Effects of ice particle shape and orientation on polarized microwave radiation for off‐nadir problems

The effect of ice crystal shape and orientation from high altitude clouds (9 to 10 km height) on the angular distribution and state of polarization of microwave radiation emerging from the earth's atmosphere is investigated. The potential effects of nonspherical shapes are studied at 200 GHz and for two different shapes: Oblate and prolate spheroids with a preferred orientation of the axis of symmetry and an aspect ratio of 5.0 and 0.2, respectively. The results show strong effects of shape and orientation on both the total intensity and polarization state. Propagation directions close to the horizontal are of special interest to troposphere/lower stratosphere microwave limb-sounding investigations. Although the presented calculations do not consider realistic ice clouds with hexagonal particles and the limb sounding geometry is not explicitly taken into account, the results obtained for large off-nadir angles lead to the conclusion that particle shapes, especially in case of particles with preferred axis of orientation, have a significant effect on intensity (up to 15 K) and polarization difference (up to 30 K).

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