Maho Nakamura

Anomalous enhancement of ionospheric electron content in the Asian-Australian region during a geomagnetically quiet day

National Natural Science Foundation of China[40725014]; National Important Basic Research Project[2006CB806306]; Knowledge Innovation Program of the Chinese Academy of Sciences

Using a neural network to make operational forecasts of ionospheric variations and storms at Kokubunji, Japan

An operational model was developed for forecasting ionospheric variations and storms at Kokubunji (35⊙N, 139⊙E), 24 hours in advance, by using a neural network. The ionospheric critical frequency (foF2) shows periodic variabilities from days to the solar cycle length and also shows sporadic changes known as ionospheric storms caused by geomagnetic storms (of solar disturbance origin). The neural network was trained for the target parameter of foF2 at each local time and input parameters of solar flux, sunspot number, day of the year, Kindex at Kakioka. The training was conducted using the data obtained for the period from 1960 to 1984. The method was validated for the period from 1985 to 2003. The trained network can be used for daily forecasting ionospheric variations including storms using prompt daily reports of K-index, sunspot number, and solar flux values available on-line.

Dissemination of UTC(NICT) by means of QZSS

The Japanese Quasi-Zenith Satellite System (QZSS) offers the possibility to transmit information with unprecedented bit rates via the L-band experimental (LEX) signal. This feature can be used to disseminate Japan Standard Time, i.e. UTC(NICT) to any user who is capable to receive the new QZSS signal. Various modes for the transmission of the timing information as well as a dedicated ionosphere correction model allow the users to instantaneously realize UTC(NICT) across Japan with an uncertainty of a few nanoseconds.

Error correction of precise time transfer experiment between ground and ETS-VIII

The Engineering Test Satellite-VIII (ETS-VIII) is a Japanese geostationary satellite. Its missions include basic satellite positioning experiments using onboard atomic clocks. The National Institute of Information and Communications Technology (NICT) developed special equipment for this time transfer link. This link makes precise time transfer between the onboard atomic clock and a ground reference clock using two way time transfer method and carrier phase measurement for the first time in the world. We have corrected ionosphere error by two received downlink measurement data and compared to obtain a precision as better than 3ps between both clocks.

Correction to ''Ionospheric responses to the October 2003 superstorm: Longitude/local time effects over equatorial low and middle latitudes''

] In the paper ‘‘Ionospheric responses to the October2003 superstorm: Longitude/local time effects over equato-rial low and middle latitudes’’ by Mangalathayil A. Abdu,Takashi Maruyama, Inez S. Batista, Susumo Saito, andMaho Nakamura (Journal of Geophysical Research, 112,A10306, doi:10.1029/2006JA012228, 2007), the LT datesshown at the top of Figures 6a, 6b, and 7 are incorrect. Thecorrected figures are shown here.Figure 6a. F layer peak height hmF2 deviation from its reference day curve, hmF2, during the periodfrom 1500 UT of 28 October (0000 LTof 29 October) to 0000 UT (0900 LT) of 1 November 2003. ThehmF2 variations are shown from bottom to top for Okinawa, Yamagawa, Kokubunji, and Wakkanai. Theshaded areas represent the local night hours.

Development of QZSS-mobile station

As we designed and constructed the QZSS mobile station, we transported it to Okinawa Electromagnetic Technology Center and Kashima Space Technology Center. At each place we carried out time comparison experiments. This paper describes some results of the time comparison experiments.

Time management system of the QZSS and time comparison experiments

National Institute of Information and Communications Technology, Japan (NICT) developed the time management system of the first Quasi-Zenith Satellite (QZS-1), which consisted of on-board time transfer subsystem (TTS) and related ground systems such as time management stations (TMS). TTS can measure the time differences between an on-board Rb clock and an atomic clock of the TMS. TTS can also measure the time differences between the on-board Rb clocks and the satellite reference clock, moreover between the L-band signals and the satellite reference clock. This paper describes about the time management system and shows results of a time comparison experiment between the QZS-1 and the ground TMSs using TTS.