Solar-Terrestrial Environment Laboratory Nagoya University Annual Report

Transcription

1 Solar-Terrestrial Environment Laboratory Nagoya University Annual Report

2 The Annual Report was published in October 2007 by the Solar-Terrestrial Environment Laboratory of Nagoya University. Copies of this report are available from the Director s office of the Laboratory. published by Solar-Terrestrial Environment Laboratory Nagoya University Furo-cho, Chikusa-ku, Nagoya , Japan TEL FAX Toyokawa Branch on the Toyokawa campus of Nagoya University Honohara 3-13, Toyokawa, Aichi , Japan TEL FAX

3 Foreword The movement of the Solar-Terrestrial Environment Laboratory (STEL) from the Toyokawa campus to the main campus of Nagoya University commenced at the end of FY Although all students have moved to the main campus, lack of space in our main building due to reconstruction of several buildings to withstand earthquakes in the main campus has prevented us from completing the movement of the remaining part of the research group and technical staff, and the library and workshop until the end of FY As a major change of our organization structure, the three administrative offices of STEL, the Research Institute of Environmental Medicine and the EcoTopia Science Institute were unified in October 2006 in order to increase the efficiency and strength of the administrative capability. One of our observatories, Sakushima Observatory, which had completed its purpose, was abolished in 2006 after 40 years since its establishment in Nagoya University has placed its present research laboratory and research center under the inter-university collaborative system that respectively has a mission to develop the most advanced research and education in a specified field within the framework of seamless linkage between space science and earth and environmental science, and it has made a strong commitment to enhance developments of the laboratory and center as leading organizations. Additionally, STEL, which is deeply related not only to space science but also to earth and environmental science, has been contributing to education and research in cooperation with the Graduate Schools of Science, Engineering and in cooperation with the 21st Century COE Program Dynamics of Sun-Earth-Life Interactive System which consists of the Graduate School of Environmental Studies, Hydrospheric Atmospheric Research Center and STEL. Since the above COE program will cease to exist in FY 2007, it is very urgent for us to discuss our next Global COE Programs extensively with the Graduate Schools of Science, Engineering and Environmental Studies. STEL hopes to enhance collaboration not only in education but also in research with these schools. The Scientific Committee on Solar-Terrestrial Physics (SCOSTEP) under International Council for Science (ICSU) has implemented Climate And Weather of Sun-Earth System (CAWSES) since 2004, aiming at the full understanding of the entire Sun-Earth domain as one system while fostering a scientific approach to better understanding the short-term (Space Weather) and long-term (Space Climate) variability. STEL has been applying this CAWSES as the central project during the present medium-term plan period, and STEL has fostered leading research under the inter-university collaborative system as a national and international research center. The project has been supported by a newly introduced governmental research fund for a 5 year period starting fiscal year This presents us with a significant possibility of research development and enables us to construct new costly observation/experiment instruments necessary for successful implementation of CAWSES. In 2005, construction began on a new interplanetary scintillation (IPS) phased array antenna system called the Solar Wind Imaging Facility on the Toyokawa campus which will be completed in An HF Radar at Rikubetsu, Hokkaido, which is part of the SuperDARN HF radar network, was completed in December 2006 and has started continuous observations. This Hokkaido radar provides a unique and powerful tool to i

4 examine a number of thus far unsolved important physical processes in the sub-auroral zone and can be used for inter-university collaboration studies. In FY 2006, development began of both a millimeter-wave band radiometer for measuring ozone, water-vapor and chlorine monoxide in the middle and upper atmosphere and a spectrometer for measuring methane, carbon dioxide. Also, there is a plan in 2007 to set up a meteor radar at Bear Island which lies halfway between Svalbard and Tromsø EISCAT radars. Another plan is to establish Fabry-Perot interferometers which are state-of-the-art instruments for observations in the thermosphere and mesosphere and place them up at the EISCAT Tromsø site and at middle latitude magnetic conjugate observatories that STEL has been operating. This fund allows us to provide outside STEL researchers with traveling expenses necessary for overseas observations, which has been our desire for a long time but not possible previously. We formed a new committee under the Geospace Research Center by reconstructing the Technical Committee of Overseas Observations in 2006 and the committee invites requirement/application from collaborative researchers for this purpose. We will of course continue to support individual collaborative researchers and sponsor topical symposia/workshops to provide a forum for stimulating discussions on solar-terrestrial science. In order to foster collaborative research activity and conduct cutting edge research of solar-terrestrial science, a scientifically attractive future plan based on a well-thought out long-term plan is definitely needed. Based on objective evaluation to reveal problems to overcome and future direction to pursue, we have decided to conduct an external evaluation in FY We have started to discuss this urgent issue more concretely and are attempting to design the next 5 year plan as early as possible, for which valuable suggestions/discussions/requirements from nationwide researchers/institutions are critically important. We are pleased to report that leading and active research has been conducted ranging from solar flare, past solar activity more than 2000 years ago, solar wind, magnetosphere, ionosphere, thermosphere to middle and lower atmosphere. This Annual Report for FY 2006 (April 2006 March 2007) summarizes the scientific accomplishments that each research group has achieved, as well as an account of the STEL s activity as an institute which operates under Japan s inter-university collaborative system. It also contains activity reports of a number of committees inside STEL that promote space science and geospace research and education. October 2007 R. Fujii Director ii

5 Table of Contents Foreword... i 1. Progress in Research... 1 Atmospheric Environment Ionospheric and Magnetospheric Environment Heliospheric Environment Integrated Studies 2. Publications and Presentations Published Books and Papers International Conferences 3. Staff Organization Staff List 4. Management System Committee System Advisory Board 5. Collaborative Research Activities Collaborative Research Program Symposia/Workshops Reports from Collaborative Research Committee on STER CAWSES Space Weather Database in Japan 6. International Relations Academic Exchange International Collaboration Visitors iii

6 7. Education Graduate Programs Undergraduate Education 8. Research-Related Activities Computer/Network 9. Public Service Open Symposium Open House Outreach Activities 10. Geospace Research Center Projects Observatories 11. Facilities Library Properties iv

7 1. Progress in Research ATMOSPHERIC ENVIRONMENT The chemical composition of the terrestrial atmosphere, which has evolved with life on Earth, is quite different from that of other solar planets. In recent years, the exhaustion of minor molecular species by human activity has destroyed the balance of the atmospheric environment, causing global warming, the destruction of the stratospheric ozone layer, air pollution, and so on. In order to understand these phenomena more thoroughly, the Division of Atmospheric Environment is investigating: (1) the time variations and circulation of minor molecular constituents, (2) the fundamental processes of chemical reactions, and (3) the composition of aerosol and its influence on the atmospheric environment. To enhance our laboratory research and remote field observations, we are developing several original instruments and methodologies. Observational and Laboratory Studies of the Upper and Middle Atmosphere (1) Millimeter-Wave Band Observations of Stratospheric and Mesospheric Water-Vapor Using a Highly Sensitive Radiometer at Atacama Highland Atmospheric water-vapor, one of the richest minor constituents in the terrestrial atmosphere, is closely linked to global warming and ozone depletion via the HO x cycle. Recent research shows stratospheric water-vapor has been increasing at a rate of ~1%/year over the last two decades. However, the mechanism driving the increase is not yet fully understood. In addition, the increase in water-vapor may further reduce the stratospheric temperature in the polar region, which, in turn, affects the ozone hole through the formation of polar stratospheric clouds. The millimeter-wave band radiometer spectrometer (Atacama Highland, Chile; 23.0 S, 67.7 W, altitude 4800 m) permits us to observe simultaneously the emission lines of the stratospheric and mesospheric water-vapor isotopes (H 2 O at GHz and H 2 18 O at GHz). Observational conditions at the site are excellent since the lack of thick tropospheric water-vapor results in high atmospheric transparency. The isotopic ratio changes in accordance to chemical fractionation as the water-vapor enters the stratosphere through the tropical tropopause. This ratio is also influenced by methane oxidization through photochemical reactions. Almost all molecular species excited thermally in the Earth s atmosphere have radiative emission lines at the millimeter to submillimeter-wave bands. In our radiometer system, an incident radio-wave signal is fed to a highly sensitive Superconductor-Insulator-Superconductor (SIS) heterodyne mixer through mirrors and a 1/4 path length modulator (PLM). The mixer is cooled by a 4K-closed cycle Gifford-McMahorn/Joule-Thomson (GM/JT) cryocooler. The intermediate frequency (IF) signal down-converted in the mixer is amplified by a low-noise cooled High Electron Mobility Transistor (HEMT) amplifier. An acousto-optical spectrometer (AOS) is used to analyze the signal spectrally. The observed data, instrumental status, and other environmental information such as room temperature are automatically transferred to our 1

8 Time-variations of H 2 O and H 2 18 O column densities at 50 km and 40 km alt. observed in Atacama Highland. domestic laboratory by satellite. Ground-based heterodyne observations have several advantages: (a) twenty-four hour continuous observations can be performed without the need of a background source like the Sun; (b) the data is less influenced by aerosol; and (c) the minor molecular constituents can be remotely observed under short integrational time periods. In 2006 we developed an innovative analytical algorithm to retrieve simultaneously the overlapped H 2 18 O and O 3 spectral lines. We derived the vertical distribution of the H 2 18 O abundance (15 to 80 km alt.) from the spectral data observed from September to December The spectral data were integrated each day. We found that the H 2 18 O volume mixing ratio (VMR) reaches maximum (12 ppbv) at km alt. The H 2 18 O VMR at around 40 km alt. showed a clear increasing trend of 1.8 ppbv during the four months, while the VMR above 50 km alt. was almost unvarying. To derive H 2 O VMR we analyzed the data observed by the Microwave Limb Sounder of AURA satellite. The H 2 O VMR decreased around 40 km and held steady above 50 km alt. These results suggest that in the Atacama Highland the 18 O at around 40 km alt. increased, while the 18 O at above 50 km alt. held relatively steady during the observed period. (2) Development of a 22 GHz-Band Compact Radiometer for Water Vapor Observations We are developing a compact radiometer system for the observation of 22 GHz-band H 2 O emission line. The 183 GHz frequency band H 2 O line mentioned above is two orders greater than that of the 22 GHz band lines. The 183 GHz strong line is useful to precisely derive the isotope ratio of stratospheric and mesospheric water-vapor. On the other hand although the 22 GHz week line needs long integration time, it is observable even at low-altitudes because of its good atmospheric transparency. In addition the 22 GHz band radiometer can be constructed without any cryogenic devices, which is therefore considered to be adequate for exploring global ground-based network system for the observations of the water-vapor in middle atmosphere. In this system an input signal is directly amplified by super low-noise HEMT amplifiers (made in Germany, GHz) which is operated at room temperature. In 2006 we developed a focus mirror system which slides as 1/4- PLM to cancel standing waves appeared on spectral baseline. In addition we newly installed a commercial digital spectrometer with high frequency resolution (bandwidth: 1 GHz, resolution 60 khz) and a phase locked oscillator with a GPS reference signal. In February 2007 with this system we 2

9 Long-term variability and 12-month moving average of O 3 and HNO 3 column densities observed with FTIR in Rikubetsu. succeeded a detection of 22 GHz band H 2 O lines at Toyokawa campus. The system noise temperature is achieved to be 158 K (single side band). (3) Study of the Correlation Between Short-term Changes in Stratospheric Ozone and Dynamical Variability Recent researches have shown that short term variations in ozone column density are directly related to atmospheric dynamics [SPARC Report, 2001]. In order to study in detail the mechanism behind the variability in stratospheric ozone we investigated the correlation between short-term fluctuations of ozone abundances and dynamics for each altitude based on multiple regression analysis. The vertical distribution and total column density of ozone were derived from the data obtained between November 1999 and December 2002 using (1) a ground-based millimeter-wave band superconducting radiometer at the Rikubetsu Stratospheric Monitoring Station of the National Institute for Environmental Studies (NIES) and (2) a Dobson spectrometer at the Aerogical Observatory of the Japanese Meteological Agency, respectively. Under this analysis the horizontal and vertical advection of the ozone were expressed by potential vorticity on an isentropic surface and potential temperature, respectively, using NCEP Reanalysis DATA for each altitude. We found that the ozone VMR at 20 km and 26 km alt. correlated well with the potential temperature and the potential vorticity, respectively. This suggests that the short-term fluctuations in the ozone VMR at 20 km and 26 km alt. can be explained by vertical displacement and horizontal advection, respectively. We found also that the short-term fluctuations in the total ozone column density were well explained by using potential temperature. Since the ozone VMR in Sapporo reach maximum at around 20 km alt., the short-term fluctuations in the total ozone column density appear to be affected primarily by the atmospheric dynamics occurring around 20 km alt. (4) Data Analysis of Ozone and Nitric Acid Observed by a Ground-Based FTIR Spectrometer in Rikubetsu We have witnessed a trend toward a decreasing global average of stratospheric chlorine loading following the Kyoto Protocols. However, neither the Antarctic ozone hole nor the total ozone column density has exhibited any corresponding trend toward recovery. NO x in 3

10 Left: 22 GHz band radiometer system operated at ambient temperature. The spectral line of H 2 O detected at Toyokawa campus is superimposed. Right: Portable millimeter wave-band radiometer system with low consumption 4K-GM cryostat newly developed for observational mission at Showa Station in Antarctica. the lower stratosphere, known to be one of the greatest contributors to ozone destruction, ultimately converts to reservoirs such as HNO 3 due to the oxidization. To investigate more fully the correlation between the long-term changes in HNO 3 and O 3 abundances, the time-variations in their total column densities and vertical distributions were analyzed using SFIT2 retrieval software (version 3.92). We used Fourier Transform Infrared (FTIR) spectrometer data taken from the Rikubetsu Observatory from 1995 to 2005 ( cm 1 and cm 1 for O 3 and HN O 3, respectively). In the short-term range, the O 3 total column density reached maximum and minimum in spring and fall, respectively. The HNO 3 total column density showed a similar trend. On the other hand, the long-term changes in the O 3 and HNO 3 moving averages were %/yr and %/yr, respectively, indicating no significant trends. (5) Development of a Millimeter-Wave Band Radiometer for Observations at the Showa Station in Antarctica Atmospheric observations in Antarctica are key to understanding heterogeneous chemical reactions in polar stratospheric clouds, the influence of the midnight Sun and atmospheric convection on photochemical reaction processes, and so on. We, in collaboration with the National Institute of Polar Research, are promoting atmospheric observations at the Showa Station in Antarctica using our millimeter-wave band radiometer system. The station is limited in both electric power and weight. Accordingly, we constructed a portable radiometer system using a low-consumption 4 K GM cryocooler newly developed. The cooling capacity of the 4 K stage and the power consumption are 0.3 W and 2.1 kw, respectively. We plan to assemble low-noise superconducting SIS heterodyne receiver on this system for 100 to 250 GHz frequency bands. (6) Laboratory Study of the O( 1 S) Formation Process in the Photolysis of O 3 and its Atmospheric Implications We used a highly-sensitive technique to detect O( 1 S) atoms (vacuum ultraviolet laser-induced fluorescence (VUV-LIF) spectroscopy) to study O( 1 S) production from the UV 4

11 O( 1 D) H 2 O OH Φ(λ) k = N 2, O 2 k ~10-11 Known process O 3 O( 3 P) O k ~ New process H 2 O Φ(λ) O( 1 S) OH k = Branching to OH formation: 0.61 Altitude (km) (R 1S OH /R 1D OH ) 100 ( ) Left: New process proposed for OH formation in the stratosphere. We have found a new important reaction process of O( 1 S) + H 2 O in addition to the known process of O( 1 D) + H 2 O. Right: Percentage fraction of the calculated OH production from O( 1 S) + H 2 O relative to O( 1 D) + H 2 O, R OH 1S /R OH 1D 100, as a function of altitude in the mid-latitudes. photodissociation of O 3, N 2 O, and H 2 O 2. The quantum yields of O( 1 S) from O 3 photolysis at 215 and 220 nm were ( ) 10 4 and (5 3) 10 5, respectively. From a thermo-chemical standpoint, the O( 1 S) formation from O 3 photolysis at 215 and 220 nm can be attributed to a spin-forbidden process: O( 1 S) + O 2 (X 3 g ). An analysis of the Doppler profile of O( 1 S) produced from O 3 photolysis at 193 nm also indicates that O( 1 S) atoms are produced by the spin-forbidden process. During the photolysis of N 2 O and H 2 O 2 at 193 nm, no discernible signal of O( 1 S) atoms was detected. The upper limit values of the quantum yields of O( 1 S) from N 2 O and H 2 O 2 photolysis at 193 nm was estimated to be and , respectively. Based on these findings, the impact of O( 1 S) formation from O 3 photolysis on atmospheric OH radical formation through the reaction of O( 1 S) + H 2 O was estimated. We found that the contribution of the O( 1 S) + H 2 O reaction to the OH production rate was ~2 % of the O( 1 D) + H 2 O contribution at 30 km alt. at mid-latitudes. We also investigated the implications of these experiments to the terrestrial airglow of O( 1 S) at nm. Observational and Laboratory Studies of the Lower Atmosphere (1) Atmospheric Oxidation Processes of Ketone Molecules in the Troposphere In recent years it has become evident that significant concentrations of oxygenated volatile organic compounds (OVOCs) are present in the global troposphere. Ketones represent an important class of OVOCs, which are emitted into the atmosphere from a variety of anthropogenic and natural sources, where they eventually become available for photochemical transformations. Ketones are of particular interest to atmospheric chemists for a number of reasons, including their potential toxicity, their ability to photolyze and produce free radicals, their ability to form stable atmospheric products, and their contributions to the smog cycles. The gas-phase reactions of Cl atoms with acetone, butanone, 2-pentanone, 3-pentanone, 2-hexanone, 3-hexanone, and cyclopentanone at K were studied using pulsed laser photolysis vacuum UV laser-induced fluorescence (PLP-LIF) techniques. Cl( 2 P 3/2 ) atoms were produced by Cl 2 photolysis at 351 nm and monitored using LIF spectroscopy at nm (3p 5 2 P 3/2 3p 4 4 s 2 P 3/2 transition). The rate 5

12 LIF Intensity / arb.units ln(lif Intensity) Delay Time / µs Delay Time / µs Decay Rate / 10 4 s Butanone Acetone [Reactants] / molecule cm -3 Left: Typical Cl( 2 P 3/2 ) (= denoted Cl) decay profile observed in an experiment using a mixture of Cl 2 and butanone. The insert shows a semilogarithmic plot of the temporal decay of the VUV-LIF signal of Cl. Right: Pseudo-first-order plots for acetone and 2-butanone. coefficients for reactions of Cl atoms with acetone, butanone, 2-pentanone, 3-pentanone, 2-hexanone, 3-hexanone, and cyclopentanone were: ( ) 10 12, ( ) 10 11, ( ) 10 10, ( ) 10 11, ( ) 10 10, ( ) 10 10, and ( ) cm 3 molecule 1 s 1, respectively. The results for acetone and butanone were consistent with previous studies. The results for 2-pentanone, 3-pentanone, 2-hexanone, and 3-hexanone were higher by a factor of 2-3 over those from previous absolute rate studies. Likely explanations for these discrepancies are discussed. The tropospheric lifetimes of ketones with respect to the reaction with Cl atoms were estimated. The calculated lifetimes of ketones indicate that a reaction with Cl will dominate over a reaction with OH in marine boundary and coastal regions. Cl atoms may play a more important role in the oxidation of ketones than previously thought. (2) Real-Time Analysis of SOA Particles Using a Laser-Ionization Single-Particle Aerosol Mass Spectrometer We recently developed a laser-ionization single-particle aerosol mass spectrometer (LISPA-MS) for real-time single-particle measurements. The LISPA-MS is capable of high time-resolution measurements of the size and chemical compositions of individual particles. Changing the voltage polarity of the instrument produces both positive and negative-ion mass spectra for individual particles. We performed a real-time analysis of secondary organic aerosol (SOA) particles formed from cyclohexene ozonolysis in a smog chamber using the LISPA-MS. The instrument found both size and chemical compositions of individual aerosol particles at a high time-resolution (~ 2 s at the maximum). Both positive and negative-ion mass spectra were detected. Standard particles generated from dicarboxylic acid solutions using an atomizer were also analyzed. For both standard and SOA particles, the negative-ion mass spectra provided information about the molecular weights of the organic compounds in the particles, since the intense ions in the negative-ion mass spectra are primarily attributable to the molecular-related ions [M H]. It was demonstrated that real-time single-particle analysis of SOA particles using the LISPA-MS can accurately provide data on the formation and transformation processes of SOA particle in smog chambers. 6

13 Left: Schematic diagram of the single-particle aerosol mass-spectrometer developed in our laboratory. The air sample with aerosols is introduced into the vacuum chamber through differential pumping stages. Particles are detected by the detection of scattering light using the cw laser (532 nm). The particle detected is vaporized and ionized by a pulsed laser (248 nm). The produced ions are accelerated by the electric field and detected through the time-of-flight mass spectrum region. Right: Photograph of the experimental apparatus. The large cylindrical vessel at the back is the photochemical smog chamber. The equipment in front is the single-particle mass spectrometer. The white box in the left is the excimer laser for the particle vaporization and ionization. (3) Development of THz Band Superconducting Devices for Remote Observations of OH Radical OH is one of the most important radicals in atmospheric chemistry because it is a strong oxidant linked to destructive processes of various atmospheric molecules. However, remote measurement methods of OH radicals are not fully established due to their short lifetime and low abundance, the result being an insufficient understanding of HO x chemistry. OH has transition lines at 2.5 and 1.8 THz (1 THz = Hz). THz is an unexplored frequency band in heterodyne sensing technology fields, since a conventional niobium-based SIS mixer cannot function properly due to the breakdown of superconducting cooper pairs by photon absorption. To overcome these obstacles, we are developing an alternative THz band heterodyne device known as a hot electron bolometer mixer (HEBM) in collaboration with the University of Tokyo. In 2006 we established the fabrication processes of superconducting thin NbTiN nano-bridge integrated with a quasi optical two-dimension antenna at the 2 THz frequency band. By adopting a thick lithography resist the bridge structures and the large antenna structures are patterned by using an electron-beam drawing system with a scanning electron microscope. We also fabricated a quasi optical mixer mount with an offset-axis parabolic mirror and a hyper-hemisphere lens into which an HEB chip was integrated. The IF port on the HEB chip was connected to the micro-strip line with aluminum wiring. We tested the mechanical and electrical durability of the mixer by repeatedly cooling the mount to 4 K using a closed cycle GM/JT mechanical cryocooler. The bolometric response of the HEBM was also checked. 7

14 Left: Quasi-optical HEB mixer mount with offset-axis parabolic mirror and hyper-hemisphere lens. Center: Quasi-optical twin-slot antenna for 2 THz frequency band. Right: NbTiN nano-bridge integrated at antenna feed point observed by Scanning Electron Microscope. Submillimeter-Wave Band Observations of the Planetary Atmosphere Investigating the constituents and isotope ratios of the planetary atmosphere is key to understanding the physical and chemical environment and the evolutionary processes of the solar planetary system. In order to study how solar activity, galactic cosmic rays, and the physical environment influence the chemical composition of the planetary upper atmosphere, we tested line survey observations of Mars, Jupiter, and Neptune at GHz using an ASTE 10-m radio telescope constructed at Pampa La Bola of Atacama Highland by the National Astronomical Observatory of Japan. Pointing accuracy was checked by scanning the continuum emission radiated from the disk of Jupiter every two hours. The 1 rms pointing error was about 2, sufficiently lower than the telescope beam width (22 FWHM at 345 GHz). Interference from strong absorption lines of terrestrial ozone with the spectral lines observed in 2005 made it difficult to identify the weak lines from the planets. In 2006 we developed a simulation tool based on a radiative transfer model simple enough to be used on a laptop computer. By optimizing the observational frequency band and system setting according to the simulated results, we could carry out the line survey observations toward the planets without any interference from the terrestrial ozone lines. 8

15 IONOSPHERIC AND MAGNETOSPHERIC ENVIRONMENT The Division of Ionospheric and Magnetospheric Environment is concerned with the physical processes of energy transfer (1) from the magnetosphere into the ionosphere and thermosphere, and (2) from the lower atmosphere to the upper atmosphere. Current research areas are the structure, electrodynamics, and neutral dynamics of the ionosphere and thermosphere at various latitudes. Particles and fields in the magnetosphere and high- and low-latitude auroral phenomena are also studied. These research activities are mainly achieved through ground-based observations using radio and optical equipment at widely dispersed stations, and analyses of observational data in collaboration with other research organizations. Studies using the European incoherent scatter radars have provided new insights into auroral phenomena and the high-latitude lower thermosphere. Optical, radar, and GPS satellite observations have greatly contributed to an increased understanding of the ionosphere, thermosphere, and upper mesosphere. OMTIs Optical mesosphere thermosphere imagers (OMTIs) have been developed since 1997 to study the dynamics of the thermosphere and near the mesopause. OMTIs consist of a scanning Fabry-Perot interferometer (FPI), nine all-sky CCD imagers, three tilting photometers, a spectral airglow temperature imager (SATI), and three airglow temperature photometers. OMTIs are located at several key points around the world: Shigaraki (34.8 N, E), Rikubetsu (43.5 N, 143.8ºE), Sata (31.0 N, E), Yonaguni (24.5 N, E), Darwin (12.4 S, E), Kototabang (0.2 S, E), Resolute Bay (74.7 N, E), Athabasca (54.7 N, E), and Ithaca (42.5 N, E). These instruments measure nightglow emissions, neutral wind, and neutral temperature at an altitude range of km. All of the OMTIs are fully automated. (1) Auroral Observations The measurements at Athabasca revealed a one-to-one correspondence between isolated auroras at subauroral latitudes and Pc 1 geomagnetic pulsations, suggesting the pitch-angle scattering of ring current particles by electromagnetic ion cyclotron waves (Pc 1 pulsations) in the inner magnetosphere. The isolated auroral arcs are narrow latitudinally (less than 170 km) and limited longitudinally ( km), suggesting that the scale of the pitch-angle scattering is very small in the inner magnetosphere. We also studied auroral broadband electrons (BBEs), which are sometimes observed by ionospheric satellites during magnetic storms and can produce low-latitude auroras. Using auroral particle data obtained by the FAST satellite, we found that the pitch-angle distribution of BBEs was isotropic at a higher-energy range above ~1 kev, while field-aligned electron fluxes were larger than the perpendicular fluxes below ~1 kev. These results imply that the higher-energy portion of the BBEs originates at higher altitudes in the inner magnetosphere and that the lower-energy portion is the result of acceleration parallel to the local magnetic field at lower altitudes near the satellite. 9

16 (2) Estimating Momentum Fluxes Carried by Mesospheric Gravity Waves Automated procedures were developed to identify small-scale ( km) atmospheric gravity waves observed in airglow images and to estimate momentum fluxes carried by the waves. The procedures included assessing noise emissions and making two-dimensional Fourier analysis. The estimated momentum flux was ~1 10 m 2 /s 2. Such a large flux can significantly accelerate/decelerate wind in the mesopause region, indicating that the small-scale gravity waves in the mesosphere carry a significant amount of momentum flux to the mesopause region. Mid-Latitude Ionospheric Disturbances (1) GPS Observations of TIDs Using GPS data obtained in 2006 from the GPS networks in North America, we investigated total electron content (TEC) variations caused by traveling ionospheric disturbances (TIDs) to find the following new characteristics of medium-scale TIDs (MSTIDs) and large-scale TIDs (LSTIDs): (1) Nighttime MSTIDs propagating southwestward with wavelengths of km are frequently observed in summer and winter, similar to the nighttime MSTID characteristics over Japan. Their wavefronts extend from 30 to 50 N. (2) Daytime equatorward-propagating TIDs with wavelengths of km are frequently observed in winter, similar to daytime MSTIDs over Japan and Southern California. (3) In rare cases, northward-propagating LSTIDs occur even during geomagnetically quiet conditions. (2) Ionospheric Disturbances Induced by Earthquakes An earthquake occurred east of the Kuril Islands at 0423 UT on January 13, Approximately 30 minutes after the earthquake, a TEC perturbation with an amplitude of approximately 0.03 TECU (1 TECU = electrons/m 2 ) propagated southwestward (azimuth Examples of (left) nighttime and (right) daytime MSTIDs detected with the GPS receiver network in North America, consisting of about 1400 receivers (as of December, 2006). These TEC maps are obtained by subtracting 60-minute running average from original TEC data and plotted by assuming an ionospheric altitude of 300 km. 1 TEC unit = electrons/m 2. 10

17 of 220 from the north) at 970 m/s at approximately N and E. The observed TEC perturbation could have been caused by earthquake-induced acoustic waves that propagated into the ionosphere. Moreover, 7 15 minutes after the earthquake, the Super Dual Auroral Rader Network (SuperDARN) Hokkaido radar at Rikubetsu, Japan (see below) detected a westward-moving altitude variation at the bottomside of the ionosphere. (3) Electrodynamical Coupling Between the E and F Region Ionosphere We developed a numerical model of the mid-latitude ionosphere including the E and F regions to study the mechanism for generating MSTIDs. By combining this model with a neutral atmosphere model, we were able to demonstrate that atmospheric gravity waves can produce polarized electric fields by modulating sporadic E layer and seed plasma instability in the F region. (4) Effect of Solar Flares on the Ionosphere Using global TEC data from multiple GPS networks, we investigated 109 sudden increase in total electron content (SITEC) events associated with solar flares (greater than M5 class X-rays) from 2000 through The global TEC maps revealed that the SITEC magnitudes basically depend on the cosine of the solar zenith angle (SZA) with significant residuals (δ) from the linear fitting to SZA for almost all the flare events. The value of δ is statistically greater in the winter hemisphere than in the summer hemisphere. The magnitude of the summer-winter hemispheric asymmetry (SWHA) diminishes as the solar activity approaches its minimum. Both the NRLMSISE-00 model and TIMED/GUVI observations indicate that the SWHA is also present in the dayside distribution of the O/N 2 density ratio. These results indicate that SITEC depends on not only SZA, but also the O/N 2 ratio. Observations of the Equatorial Thermosphere/Ionosphere Over Indonesia (1) Radar Observations of Ionospheric Irregularities A VHF Doppler radar with a carrier frequency of 30.8 MHz and a peak power of 20 kw has been operating at Kototabang, Indonesia (0.20 S, E; dip latitude 10.4 S) since March We found that field-aligned irregularities (FAIs) appeared frequently in the pre-midnight in March and April and in the post-midnight in July and August. The pre-midnight FAIs, propagating mainly eastward, are unquestionably associated with equatorial plasma bubbles, while the post-midnight FAIs, propagating westward, had no such association. The post-midnight FAIs are similar to FAIs at mid-latitude. (2) Radar and Satellite Observations of Plasma Blobs Plasma blob phenomena peculiar to the low-latitude ionosphere were studied using the Equatorial Atmosphere Radar (EAR) in conjunction with the ROCSAT-1 satellite. During the appearance of the plasma blobs, the radar backscatter plumes grew upward with a large upward Doppler velocity in the late pre-midnight sector. The zonal structure and upward drift velocity of the blobs correspond to those of the radar plumes on the common magnetic flux tubes. 11

18 Left: Latitude-altitude cross-section of the geometry of the ROCSAT-1 satellite and EAR along a geomagnetic meridian. Right: Fan-sector map of EAR echoes and plasma density measured by ROCSAT-1. Radar beam directions and Doppler velocities along each direction are indicated by dotted and solid lines, respectively. The ROCSAT-1 path and density perturbation along the path are overlaid. (3) Relationship Between Plasma Bubbles and Tropical Convection Activity Plasma bubbles in the equatorial F region ionosphere are known to be generated in the bottomside of the F region after sunset via the Rayleigh-Taylor (R-T) plasma instability. However, the seeding processes of plasma perturbations that ultimately develop into bubbles via the R-T instability are unknown. To investigate the relationship between bubble occurrences and atmospheric gravity wave (AGW) activity in the troposphere, we analyzed Generation and development processes of plasma bubbles. Various atmospheric waves (short-period gravity, tidal and planetary waves) generated by tropospheric activities in the west of Kototabang propagate toward the thermosphere and trigger the generation of plasma bubbles near the sunset terminator. Eastward moving bubbles induce GPS scintillations. 12

19 Antenna array (Left) and transmitter/receiver system of the SuperDARN Hokkaido radar (right). both the GPS ionospheric scintillation index (S4: a proxy of bubble occurrence) and the Earth s infrared brightness temperature (Tbb) over the Indian Ocean as measured by meteorological satellites. The results suggest a meaningful correlation between S4 and Tbb, and that the time variations of S4 and Tbb have common periods of a few to 13 days, perhaps due to planetary waves. It is postulated that short-period (< 2 hours) AGWs are responsible for the direct seeding of bubbles. Hokkaido HF Radar The SuperDARN Hokkaido radar at HF band at Rikubetsu (43.53 N, E) began continuous operation in November Since the radar is situated at a much lower latitude than the preexisting SuperDARN radars, a number of new findings regarding the dynamical coupling processes in the high- to mid-latitude upper atmospheres are expected. So far we have observed a wide variety of interesting phenomena such as sub-auroral ion drift (SAID)-type westward plasma flows in the dusk region, TIDs, and poleward plasma flows near the cusp region during a large geomagnetic storm. During the forthcoming solar maximum period, the radar is expected to play an important role in our understanding of the physical processes in the ionosphere and thermosphere under geomagnetically disturbed conditions. Data Archives The following data archives are available to the public: 210 MM magnetic field database ( Ground-based network observations of the geomagnetic field along the meridians at geomagnetic longitudes 190, 210, and 250. This database was created in collaboration with Kyushu University and a number of other institutions and organizations in Australia, Indonesia, Japan, Palau, Papua New Guinea, the Philippines, Russia, Taiwan, and the U.S.A. Database of OMTIs ( Quick-look plots of OMTI data since GPS scintillation database ( Quick-look plots of GPS scintillation data obtained at Kototabang, Indonesia. 13

20 VHF radar database ( Quick-look plots of VHF coherent echo data obtained at Kototabang, Indonesia. SuperDARN Hokkaido radar database ( Quick-look plots of SuperDARN HF radar data obtained at Rikubetsu, Japan. Ionosphere Studies with Incoherent Scatter Radar (1) Promotion of the EISCAT Project The European Incoherent Scatter (EISCAT) Radar Scientific Association is an international organization concentrating on operating radar systems to further research on the Earth s atmosphere, ionosphere, and magnetosphere. STEL researchers have participated in numerous EISCAT special experiments (SPs) and have established data archives from regular observations carried out using the EISCAT radars. Most of these activities are performed as part of national and/or international collaborations. We conducted 10 SPs in fiscal year Four research topics in recent years are shown below. (2) Contribution of Ion Drag to the Lower Thermospheric Wind We studied the contribution of ion drag to the lower thermospheric wind dynamics using data taken on July 1 7, 1999 with the EISCAT Svalbard radar (ESR) located at Longyearbyen (78.2 N, 16.0 E) and the EISCAT UHF radar located at Tromsø (69.6 N, 19.2 E). Of particular interest was the diurnal variation in the electric field observed during the first half of the interval (approximately three days) at Longyearbyen because the lower thermospheric tidal wind also had notable diurnal component due to ion drag. Notable diurnal components in the lower thermospheric wind at Tromsø and Longyearbyen did not appear when the electric field did not have clear diurnal variations. NCAR Thermosphere-Ionosphere-Mesosphere-Electrodynamics general circulation model (TIME-GCM) also supported the observational evidence. Averaged height-profiles of tidal component of (left) meridional and (right) zonal winds in the lower thermosphere at Longyearbyen when clear (active) and unclear (quiet) tidal variations in electric field appeared. Notable effect on the electric field variations can be seen in the meridional component. 14

21 Left: Ion-line spectrum measured with the ESR at 10:59:10 UT on 28 July Right: Ion speed (solid line) and ion acoustic speed (dashed line) at that time. (3) Naturally Enhanced Ion-Acoustic Lines The characteristics of naturally enhanced ion-acoustic lines (NEIALs) appeared in the ion line between 1200 and 1900 km altitude were investigated with the ESR. Asymmetry in the ion acoustic line with the stronger downshifted line (corresponding to the upward-propagating ion-acoustic wave) was always observed above 1000 km than upshifted one. The ratio of the downshifted to the upshifted peaks remained constant at this height range. The Doppler shift of the ion line suggests that the background ion speed was slower than the ion-acoustic (sound) speed below 1500 km. The greatest ion-acoustic speed was found near 600 km, above the density peak, indicating that electrons were heated not only by ionizing precipitation but also by the upward-propagating waves. (4) EISCAT Observations During the DELTA Campaign The semidiurnal tidal amplitude and phase of the lower thermospheric wind were derived using data taken during five 12-hour runs of the EISCAT UHF radar on December 8 13, Left: Altitude profiles of neutral and ion temperatures: ion temperature by EISCAT, neutral temperature by EISCAT, neutral temperature by NTV during DELTA rocket ascent and descent. Model neutral temperature profile from MSIS90 is also shown by thick dashed-line. NTV values are averaged over 1 km in altitude. Right: Altitude profiles of electron temperature by EISCAT and FLP during the rocket ascent and descent. FLP values are averaged over 1 km in altitude. 15

22 2.0 mw/m mw/m mw/m mw/m 2 15 MLT 0.7 mw/m 2 09 MLT dusk dawn 21 MLT 03 MLT midnight Local-time dependency of particle heating rate under sunlit and shaded (gray-shaded) conditions for 3 Kp < 6 in spring and fall. The data number used for each statistics is indicated in each box In conjunction with these EISCAT observations, Dynamics and Energetics of the Lower Thermosphere in Aurora (DELTA) rocket was launched from Andenes, Norway (69.3 N, E) at 0033:00 UT on December 13. A comparison between the neutral temperatures measured by Nitrogen Temperature Vibration (NTV) instrument onboard the rocket and the ion temperatures measured by the EISCAT radar showed reasonable agreement. By contrast, the electron temperatures measured by Fast Langmuir Probe (FLP) onboard the rocket and the EISCAT radar were inconsistent. (5) Relationship Between Electromagnetic Energy and Precipitating Particle Energy We performed a statistical study of electromagnetic and precipitating particle heating rates using Tromsø EISCAT UHF radar data to investigate dependencies of the rates on solar irradiation. It was difficult to estimate the particle heating rate under sunlit conditions, because ionization due to solar EUV radiation is strong even during high auroral activity. We developed a methodology to estimate the relationship between the height-resolved electron density and the solar radiation. The results show that the electromagnetic energy heating rate is always greater than the particle heating rate, independent of local time. However, the difference in the particle heating rate between the sunlit and shaded conditions at the dusk sector was clearly greater than that at the dawn sector. Moreover, the particle heating rate at the dawn sector was greater than that at the dusk sector, independent of sunlight or lack thereof. (6) EISCAT Data Archives The analyzed data and quick-look figures can be downloaded at The web site provides physical parameters such as electric fields and ionospheric conductivity together with ionospheric parameters estimated using the EISCAT radar. The data base includes Tromsø UHF radar data from 1987 to 2005, Tromsø VHF radar data from 1990 to 1999, and ESR data from 1998 to

23 HELIOSPHERIC ENVIRONMENT The research goal of the Division of Heliospheric Environment is to understand the heliosphere within the context of the Earth s environment. Our primary interest now is in the physical processes of the Sun, interplanetary space, the heliospheric boundary, and other astrophysical phenomena. In addition, we study the paleoenvironment of the heliosphere. We carry out our research using ground-based observations, satellite data, and computer simulations. The major subjects of our ground-based observations are cosmic rays, solar energetic particles, the solar wind, extra-solar planets and dark matter. IPS Observations In 2006, we carried out interplanetary scintillation (IPS) solar wind measurements using three antennas (excluding the Toyokawa antenna) of the STEL multi-station system. A mechanical failure in the Fuji antenna in spring resulted in the delayed start of the IPS measurements; the solar wind speed data of 2006 became available on May 30. Owing to a failure of the Sugadaira antenna in September, the IPS observations were interrupted for 10 days. The IPS observations ended on December 7. The solar wind data obtained from these observations are available online at html. We also developed a highly-sensitive IPS antenna referred to as the Solar Wind Imaging Facility at Toyokawa. The construction of the antenna structure is now complete, and the development of the receiving system is in progress. International Collaboration During the IPS observations, a solar wind prediction experiment was performed in collaboration with UCSD using computer-assisted tomography (CAT). The results of the Antenna structure of the Solar Wind Imaging Facility. 17

24 Three-dimensional solar wind density distribution determined from (left) IPS and (right) SMEI observations of the halo CME event on October 28, solar wind predictions were displayed in real-time via STEL and UCSD web servers ( and index.html). Study of ICME; Structure and Propagation We deduced a loop-shaped high-density structure from the STEL IPS observations of a halo coronal mass ejection (CME) event which occurred on October 28, We compared this reconstructed feature with the three-dimensional distribution of the solar wind density reconstructed from Solar Mass Ejection Imager (SMEI) observations and found that they were in good agreement (correlation coefficient ~0.6). We also found that the loop structure was roughly aligned in the direction of the magnetic flux rope inferred from cosmic ray modulation data and in situ solar wind data. Consequently, we concluded that the loop structure identified from the IPS observations corresponded to the coronal ejecta confined within the magnetic flux rope. Cosmic ray modulation network observations provide information on the (large-scale) interplanetary magnetic field which cannot be obtained from IPS observations. We are collaborating with the Shinshu University group to understand the magnetic and plasma properties of CMEs in the solar wind (a Geospace Research Center project program entitled, Study of elementary plasma processes in coronal mass ejections ). In FY 2006, we established a global network system for cosmic ray observations with near-all-sky coverage and high temporal resolution. A new FPGA data recorder, which enabled us to carry out fully-automated continuous observations and process data rapidly, was installed at each observatory. The time resolution for the cosmic ray observations was raised from 1 hour to 1 second (the best value). We also developed an online database which enabled us to display and distribute cosmic ray data in real-time. This database has been available since the end of FY 2006 at 18

25 Observational Studies of Solar Wind Acceleration CAT applied to the IPS data can improve spatial resolution and accuracy of solar wind measurements. However, the CAT method should only be used for observations in weak radio scattering regions, since it employs Born approximation. Although radio scattering at 327 MHz exhibits strong scattering around 0.2 AU, the solar wind velocity structure derived using the CAT method for observations at AU was quite similar to that at AU. The acceleration profile was also similar between STEL (327 MHz) and EISCAT (933 MHz) observations at distances beyond 0.1 AU, but the velocities observed at STEL were slightly higher than those observed at EISCAT. In order to verify the accuracy using the CAT method at AU, we conducted simultaneous IPS observations at STEL and EISCAT from July to September Data analysis is now in progress. Recent studies reveal that solar wind speed (V) highly correlates with coronal magnetic parameters (B/f) during the solar activity minimum, where B represents the photospheric magnetic field strength and f represents the magnetic flux expansion rate. We analyzed solar wind IPS data from 1995 to 2005 to verify this relationship. We found that V depends linearly on B/f through the solar cycle and that the proportional coefficient peaks at the solar activity minimum and reaches its lowest level at the solar activity maximum. An abnormally low-density event referred to as a disappearing solar wind event occurred on May 11 12, We posited that this event was caused by a transient tenuous slow solar wind stream originating from a small coronal hole. We searched for similar events such as low-density, low velocity and non CME. In an attempt to clarify the general properties underlying this type of low-density event, we analyzed solar wind data measured by the ACE satellite from 1998 to We identified 22 low-density events with the following properties: (1) a positive correlation between magnitude of solar wind density drop and duration; (2) very minor fluctuations in magnetic field strength; and (3) a large negative Vy component in the GSE coordinate (10 of the 22 events). We concluded that half of these events could be considered disappearing solar wind events. Relationship between V and B/f during solar activity minimum (CRN=1896) and maximum (CRN=1976). 19

26 Using Solar Neutron Telescopes to Study the Acceleration Mechanism of Solar Particles The Cosmic Ray Group at STEL studies particle acceleration mechanisms associated with solar flares. For this research, measuring neutrons is preferable to measuring charged particles such as protons, since the propagation of neutrons is not affected by the interplanetary magnetic field (IMF). The precise moment of an emittance of neutron, however, cannot be determined without knowing the neutron energy, since neutrons have mass. Since 1990, we have constructed mountain-based solar neutron telescopes which measure the energy and direction of neutrons. Because neutrons are attenuated in the atmosphere, several detectors must be constructed at various longitudes in order to detect solar neutrons over the course of an entire day. A network promoted by STEL to observe solar neutrons has been in operation since the beginning of solar cycle 23, thanks to the support of various groups and institutions. The solar neutron telescope located at the Norikura Cosmic Ray Laboratory of the Institute for Cosmic Ray Research at the University of Tokyo has an area of 64 m 2, making it the largest solar neutron telescope in the world. Details of the seven solar neutron telescopes in this network are summarized in the table below: Solar cycle 23 is now in the declining phase and will presumably end in X class solar flares, however, occurred 4 times in December, During the X3.4 flare on December 13, 2006, many neutron monitors in the world detected increases of the counting rate of cosmic rays (ground level enhancement: GLE). This GLE is also detected by the solar neutron telescope at Gornergrat, rigidity cutoff of which is 4.5 GV. Solar neutrons associated with these 4 X class flares have not been detected by our analysis so far. This work was performed in collaboration with Nihon University, Chubu University, Shinshu University, the Tokyo Institute of Technology, Yamanashi Gakuin University, the National Astronomical Observatory of Japan, Ehime University, the Institute of Physical, Chemical Research, and the Institute for Cosmic Ray Research at the University of Tokyo, and many institutions in the world. Research on Astrophysical Neutrinos and Cosmic Ray Acceleration Neutrinos are the products of the decay of charged pions produced by interactions between Location Country Longitude Altitude Area Year Built Norikura Tibet Aragats Gornergrat Chacaltaya Sierra Negra Mauna Kea Japan Tibet Armenia Switzerland Bolivia Mexico U.S.A. 137 E 91 E 44 E 8 E 68 W 97 W 155 W 2770 m 4300 m 3250 m 3135 m 5250 m 4600 m 4200 m 64 m 2 9 m 2 4 m 2 4 m 2 4 m 2 4 m 2 8 m Locations, altitudes, and surface areas of solar neutron telescopes used to detect solar neutrons over the course of an entire day. 20

27 high energy protons and matter. Using a Super-Kamiokande (a 50 kt water Cherenkov detector in the Kamioka Mine) we searched for cosmic neutrinos in order to obtain direct evidence for proton acceleration. In FY 2006 we mainly contributed for reconstruction of the detector, calibration of electronics and data reduction of upward going muon sample in the Super-Kamiokande phase 3. We also studied high energy electron neutrino events using Flash Analog to Digital Converter (FADC) data. We developed a new method for reconstructing energy using PMT pulse shape information recorded in FADC. This method yielded a correction by a factor of two at most for neutrinos at the 100 GeV region. We studied the applied energy spectrum for high energy fully-contained events using the FADC method with additional cuts to enhance the electron neutrino charged current. We observed no events above 100 GeV in the SK2 data sample. It is consistent with expected flux for atmospheric electron neutrinos. This work is collaboration with the Institute for Cosmic Ray Research, University of Tokyo. A New Accelerator Experiment to Aid in Understanding Cosmic-Ray Interactions High energy cosmic-rays interacting with atmospheric molecules generate child particles resulting in a cluster of particles called air showers. By measuring these shower particles, highest energy cosmic-rays are observed by some large international collaborations. However, the compilation of the observational results is affected by the uncertainty of the nuclear interaction model. Therefore we started a new experiment named LHCf that can discriminate the different nuclear interaction models by using the Large Hadron Collider (LHC) accelerator where the most energetic particles are artificially generated. LHC is under construction at Conseil Européen pour la Recherche Nucléaire (CERN) in Switzerland. It is a proton collider of 14 TeV that corresponds to ev in the laboratory system. LHCf is planned to operate at the beginning of the LHC commissioning in when the luminosity of LHC is low. Calibration of photomultiplier tubes used in the LHCf experiment. The relation between incident light intensity (expressed in the corresponding number of particles passing a scintillator) versus ADC value. Similar curves were obtained for 72 tubes. 21

28 In June 2006, LHCf was officially approved by the LHC committee. Each detector component was calibrated and (Detector #1) constructed in Nagoya. Detector #2 was pre-constructed at the University of Florence. Both detectors were tested in August at the SPS Accelerator at CERN. In January, pre-installation of Detector #1 was successfully carried out in the LHC tunnel. In February, a radiation-damage test for each component was performed at the HIMAC accelerator in Chiba. The initial start-up date was moved to 2007 at which time 900 GeV collisions will commence. We performed a new Monte Carlo calculation and concluded that we can conduct accurate measurements even at this lower energy. The LHCf experiment is a collaboration with the Shibaura Institute of Technology, Waseda University, Kanagawa University and institutions in U.S.A., France, Italy, Switzerland and Spain. Observing Dark Objects It is well known that the universe contains a significant amount of dark matter which cannot be observed directly using photons. One theory suggests that the dark matter consists of massive star-sized objects referred to as Massive Compact Halo Objects (MACHOs). To detect these MACHOs we can use the gravitational microlensing technique, wherein the gravitational field of a dark object passing across the line of sight toward a star amplifies the light from the star, thereby acting like a lens. However the efficiency of gravitational microlensing is low, since on average, only one such event occurs each year during which millions of stars are being observed. Gravitational microlensing is also a very effective tool for searching for extra-solar planets. To detect gravitational microlensing events effectively, we observe dense stellar fields such as the Large Magellanic Cloud, the Small Magellanic Cloud, and the Galactic Bulge using a The light curve of the event with time scale of 1 day. Top panel shows for 1 year. Bottom panel shows zoom up during the event. The event could be caused by a free floating planet. 22

29 large area CCD camera and a wide field telescope. We installed a 1.8 m telescope and a large CCD camera in New Zealand, and began observations in May We found exciting microlensing event (OGLE-2005-BLG-390) occurred in the Galactic bulge, which have 5.5 Earth mass planet. In 2006, we completed detailed setups (including adjusting the optics) of a new 1.8 m telescope. In April we began regular surveys of the Galactic Bulge and Magellanic Clouds. In 2006, we detected ~170 microlensing events in the Galactic Bulge and issued alerts to other researchers around the world ( We observe stars very frequently, at least 10 times per night (50 times in some fields) to detect events with very short time scales. Accordingly, we found four events with time scales of ~1day. The figure shows one of these events. These discoveries could represent the first-ever detection of free floating planets. Members of the research team came from the School of Science of Nagoya University, the Tokyo Metropolitan College of Astronautical Engineering, the Nagano College of Engineering, the Carter National Observatory, the University of Auckland, Massey University, the University of Canterbury, and Victoria University of New Zealand. This project is supported by the Ministry of Education, Culture, Sports, Science and Technology (MEXT). Radiocarbon Measurements of Past Solar Activity The intensity of the galactic cosmic rays entering the terrestrial atmosphere is influenced by solar activity. Radiocarbon ( 14 C) is produced in the upper atmosphere by nuclear reactions initiated by cosmic rays. The radiocarbon turns into carbon dioxide, which circulates throughout the atmosphere with a portion being transported into the biosphere. By measuring the concentration of 14 C in biological samples such as tree rings, one can ascertain variations in cosmic ray intensity and consequently variations in solar activity during the years when the 14 C was absorbed by the sample. We previously measured the concentration of 14 C in tree ring samples corresponding to the Maunder Minimum ( AD) and the Spoerer Minimum ( AD). We found that the activity of the Sun varied periodically even during these solar grand minima and that the cycle lengths of the periodicity during the Maunder Minimum was 14 and 28 years, corresponding to the present cycle lengths of 11 and 22 years. We also measured the concentrations of 14 C during the periods between the two minima ( AD) and a period covering the 9 10th centuries ( AD). The analysis revealed a consistent 11-year periodicity throughout normal solar activity. In the current fiscal year, we began to measure concentrations of 14 C during other minima to compare the cycles with those during the Maunder and the Spoerer Minima. The sample tree was a 300-year-old buried camphor tree from Kushima, Miyazaki in southern Japan estimated to date back to the 4th century BC. The single-year samples were pretreated chemically to obtain cellulose, which was then converted to graphite in order to conduct measurements of radiocarbon concentrations by an accelerator mass spectrometer. Measurement accuracy was 3 permil on average. 23

30 We measured the 14 C concentrations for alternate years during the initial 110 years of tree growth. We estimated the date of the innermost ring to be 431 (+/- 12) BC by comparing the measured 14 C concentrations with the INTCAL decadal standard data. It is believed that during the 4 5th centuries BC solar activity was at a level similar to the Maunder Minimum; accordingly, our tree could be used to analyze the Maunder Minimum. According to the preliminary results, the cycle of the minimum exhibited by our tree was approximately 15 years, rather than 11 years roughly parallel to that during the Maunder Minimum. We will work to verify this result and conduct similar measurements for the Spoerer Minimum, whose periodicity was not prolonged. It is expected that by defining the characteristics of periodic change in various grand minima, the mechanism underlying long-term variations in solar activity will be clarified. This research was performed in collaboration with the Nagoya University Center for Chronological Research. 24

31 INTEGRATED STUDIES The Integrated Studies Division aims at tracing the flow of energy from the solar surface into the Earth s upper atmosphere and its transformation on the way. The primary method of this research is to analyze data obtained from various points in the solar terrestrial environment. The data studies are complemented by computer simulations and modeling to help understand a number of phenomena in the coupled Sun-Earth system, such as solar flares, CMEs, interplanetary disturbances, boundary processes, plasma convection, magnetic storms, substorms, and auroras. The study of space weather has evolved over the past decade for identifying and predicting space environment variations. Using the Geospace Environment Data Analysis System (GEDAS), which provides near real-time data from around the world, basic research of space weather is also performed. In 2006, we made a strategic plan, Geospace Environment Modeling System for Integrated Studies (GEMSIS) to advance geospace models based on simulation and data analyses. Areas of research are set forth below: 1. Acceleration mechanism of solar energetic particles 2. Inner magnetosphere-ionosphere coupling 3. Numerical simulation of the energetic in the inner magnetosphere particles 4. Solar wind-magnetosphere-ionosphere coupling 5. Upward flow of O + into the inner magnetosphere during major geomagnetic storms 6. Space weather charts based on data assimilation of the ionospheric parameters Particle Acceleration in Solar Flares In H-alpha, the so-called two-ribbon structure is observed during solar flares, especially during long-duration events. In hard X-rays, however, a pair of compact footpoint sources can be observed. To solve this problem, Asai et al. (2002) showed that hard X-ray emissions strongly depend on the magnetic field strength under the magnetic reconnection flare model. To confirm their line of reasoning, we investigated the spatial relationship along each ribbon between the magnetic field strength and hard X-ray intensity, using the July 14, 2000 event (which contained a two-ribbon structure even in hard X-rays). While the distribution patterns were roughly similar, there was no clear one-to-one correspondence. This discrepancy may have been the result of our failure to consider the magnetic connectivity between the two ribbons. Including simple magnetic connectivity in our analysis produced a higher correlation between the hard X-ray intensity and the magnetic field strength. These improved results, however, were not sufficient to explain why the two-ribbon structure is not usually observed in hard X-rays. We are continuing our analysis using more realistic magnetic connectivity model. Modeling of Coronal Magnetic Fields Space weather forecasters need to understand thoroughly solar active phenomena such as solar flares and CMEs. The modeling of coronal magnetic fields plays an important role in revealing their trigger mechanism. However, since the equilibrium equation of coronal magnetic fields is nonlinear, the triggering mechanism cannot be obtained analytically. A numerical method is required. 25

32 We developed a numerical code to reconstruct three-dimensional coronal magnetic fields from photospheric vector magnetic field data. A performance test confirmed that our code reconstructed coronal magnetic fields with very good precision and that the calculation period was faster than that of the codes developed by other research groups. The new solar satellite HINODE launched last year provides a large amount of high-resolution magnetic field data. In order to deal with such high-resolution data, we employed the multi-grid technique, resulting in a drastic shortening of the calculation time. The Importance of the Tail Current in Expanding Storm-Time Auroral Belt The importance of the tail current in expanding the auroral belt toward lower latitudes was examined. It is generally accepted that the equatorward edge of the auroral oval at the nightside is coincident with the outer boundary of the trapping region of energetic electrons. We should then explain why the boundary between the inner and outer magnetospheric regions moves earthward during magnetic storms. Schulz [1997] obtained theoretically that every 130 nt of the magnetic disturbance in the Earth s center associated with the ring current can displace the auroral oval toward the equator by 2. In reality, however, this displacement is, at least, two times greater. The reason why the ring current can only slightly affect the magnetic flux redistribution between the inner and outer magnetosphere is that the area of the magnetic depression region associated with the ring current is rather small, compared to that of the cross-tail current. Following the formulation of Maltsev et al. [J. Geophys. Res., 1996], where the solar wind dynamic pressure and the magnetic field of the ring current are parameterized, it was shown Latitude of the equatorward edge of the auroral oval, Λ, versus the magnetic storm intensity (Dst). The solid lines indicate the calculations, and the dashed line refers to the observations by Feldstein et al. [J. Geophys. Res., 1997]. The solid lines show the dependence Λ (Dst) for three levels of the solar wind dynamic pressure: P = 0, 4, and 100 npa. The circles show individual observations at the main phase of five geomagnetic storms: the numbers alongside the circles indicate the dynamic pressure of the solar wind. 26

33 that the observed dependence of the auroral belt latitude on Dst values is close to the calculated one, indicating that the cross-tail current, or the magnetic flux in the tail, is as important as the ring current. A major role of the magnetotail currents in the storm time decrease of the auroral oval latitude has also been pointed out by other observations. Red Arcs in Subauroral Regions as Observed by the Athabasca ALL-Sky Camera Stable auroral red (SAR) arcs consist of global red (630 nm) emissions without green (558 nm) emissions in the subauroral region. SAR arcs are often observed during geomagnetic storms. However, it is less clear how they begin in terms of their association with disturbances in the main oval. Previous studies have demonstrated that SAR arcs lacked green emissions both during initiation and afterward. On the other hand, we have observed SAR arcs bifurcating from the main oval. SAR arcs are usually observed at 2 < L < 4, the same location as the plasmapause during storms. Using a multi-spectral all-sky imager at Athabasca, Canada (L = 4.6, MLAT = 62), we simultaneously observed SAR arcs and the auroral oval. We observed four separate instances of isolated red arcs from September 2005 through June The red arcs were selected as not seen in the green line (558 nm) and were located equator ward from the main auroral oval. Red arcs were observed during non-storm times. The Dst index was greater than 30 nt. These arcs appeared to initiate by bifurcating from the main oval during the northward-turning of the green/red arcs in the main oval, which was previously expanding equatorward. These observations suggest that the isolated arcs were generated by the interaction of plasma sheet particles with particles in the plasmasphere located at higher latitudes during quiet times. Auroral Dynamics Two fortuitous events occurring during enhanced solar wind density suggested that the intensity of the westward auroral electrojet increased significantly. However, the total night side auroral power did not increase significantly in response to the density enhancement. Since the auroral electrojet is determined by the electric field and conductance in the ionosphere, this result indicates that the westward auroral electrojet driven by the density enhancement is electric field dominant. Geotail plasma and magnetic field measurements in conjunction with night side auroral power data derived from Polar Ultraviolet Imager auroral images indicate that earthward plasma sheet fast flows can be classified into two categories: (1) near X = 10 Re and (2) X < 15 Re. Rates of change in the auroral intensity for the former category were found to be greater than those for the latter category. The former category of the fast flows can be understood in terms of the current disruption (near-earth neutral line theory), the latter in terms of the bubble theory. Storm Time Electric Field in the Global Ionosphere and Inner Magnetosphere The magnetospheric electric field produced by the interaction between the southward IMF and the magnetosphere propagates to the polar ionosphere along the magnetic field lines. The storm time electric field drives DP2-type currents in the global ionosphere (as observed 27

34 by the magnetometer network), particularly at the dayside geomagnetic equator. The magnitude of the electric field associated with the storm main phase was several times that of the ionospheric dynamo electric field, resulting in space weather effects in the low latitude ionosphere. The electric field changed direction from the dawn-to-dusk to dusk-to-dawn at the beginning of the recovery phase of the storm. This overshielding electric field induced the equatorial counter electrojet, which amplified the amplitude of the geomagnetic storm together with the DP2 currents by a factor of 2.7 as compared with the geomagnetic storm at a low latitude. In order to understand the temporal and spatial distribution of electric fields in the inner magnetosphere during geomagnetic storms, we analyzed the electric field data from the Akebono satellite from March 1989 to January During a magnetically quiet period, the electric field s maximum magnitude was 0.5 mv/m, the distribution identical to that deduced from previous models. However, we found that the plasmasphere did not strictly co-rotate with the Earth s rotation due to the presence of the ionospheric dynamo field. During the main phase, a localized electric field was observed with a remarkable dawn-dusk asymmetry at the inner magnetosphere where L < 6. This result showed that the intensity in the dusk sector was 2 3 times greater than that in the dawn sector. The enhancement of the electric field corresponded to the development of the ring current. Moreover, the maximum intensity of the electric field corresponded to the greatest temporal change in the ambient magnetic field. During the recovery phase, the localized electric field intensity abruptly decreased to that of the quiet time, the dawn-dusk asymmetry gradually disappearing. During the early recovery phase, the over-shielding electric field formed at the daytime sector (13 16 h) and midnight sector (23 02 h), the intensity in the midnight sector being 2 3 times greater than that in the daytime sector. Transmission of the convection electric field to the inner magnetosphere and to the equatorial ionosphere was studied using a transmission line model consisting of the field-aligned currents (FACs) and the earth-ionosphere waveguide. By replacing the FACs with a perfectly conducting transmission line and the earth-ionosphere waveguide with a lossy transmission line, we were able to demonstrate that electromagnetic energy is transmitted to the equatorial ionosphere through a magnetosphere-ionosphere-ground current circuit, which is extended to low latitudes by TM0 mode waves in the earth-ionosphere waveguide. Statistical distribution of the electric field in the inner magnetosphere, observed by AKEBONO for the quiet period (left), storm main phase (middle) and storm recovery phase (right). 28