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Communication Dans Un Congrès Année : 2020

A Microwave Closure Experiment: Testing the Physical Consistency of Microwave Scattering Models.

Résumé

A microwave closure experiment is presented that is used to test the physical consistency of the single-scattering properties of ice aggregate models using the Independent Monomer Approximation (IMA). The IMA is an approximation where the interacting fields between the monomers that make up the ice aggregate are ignored, but other interactions are included. IMA has been applied to interpret radar reflections at 35 and 95 GHz, as well as observed polarised brightness temperature depressions (btds) at 243 GHz. This unique set of observations were obtained over deep frontal ice cloud, from the German HALO, the French Falcon 20, and the FAAM BAe-146 aircraft. On board these aircraft were the 35, 95 GHz radars, and the ISMAR spectral-like radiometer, which measured polarised btds at 243 GHz. The FAAM aircraft also carried a microphysics suite of instrumentation, which made vertical profile measurements of the ice crystal shapes, bulk ice water content, and particle size distributions. From the measurements, the ice crystal shapes and mass-dimension were obtained as functions of distance from the cloud top. The various cloud layers were modelled using columnar and dendritic particles, following the observed mass-dimension relations to within 20%. From the models, and under the assumption of horizontal orientation but randomly oriented in the horizontal plane, the radar backscattering cross sections and the SSPs were obtained at the three different frequencies. The radar reflectivity at the two frequencies was obtained from the radar backscattering cross sections, inclusive of attenuation at 95 GHz, and the measured ISMAR polarisation at 243 GHz was simulated using the ARTS model. It is shown that the two radar reflectivities can be simulated to generally within the standard deviations of the measurements at all altitudes considered using the theoretical models. Btds of up to about 8 K were observed using ISMAR. Such large btds can only be simulated using the assumption of horizontally oriented ice crystals, using a single dendrite model to represent the very lowest layer of the model cloud. We show that it is possible to simulate consistently the observed radar reflections and the ISMAR observed btds using microwave scattering models that are consistent with in-situ microphysics observations.
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Dates et versions

insu-04463124 , version 1 (16-02-2024)

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K. Mccusker, C. Westbrook, A. J. Baran, P. Eriksson, S. Fox, et al.. A Microwave Closure Experiment: Testing the Physical Consistency of Microwave Scattering Models.. American Geophysical Union, Fall Meeting 2020, Dec 2020, Online, Unknown Region. pp.abstract #A197-05. ⟨insu-04463124⟩
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