Transpacific Transport of Dust and Pollution around Mid-Latitude Cyclones as Revealed by Fine-Resolution Satellite Observations and GEOS-5 Simulations

Trans-Pacific transport of desert dust and man-made pollution is a year-round phenomenon that has important implications for air quality, weather, and climate in North Pacific basin, North American continent, and even beyond. Mid-latitude cyclones (MCs), which are frequently developed over North Pacific and form the storm tracks, play an important role in determining the route and efficiency of dust and pollution being transported from Asia to North America and the Arctic. The atmospheric circulations and weather patterns around MCs have complex, fast evolving, and distinctive structures in both horizontal and vertical dimensions. However, it is not fully understood how the dust and pollution are processed and redistributed often by multiple MCs during a week-long trans-Pacific journey, because of the lack of systematic in situ measurements and the oversimplified representations of complex processes in models. Owing to their routine sampling over a decadal time span, fine-resolution satellite measurements offer an unprecedented opportunity of revealing the evolution of aerosol during the lifecycle of MCs and providing a climatology of aerosol structures around MCs. In this study, we investigate the evolution of three-dimensional aerosol distribution during the lifecycle of two MCs over North Pacific in January- March, 2017 by using the CALIPSO lidar measurements of aerosol vertical profiles in clean columns between clouds and above clouds and the MODIS 3km-resolution measurements of aerosol optical depth. The MODIS measurements clearly show that aerosol swirls into the cyclone center through the warm sector. The CALIPSO lidar passing through the storm center reveals a poleward, slant rise (up to 8 km) of dust and pollution mixture in the warm sector that is detached from the boundary layer aerosol and persists throughout the lifecycle of MCs. This provides a line of observational evidence that MCs may contribute to the formation and persistence of the observed high-altitude dust layer across North Pacific. The GEOS-5 simulations well capture the poleward rise of aerosol plume structure but significantly underestimate the magnitude of aerosol extinction. Future work will include more case studies and the composite analyses of all identified North Pacific MCs over the 2007-2018 period.