Report on the Activity
of Commission G
(15 November
2004)
1. Studies on
topside ionosphere
In the
evaluation of radio propagation delays through the ionosphere when the satellite
elevation angle is low, so-called thin layer model of the ionosphere leads a
large error depending on the azimuth angle. Thus we need information on the
vertical distribution of the ionosphere. Topside electron density modeling is
going on by comparing GPS derived total electron content (TEC) and ionospheric critical frequency (foF2) by National Institute
of Information and Communications Technology (NICT) and Institute of Space and Aeronautical Science (ISAS)/JAXA
groups. Topside electron density distribution shape is estimated by using
non-diffusive equilibrium distribution model, i.e., the combination of the
diffusive equilibrium and flux solution terms.
To verify an
additional ionization layer predicted in the equatorial ionosphere, topside
ionograms obtained by the Planetary Plasma Sounder
(PPS) system on-board the Ohzora (EXOS-C) satellite
were analyzed by the Tohoku University group. Based on the analysis of
the PPS data of 8 passes in March and 11 passes in May, 1987, the ionization
ledge observed in the local noon time period shows nature theoretically
predicted for the F3 layer by Balan and Bailey (1995);
namely, the ionization ledge has a tendency to rise with the upward velocity of
about 32 m/s in this local time period. It was noted that some peaks of the
ledge structure were located on the field line of higher latitude region than
the field line of the equatorial anomaly crests. Also in their study, the
occurrence probability of the ionization ledge shows a tendency contrary to that
of the F3 layer reported by Balan et al. (2000). This
difference may be due to the lack of data number. An extended statistical study
is needed to clarify the seasonal dependence of the occurrence probability in
the future studies.
2.
Observation Campaigns
Geomagnetic-conjugate
experiment of equatorial ionosphere over Indonesia-Thailand
region
There are two
research projects for studies of equatorial ionosphere in Southeast Asia. One is “Southeast Asia Equatorial Ionospheric Network (SEALION)” leaded by NICT. SEALION
consists of three FM/CW ionosondes located along the
longitude of 100 degrees East; two of them are at the
magnetic conjugate points and one is near the magnetic equator. Another research
project is “Coupling Processes in the Equatorial Atmosphere (CPEA)” that studies
dynamical coupling processes in the equatorial atmosphere from the troposphere to the ionosphere. Research Institute of
Sustainable Humanosphere (RISH), Kyoto University and Solar-Terrestrial Environmental
Laboratory (STEL), Nagoya University jointly participate ionospheric studies under the CPEA. In October 2004, SEALION
and CPEA conducted collaborative observation campaign with all of their
instruments. Echoes from ionospheric irregularities
associated with plasma bubbles were observed by the Equatorial Atmosphere Radar
(EAR), while meridional structure of the ionosphere
was observed by SEALION. In the EAR site CPEA team operated an airglow imager,
GPS scintillation receivers, a magnetometer, etc. This is a very unique
observation network for the study of the equatorial atmosphere. We anticipate
revealing dynamical processes of the equatorial ionosphere and generation
mechanisms of the plasma bubbles.
Rocket
Experiment of momentum transfer between neutral atmosphere and
ionosphere
A rocket
experiment to observe F-region ionosphere is planned and proposed to ISAS/JAXA
to be conducted in summer 2006 with an S-520 sounding rocket. The PI of the
experiment is Prof. Ono, Tohoku University, and is joined by researchers
from Hokkaido
University, Tohoku University, Toyama Prefectural University, Nagoya University, Kyoto University, and NICT. Indian and Canadian
researchers join the project, too. The S-520 rocket will be equipped with
in-situ instruments to measure plasma parameters, i.e., plasma density, electric
field, electron temperature, etc. A unique part of the rocket experiment is the
Lithium (Li) release experiment in the ionosphere, which will measure neutral
atmospheric winds. This experiment will observe both ionospheric plasma and neutral atmosphere, which will reveal
momentum transfer between the neutral atmosphere and ionosphere. Ground-based
observations are also planned in association with the rocket experiment. Dr.
Yamamoto, Kyoto
University is planning to
operate a portable radar for observation of E-region irregularities and meteors.
The radar experiment adds simultaneous data of electric field and neutral winds
in the lower ionosphere, and would help study of ionospheric E- and F-region coupling
processes.
Geomagnetic
Conjugate Observations of Medium-Scale Traveling Ionospheric Disturbance (MSTID)
Prof. Ogawa
and his research group in STEL, Nagoya University conducted geomagnetic conjugate
observations of 630-nm airglow at Sata, Japan, and Darwin, Australia, with two all-sky CCD
imagers. The observations were conducted in association with the CPEA project
that studies coupling processes in the equatorial atmosphere. In their
experiment, airglow perturbations caused by MSTIDs
were simultaneously observed at both sites near midnight of August 9, 2002. The MSTID structures were mirrored in the
northern and southern hemispheres connected by the geomagnetic field lines. This
result suggests that polarization electric field (Ep) plays an important
role in MSTIDs set up and grow in the ionosphere.
Ep maps along B and drives the F-region plasma upward and downward in
the direction of EXB,
causing plasma density perturbations with mirrored structures in both the
hemispheres. This electromagnetic coupling process between both the hemispheres
is associated with the equatorial atmosphere at very high altitude. The research
group now proposes a future plan to expand the inter-hemisphere comparisons of
the mid-latitude ionosphere by including neutral-wind experiment with Fabry-Perot interferometries and
ionospheric irregularity experiment with VHF/HF radars
at the conjugate points in Japan and Australia. The
experiment would be very helpful to reveal generation processes of the
polarization electric field and source of the MSTIDs.
Reference
Otsuka,
Y., K. Shiokawa, T. Ogawa, and P. Wilkinson (2004),
Geomagnetic conjugate observations of medium-scale traveling ionospheric disturbances at midlatitude using all-sky airglow imagers, Geophys. Res. Lett., 31, L15803,
doi:10.1029/2004GL020262.
Figure
1:
(a) Map
showing the locations of observational sites and coverage of the airglow imagers
(radius of 500 km). One site is located at Sata
(31.0N, 130.7E), Japan and the other site at Darwin (12.4S, 131.0E),
Australia. The geomagnetic field line
connecting Darwin and its conjugate point is shown by a
black curve. Red circle shows conjugate area connected by the geomagnetic field
lines to the observational coverage of the Darwin imager. (b and c) Two-dimensional maps
of 630-nm airglow intensity at (b) Sata and (c) Darwin
at 1502 UT (2402 LT) on August
9, 2002. The all-sky images are converted to geographical coordinates
assuming the emission layer at an altitude of 250~km. Color levels in each image
show percentage of the airglow intensity deviations from 1-hour average to the
background.
3. Coming
Workshops
Domesitic
(1) Space
Weather/Climate Symposium (24-26 November at Nagoya University)
(2)
Mesosphere Thermosphere Ionosphere Workshop (25-26 November at Nagoya University)
(3) GPS/GNSS
Symposium 2004 (17-19 November at Tokyo University of Marine Science and
Technology.
International
(1)
International Workshop on Seismo Electromagnetics (15-17 March 2005, Chofu, Tokyo, Japan)
(2) The 11th
International Symposium on Equatorial Aeronomy
(ISEA-11) (9-14 May2005 in Taipei, Taiwan)
http://csrsddc.csrsr.ncu.edu.tw/isea-11.html
(Prepared by T. Maruyama and M.
Yamamoto)