MODIS comparisons with northeastern Pacific in situ stratocumulus microphysics.

Area of Science:

• Atmospheric Science
• Remote Sensing
• Cloud Physics

Background:

• Stratocumuli clouds play a crucial role in Earth's radiative balance.
• Accurate retrieval of cloud properties from satellite data is essential for climate modeling.
• Aircraft-based in situ measurements provide ground truth for validating satellite retrievals.

Purpose of the Study:

• To validate Moderate Resolution Imaging Spectroradiometer (MODIS) retrievals of cloud optical thickness (COT), cloud liquid water path (LWP), and cloud effective radius (re).
• To assess the performance of MODIS cloud property retrievals using data from the Marine Stratus/stratocumulus Experiment (MASE) and Physics of Stratocumulus Top (POST) campaigns.
• To identify factors contributing to discrepancies between MODIS and in situ measurements.

Main Methods:

• Utilized vertical sounding measurements from two aircraft field campaigns (MASE and POST).
• Calculated in situ COT, LWP, and re from 5m vertically averaged droplet probe measurements.
• Averaged MODIS 1km pixels along aircraft penetrations for direct comparison.

Main Results:

• MODIS COT showed strong correlations and a near 1:1 relationship with in situ measurements in the POST campaign.
• MODIS COT exceeded in situ COT in the MASE campaign, likely due to temporal differences.
• MODIS re exhibited a positive bias (20-30% greater than in situ) in POST, contributing to LWP biases (14-36% higher than in situ).
• Comparisons were best when temporal differences between MODIS and in situ data were under 20 minutes.

Conclusions:

• POST data validate MODIS COT retrievals.
• A positive MODIS effective radius bias was identified, which propagates to cloud liquid water path estimates.
• Temporal differences and potential cloud probe artifacts can affect the accuracy of satellite data validation.