3-D polarised simulations of space-borne passive mm/sub-mm midlatitude cirrus observations: a case study

Abstract

Abstract. Global observations of ice clouds are needed to improve our understanding of their impact on earth's radiation balance and the water-cycle. Passive mm/sub-mm has some advantages compared to other space-borne cloud-ice remote sensing techniques. This paper presents detailed simulated observations for three such instruments, AMSU-B, CIWSIR, and EOS-MLS. The Monte-Carlo radiative transfer code, ARTS-MC, makes proper account of polarisation and uses 3-D spherical geometry. The actual field of view characteristics for each instrument are also accounted for. A 3-D midlatitude cirrus scenario is used, which is derived from Chilbolton cloud radar data and a stochastic method for generating 3-D ice water content fields. Although the main purpose of the work was to demonstrate the capability of accurately simulating observations of this type, the results suggest that cloud inhomogeneity will affect CIWSIR, and EOSMLS low tangent height observations via the beamfilling effect. Also, the results confirm that preferentially oriented ice crystals will produce significant polarisation effects.