Report on the Activity of Commission G

(11 March 2005)

 

 

1. Development of Ionospheric observation facility

Multi-functional Transport Satellite (MTSAT) was successfully launched on 26 February 2005. One of the missions of the satellite is Satellite-Based Augmentation System (SBAS) supporting GPS application in aircraft navigation. In order to investigate and evaluate the ionospheric effects on the GPS signals, Electronic Navigation Research Institute (ENRI) installed 12 GPS receivers in Ishigaki Island, South of Japan. Five receivers among them are capable of observing ionospheric scintillations, and the others are total electron content (TEC). These receivers are aligned the East-West and North-South baselines with a separation of 100 to 1000 m. Characteristics of plasma bubbles including onset times, density depletions, drift velocities, significance of scintillations will be observed. Based on the observations, empirical model of ionospheric degradation of the GPS signals will be constructed and provided for aviation users and system designers.  

STELAB, Nagoya University installed an all-sky airglow imager at the Resolute Bay Observatory (74.7N, 265.1E) in collaboration with the SRI International. The imager started automatic measurements from 11 January 2005. Quick-look data (deviation from one-hour running averages to see gravity waves) are available at http://stdb2.stelab.nagoya-u.ac.jp/omti/index.html (please see Imager #6.) The information of filters, exposures, and time resolutions is as follows.

Resolute Bay : (74.7N, 265.1E)

All-Sky Imager #6 (Jan.11, 2005-)   (2x2 binning = 256x256pixels)

OI (557.7nm, expo: 30s), OI (630.0nm, 30s),

OH-bands(2s), Na (589.3nm, 30s)  : every 2min

OI (777.4nm, 45s) : every 20 min

 

2. Observation Campaigns

The rocket campaign DELTA (Dynamics and Energetics of the Lower Thermosphere in Aurora) was carried out on 13 December 2004 in Norway. The sounding rocket S310-35 was launched at 0:33 (UT) to measure the ionospheric plasma and neutral gasses during the diffuse aurora. Ground-based observations were simultaneously made by using EISCAT radar and Fabry-Perot interferometer during the rocket flight. This campaign aimed to clarify the driving factor of strong neutral wind, in particular, horizontal wind. The new experiment in this campaign is neutral (N₂) temperature measurement which is planned to measure the neutral atmospheric heating due to the auroral precipitation or joule heating. It is possible to discuss the physical process of atmospheric heating and effect on the driving wind system in comparison with the results of other instruments as the electron density, temperature or aurora glowing intensity. Electron number density measurement was made by using instrument provided by the Tohoku University group, namely, the NEI instrument on-board the S310-35. NEI is the impedance probe which is developed by Oya [1966]. The NEI sensor was BeCu ribbon antenna, and extended at the altitude of 72.9 km. During the ascending period, electron density enhancements were observed in the altitude ranges from 100 to 110 km and from 125 to 130 km with the electron densities of about 1×10⁶ cm^-3 and 6×10⁵ cm^-3, respectively. In the descending phase, electron density enhancement was in the altitude range from 108 to 115 km, and there were many periodic density fluctuations due to the rocket wake. These electron density enhancements seem to be associated with the enhancement of neutral temperature at auroral altitudes. It is interesting to compare with the other observation results during the DELTA campaign, not only the on-board instruments but also ground-based instruments as the EISCAT radar.

 

3. Data Analyses

For clarifying the structure and occurrence characteristics of the ionization ledge, the topside sounder data observed by the Ohzora (EXOS-C) and ISIS-2 satellites in the equatorial ionosphere were analyzed. We analyzed topside ionograms of 19 and 430 passages observed by Ohzora in March and May, 1987 and ISIS-2 in 1973-1979, respectively. Also the variations of the geomagnetic field were analyzed to deduce the electric field. The ionization ledge was found in a dip latitude range from –13.5 to 19.3°, at the limited region around the dip equator. The ionization ledge appears in the local time sector from 9-11 LT to 0-2 LT. The occurrence probability is highest in the noon sector and tends to decrease gradually with local time. These results are consistent with the previous studies of the ionization ledge. The occurrence probability of the ionization ledge is higher in equinox seasons and lower in solstice seasons, which is consistent with the seasonal variation of the upward plasma drift derived by the AE-E satellite. Comparing with the eastward electric field deduced by the variations of the horizontal component of the geomagnetic field, the occurrence probability of the ionization ledge obtained by analyzing the Ohzora sounder data tends to be higher when the time integrated electric field shows a large value. These results indicate that the upward drift caused by the E×B term is the major source of the generation mechanism of the ionization ledge as reported in the previous studies. On the other hand, the present data analysis revealed the following important character of the ionization ledge. The ledge altitude has no clear dependence on the local time. However, the magnitude of the plasma density enhancement tends to become higher depending on the local time. The ionization ledge sometimes occurred even when the magnitude of the time integrated electric field variation was small. Therefore, in addition to the electric field effect, another control mechanism is possibly affecting the generation or containment of the ionization ledge structure. Majority of the character of the ionization ledge is basically the same with the character of the F₃ layer in terms of the local time dependence of occurrence (Balan et al., 1998). However, the seasonal dependence of the occurrence probability has a tendency contrary to that of the F₃ layer reported by Balan et al. (2000).

 

4. Ionospheric response to the December 26, 2004 Sumatra-Andaman Islands Earthquake

Total electron content fluctuations as observed by the meridional GPS receiver chain over Indonesia and Thailand (Chiang Mai, Bangkok, Chumphon, Medan, and Padang) were analyzed by the scientists of STEL, Nagoya University. In response to the atmospheric perturbation over the epicenter, the ionospheric total electron content increased stepwise by more than 7 TEC units (1TEC unit=1×10¹⁶ electrons/m³). They interpret the TEC fluctuation was caused by a sonic wave launched by the earthquake, and its efficiency to modify the ionosphere depended on the geometry of the earth’s magnetic field inclination and the sonic wave propagation path, which can explain the observed geographical and temporal changes in the TEC perturbation.  

 

 

 

TEC perturbation caused by the earthquake

　　

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Chiang Mai, Bangkok, Chumphon (NICT), Medan (SOPAC), Padang (STEL, Nagoya U.)

 

 

 

 

 

 

 

 

 

 

↑

           0058 UT: Earthquake

                    The first signal was detected 14 min after the earthquake at Padang

 

5. Coming Workshops

(1) Space Environment Center Space Weather Week, in Boulder, CO, USA, 5-8 April 2005,

http://www.sec.noaa.gov/sww/

(2)  The 11th International Ionospheric Effects Symposium, in Alexandria, VN, USA, 3-5 May 2005,

http://www.ies2005.com/

(3)  The 11th International Symposium on Equatorial Aeronomy (ISEA-11), in Taipei, Taiwan, 9-14 May 2005, http://140.115.111.70/ISEA-11/3rd_circular.html

(4)  IAGA Scientific Assembly, in Toulouse, 18-29 July 2005, http://www.iugg.org/IAGA/index.htm

(5)  URSI General Assembly, in New Delhi, India, 23-29 October 2005,

http://www.ursiga2005.org/ecm/index.php

During URSI General Assembly cited above, a General Lecture and an intercommission session on Solar Power Satellite (SPS) are arranged as below. Dr. Michael Rietveld of EISCAT will also give a talk entitled, "Interactions between microwave power transmissions from a solar power station and the ionosphere-atmosphere system" based on the recommendation of Commission G.

U1 - GENERAL LECTURE 1 (Monday 24/10/2005 14:00-15:20)

“Solar Power Satellite (SPS) for Sustainable Clean Energy Humanosphere” by Prof. Hiroshi Matsumoto

HX - INTERCOMMISSION SESSION - Solar power satellites (SPS) (I,C,P)

(Tuesday 25/10/2005 14:00-16:20) Session subjects include: passive and active microwave devices, antenna and rectenna, huge antenna arrays, retrodirective systems, antennas in plasma, self calibration, compatibility with telecommunications and radio astronomy, radio frequency interference and electromagnetic compatibility (RFI and EMC), the interaction of heavy ions ejected from the electric spacecraft propulsion engine. (Conveners: H.Kozo Hashimoto, Japan: kozo@rish.kyoto-u.ac.jp and D. Tatsuo Itoh, USA: itoh@ee.ucla.edu)

 

(Prepared by T. Maruyama and M. Yamamoto)