Submitted as: model description paper 14 Jun 2021

Submitted as: model description paper | 14 Jun 2021

Review status: a revised version of this preprint is currently under review for the journal GMD.

Bulk hydrometeor optical properties for microwave and sub-mm radiative transfer in RTTOV-SCATT v13.0

Alan Jon Geer1, Peter Bauer1, Katrin Lonitz1, Vasileios Barlakas2, Patrick Eriksson2, Jana Mendrok2,a, Amy Doherty3, James Hocking3, and Philippe Chambon4 Alan Jon Geer et al.
  • 1ECMWF, Shinfield Park, Reading, RG2 9AX, UK
  • 2Department of Space, Earth and Environment, Chalmers University of Technology, Gothenburg, Sweden
  • 3Met Office, UK
  • 4CNRM, Université de Toulouse, Météo-France, CNRS, Toulouse, France
  • anow at: Deutscher Wetterdienst, Offenbach, Germany

Abstract. Satellite observations of radiation in the microwave and sub-mm spectral regions (broadly from 1 to 1000 GHz) can have strong sensitivity to cloud and precipitation particles in the atmosphere. These particles (known as hydrometeors) scatter, absorb and emit radiation according to their mass, composition, shape, internal structure, and orientation. Hence, microwave and sub-mm observations have applications including weather forecasting, geophysical retrievals and model validation. To simulate these observations requires a scattering-capable radiative transfer model and an estimate of the bulk optical properties of the hydrometeors. This article describes the module used to integrate single-particle optical properties over a particle size distribution (PSD) to provide bulk optical properties for the Radiative Transfer for TOVS microwave and sub-mm scattering code, RTTOV-SCATT, a widely-used fast model. Bulk optical properties can be derived from a range of particle models including Mie spheres (liquid and frozen) and non-spherical ice habits from the Liu and Atmospheric Radiative Transfer Simulator (ARTS) databases, which include pristine crystals, aggregates and hail. The effects of different PSD and particle options on simulated brightness temperatures are explored, based on an analytical two-stream solution for a homogeneous cloud slab. The hydrometeor scattering "spectrum" below 1000 GHz is described, along with its sensitivities to particle composition (liquid or ice), size and shape. The optical behaviour of frozen particles changes in the frequencies above 200 GHz, moving towards an optically thick and emission-dominated regime more familiar from the infrared. This region is previously little explored but will soon be covered by the Ice Cloud Imager (ICI).

Alan Jon Geer et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on gmd-2021-73', Anonymous Referee #1, 14 Jul 2021
  • RC2: 'Comment on gmd-2021-73', Anonymous Referee #2, 14 Jul 2021
  • AC1: 'Author comment on gmd-2021-73', Alan Geer, 06 Sep 2021

Alan Jon Geer et al.

Alan Jon Geer et al.


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Short summary
Satellite observations of radiation from the earth can have strong sensitivity to cloud and precipitation in the atmosphere, with applications in weather forecasting and the development of models. To compute the radiation received at the satellite sensor using radiative transfer theory requires a simulation of the optical properties of a volume containing a large number of cloud and precipitation particles. This article describes the physics used to generate these “bulk” optical properties.