ALBERT

Description: Chondrules in chondritic meteorites are unique witnesses of nebular and asteroidal processes that preceded large-scale planetary accretion. Together with refractory calcium-aluminium-rich inclusions (CAIs), they are the sources of our knowledge of the initial evolution of the early Solar System. We have investigated a single very large (〉10 mm in longer dimension) chondrule, hereafter, the mega-chondrule A25-2, extracted from the Allende CV3 chondrite. We characterised texture, mineralogy and mineral chemistry of this chondrule, and studied its Al-Mg, U-Pb and U-isotope systematics. We also studied the distribution of U, Th and Pb, and measured Pb isotopic composition in individual minerals of A25-2 by secondary ion mass-spectrometry (SIMS). The main difficulty in absolute age determination was the presence of pervasive and resilient non-radiogenic Pb. In the search for the best way to separate radiogenic Pb from non-radiogenic Pb components of terrestrial and asteroidal origins, we used various protocols of multi-step leaching and assessed their efficiency in generating data suitable for the construction of an isochron. Testing the data filtering procedure led us to explore the behaviour of the stepwise leaching method in the presence of pervasive and resilient non-radiogenic Pb. The model age patterns observed in the final HF partial dissolution steps were probably induced by isotopic fractionation. Although step leaching did not yield fractions with highly radiogenic Pb, a Pb-Pb isochron age corrected for measured 238U/235U was obtained by: (1) data filtering process based on strict analytical and geochemical criteria to include in the Pb-Pb isochron only leaching steps free from terrestrial contamination and (2) arithmetically recombined analyses to cancel the effects of leaching-induced isotopic fractionation. This extensive data processing yielded the age of 4568.5±3.0 Ma, which we consider reliable within its uncertainty limits, although it is not as precise as, and more model dependent than, the age that could have been obtained if Pb isotopic compositions were more radiogenic. The 238U/235U ratio of the mega-chondrule is 137.764±0.016, which is similar to the ratios obtained from single chondrules yet slightly different from small pooled Allende chondrules. The initial 27Al/26Al ratio inferred from internal isochron obtained from SIMS Al-Mg isotope measurements is (5.4±6.5)×10–6, which corresponds to 4565.0 +0.8/-∞ Ma, assuming homogeneous distribution of 26Al throughout the protoplanetary disk at the canonical level (∼5.2×10−5). This age is 3.5±3.1 Ma younger than the Pb-isotopic age. Calculation of 26Al-26Mg age assuming initial (27Al/26Al)0 of (1.36±0.72)×10–5 in the chondrule-forming region yields the age of 4566.4+0.8/-∞, which is consistent with the Pb-isotopic age.

Description: To investigate the feasibility of rain enhancement by cloud seeding over the target area in early summer, the effects of salt micro-powder (MP) seeding and hygroscopit flare (HF) seeding on the initial cloud microphysical structures were investigated using a detailed bin microphysics parcel model with the background atmospheric aerosol data collected from ground-based monitoring observations carried out on the windward side of the target area and seeding aerosol data collected from the coordinated flghts of seeding helicopter and in-situ measurement aircraft. Numerical seeding experiments show that size distributions of cloud droplets are broadened and onset of the rain drop formation is fastened by MP and HF seeding although MP seeding shows more remarkable seeding effects than HF seeding. MP seeding increases the mean droplet size and decreases total number concentration of cloud droplets whereas HF seeding does vice versa. According to the relationship between the increase/decrease ratio of cloud droplet number concentration and the increase/decrease ratio of surface precipitation by hygroscopic seeding obtained in previous studies, it is shown that MP seeding has a positive seeding effect, and HF seeding has a negative effect. In the numerical seeding experiments, although a range of variation in the number concentration and hygroscopicity of background aerosol particles, the amount of seeding material applied, and the change in the physico-chemical properties of the seeding aerosols for an improvement of seeding effects were also considered, the outline of the results described above remained unchanged.

Description: Japan has a wide variation in the snowy environments and it is anticipated that climate change will alter the snow-cover conditions. Although a lot of meteorological observation sites managed by the Japan Meteorological Agency are located in the low altitude areas, few observation sites are located in the high altitude areas. Therefore, quantitative variations in snow conditions in Japan's mountainous regions are not yet well understood due to the lack of long-term observational data. The Snow and Ice Research Center, National Research Institute for Earth Science and Disaster Resilience has managed a Snow and Weather Observation Network, operating for over 25 years, covering the northern part to the western part of Japanese mountains, which monitors fluctuations in meteorological and snow cover conditions in high altitude areas. These data are used not only to investigate the influence of climate change on snowy environments in Japan but also to mitigate snow disasters which have changed drastically in frequency and intensity owing to the changes in climatic conditions. Our long-term observations revealed that the trends of variation of maximum snow depth and maximum snow water equivalent are almost the same, but the range of variation of maximum snow water equivalent is larger than that of maximum snow depth. It was also found that the trend of variation of the maximum snow depth depends on elevation and that the variation may differ between mountainous and flat areas.