Fast and slow timescales in the tropical low-cloud response to increasing CO2 in two climate models     

Masahiro Watanabe  Hideo Shiogama  Masakazu Yoshimori  Tomoo Ogura  Tokuta Yokohata  Hajime Okamoto  Seita Emori  Masahide Kimoto 《Climate Dynamics》2012,39(7-8):1627-1641

To obtain physical insights into the response and feedback of low clouds (C _l ) to global warming, ensemble 4?×?CO₂ experiments were carried out with two climate models, the Model for Interdisciplinary Research on Climate (MIROC) versions 3.2 and 5. For quadrupling CO₂, tropical-mean C _l decreases, and hence, acts as positive feedback in MIROC3, whereas it increases and serves as negative feedback in MIROC5. Three time scales of tropical-mean C _l change were identified—an initial adjustment without change in the global-mean surface air temperature, a slow response emerging after 10–20?years, and a fast response in between. The two models share common features for the former two changes in which C _l decreases. The slow response reflects the variability of C _l associated with the El Ni?o-Southern Oscillation in the control integration, and may therefore be constrained by observations. However, the fast response is opposite in the two models and dominates the total response of C _l . Its sign is determined by a subtle residual of the C _l increase and decrease over the ascending and subsidence regions, respectively. The regional C _l increase is consistent with a more frequent occurrence of a stable condition, and vice versa, as measured by lower-tropospheric stability (LTS). The above frequency change in LTS is similarly found in six other climate models despite a large difference in both the mean and the changes in the low-cloud fraction for a given LTS. This suggests that the response of the thermodynamic constraint for C _l to increasing CO₂ concentrations is a robust part of the climate change.  相似文献   

Anomalous Love-wave phase velocities in the Pacific: sequential pure-path and spherical harmonic inversion     

Clyde E. Nishimura  Donald W. Forsyth 《Geophysical Journal International》1985,81(2):389-407

Summary. We have determined the lateral distribution of Love-wave phase velocities in the Pacific for the periods 40, 67, 91 and 125 s. Application of the pure-path and spherical harmonic representation methods indicates that the velocities are primarily a function of the age of the seafloor. A comparison of the results from these two techniques indicates inherent modelling constraints in both methods. The pure-path method is limited by its a priori nature while the spherical harmonic approach is unsuitable in describing sharp lateral velocity gradients. To circumvent these limitations, we propose the sequential application of the pure-path and spherical harmonic methods. The sequential inversion separates the velocity distribution into two separate components; velocity as a function of the age of the oceanic plate and variations superimposed on this relationship. Application of this method demonstrates the presence of velocity anomalies which cannot be modelled by an age–velocity relationship. These anomalies are tentatively correlated with regions of anomalous seafloor depths and/or the presence of active hot-spots. In the central south Pacific, an area with numerous active hot-spots coincides roughly with a region of anomalously slow Love wave velocities. A method for determining the errors associated with the slowness distributions calculated by the spherical harmonic method is presented and provides a means for determining the resolvability of these features.  相似文献   

High-Unblocking-Temperature Haematite Magnetizations of Late Palaeozoic Red Beds From the Okcheon Zone, Southern Part of the Korean Peninsula     

Y. S. Lee  S. Nishimura  K. D. Min 《Geophysical Journal International》1996,125(1):266-284

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Development of a Ground-Based LIF Instrument for Measuring HOx Radicals: Instrumentation and Calibrations     

Yugo Kanaya  Yasuhiro Sadanaga  Jun Hirokawa  Yoshizumi Kajii  Hajime Akimoto 《Journal of Atmospheric Chemistry》2001,38(1):73-110

An instrument for measuringtropospheric OH/HO₂ radicals by laser-inducedfluorescence developed in our laboratory is presentedin detail. It is based on FAGE (fluorescence assay bygas expansion) technique and OH is both excited anddetected at 308 nm corresponding to its A-X(0,0) band.The alignment of the laser beam, the design of thesample gas inlet, and the devices for the fluorescencedetection are optimized so as to reduce the backgroundsignal while keeping the OH sensitivity as high aspossible. A thermalized position of the expanding gasbeam is probed in our system and we did not observe asevere decrease of the HO_x sensitivities under humidconditions. An optical fiber is used for deliveringthe laser light to the fluorescence detection cellmounted outside at a high position. Thus the laserbeam alignment is by far simplified and is made highlyreproducible, once settled properly. For thecalibration, two methods are employed: a system withlaser absorption measurements of OH and a system ofsimultaneous photolysis of H₂O and O₂. Thecalibration factors are compared well within thecombined uncertainty. Using the latter system, theconversion efficiency of HO₂ to OH by NO additionis measured to be around 90%. The detection limitsfor OH and HO₂ (S/N = 2) are estimated to be3.3 × 10⁶ and 3.6 × 10⁶cm^–3 at noon,respectively, with an integration time of 1 min. Theresults of test observations at our institute are alsopresented.  相似文献   

Raman spectroscopy and heat capacity measurement of calcium ferrite type MgAl2O4 and CaAl2O4     

Kojitani  H.  Nishimura  K.  Kubo  A.  Sakashita  M.  Aoki  K.  Akaogi  M. 《Physics and Chemistry of Minerals》2003,30(7):409-415

Raman spectroscopy of calcium ferrite type MgAl₂O₄ and CaAl₂O₄ and heat capacity measurement of CaAl₂O₄ calcium ferrite were performed. The heat-capacity of CaAl₂O₄ calcium ferrite measured by a differential scanning calorimeter (DSC) was represented as C_P(T)=190.6–1.116 × 10⁷T^–2 + 1.491 × 10⁹T^–3 above 250 K (T in K). The obtained Raman spectra were applied to lattice dynamics calculation of heat capacity using the Kieffer model. The calculated heat capacity for CaAl₂O₄ calcium ferrite showed good agreement with that by the DSC measurement. A Kieffer model calculation for MgAl₂O₄ calcium ferrite similar to that for CaAl₂O₄ calcium ferrite was made to estimate the heat capacity of the former. The heat capacity of MgAl₂O₄ calcium ferrite was represented as C_P(T)=223.4–1352T ^–0.5 – 4.181 × 10⁶T ^–2 + 4.300 × 10⁸T ^–3 above 250 K. The calculation also gave approximated vibrational entropies at 298 K of calcium ferrite type MgAl₂O₄ and CaAl₂O₄ as 97.6 and 114.9 J mol^–1 K^–1, respectively.  相似文献   

Geochemical characteristics of the high reduction zone of stenols in Suwa sediments and the environmental factors controlling the conversion of stenols into stanols     

Mitsugu Nishimura 《Geochimica et cosmochimica acta》1978,42(4):349-357

Detailed geochemical analyses of the high reduction zone in Lake Suwa sediments suggested that the stenol to stanol conversion rate in this zone is primarily controlled by the proportion of autochthonous contribution to organic matter and the redox potential in these sediments, and that land-derived stenols were kept insensitive to hydrogenation in lacustrine sediments as compared with those derived from plankton. These results indicate that stanols derived directly from organisms on land may contribute significantly to stanols found in lacustrine sediments which contain minor proportions of autochthonous organic materials.In order to express the relative autochthonous vs terrigenous contribution to organic matter in lacustrine sediments, the autochthonous contribution index (ACI) was defined based on the characteristic distribution of sterol in plankton and land plants. It systematically increased from river inlet towards lake center and correlated closely with the δ¹³C value in same sediments. This strongly indicates that ACI is a useful indicator providing informatiom on autochthonous vs terrigenous contribution to the organic material in lacustrine sediments.  相似文献   

The occurrence of stanols in various living organisms and the behavior of sterols in contemporary sediments     

Mitsugu Nishimura  Tadashiro Koyama 《Geochimica et cosmochimica acta》1977,41(3):379-385

Unsaturated sterols (stenols) and saturated sterols (stanols) in phytoplankton and Zooplankton from Lake Suwa and from higher plants around the lake were analyzed by combined GLC and MS. In all the organisms investigated, 5α-cholestanol, 24-methylcholestan-3β-ol and 24-ethyl-5α-cholestanol were found, although in low concentrations, together with large quantities of stenols. This strongly suggests the contribution of stanols from living organisms to recent sediments.Findings from incubation experiments of cholesterol and 5α-cholestanol in the surface sediment from Lake Suwa extending through 450 days suggest the following: (1) stanols are slowly degraded and tend to survive unaltered in sediments in comparison with stenols, (2) in a relatively oxidative depositional environment such as Lake Suwa, the greater part of the stanols in the surface sediment originates from living organisms, (3) the reduction zone in which the degradation of sterols is suppressed and the rapid hydrogenation of stenols takes place may be in the microbiologically active sediment from 1 cm to about 10 cm in Lake Suwa, and (4) the increase in the ratio of stanols to stenols with depth below the zone may be caused by the simultaneous progress of preferential degradation and slow hydrogenation of stenols during long-term preservation in sediments.  相似文献   

The Preparation and Preliminary Characterisation of Four New Geological Survey of Japan Geochemical Reference Materials: Soils, JSO-1 and JSO-2; and Marine Sediments, JMS-1 and JMS-2   总被引：1，自引：0，他引：1  

Shigeru Terashima  Noboru Imai  Masahiro Taniguchi  Takashi Okai  Akira Nishimura 《Geostandards and Geoanalytical Research》2002,26(1):85-94

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Deep-sea coral geochemistry: Implication for the vital effect   总被引：2，自引：0，他引：2  

Kotaro Shirai  Minoru Kusakabe  Teruaki Ishii  Hajime Hiyagon 《Chemical Geology》2005,224(4):212-222

Deep-sea corals hold a great potential as a key to important aspects of paleoceanography for at least two reasons, 1) they offer temporal high resolution records of deep-sea environment, because they have growth banding structures, 2) and they are well suited for studying vital effects, because the deep-sea environment does not change over short time scales. However, the relationship between the chemical composition of deep-sea coral skeletons and environmental factors is not well understood. In this study, the chemical composition of deep-sea corals was measured in bulk individuals and along skeletal micro-structures. Among the bulk individuals, δ¹⁸O value and Sr / Ca ratio show a negative but weak correlation with ambient temperature. On the other hand, the Mg / Ca ratio has a positive, weak correlation with the temperature. Large variations were found among samples collected from similar temperature. The variation is up to 3.8‰ for δ¹⁸O, 0.9 mmol/mol for Sr / Ca ratios, and 0.78 mmol/mol for Mg / Ca ratios among samples with ambient average temperature within 1 °C. This variation may be due to a large vital effect. The centers of calcification (COCs), which were formed at high calcification rate, have lower Sr / Ca, U / Ca and higher Mg / Ca ratios than surrounding fasciculi. This chemical distribution supports the model that elemental incorporation depends on calcification rate. This suggests that calcification rate is a very important factor for the chemical composition in deep-sea corals and is one of the most significant mechanisms of the vital effect. Because of this large vital effect, further investigations are essential to use the deep-sea coral as a temperature proxy.  相似文献   

The nature of volcanic earthquake swarm preceding the 2000 flank eruption at Usu volcano, Hokkaido, Japan   总被引：1，自引：0，他引：1  

Vyacheslav M. Zobin  Yuichi Nishimura  Jun'ichi Miyamura 《Geophysical Journal International》2005,163(1):265-275

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