, we utilize an 18-year record of AR dust scores combined with satellite, reanalysis, and observational meteorological data to understand the drivers of ARs embedded within dusty environments, or "dusty ARs", as compared to ARs in more pristine environments. We find that dusty ARs are associated with transport of dust from the east Asian coast to North America. Dusty ARs are associated with conditions that are especially conducive to transport of dust across the Pacific; namely, enhanced mid- to upper-tropospheric westerly winds over Asian dust source regions and over the Pacific. In contrast, ARs in more pristine environments are associated with a persistent ridge over the central Pacific, which blocks zonal westerly flow, as well as continental dust. The vertical structure of dust within AR-associated extra-tropical cyclones is characterized by descent of dust layers across the cold-frontal boundary associated with cold dry air that is forced below the warm air on the warm side of the front. This may allow dust transported in the mid- and upper-troposphere to descend to the level of moisture transport within an AR.