Long-Range Aerosol Transport via Rossby Wave Breaking during Atmospheric River Events on the Western U.S.

Previous studies show that heavy precipitation events, known as Atmospheric Rivers (ARs), are highly affected by upper-level Rossby Wave Breaking (RWB), also known as Potential Vorticity (PV) intrusion. However, the impact of long-range aerosol transport on ARs remains elusive. In this study, the role of PV (RWB) on long-range aerosol transport is demonstrated by linking the two with convection and its relationship with precipitation. Using March 2016 and February 2017 AR events, this study aims to understand the exact link between convection associated with RWB, and surface-based and airborne aerosol transport and precipitation. Synoptic conditions were investigated for ARs in terms of sea level pressure and clouds associated with PV before, during, and after AR events. Datasets employed include NASA Modern Era Retrospective analysis for Research and Applications 2 (MERRA2), NASA Moderate Resolution Imaging Spectroradiometer (MODIS) satellite, and European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-interim.

Preliminary results show that convection likely occurs behind high PV troughs, causing lower troposphere destabilization in the course of AR events. MODIS Aerosol Optical Depth (AOD) data clearly showed high AOD moving across the northern Pacific from Asia over time, peaking over the western U.S. around the time of ARs. Additionally, over the western US, aerosol impact of: dust, black carbon (BC), sulphate aerosol (SO4), and organic carbon (OC) on AR precipitation and air quality was examined to see whether they are transported with clouds associated with RWB to the remote region. Trajectory analysis confirmed that the significant portion of air mass came from the regions with relatively high aerosols. Regression analysis indicated that there was a relatively high negative correlation between BC (SO4, dust) and precipitation during the March 2016 (February 2017) case. The study favors the hypothesis that convection associated with RWB can act as a potential carrier of aerosol at a distance during AR events.