CloudSat and Aura MLS Constrain upon Ice Cloud Particle Size Distribution

Abstract:

Despite years of measurements, ice clouds remain one of the largest uncertainties in climate models. In part, because individual cloud ice remote sensing techniques or instruments observe only portions of the complete ice particle size distribution (PSD) and therefore, to deduce cloud ice water, the retrievals need to assume a given PSD. Uncertainty in such knowledge currently accounts for most of the factor of two or greater uncertainties in satellite based cloud ice water content measurements. The Aura-Microwave Limb Sounder (MLS) observes limb microwave emissions from the Earth’s atmosphere at 118, 191, 240, 640 and 2500 GHz enabling cloud ice measurements across a large range of particle sizes.
This study explores the synergy of collocated A-train radar backscatter CloudSat measurements and MLS radiances in search of a better understanding of cloud ice PSDs. For each “scene” jointly observed by CloudSat and MLS, we quantify the ability of each of several candidate PSDs to account for the observed signals. First, a CloudSat retrieval is used to determine the cloud altitude and location along the MLS line of sight as well as the cloud ice water content that, for a given PSD, would give rise to the observed CloudSat signal. Then, for each PSD, estimated MLS measurements are reconstructed, compared to those actually observed and a chi-squared metric is used to determined which PSD gives the best fit. We will discuss potential applications of this technique to studies of convection and the impacts of aerosol pollution on ice PSD.