台风原因英文版

台风（英语：Typhoon）是赤道以北，日界线以西，亚洲太平洋国家或地区对热带气旋的一个分级。在气象学上，按世界气象组织定义，热带气旋中心持续风速达到12级（即64节或以上、每秒32.7米或以上，又或者每小时118公里或以上）称为飓风（Hurricane）或其他在地近义字。西北太平洋地区采用之近义字乃台风。

在海洋面温度超过26℃以上的热带或副热带海洋上，由于近洋面气温高，大量空气膨胀上升，使近洋面气压降低，外围空气源源不断地补充流入上升去。受地转偏向力的影响，流入的空气旋转起来。而上升空气膨胀变冷，其中的水汽冷却凝结形成水滴时，要放出热量，又促使低层空气不断上升。这样近洋面气压下降得更低，空气旋转得更加猛烈，最后形成了台风。

从台风结构看到，如此巨大的庞然大物，其形成主要原因有四个：

一、要有广阔的高温、高湿的大气。热带洋面上的底层大气的温度和湿度主要决定于海面水温，台风只能形成于海温高于26℃-27℃的暖洋面上，而且在60米深度内的海水水温都要高于26℃-27℃

二、要有低层大气向中心辐合、高层向外扩散的初始扰动。而且高层辐散必须超过低层辐合，才能维持足够的上升气流，低层扰动才能不断加强

三、垂直方向风速不能相差太大，上下层空气相对运动很小，才能使初始扰动中水汽凝结所释放的潜热能集中保存在台风眼区的空气柱中，形成并加强台风暖中心结构

四、要有足够大的地转偏向力作用，地球自转作用有利于气旋性漩涡的生成。地转偏向力在赤道附近接近于零，向南北两极增大，台风基本发生在大约离赤道5个纬度以上的洋面上。

The formation of tropical cyclones is the topic of extensive ongoing research and is still not fully understood.[35] While six factors appear to be generally necessary, tropical cyclones may occasionally form without meeting all of the following conditions. In most situations, water temperatures of at least 26.5 °C (79.7 °F) are needed down to a depth of at least 50 m (160 ft);[36] waters of this temperature cause the overlying atmosphere to be unstable enough to sustain convection and thunderstorms.[37] Another factor is rapid cooling with height, which allows the release of the heat of condensation that powers a tropical cyclone.[36] High humidity is needed, especially in the lower-to-mid troposphere; when there is a great deal of moisture in the atmosphere, conditions are more favorable for disturbances to develop.[36] Low amounts of wind shear are needed, as high shear is disruptive to the storm's circulation.[36] Tropical cyclones generally need to form more than 555 km (345 mi) or 5 degrees of latitude away from the equator, allowing the Coriolis effect to deflect winds blowing towards the low pressure center and creating a circulation.[36] Lastly, a formative tropical cyclone needs a pre-existing system of disturbed weather, although without a circulation no cyclonic development will take place.[36]

台风是怎样形成的？