Retrieving cirrus properties over the ARM tropical Western Pacific sites using AIRS observations (Formerly P1.35)

We present retrievals of cirrus optical depth (Tau) and effective particle size (Deff) using the high-spectral-resolution measurements of the Atmospheric Infrared Sounder, emphasizing nighttime, using the methodology of Kahn et al (2005, JGR) to detect candidate cases. Cirrus Tau and Deff are retrieved over the Atmospheric Radiation Measurement (ARM) program Tropical Western Pacific sites from AIRS radiances. The ARM cloud boundaries, as well as T(z) and RH(z) measurements from coincident sondes, are used as input to two different radiative transfer (RT) models: CHARTS, a high spectral resolution RT model with multiple scattering coupled to the LBLRTM, and OPTRAN, a fast RT model used in NWP modeling, that has been modified with a cirrus parameterization. The results of CHARTS is used to validate the accuracy of the parameterized OPTRAN model; this comparison will begin with clear sky cases. Next, the AIRS standard product cloud top pressure (CTP), T(z), and RH(z) that are coincident with the ARM site measurements are used as inputs to both RT models, and are compared to the ARM measurement-derived Tau and Deff. By using the ARM measurements as inputs to CHARTS, this serves as the "best guess" Tau and Deff retrieval. Applying the same methodology to the modified OPTRAN model, along with AIRS standard product retrievals, and comparing to the CHARTS simulations will allow us to extend cirrus Tau and Deff retrievals beyond the ARM sites and understand their error characteristics with increased confidence.