西藏上空的气辉涟漪

2022年11月20日

Airglow Ripples over Tibet
Image Credit & Copyright: Jeff Dai

Explanation: Why would the sky look like a giant target? Airglow. Following a giant thunderstorm over Bangladesh in late April, giant circular ripples of glowing air appeared over Tibet, China, as pictured here. The unusual pattern is created by atmospheric gravity waves, waves of alternating air pressure that can grow with height as the air thins, in this case about 90-kilometers up. Unlike auroras powered by collisions with energetic charged particles and seen at high latitudes, airglow is due to chemiluminescence, the production of light in a chemical reaction. More typically seen near the horizon, airglow keeps the night sky from ever being completely dark.

Tomorrow’s picture: butterfly sky

西藏上空的气辉涟漪
图像提供与版权: Jeff Dai（戴建峰）

说明: 为何天空会看起来像个巨型的标靶呢？因为有气辉。2014年4月，在追踪孟加拉国上方的一个大型雷暴系统之时，见到了上面这个出现在中国西藏上空的庞大圆形气辉涟漪。这种不寻常的图案，是由大气重力波所产生的；这种大气压力高低交替的波，其波长会随着标高而增加，在此例之中，波传递到了90公里以上的高空。然而，有别于极光是空气分子受到高能粒子冲撞所发的光，气辉则是源自空气分子参与化学反应的化学发光。一般来说，出现在地平线附近的气辉较易分辨，而气辉也让夜空不会完全黝黑。

明日的图片: butterfly sky