Simulated interannual variation in summertime atmospheric circulation associated with the East Asian monsoon     

Miki Arai  Masahide Kimoto 《Climate Dynamics》2008,31(4):435-447

The reproducibility of the interannual variability of the summertime East Asian circulation is examined using an atmospheric general circulation model (AGCM). An ensemble experiment is conducted using observed sea surface temperature (SST) of recent 20 years as a lower boundary condition. The spatial pattern associated with the first principal mode of observation of geopotential height at 500 hPa is characterized by a meridional wavy pattern extending over eastern Siberia, the vicinity of Japan and the subtropical western Pacific. The principal component (PC) time series of the leading mode is represented well by a high-resolution version of the AGCM with horizontal resolution T106 and with 56 vertical levels (T106L56), while with a lower resolution version, T42 and 20 vertical levels, the reproducibility is considerably degraded. The reproducibility by the AGCM suggests the importance of SST as a boundary condition. However, the simulated interannual variations show the alternating appearance of two distinct circulation regimes, a cold summer regime and a hot summer regime, exhibiting interesting bimodality in probability density distribution in PC phase space. This implies that the system’s response to the continuously varying boundary condition includes nonlinearity. The nature of this nonlinearity is suggested to be wave breaking in the westerly region of the high latitudes that requires high resolution for the reproduction. Using the T106L56 model, another ensemble experiment was carried out with doubled CO₂. The climate change appears as an increase in residence frequency of the cold summer regime of the principal patterns of the present-day climate. This paper is a contribution to the AMIP-CMIP Diagnostic Sub-project on General Circulation Model Simulation of the East Asian Climate, coordinated by W.-C. Wang.  相似文献   

Monte Carlo modeling of Io’s [OI] 6300 Å and [SII] 6716 Å auroral emission in eclipse     

C. Moore  K. Miki  K. Stapelfeldt  P.L. Varghese  R.W. Evans 《Icarus》2010,207(2):810-833

We present a Monte Carlo (MC) model of [OI] 6300 Å and [SII] 6716 Å emission from Io entering eclipse. The simulation accounts for the 3-D distribution of SO₂, O, SO, S, and O₂ in Io’s atmosphere, several volcanic plumes, and the magnetic field around Io. Thermal electrons from the jovian plasma torus are input along the simulation domain boundaries and move along the magnetic field lines distorted by Io, occasionally participating in collisions with neutrals. We find that the atmospheric asymmetry resulting from varying degrees of atmospheric collapse across Io (due to eclipse ingress) and the presence of volcanoes contributes significantly to the unique morphology of the [OI] 6300 Å emission. The [OI] radiation lifetime of ∼134 s limits the emission to regions that have a sufficiently low neutral density so that intermolecular collisions are rare. We find that at low altitudes (typically <40 km) and in volcanic plumes (Pele, Prometheus, etc.) the number density is large enough (>4 × 10⁹ cm⁻³) to collisionally quench nearly all (>95%) of the excited oxygen for reasonable quenching efficiencies. Upstream (relative to the plasma flow), Io’s perturbation of the jovian magnetic field mirrors electrons with high pitch angles, while downstream collisions can trap the electrons. This magnetic field perturbation is one of the main physical mechanisms that results in the upstream/downstream brightness asymmetry in [OI] emission seen in the observation by Trauger et al. (Trauger, J.T., Stapelfeldt, K.R., Ballester, G.E., Clarke, J.I., 1997. HST observations of [OI] emissions from Io in eclipse. AAS-DPS Abstract (1997DPS29.1802T)). There are two other main causes for the observed brightness asymmetry. First, the observation’s viewing geometry of the wake spot crosses the dayside atmosphere and therefore the wake’s observational field of view includes higher oxygen column density than the upstream side. Second, the phased entry into eclipse results in less atmospheric collapse and thus higher collisional quenching on the upstream side relative to the wake. We compute a location (both in altitude and latitude) for the intense wake emission feature that agrees reasonably well with this observation. Furthermore, the peak intensity of the simulated wake feature is less than that observed by a factor of ∼3, most likely because our model does not include direct dissociation-excitation of SO₂ and SO. We find that the latitudinal location of the emission feature depends not so much on the tilt of the magnetic field as on the relative north/south flux tube depletion that occurs due to Io’s changing magnetic latitude in the plasma torus. From 1-D simulations, we also find that the intensity of [SII] 6716 and 6731 Å emission is much weaker than that of [OI] even if the [SII] excitation cross section is 10³ times larger than excitation to [OI]. This is because the density of S⁺ is much less than that of O and because the Einstein-A coefficient of the [SII] emission is a factor of ∼10 smaller than that of [OI].  相似文献   

Mountain influence on the areal characteristics of types of convective precipitation     

M. Ćurić  D. Janc 《Theoretical and Applied Climatology》1992,45(1):71-76

Summary The unique detailed precipitation data from a dense network operated in Serbia during the project of hail suppression have been used to define the relationship between a convective storm and associated precipitation.The data analysed were from 1982–1986 and from 120 firing stations in mountainous terrain and 115 in flat areas. The firing stations are those manned 24 hours a day by cooperative observers. The average distance between sites is 5 km.Detailed maps of the frequency of different precipitation types at all points of the network are plotted. A comparison is made between the results obtained from both mountainous and flat land networks. It is shown that alternate changes of the local maxima and minima of rain and hail shower frequency exist for the air mass (Cb) clouds. The air mass tracks from a NW direction in the river valley where it is flanked by orography.With 8 Figures  相似文献   

Determination of Multiple Trace Element Compositions in Thin (> 30 μm) Layers of NIST SRM 614 and 616 Using Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS)     

Tomoaki Morishita  Yoshito Ishida  Shoji Arai  Miki Shirasaka 《Geostandards and Geoanalytical Research》2005,29(1):107-122

To understand and/or avoid small-scale chemical heterogeneities within geological materials prepared as normal thin sections, in situ multiple trace element determination coupled with the simultaneous microscopic observation of the sample during analysis is preferable. We have examined fifty trace elements in thin (< 30 μm) layers of the NIST SRM 614 and 616 glass reference materials by LA-ICP-MS using different pit diameters and internal standard elements (Ca and Si). Compositional heterogeneities of Tl, Bi, As and Cd were found in NIST SRM 614 and 616 at the spatial resolution of ca. 10 0 μm. Except for these elements, the RSDs of six determinations for most elements were better than 10% in NIST SRM 614 when ablation diameters were < 50 μm. The measured concentrations for most elements in NIST SRM 614 and 616 agree with previous values in the literature at the 95% confidence level with the exception of W and Bi. New LA-ICP-MS data for K, As and Cd are also reported. The results support the view that the latest LA-ICP-MS is a powerful and flexible analytical technique for the determination of multiple ultra-trace element compositions in geological materials prepared as normal thin sections of the type that has been used for polarising optical microscopic observations since the end of the 19th century.  相似文献   

Sensitivity analysis of the 1-D convective cloud model outputs on the dynamical parameters     

M. Ćurić  D. Janc 《Theoretical and Applied Climatology》1989,40(4):237-246

Summary Forced 1-D time-dependent numerical model of Cb cloud is used to analyse the sensitivity of the model products on dynamical parameters. The model considers the processes of horizontal entrainment, forced lifting through the cloud base as well as the six forms of water substance: water vapour, cloud water, cloud ice, rain, snow and hail. Atmospheric soundings for deep storm situation are used as initial and evironmental conditions.The maxima model values of vertical velocity, cloud water, rain water and ice mixing ratios, temperature excess, cloud top height and radar reflectivity are under the strong influence of the parameters of entrainment, amplitude of initial vertical velocity and forced vertical velocity. The most visible influence is that of forced vertical velocity on the ice content.The model values agree well with observations in one case for selected dynamical conditions.

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Zusammenfassung Ein 1-D-zeitabhängiges numerisches Modell einer Cumulonimbuswolke wird für eine Sensitivitätsanalyse der Modellergebnisse nach dynamischen Parametern herangezogen. Im Modell werden Prozesse des horizontalen Entrainments und der erzwungenen Hebung durch die Wolkenbasis sowie Wasser in sechs Erscheinungsformen beachtet: Wasserdampf, Wolkenwasser, Wolkeneis, Regen, Schnee und Hagel. Atmosphärische Sondierungen von heftigen Sturmsituationen werden als Anfangs- und Randbedingungen verwendet.Die maximalen Modellwerte der Vertikalgeschwindigkeit, des Wolken- und Regenwassers und des Eismischungsverhältnisses, des Temperaturüberschusses, der Höhe der Wolkenobergrenze und der Radarreflektivität werden stark von den Entrainmentparametern und der Amplitude der ursprünglichen wie der erzwungenen Vertikalgeschwindigkeit beeinflußt. Am sichtbarsten ist der Einfluß der erzwungenen Vertikalgeschwindigkeit auf den Eisgehalt.Die Modellwerte stimmen gut mit Beobachtungen für einen Fall mit ausgesuchten dynamischen Bedingungen überein.

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With 7 Figures  相似文献   

Collapse mechanism of the Paleogene Sakurae cauldron, SW Japan   总被引：1，自引：0，他引：1  

Hiroaki Komuro  Miki Aoyama  Tahei Arayashiki 《Bulletin of Volcanology》2006,68(7-8):631-640

The Paleogene Sakurae cauldron of SW Japan is characterized by a nested structure with a polygonal outline (21×13 km²) including a circular collapsed part (5 km in diameter). Total thickness of the caldera infill amounts to 2,000 m. The lower member of the infill consists mainly of felsic crystal tuff and lesser intercalated andesitic lava flows, whereas the upper member is composed of high-grade ignimbrite capped with a large rhyolitic lava dome. These members represent the first and second stage eruptions, respectively. Faults bounding the cauldron rim comprise intersecting radial and concentric faults, producing the polygonal outline of this cauldron. The primary collapse of this cauldron thus occurred as a polygonal caldera basin where products of the first stage eruption accumulated. In contrast, the inner collapse part is defined by a ring fracture system. This sector subsided concurrently with accumulation of the high-grade ignimbrite of the second stage eruption. This inner circular collapse thus represents syn-eruptional subsidence concurrent with the climactic eruption. Magma drainage during the first stage probably induced outward-dipping ring fractures in the chamber roof. Opening of the ring fractures following subsidence of the central bell-jar block caused rapid evacuation of magma as voluminous pumice flows, even though magma pressure may have decreased to some degree.  相似文献   

Melting and Multi-stage Metasomatism in the Mantle Wedge beneath a Frontal Arc Inferred from Highly Depleted Peridotite Xenoliths from the Avacha Volcano, Southern Kamchatka   总被引：3，自引：0，他引：3  

Ishimaru  Satoko; Arai  Shoji; Ishida  Yoshito; Shirasaka  Miki; Okrugin  Victor M. 《Journal of Petrology》2007,48(2):395-433

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Cooling Radius vs. Absorption Size of Galaxies     

Milan M. Ćirković  Srdjan Samurović  Aleksandra Djorić 《Astrophysics and Space Science》2000,274(4):867-875

The discussion of the relationship between cooling radius in two-phaseadiabatic halo models and observationally established maximal radiusof absorption in luminous galaxies at low redshift is presented. It isof paramount importance that any viable model of the halo is able toreproduce empirical value of the absorption cross-section of normalgalaxies and its scaling with luminosity. Several ways for bringingthe theoretical and observational values into agreement are outlined.It is of great methodological importance to fully assess the difficultiesany model is likely to encounter when testing predicted extent ofabsorption and column density distribution against recently obtainedlow-redshift Ly absorption data.  相似文献   

Transport properties of olivine grain boundaries from electrical conductivity experiments     

Anne?Pommier  David?L.?Kohlstedt  Lars?N.?Hansen  Stephen?MackwellEmail authorView author&#;s OrcID profile  Miki?Tasaka  Florian?Heidelbach  Kurt?Leinenweber 《Contributions to Mineralogy and Petrology》2018,173(5):41

Grain boundary processes contribute significantly to electronic and ionic transports in materials within Earth’s interior. We report a novel experimental study of grain boundary conductivity in highly strained olivine aggregates that demonstrates the importance of misorientation angle between adjacent grains on aggregate transport properties. We performed electrical conductivity measurements of melt-free polycrystalline olivine (Fo₉₀) samples that had been previously deformed at 1200 °C and 0.3 GPa to shear strains up to γ?=?7.3. The electrical conductivity and anisotropy were measured at 2.8 GPa over the temperature range 700–1400 °C. We observed that (1) the electrical conductivity of samples with a small grain size (3–6 µm) and strong crystallographic preferred orientation produced by dynamic recrystallization during large-strain shear deformation is a factor of 10 or more larger than that measured on coarse-grained samples, (2) the sample deformed to the highest strain is the most conductive even though it does not have the smallest grain size, and (3) conductivity is up to a factor of ~?4 larger in the direction of shear than normal to the shear plane. Based on these results combined with electrical conductivity data for coarse-grained, polycrystalline olivine and for single crystals, we propose that the electrical conductivity of our fine-grained samples is dominated by grain boundary paths. In addition, the electrical anisotropy results from preferential alignment of higher-conductivity grain boundaries associated with the development of a strong crystallographic preferred orientation of the grains.  相似文献   

A new high-pressure phase of strontium carbonate     

Shigeaki Ono  Miki Shirasaka  Takumi Kikegawa  Yasuo Ohishi 《Physics and Chemistry of Minerals》2005,32(1):8-12

High-pressure and high-temperature experiments conducted in a laser-heated diamond-anvil cell with a synchrotron X-ray diffraction method have revealed a phase transformation in the aragonite-type SrCO₃ at pressures above 10 GPa. The new phase has an orthorhombic symmetry and was confirmed to remain stable to 32 GPa. The Birch-Murnaghan equation of state for new phase was determined from the experimental unit cell parameters, with K₀ = 101 (± 16) GPa, K₀ = 4 (constrained value), and V₀ = 111.9 (± 2.2). This transformation in SrCO₃ is different from that in BaCO₃ as reported in previous studies. After decompression at ambient pressure, the high-pressure phase transforms to a metastable structure, which has an orthorhombic symmetry. This result should also resolve a dispute regarding the stable high-pressure phases in BaCO₃, which is an analog material of CaCO₃ and SrCO₃.This revised version was published in February 2005 with corrections to the Introduction and to the References.  相似文献