Colloquium: Thurs, 4/26, 3:00 pm, EN6085A:

Abstract:

Atmospheric infrared sounder (AIRS), along with microwave sounders advanced microwave sounding unit A (AMSU-A), and humidity sounder for Brazil (HSB) form a sophisticated sounding suite deployed in NASA earth observing system (EOS) satellite Aqua. The sounding suite is designed to measure water vapor and temperature profiles on global scale at radiosonde accuracy. However, a study led by Dr. Whiteman at NASA/GSFC has shown that retrieved water vapor profiles show a persistence bias of up to 90% in the upper troposphere in the presence of, or in the vicinity of cirrus clouds. In an approach to improve the retrieval from this sounding suite a database of the best-estimate profiles of the atmospheric state variables is being constructed using dedicated radiosondes and Raman lidar measurements at two atmospheric radiation measurement (ARM) validation sites at Southern Great Plains (SGP) site in northern Oklahoma and tropical Western Pacific (TWP) site in Nauru Island. The database also contains radiance measurements from the AIRS, and cloudy condition information within the AIRS footprint.

This research is part of the process of the development of the database and focuses on providing cloudy condition database within the AIRS footprints by using moderate resolution imaging spectroradiometer (MODIS) measurements that have higher spatial resolution than AIRS. A collocation algorithm is developed to find MODIS pixels with AIRS pixels. Cloud fraction as well as cloud top height, optical depth, and effective radius are provided to characterize cloud condition within AIRS pixels. A comparison between the MODIS retrieved cloud top pressure (CTP) and AIRS retrieved CTP is presented to evaluate AIRS cloud detection. The MODIS cloud detection and CTP retrievals are validated by micro pulse lidar (MPL) and millimeter wave cloud radar (MMCR) measurements at the ARM validation sites. The validation results show that MODIS measurements give a good estimate of the cloudy condition within the AIRS footprint though MODIS retrievals have difficulties in detecting optically thin upper tropospheric cirrus clouds, especially in the presence of lower level clouds.