First determination of the fractal perimeter dimension of noctilucent clouds

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Abstract

[1] We report on the first determination of the fractal perimeter dimension of noctilucent clouds using satellite images of cloud fields taken with the CIPS (Cloud Imaging and Particle Size) experiment on NASA's AIM (Aeronomy of Ice in the Mesosphere) spacecraft. The area and perimeter of individual clouds exceeding a certain albedo threshold are used to infer the fractal perimeter dimension. We find scaling behavior of cloud area as a function of cloud perimeter over more than 2 orders of magnitude. The cloud perimeters are fractals and the derived fractal perimeter dimensions decrease slightly with increasing NLC albedo threshold from DNLC = 1.35 ± 0.04 for an albedo threshold of 20 × 10−6 sr−1 to DNLC = 1.23 ± 0.05 for an albedo threshold of 60 × 10−6 sr−1. The fractal dimension for the lower albedo thresholds is in remarkably good agreement with the fractal perimeter dimension of tropospheric clouds and rain fields, possibly suggesting that similar physical processes govern the distribution and shape of both tropospheric and noctilucent clouds.

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