Tomoyuki Nakajo

Simultaneous observations of tropospheric turbulence from radiosondes using Thorpe analysis and the VHF MU radar

This paper deals with the detection and quantification of refractivity turbulence in the troposphere from radiosonde and very high frequency (VHF) band radar data. Balloon data processing methods based on Thorpe sorting and recently developed by Wilson et al. (2010, 2011, and 2013) can be applied for a direct identification of turbulent layers from the in situ profiles. The VHF band mid and upper atmosphere radar (MUR) can be operated in range-imaging mode for detecting and monitoring turbulent layers at high time and range resolutions (of the order of 10 s and a few tens of meters, respectively). For cross validating the techniques, concurrent MUR and RS92-SGP Vaisala radiosonde observations were made at the Shigaraki Middle and Upper atmosphere (MU) observatory (34.85°N, 136.15°E; Japan) during a field campaign of 3 weeks in September 2011. The radar signature, in terms of echo power and aspect ratio, of the turbulent layers identified from balloon data analyses is investigated from case studies and statistics. The deep (>~100 m) layers are very often associated with echo power maxima and weak aspect ratios suggesting that the same events of isotropic turbulence were detected by both instruments. Some others are associated with relative minima of isotropic echo power, possibly indicating a later stage of turbulence. The ranges of strong aspect ratios are generally not associated with turbulent events in the balloon data supporting the hypothesis that anisotropic turbulence is not the cause of vertically enhanced radar echoes. Quantitative comparisons are made between radar echo power and refractive index constant structure C2n estimated from temperature variance and additional parameters in the selected layers. Despite a large scatter between the radar and balloon estimates, the results are statistically significant (correlation coefficients ~0.5–0.88) even when the causes of systematic decrease with height of C2n (humidity and density) are removed. Our studies therefore demonstrate that radar and balloon observations of turbulence are consistent between each other and that new insights on tropospheric turbulence can be obtained by the two techniques as stand-alone systems.

Development and Operation Results of Cubesat RAIKO Using Ground Network System

The 2U-size cubesat RAIKO was launched to the International Space Station (ISS) in July 2012, and released to space in October 2012. The preset sequences of the 30-min initial separation phase were successfully carried out, and 46 photos were taken and stored to memory by the onboard CMOS and CCD sensors. Four Japanese universities collaborated in joint operations of RAIKO, which included successful S-band command/telemetry operations at a telemetry downlink rate of 100 kbps using the 100-mW onboard transmitter. In addition, Ku-band beacon signals were successfully monitored to determine the orbit and atmospheric disturbances. This paper presents an outline of RAIKO, the ground station network, the operation method, and associated results. The cubesat RAIKO inherited the satellite bus technology of a 50-kg microsatellite, and various technology demonstrations were achieved. Through the joint operation of RAIKO, the ground station network was practically improved and will contribute to the operations of future microand nanosatellites.