东风波是在副高南侧对流层中、下层的东风带中，常存在一个槽或气旋性曲率最大区，呈波状形式自东向西移动。

东风波的成因，可能是高层对流层的一个热带性低压或中纬度低槽向赤道伸展的反映，也可能是低纬度的气旋向极地方伸展引起的弯曲。槽线附近300hpa以下是气旋性涡度，以上是反气旋性涡度。最大的上升运动中心有两个，一个在槽前的750hpa高度上，另一个在槽线附近300hpa的高度上。槽线附近600hpa以下是冷性的，以上为暖性。近地面层槽区为高湿区，槽线前后湿度相差不大，700hpa以上，槽前为干区，槽后为湿区。在夏季和初秋季节，当西太平洋副高位置偏北呈东西向带状分布时，副高南侧常有东风波进入中国沿海，影响广东、福建、浙江、江苏及山东等地区。

Tropical waves, easterly waves, or tropical easterly waves, also known as African easterly waves in the Atlantic region, are a type of atmospheric trough, an elongated area of relatively low air pressure, oriented north to south, which moves from east to west across the tropics causing areas of cloudiness and thunderstorms. West-moving waves can also form from the tail end of frontal zones in the subtropics and tropics and may be referred to as easterly waves, but these waves are not properly called tropical waves; they are a form of inverted trough sharing many characteristics with fully tropical waves. All tropical waves form in the easterly flow along the equatorward side of the subtropical ridge or belt of high pressure which lies north and south of the Intertropical Convergence Zone (ITCZ). Tropical waves are generally carried westward by the prevailing easterly winds along the tropics and subtropics near the equator. They can lead to the formation of tropical cyclones in the north Atlantic and eastern north Pacific basins. Tropical wave study is aided by Hovmöller diagrams, a graph of meteorological data.