Cloud Trends from 15 Years of Atmospheric Infrared Sounder Observations

Establishing robust satellite-based benchmarks of secular cloud trends is an ongoing challenge because of imperfect radiometric calibration, sampling, and sensitivity limitations, and many additional reasons related to the satellite orbit, instrument, and retrieval algorithm. The Atmospheric Infrared Sounder (AIRS) has now provided 15+ years of radiances with very stable infrared radiometry that has enabled the detection of statistically significant trends in some cloud properties. We describe trends in effective cloud fraction (ECF), cloud top temperature (CTT), cloud thermodynamic phase (liquid and ice), and ice cloud optical thickness (COT) and cloud effective radius (CER) with AIRS observations. While the ECF does not exhibit statistically significant trends in the extratropical storm tracks, statistically significant trends emerge when liquid and ice phase clouds are partitioned, with clear decreases in ice cloud frequency and COT, and increases in liquid cloud frequency. Statistically significant increases in ice CER are observed over most of the globe. Trends in CTT strongly depend on whether the clouds are liquid or ice phase, with liquid clouds warming and ice clouds cooling. The cloud trends inferred from AIRS appear to exhibit similarity to climate GCM predictions in the Coupled Model Inter-comparison Project Phase 5 (CMIP5) model ensemble results.