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Long-term field observation of carbon dioxide concentrations in soil air and soil temperature and moisture was conducted in a forested (oak and Japanese larch) headwater basin. The soil CO2 concentration was measured monthly from the ground surface to a depth of 2 m using gas detection tubes. The data were then averaged monthly to show general annual trends. The temporal and spatial distribution of carbon dioxide showed generally constant annual patterns of concentration increase from spring to summer and decrease from autumn to winter in response to soil temperature changes. The concentration increased exponentially with soil temperature ≥5 °C at the same depth, suggesting a close relationship between the concentration and production of carbon dioxide. From late winter to early spring a frozen layer formed at the top of the soil profile that inhibited the escape of carbon dioxide into the atmosphere. The soil CO2 concentrations in the oak forest were generally higher than those in the Japanese larch forest, although both soil respiration rate and soil organic carbon contents were lower in the oak forest. Considerable interannual differences in the distribution of carbon dioxide were observed with coincident differences in precipitation. Concentrations at shallow depths were relatively low in dry summers. When the frozen layer was not formed under thick snow cover, soil CO2 concentration did not increase. In deep soils, where the influence of precipitation was not significant, the interannual difference was almost always within ±20% of the monthly average. Copyright © 2001 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Magnetic, density and potential fluctuations up to 500 kHz at several spatial points have been observed in the core region of JIPPT-IIU tokamak plasmas using a heavy ion beam probe. The frequency spectra of the density and magnetic oscillations are found to be similar, whereas there are large differences in the phase, coherence and frequency dependences deduced from signals at adjacent sample volumes. These differences allow us to ascribe the detected magnetic fluctuations to the microtearing mode (MTM) by simple dispersion relations of the MTM in collisionless and intermediate regimes. The frequency-integrated level of magnetic fluctuations around 150 kHz (100–200 kHz) is , a level high enough for the ergodization of the magnetic surface and enhanced electron heat loss as derived by Rechester and Rosenbluth (1978 Phys. Rev. Lett.40 38). This level is consistent with the measurements performed using cross-polarization scattering of microwaves in the Tore Supra tokamak. Our results are the first direct experimental verification of the MTM in the core region of tokamak plasmas, which has been recently observed in gyrokinetic simulations using a very fine mesh in tokamak and ST plasmas. [ABSTRACT FROM AUTHOR]