A Far Infrared Radiative closure experiment for Antarctic Clouds

Most uncertainties in the characterization of the longwave emission of cirrus clouds come from the lack of spectrally resolved measurements in the far-infrared (FIR) spectral region from 100 to 667 cm-1 (100-15 ?m). The Antarctic Plateau represents one of best place where these measurements can be performed because the high-altitude and the very dry conditions allow to sound efficiently the infrared spectrum down to the FIR region. The purpose of this research is the spectral characterization of ice and mixed-phase clouds in order to evaluate the radiative models in the FIR regime, where the clouds effect is very strong, and systematic spectral measurements are scarcely available. This can be accomplish by means of the synergy of different instruments installed at Dome-C, such as a Fourier transform spectroradiometer (REFIR-PAD), operating in the spectral broad band between 100-1600 cm-1 (6-100 mu) since 2012, the backscattering/depolarization lidar at 532/1064 nm, a micro rain radar (MRR) at 24 GHz , an ice-camera and halo-camera. The retrieval of the optical and micro-physical properties (effective diameters of the ice crystals and optical depth) of ice and mixed-phase precipitating clouds is performed by using a suitable code with the REFIR-PAD and lidar measurements, and they can be used to estimate the cloud reflectivity at the radar frequency for comparison with the MRR and ice camera data.