Abstract
Abstract. The next generation of European polar orbiting weather satellites will carry a novel instrument, the Ice Cloud Imager (ICI), which uses passive observations between 183 and 664 GHz to make daily global observations of cloud ice. Successful use of these observations requires accurate modelling of cloud ice scattering, and this study uses airborne observations from two flights of the Facility for Airborne Atmospheric Measurements (FAAM) BAe 146 research aircraft to validate radiative transfer simulations of cirrus clouds at frequencies between 325 and 664 GHz using the Atmospheric Radiative Transfer Simulator (ARTS) and a state-of-the-art database of cloud ice optical properties. Particular care is taken to ensure that the inputs to the radiative transfer model are representative of the true atmospheric state by combining both remote-sensing and in situ observations of the same clouds to create realistic vertical profiles of cloud properties that are consistent with both observed particle size distributions and bulk ice mass. The simulations are compared to measurements from the International Submillimetre Airborne Radiometer (ISMAR), which is an airborne demonstrator for ICI. It is shown that whilst they are generally able to reproduce the observed cloud signals, for a given ice water path (IWP) there is considerable sensitivity to the cloud microphysics, including the distribution of ice mass within the cloud and the ice particle habit. Accurate retrievals from ICI will therefore require realistic representations of cloud microphysical properties.
Highlights
Ice cloud properties including column-integrated ice mass, particle size and cloud altitude can have an important impact on weather and climate prediction
Results are shown for the particle habits, which give an ice mass that is consistent with the in situ observations as described above
In this paper we have performed a closure study comparing millimetre and sub-millimetre passive observations to radiative transfer simulations for two cirrus cloud cases. These two cases represent the best available FAAM aircraft observations for such a study and care was taken to ensure that the inputs to the radiative transfer model were as realistic as possible and were consistent with in situ measurements of the same clouds
Summary
Ice cloud properties including column-integrated ice mass (ice water path, or IWP), particle size and cloud altitude can have an important impact on weather and climate prediction They remain poorly constrained in current weather and climate models, in part due to the limited number of high-quality global observations (Waliser et al, 2009; Eliasson et al, 2013), and a recent study (Duncan and Eriksson, 2018) has shown that significant discrepancies still remain between both state-of-the-art satellite datasets and reanalyses. Visible and infrared observations are mostly sensitive to particles close to the cloud tops, whilst current microwave observations, which are capable of penetrating deeper into the clouds, are restricted to frequencies of up to 190 GHz and are relatively insensitive to all but the largest ice particles Active sensing techniques, such as the combined lidar–radar DARDAR dataset (Delanoë and Hogan, 2010), are capable of sensing the full cloud depth with ex-. Validation of radiative transfer models at submillimetre frequencies is currently rather limited due to the small number of available observations and the difficulty in obtaining co-located “ground truth” measurements
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
