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别让冬天的灾难影响您的飞行
了解大气天气条件的季节性变化及其影响。
来源:飞行杂志For meteorologists, one of the big indicators that marks wintertime is the enormous increase in wind speed and atmospheric momentum in the Northern Hemisphere.
At the jet stream level, winds across the U.S. during July average about 20-40 knots, but in January these speeds rise to 60-80 knots and often much higher.这显着增加了天气系统可用的能量。
急流也有向南移动。七月，急流穿过阿拉斯加湾、加拿大和加拿大沿海地区。然而，到一月份，急流已完全扎根于美国和邻近海域。 This brings a smorgasbord of weather systems during the cold season, ranging from weak, transitory upper level disturbances to well-developed frontal systems.
冬季也会带来对流层低层和高层之间更大的温差。我们可能认为夏天炎热且不稳定，但对于稳定性来说，重要的是对比度，而不是炎热本身。 The more the atmosphere leans vertically toward “cold over warm,” the higher the static instability.
In such an environment, lapse rates are steeper, and that means much greater potential for not only severe weather but also mechanical turbulence.最有可能发生湍流的地方是新鲜的冷气团在被太阳强烈加热的地形上滚动的地方。当风向差异足够大时，风切变也会产生。
Clear air turbulence (CAT) and mountain waves also deserve attention. For these phenomena, forecasters look for large wind components perpendicular to mountain ranges.穿过落基山脉的强烈西风气流是 CAT 和山浪的特别有效的来源。 What differentiates a weak from a strong CAT environment boils down to the vertical shear, the instability, and the type of air mass overlying the mountain range itself.