Interpretation of Crystallographic Orientations in Accreted Ice

P. J. Rye Department of Physics, University of Western Australia, Nedlands

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W. C. Macklin Department of Physics, University of Western Australia, Nedlands

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Abstract

Measurements of c- and c′-axis orientation distributions in accreted ice deposits formed in the dry growth regime show peaks which may be related to the growth conditions. Theoretical studies of the factors governing the development of the equilibrium crystallographic orientation distributions in such deposits have been made. These show that surface roughness affects the sharpness of the peaks in both types of distributions. In addition, in the c′-axis distribution the position of the peak is shifted and hence the peak cannot be uniquely related to the growth conditions. If inferences of the growth environment of hailstones are to be made from crystal orientation measurements, the orientation distributions of the c-axes relative to the local normal to the surface of the hailstone should be used as these give the maximum possible resolution of the peaks.

Abstract

Measurements of c- and c′-axis orientation distributions in accreted ice deposits formed in the dry growth regime show peaks which may be related to the growth conditions. Theoretical studies of the factors governing the development of the equilibrium crystallographic orientation distributions in such deposits have been made. These show that surface roughness affects the sharpness of the peaks in both types of distributions. In addition, in the c′-axis distribution the position of the peak is shifted and hence the peak cannot be uniquely related to the growth conditions. If inferences of the growth environment of hailstones are to be made from crystal orientation measurements, the orientation distributions of the c-axes relative to the local normal to the surface of the hailstone should be used as these give the maximum possible resolution of the peaks.

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