Characterization of Dust Vertical Distribution and Their Impacts on Warm Clouds Using ARM Observations Over the Eastern North Atlantic

Mineral dust aerosols comprise roughly two-thirds of the total mass of all aerosols in the atmosphere, with sizes ranging more than three orders of magnitude in diameter (between 0.1 µm and 100 µm). Due to their broad size range, dust interacts with a wide spectrum of wavelengths by scattering and absorbing shortwave and longwave radiation, thereby contributing to the Earth's radiative budget and adding uncertainty to predicting future climate. A significant source of these uncertainties is the vertical distribution of aerosols. The interaction between dust and radiation, especially when clouds are present, is complex and depends on their relative vertical positioning, and its exact effects remain unclear. Here, we characterize dust’s vertical distribution and investigate its potential effects on warm low-level clouds at the U.S. Department of Energy Atmospheric Radiation Measurement (ARM) Eastern North Atlantic (ENA) site, representative of marine environments, between 2016 and 2022. We integrated multi-year sunphotometer retrievals, Raman Lidar measurements, and available Value-Added products of aerosol vertical profiles from the ARM facility with collocated data from Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) aboard the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite. Analysis of the vertically-integrated extinction coefficient over several layers of the atmosphere on clear-sky days shows that most dust loading is found between 1000 m and 3000 m over ENA. Furthermore, after classifying the dust position relative to clouds on days with single-layer clouds, we identified that most dust is located above clouds. In addition, cloud optical depth and liquid water path show a relationship with dust-layer optical depth as a function of the relative position of the dust layer; for the cases when dust was found above clouds, both cloud properties are directly proportional to dust optical depth, while the opposite is the case when the dust is below the cloud layer. Our results suggest that the vertical distribution of mineral dust aerosols influences physical and optical cloud properties, depending on the relative position of dust layers to clouds, highlighting the need to understand dust-cloud interactions better.