高速气流，或称喷射气流、高空急流、极风喷流（英语：Jet Stream），是行星尺度的大气环流。在地球上，指数条围绕地球的强而窄的高速气流带，集中在对流层顶，在中高纬西风带内或在低纬度地区都可出现。其水平长度达上万公里，宽数百公里，厚数公里。中心风速有时可达每小时200至300公里的偏西风，而且可以有一个或多个风速极大中心，具有强大的水平风切变和垂直风切变。高速气流附近亦有强大风切变，这也是所谓飞机上的乱流。

Jet streams are fast flowing, narrow, meandering, air currents found in the upper atmosphere or in troposphere of some planets, including Earth. The main jet streams are located near the altitude of the tropopause. The major jet streams on Earth are westerly winds (flowing west to east). Their paths typically have a meandering shape. Jet streams may start, stop, split into two or more parts, combine into one stream, or flow in various directions including the opposite that of the direction of the remainder of the jet. The strongest jet streams are the polar jets, at 9–12 km (30,000–39,000 ft) above sea level, and the higher altitude and somewhat weaker subtropical jets at 10–16 km (33,000–52,000 ft). The Northern Hemisphere and the Southern Hemisphere each have a polar jet and a subtropical jet. The northern hemisphere polar jet flows over the middle to northern latitudes of North America, Europe, and Asia and their intervening oceans, while the southern hemisphere polar jet mostly circles Antarctica all year round.