Researchers demonstrate high accuracy of observation device that can be dropped into typhoon without parachute

Dropped from aircraft, the dropsonde, a small, single-use instrument, measures and transmits atmospheric data, including temperature, humidity, and wind speed, as it falls. The new dropsonde, iMDS-17, weighs only 130 grams and is made mainly of a biodegradable material. With its fin and lightweight body, iMDS-17 can descend without a parachute, unlike conventional dropsondes.

To predict whether a typhoon will intensify and where it will move, it is important to know how temperature, wind, and humidity are changing. In Japan, airborne instruments called radiosondes are commonly used to observe the upper atmosphere. Radiosondes are launched from land using a rubber balloon. However, the strong winds and rain associated with typhoons, which form and develop over the ocean, make this process difficult.

To overcome this shortcoming, a research group at Nagoya University in collaboration with Meisei Electric Co. has developed Japan's first dropsonde that can be dropped from an airplane into the eye of a typhoon to obtain vertical profiles of temperature, humidity, and winds.

Designated Associate Professor Sachie Kanada and her colleagues at Nagoya University, in collaboration with researchers from Meisei Electric and the National Research Institute for Earth Science and Disaster Resilience, have conducted a study to evaluate the performance of their newly developed dropsonde. They evaluated the performance by comparing data from their dropsonde with data from an accuracy assured radiosonde used by the Japan Meteorological Agency.

Before that, dropsondes were rarely evaluated because their use was restricted to the ocean, making simultaneous comparisons with radiosondes impractical.

In their study, conducted on one of the islands of Okinawa in Japan, on March 27 and 28, the dropsonde and the reference radiosonde were launched simultaneously with the same balloon. A cutter with a timer was placed between the balloon and the two instruments. When the balloon reached an altitude of 12 km, the timer was activated, and both instruments were separated from the balloon and dropped. Each instrument measured the temperature, wind, and humidity as they descended, and the data from the dropsonde were compared with the data from the radiosonde.

Differences between the dropsonde and radiosonde data were less than 1 K and 2 m/sec. for temperature and wind, respectively, at most altitudes between 9 km and 2 km. The results showed a high performance of the dropsonde for temperature and wind observations. Humidity, however, tended to be drier than that of the radiosonde measurements and still needed improvement.

To observe the dropsonde in actual storm conditions, on October 9 and 10, 2024, Designated Associate Professor Kanada and Professor Kazuhisa Tsuboki of the Nagoya University Institute for Space and Earth Environmental Research dropped a total of 50 dropsondes from an aircraft into the eye of Typhoon Barijat.

Kanada explained: "On October 9, we had just arrived around the storm center in the typhoon genesis phase. The observed profiles of atmospheric conditions for the midlatitude typhoon were delivered worldwide via the Global Telecommunication System (GTS) of the WMO and used for the weather forecasting systems. This time, we preverified humidity data of the dropsondes and the data was improved. Using this dropsonde, we are planning to have another aircraft observation in 2025."