月亮与冒烟圈的埃特纳火山

月亮与冒烟圈的埃特纳火山

Moon and Smoke Rings from Mt. Etna
Image Credit & Copyright: Dario Giannobile

Explanation: Yes, but can your volcano do this? To the surprise of some, Mt. Etna emits, on occasion, smoke rings. Technically known as vortex rings, the walls of the volcano slightly slow the outside of emitted smoke puffs, causing the inside gas to move faster. A circle of low pressure develops so that the emitted puff of volcanic gas and ash loops around in a ring, a familiar geometric structure that can be surprisingly stable as it rises. Smoke rings are quite rare and need a coincidence of the right geometry of the vent, the right speed of ejected smoke, and the relative calmness of the outside atmosphere. In the featured image taken about two weeks ago from Gangi, Sicily, Italy, multiple volcanic smoke rings are visible. The scene is shaded by the red light of a dawn Sun, while a crescent Moon is visible in the background.

Tomorrow’s picture: sky X

月亮与冒烟圈的埃特纳火山
影像提供与版权: Dario Giannobile

说明: 对了，你看过的火山有这么神奇吗？挺令人惊讶的，埃特纳火山偶尔会冒烟圈。用专业术语来说，这种烟圈称为涡旋圈，起因是火山壁会稍微减缓排放烟柱外层的速度，而内层的气体则相对快速移动，从而造就了一圈低压环，使得排放出的火山气体和火山灰形成涡环。这种我们相当熟悉的几何结构，有时在上升时会意外的稳定。火山烟圈非常罕见，其形成要排放孔的几何形状正确、排放烟尘的速度刚好、及外部大气相对平静等条件皆同时存在。在这幅大约2周前摄于意大利西西里岛冈吉镇的主题影像里，可见到多个火山烟圈。这片景观以黎明时分太阳的泛红阳光为背光，背景里还可见到一轮蛾眉新月。

明日的图片: sky X