Buổi 72: Reading – Bài khoa học dài: diagram labelling + multiple choice (bóng thám không)

Reading the sky

(Bài đọc tự viết; trạm và nhân vật là giả định. Sơ đồ đã đơn giản hóa.)

A Twice a day at weather stations around the world, staff release large balloons into the sky. Despite the availability of satellites, these weather balloons remain one of the most important sources of information for forecasters, because they measure conditions directly as they pass through different layers of the atmosphere.

B A typical weather balloon consists of three main parts. At the top is the balloon itself, made of a thin, stretchy material and filled with a gas that is lighter than air. Attached below it by a long string is a small parachute. Hanging further down, at the end of the string, is a lightweight box of instruments, known as a radiosonde. Inside the radiosonde are sensors that measure temperature, humidity and air pressure, together with a radio transmitter.

C Once released, the balloon rises steadily. As it climbs, the air pressure around it falls, and the gas inside expands, so the balloon becomes larger and larger. Throughout the flight, the radiosonde transmits its measurements to a receiver on the ground every few seconds. By tracking the radiosonde’s position, forecasters can also calculate the speed and direction of the wind at different heights.

D Eventually, the balloon expands so much that it bursts. The parachute then opens, and the radiosonde descends slowly back to the ground. Because balloons may travel a long way before bursting, the instruments often land far from where they were released, and many are never recovered. Some have a label asking the finder to return them.

E “People are often surprised that we still use balloons,” says Tomás Ibarra, a technician at a hypothetical coastal weather station. “Satellites give us a wide view, but they measure the atmosphere from above. Balloons give us a detailed vertical picture, layer by layer. The two methods complement each other.” Ibarra acknowledges that the balloons create waste, and several organisations are now testing designs that use more environmentally friendly materials.