A study on three-dimensional structures of the ionospheric dynamo currents induced by the neutral winds simulated by the Kyushu-GCM     

Keiko Kawano-Sasaki  Saburo Miyahara 《Journal of Atmospheric and Solar》2008,70(11-12):1549-1562

Three-dimensional structures of the ionospheric dynamo currents are examined using the neutral winds in a general circulation model of the middle atmosphere at Kyushu University. A quasi-three-dimensional ionospheric dynamo model is constructed assuming an infinite parallel conductivity in the ionosphere. This model is able to simulate both the equatorial electrojet and the global Sq current system successfully. The simulated results reveal that the equatorial electrojet is confined in quite narrow latitudes around the equator accompanied with meridional current circulations and satisfies a non-divergent structure mainly within the E region. A vertically stratified double layered structure is seen in the east–west current density near the focus latitude of the global Sq current system. It is shown that the stratified structure mainly consists of the east–west Hall current associated with the eastward wind of zonal wavenumbers 1 and 2 in the lower altitudes and the westward wind of zonal wavenumber 2 in the upper altitudes. The day-to-day variation of the neutral winds can significantly vary the induced ionospheric dynamo current system, which is recognized as changes of the focus latitude and/or the maximum value of the equatorial electrojet.  相似文献   

Ionospheric electromagnetic perturbations observed on DEMETER satellite before Chile M7.9 earthquake   总被引：1，自引：0，他引：1  

Xuemin Zhang Jiadong Qian Xinyan Ouyang Xuhui Shen Jin’an Cai  Shufan Zhao Institute of Earthquake Science  China Earthquake Administration  Beijing  China 《地震学报(英文版)》2009,(3):251-255

Based on the ionospheric electromagnetic data observed on DEMETER satellite of France, the ionospheric electromagnetic signals were analyzed within 10 days before Chile M7.9 earthquake on November 14, 2007. It is found that, low frequency electromagnetic disturbances began to increase in a large scale of latitude, and reached to a maximum one week prior to the earthquake, and at about three days before the quake, the peak values shifted to lower latitude. Taking three days as a group, spatial images of a fe...  相似文献   

Modeling Arctic Ocean heat transport and warming episodes in the 20th century caused by the intruding Atlantic Water     

Jun Takahashi  Tatsuo Suzuki  Igor V Polyakov  Kohei Mizobata  Moto Ikeda  Fancois J.Saucier  Markus Meier 《极地研究(英文版)》2008,19(2):159-167

This study investigates the Arctic Ocean warming episodes in the 20th century using both a high-resolution coupled global climate model and historical observations. The model, with no flux adjustment, reproduces well the Atlantic Water core temperature （AWCT） in the Arctic Ocean and shows that four largest decadalscale warming episodes occurred in the 1930s, 70s, 80s, and 90s, in agreement with the hydrographic observational data. The difference is that there was no pre-warming prior to the 1930s episode, while there were two pre-warming episodes in the 1970s and 80s prior to the 1990s, leading the 1990s into the largest and prolonged warming in the 20th century. Over the last century, the simulated heat transport via Fram Strait and the Barents Sea was estimated to be, on average, 31.32 TW and 14.82 TW, respectively, while the Bering Strait also provides 15.94 TW heat into the west- ern Arctic Ocean. Heat transport into the Arctic Ocean by the Atlantic Water via Fram Strait and the Barents Sea correlates significantly with AWCT （ C = 0.75 ） at 0- lag. The modeled North Atlantic Oscillation （NAO） index has a significant correlation with the heat transport （ C = 0.37 ）. The observed AWCT has a significant correlation with both the modeled AWCT （ C =0.49） and the heat transport （ C =0.41 ）. However, the modeled NAO index does not significantly correlate with either the observed AWCT （ C = 0.03 ） or modeled AWCT （ C = 0.16 ） at a zero-lag, indicating that the Arctic climate system is far more complex than expected.  相似文献   

Redox Evolution of the Lithospheric Mantle beneath the North China Craton     

WANG Jian  SONG Yue  Keiko HATTORI 《《地质学报》英文版》2016,90(4):1539-1540

正Objective The North China Craton(NCC)is a large Archean craton with a long geological history,yet very few studies have been carried out on the evolution of the redox conditions of its underlying mantle.Oxidation state of the mantle is critical in controlling the formation of metallic mineral deposits because metals can be readily released from the mantle to partial melt under oxidized conditions.  相似文献   

Phosphorus and nitrogen cyclings in the pelagic system of hiroshima bay: Results of numerical model simulation     

Jutarat Kittiwanich  Tamiji Yamamoto  Toshiya Hashimoto  Keiko Tsuji  Osamu Kawaguchi 《Journal of Oceanography》2006,62(4):493-509

A numerical ecosystem model expressing both phosphorus and nitrogen cyclings in the pelagic system of Hiroshima Bay, Japan, was developed in order to investigate the seasonal variations of these elements and their annual budgets. Based on the geophysical and chemical structures of the bay, Hiroshima Bay was divided into northern and southern boxes, themselves divided into two layers of an upper 5 m and a lower layer according to the stratification of the water column. The model consists of equations representing all relevant physical and biological processes. The results revealed that the internal regeneration of materials was an important source of bioavailable nutrients for phytoplankton growth in the water column. The incorporation of phytoplankton aggregation improved the accuracy of the outputs in comparison to the observed data, especially during the stratified summer season. The results also indicated that phosphorus limitation of phytoplankton growth occurs in the upper layer during summer while light limitation occurs in the lower layer. In addition, physical processes such as diffusion and advection were also important as they ensured that most of regenerated nutrients in the lower layer were transported to the upper layer. Thus, these processes might support the high primary production and the production of oysters that are extensively cultured in this bay. Considering the informative results obtained, the model used in this study provides a sound basis and tool to describe the dynamics of phosphorus and nitrogen cyclings in Hiroshima Bay.  相似文献   

Obliquity evolution of extrasolar terrestrial planets     

Keiko Atobe 《Icarus》2007,188(1):1-17

We have investigated the obliquity evolution of terrestrial planets in habitable zones (at ∼1 AU) in extrasolar planetary systems, due to tidal interactions with their satellite and host star with wide varieties of satellite-to-planet mass ratio (m/Mp) and initial obliquity (γ₀), through numerical calculations and analytical arguments. The obliquity, the angle between planetary spin axis and its orbit normal, of a terrestrial planet is one of the key factors in determining the planetary surface environments. A recent scenario of terrestrial planet accretion implies that giant impacts of Mars-sized or larger bodies determine the planetary spin and form satellites. Since the giant impacts would be isotropic, tilted spins (sinγ₀∼1) are more likely to be produced than straight ones (sinγ₀∼0). The ratio m/Mp is dependent on the impact parameters and impactors' mass. However, most of previous studies on tidal evolution of the planet-satellite systems have focused on a particular case of the Earth-Moon systems in which m/Mp?0.0125 and γ₀∼10° or the two-body planar problem in which γ₀=0° and stellar torque is neglected. We numerically integrated the evolution of planetary spin and a satellite orbit with various m/Mp (from 0.0025 to 0.05) and γ₀ (from 0° to 180°), taking into account the stellar torques and precessional motions of the spin and the orbit. We start with the spin axis that almost coincides with the satellite orbit normal, assuming that the spin and the satellite are formed by one dominant impact. With initially straight spins, the evolution is similar to that of the Earth-Moon system. The satellite monotonically recedes from the planet until synchronous state between the spin period and the satellite orbital period is realized. The obliquity gradually increases initially but it starts decreasing down to zero as approaching the synchronous state. However, we have found that the evolution with initially tiled spins is completely different. The satellite's orbit migrates outward with almost constant obliquity until the orbit reaches the critical radius ∼10-20 planetary radii, but then the migration is reversed to inward one. At the reversal, the obliquity starts oscillation with large amplitude. The oscillation gradually ceases and the obliquity is reduced to ∼0° during the inward migration. The satellite eventually falls onto the planetary surface or it is captured at the synchronous state at several planetary radii. We found that the character change of precession about total angular momentum vector into that about the planetary orbit normal is responsible for the oscillation with large amplitude and the reversal of migration. With the results of numerical integration and analytical arguments, we divided the m/Mp-γ₀ space into the regions of the qualitatively different evolution. The peculiar tidal evolution with initially tiled spins give deep insights into dynamics of extrasolar planet-satellite systems and discussions of surface environments of the planets.  相似文献   

Rapid contamination during storage of carbonaceous chondrites prepared for micro FTIR measurements     

Yoko KEBUKAWA  Satoru NAKASHIMA  Takahiro OTSUKA  Keiko NAKAMURA‐MESSENGER  Michael E. ZOLENSKY 《Meteoritics & planetary science》2009,44(4):545-557

Abstract— Organic contamination (?2965 and ?1260 cm^?1peaks) was found on Tagish Lake (C2) and Murchison (CM2) carbonaceous chondrites containing abundant hydrous minerals by Fourier transform infrared (FTIR) microspectroscopy on the samples pressed on Al plates. On the other hand, anhydrous chondrite (Moss, CO3) was not contaminated. This contamination occurred within one day of storage, when the samples pressed on Al were stored within containers including silicone rubber mats. Volatile molecules having similar peaks to the contaminants were detected by long‐path gas cell FTIR measurements for the silicone rubber mat. Rapid adsorption of the volatile contaminants also occurred when silica gel and hydrous minerals such as serpentine were stored in containers including silicone rubber, silicone grease, or adhesive tape. However, they did not show any contamination when stored in glass and polystyrene containers without these compounds. Therefore, precious astronomical samples such as meteorites, interplanetary dust particles (IDPs), and mission‐returned samples from comets, asteroids, and Mars, should be measured by micro FTIR within one day of storage in glass containers without silicone rubber, silicone grease, or adhesive tape.  相似文献   

Influence of weather conditions and spatial variability on glacier surface melt in Chilean Patagonia     

Keiko Konya  Takane Matsumoto 《Theoretical and Applied Climatology》2010,102(1-2):139-149

In order to clarify how differences in weather conditions affect the surface heat balance of a large maritime glacier, meteorological observations were carried out in the ablation area of Glaciar Exploradores in the Chilean Patagonia during the austral summer of 2006/2007. Under cloudy/rainy weather, when the air temperature and wind speed were high due to advection, the average melting heat was 18.8 MJ m^?2 day^?1 and the turbulent heat fluxes contributed 35% of the total melt. During clear weather, the average melting heat was 16.9 MJ m^?2 day^?1 and 13% of the total was the turbulent heat fluxes. A decrease in air temperature due to the development of the glacier boundary layer on clear days will lead to an overestimation of the melt using the air temperature at a weather station outside of the glacier.  相似文献   

Cosmic-ray-produced⁴⁰K and⁵⁰V in the metal phase of chondrites     

Keiko Imamura  Masako Shima  Masatake Honda 《Earth and Planetary Science Letters》1975,26(1):54-60

Cosmic-ray-produced⁴⁰K in the metal phase of six chondrites and⁵⁰V in that of one chondrite were determined using a surface ionization mass spectrometer. The²²Ne_total/⁴⁰K_metal ratios of the chondrites are explained in part by shielding effects during cosmic-ray irradiation. The wide variation of this ratio in some groups of meteorites is explained in terms of partial loss of rare-gas nuclides. Radiation ages for the chondrites were determined using⁴⁰K measurements and production-rate estimates from thick target calculations.  相似文献   

Surface Heat Balance and Spatially Distributed Ablation Modelling at Koryto Glacier, Kamchatka Peninsula, Russia   总被引：1，自引：0，他引：1  

Keiko Konya  Takane Matsumoto  Renji Naruse 《Geografiska Annaler: Series A, Physical Geography》2004,86(4):337-348

To investigate the characteristics of ablation at Koryto Glacier, a mountain glacier under maritime climate in Kamchatka Peninsula, Russia, we made field observations from August to early September 2000. At a site near the equilibrium line, the 31‐day average net radiation, sensible heat flux, and latent heat flux were 43, 59 and 31 W^?2, respectively. We developed a new distributed ablation model, which only needs measurements of air temperature and global radiation at one site. Hourly ablation rates at this site obtained by the energy balance method are related to measured air temperature and global radiation by linear multiple regression. A different set of multiple regression coefficients is fitted for snow and ice surfaces. Better estimates of ablation rate can be obtained by this approach than by other temperature index models. These equations are then applied to each grid cell of a digital elevation model to estimate spatially distributed hourly melt. Air temperature is extrapolated using a constant temperature lapse rate and global radiation is distributed considering topographic effects. The model enables us to calculate the hourly spatial distribution of ablation rates within the glacier area and could well provide a realistic simulation of ablation over the whole glacier.  相似文献