A new flask sampling system (Automatic Air Sampling Equipment (ASE)) was used to conduct atmospheric CO₂ measurements at about 10km altitude over the western Pacific between Australia and Japan using a Japan Airlines (JAL) airliner from December 2005 to April 2007. The observed CO₂ from the ASE agreed well with that determined by the in-situ CO₂ measuring system (Continuous CO₂ Measuring Equipment (CME)) during the same flights. The data from the ASE and CME exhibited similar mean CO₂ for 12 latitudinal bands at an interval of 5° between 30°N and 30°S, although the discrete ASE data are sparse compared to the frequent measurements by the CME. The CO₂ standard scales of the Meteorological Research Institute and the National Institute for Environmental Studies were compared to provide a consistent data set for the first and second phases of the JAL project. The new ASE data clearly depicted a seasonal cycle and increasing trend, which were reproduced by the extrapolated variations deduced from the climatology of previous observations for the past 12 years. In particular, latitudinal changes of detrended seasonal cycles obtained from the new observation were quite similar to those derived from the climatology in the previous observation. These results indicated the consistency in the continuity of the CO₂ record extended by the new JAL observations.

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   We have developed a general-purpose simple coupler (Scup) that can be used for earth system modeling. Scup allows flexible coupling among component models, for example, atmosphere and ocean general circulation models and chemical transport models. Although Scup has provided functions that are required for the efficient development of an earth system model at the Meteorological Research Institute, its fundamental design should also be applicable to other earth system models. Processes of the component models communicate with each other directly by calling the Scup library, which is necessary to efficiently exchange large amounts of grid data among the processes of the component models. Scup supports grid transformation for three-dimensional data and that for two-dimensional data with accurate local and global conservation, necessary features for coupling component models with different coordinates or grids. Simplicity and ease of use are among Scup's strong points. All of the source code is written in Fortran and can be compiled on various platforms with a Fortran 95 compiler and a Message Passing Interface library, so it has good portability.

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   Measurements of atmospheric CO₂ and O₃ were conducted on Rishiri Island (45°07′N, 141°12′E) in northern Japan from December 2006 to March 2007. Atmospheric CO₂ and O₃ varied over a time scale from a few minutes to months: from December to mid-February, atmospheric CO₂ concentration was negatively correlated with the atmospheric O₃ concentration. This negative correlation was due to the emission of CO₂ by soil respiration and decomposition of O₃ at the surface in the high latitudes of Eurasia, as well as on Rishiri Island. Contrary to the CO₂-O₃ relationship from December to mid-February, after mid-February atmospheric CO₂ concentration sometimes correlated positively with the concentration of atmospheric O₃. High atmospheric CO₂ and O₃ concentrations were probably due to the transport of the air mass affected by anthropogenic sources in densely populated areas in northeast Asia, including Japan, Korea, and China.

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   Numano-Taira Crater in Adatara volcano has shown signs of volcanic unrest such as hot mud effusion since 1996, even though no obvious changes in seismicity have been observed. We carried out observations of magnetism, deformation, gravity, and self-potential around the crater to detect volcanic activity. We found remarkable variation of up to 110 nT in total magnetic intensity, from which we inferred that demagnetization caused by rising temperatures occurred under the southeastern part of the crater bottom from around 1997 to 2000, and that magnetization increased because of falling temperatures under the northeastern part after 2000. By geodetic observations with GPS, we found inflation of the crater before 2000 and deflation after 2000. We made gravity observations taking into account the effect of the height change by using the GPS to precisely position a benchmark. A gravity increase was observed in the crater from 2001 to 2005, and the amount of change was larger than that which could be explained by the height change. We speculated that the change in gravity reflected variations in the groundwater thickness. In the self-potential observations, we maintained long-term stability by calibration with a Cu/CuSO₄ electrode, and ground temperature was measured to correct for the drift of the electrode potential. The results revealed a self-potential fluctuation probably caused by small-scale hydrothermal activity. The results of these comprehensive observations suggest that the Numano-Taira Crater was fairly active from 1996 to 2000, and that it became gradually calmer after 2000. Because the observed volcanic unrest was possibly related to the activity of hot groundwater, we used a hydrothermal simulation to study the variations in water flow and temperature distribution beneath the crater that would be expected if hot water was supplied from depth. Assuming intrinsic hydraulic permeability beneath the crater, we carried out simulations for various cases. The results showed that two hot water supplies, one in the north and the other in the south, were needed to explain the temperature changes estimated from the magnetic observations. We also calculated the changes in the magnetic and gravity fields from the results of the hydrothermal simulation, and found that they were consistent with the observed values. For volcanoes such as Adatara, it is not easy to monitor the volcanic activity by seismic observations, but comprehensive observations of magnetism, gravity, self-potential, and deformation around the crater are a powerful means of understanding the total volcanic activity when combined with a hydrothermal simulation.

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   The 2004 off the Kii Peninsula earthquake (Mj7.4) occurred near the Nankai trough axis, southeast off the Kii Peninsula, Japan, on September 5, 2004. The earthquake was estimated to have a thrust-type focal mechanism with N-S striking P-axis and was regarded as an intra-plate earthquake in the uppermost mantle of the Philippine Sea plate (PHS). In order to investigate the precise distribution and time change of the aftershock, we conducted pop-up ocean bottom seismometer (OBS) observations around the aftershock region. The observations were conducted three times intermittently for almost one year after the earthquake. A one-dimensional seismic velocity structure for hypocenter determination was derived from the survey result of the previous seismic refraction study. A station correction method using a PS conversion wave was applied to improve the hypocenter determination. Consequently, we could determine a more detailed and precise aftershock distribution compared with that of the Japan Meteorological Agency (JMA). The depth range of the OBS-located hypocenters was 5 to 30 km, about 20 km shallower than that of the JMA, and the OBS-derived epicenters were shifted about 10 km to the southeast compared to those of the JMA. The aftershocks, according to the JMA hypocenters, seem to be distributed mainly landward of the trough axis, whereas OBS-located hypocenters were distributed mainly along the trough axis. It was also found that the aftershock distribution can be divided roughly into two groups, a relatively shallower group with a depth range of 5 to10 km, and a deeper group with a depth range of 15 to 30 km. The shallower group, which is located inside the PHS or the accretionary prism just over the PHS, was distributed from the center to the north of the aftershock region. The deeper group is located in the uppermost mantle of the PHS near the Nankai trough axis, which is inferred to be the main ruptured zone of the main shock. We also detected several seismic clusters in the shallower earthquake group. They form vertical planes going down from the accretionary prism to the PHS. We are interested in the relation between the detected seismic clusters and the splay fault system in the accretionary prism.

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   A tsunami warning is issued according to the magnitude, location, and depth of an earthquake as estimated from seismograms. However, there is a large uncertainty of expected tsunami heights because of a lack of information on the rupture process immediately after an earthquake occurs. Actual tsunami heights observed by offshore tsunami recorders can reduce this uncertainty. To make it possible to predict tsunami heights on the coast from offshore tsunami heights, we investigated the statistical relationship between tsunami maximum amplitudes of offshore and coastal stations.
   We used data from ocean-bottom pressure gauges, installed as a part of the ocean-bottom seismometer system off-Tokai and off-Boso by the Japan Meteorological Agency, and off-Muroto by the Japan Agency for Marine-Earth Science and Technology. The data were contaminated with short-period variations accompanied by seismic waves as well as long-period variations, such as the tidal components. To remove noise and extract the tsunami component, we first processed time-series data of the ocean-bottom tsunami recorders with filters, and then compared the tsunami maximum amplitudes observed by the ocean-bottom tsunami recorders off-Tokai, off-Boso, and off-Muroto with those observed at coastal stations. We investigated the statistical relationship by calculating means and standard deviations of the common logarithm of the ratio of coastal to offshore tsunami maximum amplitudes. Next, following Baba et al. (2004), we considered the effects of the installation depth of the ocean-bottom tsunami recorders and the reflection at the coastline. The difference of distances to offshore and coastal stations from sources is also corrected through the tsunami magnitude.
   Making use of AIC (the Akaike Information Criterion), for each combination of offshore and coastal stations, we chose the best fitting statistical relationship between tsunami maximum amplitudes at offshore and coastal stations. As a result, we found a constant ratio or a linear relationship with offshore amplitude and/or epicentral distance, with or without the above-mentioned correction.

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   The evolution of Typhoon Tokage (0423), which made landfall in western Japan and underwent extratropical transition (ET) in October 2004 associated with strong winds and heavy rainfall on both the right and left sides of the storm track, is diagnosed using a gridded regional analysis (RANAL) data set produced by the Japan Meteorological Agency. When Tokage makes landfall, it is located in the right entrance of an upper-tropospheric jet streak and downstream of a synoptic-scale upper trough. The lack of an intense short-wave trough interacting with Tokage is consistent with the fact that the storm did not reintensify after the completion of ET. The strong cyclonic circulation in the lower troposphere associated with Tokage strengthens a preexisting lower-tropospheric front over western Japan, and Tokage eventually transformed into a frontal cyclone in the baroclinic zone. The conditional symmetric instability related to the approach of Tokage to the upper-tropospheric jet stream, as well as the conditional instability in the lower-tropospheric air on the cooler side of the frontal zone over the warm sea surface of the southern Sea of Japan, are considered to contribute to the heavy precipitation along the northern coast of western Japan, which is located on the left side of the storm track. Further study is needed to clarify the impact of air-sea interaction on the intensity and structure of a tropical cyclone in the midlatitude.

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