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The Forefront of Space Science

Research on the Upper Atmosphere Region Using Sounding Rockets
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S-520-23 Experiment (WIND Campaign)

As described above, neutral particles and plasmas coexist at the 100 to 300km altitude in the lower thermosphere. Since these particles collide with each other, the exchange of momentum occurs. Neutral atmospheric particles move independently with electromagnetic forces, while the plasma motion is influenced by electric and magnetic fields. Thus, since they move in the different directions and receive the force generated by their collisions, they begin complex movements depending on the density and electromagnetic field. Theoretical studies on momentum transfer (transport) through collisions between the particles and the electric field have been made for many years. Observational or experimental verification on this matter is still lacking, however, and simultaneous and direct observations to measure such key parameters have been rare.

The objectives of the S-520-23 experiment were: to conduct direct observations of electron density, ion density and velocity, the electric field and the neutral wind in the lower thermosphere; to understand the momentum transfer between the neutral atmosphere and plasma; and to elucidate the role of the transfer process in the generation and growth of various phenomena.

In this experiment, the observation of the neutral wind drew much attention. It was made by continuous imaging of the resonant emission of lithium vapor released from the rocket. This kind of wind observation is extremely rare and an experiment using lithium has not been conducted in the past 30 years. This method was successfully developed in Japan and we have received many inquiries about it from researchers across the world. Fig. 4 shows the lithium emission images taken at Uchinoura. The wind is estimated from temporal variation of the emission region. It is noteworthy that, after detailed analysis of the images, we found a region called the velocity shear, where the direction and strength of the wind change rapidly at about 120 km altitude.

Figure 4
Figure 4. Continuous images of lithium emission taken at Uchinoura (Courtesy of Hokkaido University and Kochi University of Technology)

The S-520-23 experiment had another mission, "ultra-multiple wavelength imaging of the climatic and oceanic phenomena." It is an attempt to take an image of cumulonimbus clouds and the ocean using ultra-multiple wavelengths at 1nm intervals from above 100km altitude to observe vapor transport, river flow and plankton distribution with high-accuracy. Unfortunately this mission failed since the despinning function did not work well, but we were able to obtain valuable data.

Sounding rockets are utilized to deepen our understanding of the upper atmosphere region. One of the benefits of sounding rocket experiments is that we can accomplish in a short time a series of processes including devising observation methods necessary for deep understanding, developing new observation instruments, and installing them on rockets to retrieve the flight data. We would like to express our appreciation for your continued understanding and support.

Takumi ABE

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