Observation-based study on aerosol optical depth and particle size in partly cloudy regions

Area of Science:

• Atmospheric Science
• Remote Sensing
• Climate Science

Background:

• Aerosol-cloud interactions are crucial for climate modeling.
• Previous studies suggest a positive correlation between aerosol optical depth (AOD) and cloudiness.
• Understanding these interactions is key to improving climate projections.

Purpose of the Study:

• To investigate the statistical relationship between aerosol properties and low-altitude cloudiness.
• To examine global patterns of aerosol-cloud interactions using satellite data.
• To determine the influence of clouds on aerosol size distributions.

Main Methods:

• Analysis of a global dataset from Moderate Resolution Imaging Spectroradiometer (MODIS) observations.
• Integration of satellite data with MERRA-2 global reanalysis data.
• Comparison of different aerosol retrieval algorithms and quality assessment flags.

Main Results:

• A strong, consistent positive correlation between cloudiness and AOD globally, across seasons and aerosol types (sulfate, dust, carbon, sea salt).
• AOD is typically 30-50% higher on cloudier days.
• Aerosol size distributions shift toward smaller particles near clouds, indicating a greater cloud-related increase in fine mode AOD.
• Aerosol particle size can increase near clouds even in regions where it generally decreases with cloudiness, suggesting environmental influences.

Conclusions:

• The observed cloudiness-AOD correlation is robust and not solely due to cloud detection uncertainties.
• Clouds appear to influence aerosol properties, particularly fine mode aerosols.
• Quality assessment flags are valuable for identifying cloud-affected aerosol observations.