Oncoming traffic in the thunderstorm. Small Raindrops carried up by windings collide with falling snow or hailstones. This causes lightning. (Source: NASA)
A NASA airplane equipped with radar equipment has been examining a tropical "hybrid storm" that is just emerging. The now completed evaluation of the data provided the scientists with a detailed picture of the physical processes within this thunderstorm. Thunderstorms often produce only one of two precipitation types. In the lower layers of the air there is rain, in the higher, colder layers hail or snow. In the "hurricane" which the Nasa plane flew over the Brazilian rainforest in February 1999, both processes took place simultaneously. "Such two-phase processes should occur in many strong storms, " ​​says David Atlas of NASA's Goddard Space Flight Center. "But you could barely watch them so far."

In such thunderstorms prevail strong updrafts. That's why ? that showed the radar recordings? The smaller raindrops that formed in the lower layers were carried upward. During the climb, they came across "oncoming traffic". Because the frozen larger drops, which were formed higher up, fell down because of their weight. Due to the friction of the two types of droplets together electrical charges were separated, which eventually caused lightning.

The task of this NASA flight was to collect supplementary data on the measurement results of the TRMM (Tropical Rainfall Measuring Mission) satellite. The tropical thunderstorms are of particular interest to the scientists because they transport considerable amounts of heat into the upper atmospheric layers. This maintains the temperature gradient between the tropics and the poles, which drives global wind circulation.

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