EXPERIMENTAL STUDY ON "HALO" FORMATION IN THE POLAR REGION

• Main Authors: フルカワ ヨシノリ /, Yoshinori FURUKAWA, John HALLETT
• Format: Report
• Language: English
• Published: ABSTRACT 1990
• Subjects: Hallett; Polar meteorology and glaciology; Proceedings of the NIPR Symposium on Polar Meteorology and Glaciology
• Online Access: https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=3616; http://id.nii.ac.jp/1291/00003616/; https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=3616&item_no=1&attribute_id=18&file_no=1

When cirriform clouds or ice fogs lie down between the observer and the sun (or moon), refraction and reflection effects of light rays by small ice crystals (diamond dust) can lead to one or more "halo" phenomena (R. GREENLER : Rainbows, Halos and Glories. Cambridge, Cambridge Univ. Press, 1980). For example, the most common-the 22°-halo, which occurs when the cloud form is a veil of cirrostratus and when the predominant ice crystal form is that of hexagonal prism of uniform size, is explained form the fact that the angle of deviation (i. e. the angle of minimum bending from a straight line by refraction) is 22°for a triangle with apex angle of 60°. However, it has not as yet been satisfactory explained how the appearance of halo phenomena and the halo intensity depend on the basic properties of ice crystals such as morphology, spatial concentration, size distribution, and falling orientation (J. HALLETT : J. Opt. Soc. Am., A4,581,1987). The purpose of this study is to observe the hal phenomena in ice fogs made artificially in the laboratory and to clarify their formation mechanisms in connection with aspects of both crystal growth and meteorology. An experiment was carried out for the 22°halo. As a result, we showed that the artificial formation of halo with enough intensity was possible and the effects of the variety of crystal forms and crystal size for halo formation were extremely severe. On the basis of these experimental results and theoretical consideration, we discuss the formation mechanism of the "halo". Finally, we mention important applications of halo study such as remote sensing of cloud particles from the ground or a satellite.