Seasonal prediction of Indian summer monsoon in NCEP coupled and uncoupled model     

Hemantkumar S. Chaudhari  Samir Pokhrel  Sachiko Mohanty  Subodh K. Saha 《Theoretical and Applied Climatology》2013,114(3-4):459-477

This study has identified probable factors that govern ISMR predictability. Furthermore, extensive analysis has been performed to evaluate factors leading to the predictability aspect of Indian Summer Monsoon Rainfall (ISMR) using uncoupled and coupled version of National Centers for Environmental Prediction Coupled Forecast System (CFS). It has been found that the coupled version (CFS) has outperformed the uncoupled version [Global Forecast System (GFS)] of the model in terms of prediction of rainfall over Indian land points. Even the spatial distribution of rainfall is much better represented in the CFS as compared to that of GFS. Even though these model skills are inadequate for the reliable forecasting of monsoon, it imparts the capacious knowledge about the model fidelity. The mean monsoon features and its evolution in terms of rainfall and large-scale circulation along with the zonal and meridional shear of winds, which govern the strength of the monsoon, are relatively closer to the observation in the CFS as compared to the GFS. Furthermore, sea surface temperature–rainfall relation is fairly realistic and intense in the coupled version of the model (CFS). It is found that the CFS is able to capture El Niño Southern Oscillation ISMR (ENSO-ISMR) teleconnections much strongly as compared to GFS; however, in the case of Indian Ocean Dipole ISMR teleconnections, GFS has the larger say. Coupled models have to be fine-tuned for the prediction of the transition of El Niño as well as the strength of the mature phase has to be improved. Thus, to sum up, CFS tends to have better predictive skill on account of following three factors: (a) better ability to replicate mean features, (b) comparatively better representation of air–sea interactions, and (c) much better portrayal of ENSO-ISMR teleconnections. This study clearly brings out that coupled model is the only way forward for improving the ISMR prediction skill. However, coupled model’s spurious representation of SST variability and mean model bias are detrimental in seasonal prediction.  相似文献   

Isotopic tracers for water masses in the coastal region of eastern Hokkaido     

Sachiko Oguma  Tsuneo Ono  Akira Kusaka  Hiromi Kasai  Yasuhiro Kawasaki  Tomonori Azumaya 《Journal of Oceanography》2008,64(4):525-539

In this study we used two stable isotopes, δ¹³C and δ¹⁸O, for water mass classification in the coastal region off eastern Hokkaido. δ¹³C* values, which were corrected for the biological effect, and δ ¹⁸O values up to 300 m depth suggested that the isotopic character of the onshore and offshore water in the southern Okhotsk Sea, the Nemuro Strait and the western North Pacific could be explained by the mixing of three source waters: the Oyashio water (OYW), Soya Warm Current water (SWCW) and East Sakhalin Current water (ESCW). In summer, δ ¹³C*-δ ¹⁸O plots indicated mixing between SWCW from the southern Okhotsk Sea and OYW in the Pacific coast of southeastern Hokkaido, while temperature-salinity plots of the onshore water showed minimal difference from the offshore OYW. In winter, on the other hand, the mixed water of ESCW and OYW (or SWCW) appeared in the Pacific coastal region, distributed as cold, low salinity onshore water. Finally, we estimated mixing ratios of OYW, SWCW and ESCW in the coastal region of western North Pacific using their mean values of δ ¹³C* and δ ¹⁸O as endmembers. These results suggest seasonal and yearly changes of water mass combination en route from the southern Okhotsk Sea to the western North Pacific.  相似文献   

A study of Mg and K isotopes in Allende CAIs: Implications to the time scale for the multiple heating processes     

Motoo Ito  Hiroshi Nagasawa  Hisayoshi Yurimoto 《Meteoritics & planetary science》2006,41(12):1871-1881

Abstract— The measurements of magnesium and potassium isotopic compositions of refractory minerals in Allende calcium‐aluminum‐rich inclusions (CAIs), 7R‐19–1, HN3–1, and EGG3 were taken by secondary ion mass spectrometry (SIMS). The 7R‐19–1 contains ¹⁶O‐rich and ¹⁶O‐poor melilite grains and define a single isochron corresponding to an initial ²⁶Al/²⁷Al ratio of (6.6 ± 1.3) × 10^?5. The Al‐Mg isochron, O isotope measurements and petrography of melilite in 7R‐19–1 indicate that ¹⁶O‐poor melilite crystallized within 0.4 Myr after crystallization of ¹⁶O‐rich melilite, suggesting that oxygen isotopic composition of the CAI‐forming region changed from ¹⁶O‐rich to ¹⁶O‐poor within this time interval. The ¹⁶O‐poor melilite is highly depleted in K compared to the adjacent ¹⁶O‐rich melilite, indicating evaporation during remelting of 7R‐19–1. We determined the isochron for ⁴¹Ca‐⁴¹K isotopic systematics in EGG3 pyroxene with (4.1 ± 2.0) × 10^?9 (2s?) as an initial ratio of ⁴¹Ca/⁴⁰Ca, which is at least two times smaller than the previous result (Sahijipal et al. 2000). The ratio of ⁴¹Ca/⁴⁰Ca in the EGG3 pyroxene grain agrees within error with the value obtained by Hutcheon et al. (1984). No evidence for the presence of ⁴¹K excess (decay product of a short‐lived radionuclide ⁴¹Ca) was found in 7R‐19–1 and HN3–1. We infer that the CAI had at least an order of magnitude lower than canonical ⁴¹Ca/⁴⁰Ca ratio at the time of the CAI formation.  相似文献   

Purely physical separation of a small fraction of the Allende meteorite that is highly enriched in noble gases     

Jun-ichi MATSUDA  Sachiko AMARI  Keisuke NAGAO 《Meteoritics & planetary science》1999,34(1):129-136

Abstract— Fine material that floats during freeze-thaw disaggregation of the Allende meteorite is greatly enriched in noble gases compared to the bulk meteorite. Not only the elemental concentrations, but also most isotopic ratios of the noble gases in this fraction, strongly suggest that this material is very similar to the gas-rich carbonaceous residue isolated from the bulk meteorite by chemical treatment. The only significant difference in noble gas signature between our separated fraction and the chemical residues is that the ¹²⁹Xe/¹³²Xe ratio in the former is significantly lower than that in the latter, which suggests readsorption of ¹²⁹Xe released from the dissolved minerals during the chemical treatment. This is the first time that a gas-rich residue of a meteorite has been separated by a purely physical method alone. We also show that noble gases in phase Q and presolar diamond may be separable physically, although both are closely associated.  相似文献   

Dust from Supernovae     

Donald D. Clayton  Sachiko Amari  Ernst Zinner 《Astrophysics and Space Science》1997,251(1-2):355-374

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Variation of rare earth concentrations in pigeonitic and hypersthenic rock series from Izu-Hakone region,Japan     

Toshihiko Yajima  Hideo Higuchi  Hiroshi Nagasawa 《Contributions to Mineralogy and Petrology》1972,35(3):235-244

The abundances of rare earth elements in 5 each of aphyric volcanic rocks of pigeonitic and hypersthenic rock series from Izu-Hakone region have been determined by neutron activation analysis. Pigeonitic rock series show rare earth patterns with relative depletion of lighter rare earths (low lanthanum type) and large increase in rare earth abundances with differentiation. Hypersthenic rock series show higher lanthanum abundances (high lanthanum type) compared with pigeonitic rock series. The differences in rare earth patterns between two rock series are compatible with the theory of independent magmatic generation of these two series. Variation of rare earth patterns in both series have been examined by a model of magmatic differentiation based on the observed rare earth partition coefficients.  相似文献   

Trace element in igneous petrology | C.J. Allègre and S.R. Hart (Editors), 1978. A Volume in Memory of Paul W. Gast. Developments in Petrology, 5. Elsevier,Amsterdam, 272 pp., Dfl. 121.00, $ 49.95     

Hiroshi Nagasawa 《Earth》1979,15(1):79-80

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Trace element distribution in mineral separates of the Allende inclusions and their genetic implications     

Hiroshi Nagasawa  Douglas P Blanchard  Jeffrey W Jacobs  Joyce C Brannon  John A Philpotts  Naoki Onuma 《Geochimica et cosmochimica acta》1977,41(11):1587-1600

Concentrations of the REE, Sc, Co, Fe, Zn, Ir, Na and Cr were determined by instrumental neutron activation and mass spectrometric isotope dilution analysis for mineral separates of the coarseand fine-grained types (group I and II of Martin and Mason's classification) of the Allende inclusions.These data, combined with data on mineral/liquid partition coefficients, oxygen isotope distributions and diffusion calculations, suggest the following: (1) Minerals in the coarse-grained inclusions (group I) crystallized in a closed system with respect to refractory elements. On the other hand, differences in oxygen isotope distributions among minerals preclude a totally molten stage in the history of the inclusion. Group I inclusions were formed by rapid condensation (either to liquid or solid) in a supercooled solar nebula; extrasolar pyroxene and spinel dust were included but not melted in the condensing inclusions, thus preserving their extrasolar oxygen isotope composition. REE were distributed by diffusion during the subsequent heating at subsolidus temperatures; because oxygen diffuses much more slowly at these temperatures, the oxygen isotope anomalies were preserved. (2) The fine-grained (group II) inclusions were also formed by condensation from a super-cooled nebular gas; however, REE-rich clinopyroxene and spinel were formed early and REE-poor sodalite and nepheline were formed later and mechanically mixed with clinopyroxene and spinel to form the inclusions. The REE patterns of the bulk inclusions and the mineral separates are fractionated, indicating that REE abundances in the gaseous phase were already fractionated at the time of condensation of the minerals. (3) Pre-existing Mg isotope anomalies in the coarse-grained inclusions must have been erased during the heating stage thus resetting the ²⁶Al-²⁶Mg chronometer.  相似文献   

High temperature heating of the Allende meteorite     

Kenji Notsu  Naoki Onuma  Norimasa Nishida  Hiroshi Nagasawa 《Geochimica et cosmochimica acta》1978,42(6):903-907

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Rotation of volcanic smoke column around a vertical axis     

R. Nagasawa 《Bulletin of Volcanology》1965,28(1):321-331

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