COMMISSION G: IONOSPHERIC RADIO AND PROPAGATION
Edited by Koichiro Oyama
G1. Ionospheric Techniques
Igi et al. [1999] studied thermospheric meridional winds for one solar cycle (1981-1991) thatwere derived from hmF2 data at Kokubunji, Japan and pointed out the solar cycle variations of
the winds over Japan to be qualitatively similar to those in other sectors.
Shiokawa et al. [1999] reported development of comprehensive optical instruments (OMTIs:
optical mesosphere thermosphere imagers) which consists of an imaging Fabry-Perot
interferometer, three all-sky cooled-CCD cameras, three tilting photometers and a Spectral
Airglow Temperature Imager (SATI). The OMTIs measure nighttime airglow at altitudes of
80-400 km.
An integrated optical/radio observations of Arctic middle and upper atmosphere at Poker Flat,
Alaska, has been conducted by a Japan-US collaboration. Middle atmosphere andthermospheric studies and scientific results arose from MF radar, Rayleigh lidar, Fabry Perot
interferometers, all-sky imagers, etc. at Poker Flat, Alaska, and Super DARN HF radar at King
Salmon, and related-funded works.
G2. Ionospheric Structure and ModelingG2.1. Ionospheric Structure
Ionosphere structure was mainly studied from electron density observation. Electron
tenperture data obtained in 1981-1982 by Japan’s sun observer Hinotori are still being
analysed to study seasonal latitude , and longitude dependence with respect to local
time .[Denton et al,1999][Dabas er al,1999],[Bailey et al 2000]. Electron Tenperature of the topside ionosphere which
is useful to calculate topside electron density was studied up to the height of 8000km using
Akebono data[Pavlov,2000a,2000b],[Pavlov,2001].
Mu radar is actively being operated and many findings have been reported[Su et al,1999],[Zhang et al,1999],[Balan et al,1999],[Kawamura et al,2000],[Zhang et al,2000],[Zhang et al,2001a,2001b],[Kawamura et al,2002],[Zhang et al,2002].

G2.2. Ionospheric Disturbances
Since the middle of 1996,University of Electro-Communication has made a routine ob
servation of TEC using GPS in Chofu, Tokyo. We examine in this paper the relation
ship between the perturbation components of TEC and geomagnetic field variations during 11 storm events for 1997-1998 to clarify the mid-latitude characteristics of TEC
variations at the time of magnetic storms(Yamamoto et al.,2000). The perturbation components of TEC were derived every 20 seconds by subtracting quiet-time TEC val
ues which are estimated as the average of both 3 days just before and after the storm period. The magnetic field data from Memanbetsu Magnetic Observatory, Hokkaido, are used for the identification of the storm-time variations. Our results show that1(1) the amplitude level of the TEC variation tends to increase during the first 24 hrof storm and then decrease below its usual-day level with recovery in one or two da
ys later for the typical magnetic storm, and (2) during a negative-value phase of the
TEC variation, which
follows the initial positive hump structure, the perturbation amplitude of TEC shows aremarkable reduction in summer compared to in winter.
Shiokawa et al. [2000] studied storm-time airglow enhancements observed at midlatitudes
using an airglow imager, a GPS receiver network, ionosondes and the DMSP satellite. The
airglow enhancement observed equatorward of Japan was explained by equatorial plasma
fountain caused by electric field penetration associated with storm-time substorms, which was
identified as an upward plasma drift by the DMSP satellite.
Kubota et al. [2000] and Saito et al. [2001] showed large-scale view of medium-scale travelingionospheric disturbances (MSTIDs) over Japan using multi-point airglow imaging observations
and a GPS receiver network. They found that MSTIDs propagated southwestward over morethan 1500 km. The correlation between MSTIDs seen in the airglow and GPS-TEC (total
electron content) was very good. Occurrence of field-aligned irregularities observed by the
MU radar was also correlated with the observed MSTIDs.
Sahai et al. [2001] studied small-scale (30-50km) airglow depletion structures in 630-nm
images during a storm of February 12, 2000, possibly caused by non-linear interactions of
mesoscale TIDs and enhanced equatorial anomaly. They also showed that enhanced
storm-time ionospheric disturbances represented by spread-F and GPS phase fluctuations wereconfined in the midlatitudes.
Minami et al. [1999] performed an experiment of artificial stimulation of the ionosphere using
high power radio waves at the HIPAS facility in Alaska. Diagnostics, using a multi-channel
30 MHz scanning cosmic radio noise absorption, at a site 35 km from the transmission site
revealed the excited height of 90 km. Atmospheric pressure waves with a period of 10 min,probably generated in the ionosphere by the high-power HF, were simultaneously observed on
the ground.
G2.3. Ionospheric Irregularities
Kagan et al. [2000] tried to explain the generation mechanism of midlatitude E region
irregularities in sporadic E layer in terms of neutral wind-driven instability instead of
traditional plasma instabilities pertinent to the E region.
Ionospheric E and F region irregularities at southern high latitudes has been explored using theSuperADRN coherent HF radars at Syowa Station. Fukumoto et al. [1999, 2000] analyzed alarge data-set of F region echoes to find relationship among echo power, Doppler velocity andspectral width, and discussed plasma instability processes capable of explaining therelationship. Ogawa et al. [2001] examined statistical characteristics of E region Doppler
velocity to show in particular that part of the velocities at near ranges represents motions of thelower thermosphere and the upper mesosphere. Makarevitch et al. [2001] compared
simultaneous HF and VHF radar echoes returned from common volume in the E region toshow dissimilarity between echo characteristics at HF and VHF bands, and pointed out theimportance of HF wave refraction due to disturbed ionosphere.[Tsunoda Many results are being
ohfained by MO radar and other radar [Tsunoda et al,1999],[Tsunoda et al,2000],[Rao etal,2000],[Maruyama et al,2000],[Otsuka et al,2002],[Saitoh et al,2002],[Maruyamaet al,2002].
G2.4. Ionospheric Dynamics
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Shiokawa et al. [2001] reported unusual appearance of an SAR arc at 34.7 MLAT (northernpart of Japan) during a weak storm of Dst = -49nT, about 2 days after the very weak solar windinterval of May 10-11, 1999.
G2.5. Particles and Auroras
From observations with a 500-MHz incoherent scatter radar on Svalbard, Buchert et al. [1999]
found unusual coherent echoes probably due to ion-acoustic plasma waves excited byfield-aligned currents.
Nishino et al. [1999a] case-studied slowly varying daytime radio wave absorption at 30 MHz
observed with an imaging riometer at Ny Alesund, Svalbard. From simultaneous F region HF
backscatter echo and electron flux observations, they concluded that the absorption was likely
caused by precipitation of eastward drifting auroral electrons generated by substorms in themidnight region.
30 MHz imaging riometers at Ny Alesund (NYA) and Danmarkshavn (DMH) in the Arctic andZhongshan (ZHS) in Antarctica were used to examine conjugate features of daytime
ionospheric radio wave absorption. Nishino et al. [1999b] studied post-noon absorption
simultaneously observed at these stations. The absorption was a spike-type with weakintensity during high solar wind dynamic pressure and was due to high-energy electrons
precipitation from the closed dayside magnetosphere. Nishino et al. [2000] identified
simultaneous afternoon and noon absorption spikes at NYA and ZHS and at DMH and ZHS,
respectively, in association with a steep increase in solar wind dynamic pressure and its
synchronized spike-type IMF excursion. Magnetic field compression associated with thesudden pressure increase might stimulate a population of magnetospheric electrons located at
the equatorward boundary of the cusp/cleft. Nishino et al. [2001] reported quasi-periodic,
conjugate absorption spikes associated with a sequence of solar wind dynamic pressure pulses
during northward interplanetary magnetic field. Comparison between absorption images andsimultaneous all-sky aurora images at ZHS showed that the spikes had a feature of small-scale,eastward-moving enhancement embedded within a large-scale absorption region
G2.6. Polar Electrodynamics
The SuperDARN HF radars have been utilized to investigate electrodynamics in the cusp
ionosphere. Nishitani et al. [1999] found very large-scale (5 hours in magnetic local time)flow burst that occurred in association with large-scale reconnection at the daysidemagnetopause under high solar wind density and strong southward interplanetary magnetic
field. In conjunction with the EISCAT Svalbard radar, Ogawa et al. [2001] case-studied indetail plasma density suppression process in the cusp ionosphere to find enhanced plasma
convection or flow burst to be important process to generate polar patches.
G2.7. Modeling of Planetary Ionospheres
Shinagawa and Bougher [1999] studied the dynamics and structure of the Martian ionosphereusing a two-dimensional MHD model. It was found that the scale height of the modeled
ionosphere is significnatly smaller than that of the observed ionosphere under typical solar
wind conditions, suggesting that the ionosphere of Mars is controlled by possible intsinsic
magnetic field or some other effects.
Shinagawa [2000] reviewed observations and modeling studies of the ionosphere of Mars.
Recently the Mars Global Surveyor has detected strong but local magnetic field of crustal
origin in various regions at Mars, while the global intirinsic magnetic field of core origin was
3

insignificant.
Although the ionosphere of Mars is basically similar to Venus, the crustal magnetic field at
Mars is likely to play an important role in the ionospheric processes.
G3. Ionospheric Radio Propagation
G3.1. ELF/VLF
An analytical time domain solution of ELF electromagnetic waves in the subionospheri
c waveguide is studied [Nickolaenko et al., 1999d]. Multiple electromagnetic pulses [Nickolaenko and Hayakawa, 1999 a] are found to turn into a single pulse when propagat
ing in the subionospheric waveguide[Nickolaenko and Hayakawa, 1999 b]. A new ELF
observing station is established in Moshiri, Hokkaido, using fully-calibrated wide-band(
1Hz < f < 1kHz) 3-component ELF measurement to study ELF transients and Schumann resonances [Hobara et al., 2000].

The continuons analog records of the horizontal magnetic field during the period ofAugust 1967 to November 1970 have been analyzed and a comparison of theseSchumann resonance data with those made recently in Europe allows us todemonstrate the similarity and stability of the global thunderstorm variations on aseasonal scale [Nickolaenko et al., 1999 e]. We suggest an algorithm forchoosing the position for the observation of Schumann resonances [Nickolaenko
and Hayakawa, 1999 c]
Detailed analysis of early/fast Trimpi phenomena revealed two different regimes intheir temporal behavior. These regimes are used to deduce the plasma structure of
the ionospheric perturbation associated with sprites [Molchanov et al., 1998]. The
effect of those Trimpi- induced ionospheric perturbations on subionospheric VLF
propagation has been studied by means of FDTD method [Otsuyama et al., 2001].
G3.2. VHF
Nishino et al. [1999c] conducted experiments, using radio links between a 30 MHz transmitter
located at Murmansk, Russia and two receivers used as an imaging riometer at Ny Alesund,Svalbard, and Tjornes, Iceland, to characterize radio wave scatter in the high-latitude
ionosphere, and found that the scatter was caused by large-scale, irregular electron density
enhancements at the lower edge of the ionosphere.
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Shinagawa, H., and S. Bougher [1999],A two-dimensional MHD model of the solar windinteraction with Mars, Earth Planets Space, 51, 55-60.
Shiokawa, K., Y. Katoh, M. Satoh, M. K. Ejiri, T. Ogawa, T. Nakamura, T. Tsuda and R. H.
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[1999],First Observations of Quasi-Periodic Radar Echoes From Stanford, California, Geophys.
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Tsunoda, R. T., M. Yamamoto, H. Mori, and S. Fukao [2000], SEEK S310-25: Quasi-Periodic
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Yamamoto, A., Y. Ohta, T. Okuzawa, S. Taguchi, I. Tomizawa and T. Shibata [2000],"Characteristics of TEC variations observed at Chofu for geomagnetic storms," Earth
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Yamazaki, R., K. Igarashi, M. Nagayama, and I. Nishimuta [2000], "The effect of signal
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Zhang, S.-R., S. Fukao, and W. L. Oliver [1999], Data Modeling and Assimilation Studies with
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Zhang, S.-R., S. Fukao, W. L. Oliver, and Y. Otsuka [1999], The Height of the Maximum
Ionospheric Electron Density over the MU Radar, J. Atmos. Solar Terr. Phys., 61, 1367-1383.
Zhang, S.-R.. W. L. Oliver, S. Fukao, and Y. Otsuka [2000], A Study of the Forenoon
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Zhang, S.-R., W. L. Oliver, S. Fukao, and S. Kawamura [2001], Extraction of Solar and
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Zhang, S.-R., W. L. Oliver, J. M. Holt, and S. Fukao [2002], Solar EUV Flux, Exospheric
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MiscellaneousAbe, T., D.J. Knudsen, A.W. Yau, and S. Watanabe, E. Sagawa [2001], “Simultaneous satellite
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Balan, N., I.S. Batista, M.A. Abdu, G.J. Bailey, S. Watanabe, J. MacDougall [2000],“Variability of an additional layer in the equatorial ionosphere over Fortaleza”, J. Geophys.
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Balan, N., R. Fujii. [2001], “Changes in the ionosphere over EISCAT during ion frictional
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11

Buchert, S.C., A.P. van Eyken, T. Ogawa, S. Watanabe [1999], “Naturally enhanced
ion-acoustic lines seen with the EISCAT Svalbard radar”, Adv. Space Res., 23, 1699-1704.
Ejiri, M. K., K. Shiokawa, T. Ogawa, T. Nakamura, R. Maekawa, T. Tsuda, and M. Kubota,[2001],Small-scale gravity waves near the mesopause observed by four all-sky airglow imagers,
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Endo, M., R. Fujii, Y. Ogawa, S.C. Buchert, S. Nozawa, S. Watanabe, N. Toshida [2000], “Ionoutflow and downflow at the topside ionosphere observed by the EISCAT VHF radar”, Ann.
Geophysicae, 18, 170-181.
Gavrilov, N. M., H. Hashiguchi, and S. Fukao [1999], Multi-Beam MU Radar Measurementsof Advective Accelerations in the Atmosphere, Geophys. Res. Lett., 26, 315-318.
Gavrilov, N. M. and S. Fukao [1999], A Comparison of Seasonal Variations of Gravity Wave
Intensity Observed by the MU Radar With a Theoretical Model, J. Atmos. Sci., 56, 3485-3494.
Gavrilov, N. M., S. Fukao, and T. Nakamura [1999] Peculiarities of Interannual Changes in the
Mean Wind and Gravity Wave Characteristics in the Mesosphere over Shigaraki, Japan,
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Gavrilov, N., and S. Fukao [1999], The MU Radar Measurements and Modeling of the Gravity
Wave Climatology and Sources in the Atmosphere, Adv. Space Res., 24, 565-574.
Gavrilov, N. M., S. Fukao, and T. Nakamura [2000], Average Statistical Characteristics ofLong Gravity Waves Observed by the Middle and Upper Atmosphere Radar in the Mesosphere,
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Gavrilov, N. M. S. Fukao, and T. Nakamura [2000], Gravity Wave Intensity and Momentum
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Gavrilov N.M., and S. Fukao [2001], Hydrodynamic tropospheric wave sources and their rolein gravity wave climatology of the upper atmosphere from the MU radar observations, J. Atmos.
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Higashikawa, A., T. Nakamura, and T. Tsuda [1999], Seasonal Variations of Gravity Waves
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Kubo K., and T. Sugiyama, and S. Fukao [2002], Evaluation of Mesospheric VHF Echoes
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OI 630-nm Nightglow Images Over Japan by Using a Multi-Point Imager Network during the
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Murayama, Y., K. Igarashi, I. Nishimura, R. Yamazaki, K. -I. Oyama, T. Tsuda, T. Nakamura, S.
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Nakamura, T., T. Tsuda, R. Maekawa, M. Tsutsumi, K. Shiokawa, and T. Ogawa[2001],Seasonal variation of gravity waves with various temporal and horizontal scales in the
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Atmos. Solar-Terr. Phys., In press.
Namboothiri, S. P., T. Tsuda, and T. Nakamura [1999], Interannual Variability of mesosphericmean winds observed with the MU radar, J. Atmos. solar Terr. Phys, 61, 1111-1122.
Namboothiri, S.P., P. Kishore, K. Igarashi, T. Nakamura, and T. Tsuda [2000], MF radarobservations of mean winds over Yamagawa (31.2N, 130.6E) and Wakkanai (45.4N, 141.7E), J.
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Nishimura, K., T. Sato, T. Nakamura, and M. Ueda [2001], High sensitivity radar-opticalobservations of faint meteors, IEICE T. Electron, E84C (12), 1877-1884.
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Pickett, J.S., D.A. Gurnett, J.D. Menietti, M.J. LeDocq, J.D. Scudder, L.A. Frank, J.B.
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R. A. Buriti, T. Nakamura, T. Tsuda, S. Fukao, M. Tsutsumi, H. Takahashi, and P. P. Batista,[2000],Mesopause Temperature Observed by Airglow OH Spectra and Meteor Echoes at
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Sato, T., T. Nakamura, and K. Nishimura [2000], Orbit determination of meteros using the MU
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Shiokawa, K. , Y. Katoh, M. Satoh, M. K. Ejiri, T. Ogawa, T. Nakamura, T. Tsuda, and R. H.
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Shiokawa, K., M. K. Ejiri, T. Ogawa, and T. Nakamura [2000], Distant lunar sodium tailobserved in the Japanese local-time sector during the Leonid meteor shower of 1998, J.
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Takeda S., T. Nakamura, and T. Tsuda [2001], An improvement of wind velocity estimationfrom radar Doppler spectra in the upper mesosphere, Ann. Geophys., 19 (8), 837-843.
Takahashi, H., P. P. Batista, R. A. Buriti, D. Gobbi, T. Nakamura, T. Tsuda, and S. Fukao[1999], Response of the airglow OH emission, temperature and mesopause wind to theatmospheric wave propagation over Shigaraki, Japan, Earth Planets and Space, 51, 863-875.
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