Bonjour à tous/toutes,
Je ne savais ou poster le sujet mais la section "physique" m'a semblé la plus adaptée.
* Selon Wiki : Phénomène aérospatial non identifié (PAN) est un terme qui désigne un quelconque phénomène atmosphérique voire extra-atmosphérique observé dont la nature n'a pu ou pas encore pu trouver d'explication.
J'en ai peut-être un à vous proposer et je suis sur une piste :
http://www.youtube.com/watch?v=1IAGE9f0K1Q
http://www.youtube.com/watch?v=1Z_-uK5Btik
http://www.youtube.com/watch?v=Sc9Ks6H3coY
http://www.youtube.com/watch?v=cUcH3VClzUI
http://www.youtube.com/watch?v=b6BSz...eature=related
La piste :
Sachant que la luminosité visible des cristaux de glace (via un changement d'alignement) en suspension peut-être influencée par les mouvements d'air (le fameux airflow ?) mais aussi par des champs électrostatiques ayant une valeur > 1V/mm, je présume qu'il serait peut-être souhaitable d'envoyer ces vidéos à ces chercheurs (?).The alignment of ice crystals in changing electric fields
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T. C. FosterE-mail The Corresponding Author, 1 and J. HallettCorresponding Author Contact Information, E-mail The Corresponding Author
Desert Research Institute, 2215 Raggio Parkway, Reno, NV 89512, USA
Received 1 August 2001;
accepted 1 December 2001.
Available online 14 February 2002.
Abstract
Orientation of ice crystals in the form of thin plates (diameter up to 30 μm, thickness 0.5 to a few μm) was investigated optically for crystals nucleated in a supercooled cloud in a laboratory cold chamber. Random orientation caused by Brownian rotation of small crystals (apparent as twinkling) and alignment caused by airflow resulting from fall motion of larger crystals was changed by application of an electric field either as a step or as an oscillating square wave of variable frequency of order 1–10 Hz. Video records and time exposed still photographs demonstrated crystal fall, oscillation, and orientation changes with electric field magnitude and frequency. Thin film interference colours provided crystal thickness, mass, and moment of inertia. Realignment began for electric fields greater than 0.5–1 kV/m and was complete above 10 kV/m. Measurements of degree of alignment (from random orientation to completely parallel to the electric field) and its time dependence (of order tenths of seconds) are consistent with predictions of a theoretical oscillator model based on electrical torques on ellipsoids in viscous air. In a changing electric field at low frequency, the crystal realignment varies along with the variation field and at high frequency they remain aligned along the average field. These results are applied to larger crystals as occur in the atmosphere with implication for remote sensing of ice by radar and lidar as influenced by local electric fields and with the possibility of their remote measurement by optical observation of changing crystal orientations.
Source : http://www.sciencedirect.com/science...6980950200008X
Qu'en pensez-vous ?
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