A radiative consistency approach to comparing AIRS and MODIS cloud retrievals

In this presentation we will introduce and demonstrate a radiative consistency approach to comparing cloud retrievals from different, but essentially coincident, satellite instruments. The Moderate Resolution Imaging Spectroradiometer (MODIS) and the Atmospheric Infrared Sounder (AIRS) are on the Aqua Satellite. Both instruments provide infrared-based retrievals of cloud top temperature and effective cloud fraction, but different techniques are used and the products are produced at different spatial resolutions. MODIS retrievals are at 5 km, with the assumption of a single cloud layer within the field of view. AIRS retrievals are at approximately 45 km resolution, with up to two cloud layers within the field of view. The MODIS retrieval algorithm is based on either CO₂-slicing channels or a window technique, depending on the type of cloud, whereas the AIRS retrieval algorithm begins with the cloud-clearing approach and uses CO₂ channels.

We will show how effective brightness temperature, which is essentially an effective cloud fraction-weighted brightness temperature, can be used as a measure of radiative consistency in cloudy scenes and to help interpret comparisons of MODIS and AIRS cloud top temperature retrievals. Application of the effective brightness temperature approach to multiple days of accurately co-located MODIS and AIRS data will show that the level of radiative consistency is high in most cloudy scenes, even when the retrievals of cloud top temperature and effective cloud fraction disagree. We will discuss causes and frequencies of MODIS and AIRS cloud property retrieval agreement and disagreement.