Eruption of Krakatoa volcano2)
In 1883, the Krakatoa volcano in Dutch Indonesia erupted. The resulting explosion blew the whole mountain away, and the smoke from the eruption reached the stratosphere and subsequently was carried along the equator, around the world in 13 days in a westward direction. As the smoke cloud covered the sun, it was said to have turned a blue-green color. From the direction the cloud was carried at the time, it was thought that

an easterly

wind blows in the stratosphere above the equator. This wind is called the Krakatoa Easterly.

However, 25 years later in 1908, when Berson carried out balloon sounding near Lake Victoria in Africa, the wind in the stratosphere above the equator was

a westerly.

This is called the Berson Westerly. In exactly what direction is the air above the equator blowing?