Global Lightning and sprIte MeasurementS on JEM-EF (JEM-GLIMS) obtained its first observation data
Global Lightning and sprIte MeasurementS on JEM-EF (JEM-GLIMS) is the equipment onboard the Multi-mission Consolidated Equipment (MCE), installed on the Exposed Facility (EF) of the Japanese Experiment Module Kibo on the International Space Station (ISS).
JEM-GLIMS was launched to the ISS on July 21, 2012, aboard the H-II Transfer Vehicle (HTV) KOUNOTORI3 and installed on the Exposed Facility (EF) of Kibo on August 9. After the installation, JEM-GLIMS successfully obtained its first observation data.
JEM-GLIMS was collaboratively developed by Osaka University, Hokkaido University, Kinki University, Stanford University, National Institute of Polar Research, Osaka Prefecture University, Tohoku University, the University of Electro-Communications and JAXA. JEM-GLIMS, composed of a CMOS camera with high spatial resolution, photometers with high temporal resolution, and VLF/VHF radio wave receivers, lead the world in the continuous observation of the lightning and sprites from just above.
By doing the just-above observations, a detailed study for the horizontal spatial distribution and temporal development process of lightning and sprites which has been difficult to derive from the on-ground observation data becomes possible. Further, since the just-above observation from space receives little impact from absorption and scattering by the Earth's atmosphere, it is possible to acquire precise data of the luminescence intensity. Initial checkout of each instrument of JEM-GLIMS was completed; and the observation equipment had been verified working normally.
The figure below is an image data captured by the CMOS camera of a just below, a lightning that occurred over Malaysia, which JEM-GLIMS observed at 11:51 p.m. and 44.408 second on November 27, 2012 (Japan time). From the figure, the lightning emissions show a non-uniform, complicated spatial distribution of an approximately 20km wide. In addition, a strong light of near-ultraviolet ray has been detected with a wavelength of 150-280nm. The light of near-ultraviolet ray is mostly absorbed to the ozone in the atmosphere and rarely reaches the ISS flying at 400km altitude. For this reason, detection of near-ultraviolet ray suggests that the occurrence of a transient luminous event (TLE) in the upper-atmosphere. The data will be validated in near future. As such, JEM-GLIMS conducts the world's first, just-above observation of lightning and TLE in the upper-atmosphere.
This example of observation is a data before it is validated. Research teams and JAXA will conduct the continuous observation and aims to detect the luminous phenomena, such as sprites. In addition, by a comparison with the observational data of lightning obtained on the ground, we will clarify the electrical characteristics of lightning that caused upper-atmospheric luminous phenomena. In addition, in collaboration with the researchers from around the world, we are planning to carry out a simultaneous observation of an upper-atmospheric luminous event using a ground-based optical observation instrument and this JEM-GLIMS.
【Remarks from PI, Tomoo Ushio, Associate Professor, Osaka University】
JEM-GLIMS experiment was chosen as one of the JAXA's port sharing utilization mission onboard Kibo-Exposed Facility of the ISS. It was launched this July without trouble. I'd like to express my gratitude to all the concerned people. This first observation proved the equipment was working normally, and interesting data was included in the obtained data. I expect to obtain important findings in the near future.
JEM-GLIMS aims to observe the lightning that occurs at an altitude of 10 km or below and the upper-atmospheric lightning such as sprites, elves, and gigantic jets that occur at altitudes between 20-90 km in connection with the lightning.
Upper-atmospheric lightning was discovered about 20 years ago. Occurrence condition and the mechanisms are still remain a mystery such as the causes of discharge type differences of columns or carrots, vertical occurrence location gap between a thunder and a sprite, and factors that determine the number of sprite discharge(s). The most effective means to solve these is a method to observe an upper-atmosphere lightning from right above from space. By doing so, spatial distribution, time development, and relationships with the parent thunders are expected to be easily clarified, which has been difficult by the optical observation on the ground.
Furthermore, JEM-GLIMS' sweep observation alongside the ISS movements, which covers the area of latitudes 51 degree in north and south enables to obtain precise data of occurrence distribution and the frequency of the upper-atmospheric lightning can be measured. This is expected to become a key for the quantitative inference of how upper-atmospheric lightning affect the change of the atmosphere constitution of the Earth and the ozone chemistry.
JEM-GLIMSの観測装置を図6に示します。JEM-GLIMSは大きく分けて、2式の光学観測器と、2式の電波受信器、およびそれらを制御する制御ユニット1式で構成されます。光学観測器は、CMOSセンサーを用いた雷放電・スプライト観測カメラ（LSI）2台と、光電子増倍管およびフォトダイオードを用いたフォトメタ（PH）6台で構成されています。 LSIは500 m/pixの空間分解能で、主に雷放電と高高度放電発光現象の発生形態をとらえるのに対し、PHは0.05 msの高い時間分解能で絶対発光強度を測定します。これらによって、雷放電と高高度放電発光現象の時間・空間変化を精密観測します。
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