Force-free magnetic fields and flares of August 1972     

K. Tanaka  Y. Nakagawa 《Solar physics》1973,33(1):187-204

On the basis of observations (Zirin and Tanaka, 1973) inferring the presence of shear in magnetic fields, the amount of extractable energy stored in a class of force-free magnetic fields is evaluated for the flares of August 1972, using the formulations developed by Nakagawa and Raadu (1972). It is shown that the evaluated energy storage could be built up by the proper motions of sunspots in the active region McMath 11976 during July 31 and August 7. Then for the flare of August 7, a detailed analysis is made of the manner of energy release in the post maximum phases deduced from the configuration of flare loops. It is shown that the observed flare loops could be represented closely by the force-free magnetic fields and that the evaluated rate of energy release is consistent with observed rate given by the soft X-ray emission. The results of analysis suggest that the flare of August 1972 could be identified with the relaxation of an energetic force-free magnetic field towards lower energy states. The limitations and possible future extension of this type of analysis are discussed.Visiting scientist from the Tokyo Astronomical Observatory, Mitaka, Tokyo, Japan.The National Center for Atmospheric Research is sponsored by the National Science Foundation.  相似文献   

Storm-time characteristics of low-latitude whistlers     

Yoshihito Tanaka  Masashi Hayakawa 《Planetary and Space Science》1973,21(10):1797-1798

Using the results from special observations, the storm-time effects on whistler characteristics at low latitudes were examined and found to agree with previous statistical studies. A short discussion is made on the link between spread-F irregularities and magnetospheric whistler ducts. The enhanced whistler activity is explained as a consequence of the stable whistler duct region during spread-F conditions.  相似文献   

Time variations of hard X-rays from Sco X-1     

M. Matsuoka  M. Fujii  S. Miyamoto  J. Nishimura  M. Oda  Y. Ogawara  S. Hayakawa  I. Kasahara  F. Makino  Y. Tanaka  P. C. Agrawal  B. V. Sreekantan 《Astrophysics and Space Science》1972,18(2):472-490

Simultaneous hard X-ray and optical observations of Sco X-1 were carried out on 1971 May 1 at Hyderabad, India, when Sco X-1 was optically bright. The X-ray intensity observed by balloon-borne counter telescopes increased in coincidence with optical enhancements, while the plasma temperature derived by fitting the X-ray spectrum in the energy range 20–40 keV to the thermal bremsstrahlung spectrum did not appreciably change over the whole period of observation.  相似文献   

Rocket observation of energy spectrum of diffuse hard X-rays     

Y. Fukada  S. Hayakawa  M. Ikeda  I. Kasahara  F. Makino  Y. Tanaka 《Astrophysics and Space Science》1975,32(1):L1-L5

The energy spectrum of diffuse hard X-rays measured in the range 10–40 keV shows a rather sharp change of slope. The logarithmic derivative of the spectrum changes around 20–30 keV by the increment significantly greater than 0.5 within an interval smaller than 50 keV.  相似文献   

The geometry of the chromosphere-corona transition region inferred from the center-to-limb variation of the radio emission     

M. Kanno  R. Tanaka 《Solar physics》1975,43(1):63-77

Based on the observations of the EUV spectroheliograms, the effective chromosphere-corona transition region is assumed to be restricted in a small volume element in the boundaries of the supergranular network. The center-to-limb variation of the quiet Sun at cm and dm wavelengths is analyzed to determine where the transition region is located in the network boundaries. Expressions are derived for the theoretical center-to-limb variation of the hypothetical brightness temperature only from the transition region, taking into account the orientation of the spicules. Comparison with the observations shows that the spicule-sheath model (Brueckner and Nicolas, 1973) and the hot plagette model (Foukal, 1974) are not compatible with the observations, because the limb brightening predicted by these models is too great. A new picture is therefore proposed that thin platelet transition regions are placed on top of the chromosphere and scattered between the network boundaries (the platelet transition-region model). This model is in accord with the observed center-to-limb variation of the radio emission.  相似文献   

Effect of Rock Hardness and Moisture Content on Tafoni Weathering in the Granite of Mount Doeg-sung, Korea   总被引：2，自引：0，他引：2  

Yukinori Matsukura  & Yukiya Tanaka 《Geografiska Annaler: Series A, Physical Geography》2000,82(1):59-67

Many tafoni occur on the granite tors of Mount Doeg-sung, Korea. Relationships are investigated between growth processes of granite tafoni and rock properties such as rock hardness and moisture content. Field evidence shows that the rock surface of the inner backwalls and ceiling of tafoni have reduced hardness and higher moisture content compared to the outer visor of tafoni and to vertical cliff walls with no tafoni. This suggests that tafoni arise in weathered rock where conditions of low strength and high moisture content are both satisfied.  相似文献   

Rapid development of arctic cyclone in June 2008 simulated by the cloud resolving global model NICAM     

Takuro Aizawa  H. L. Tanaka  Masaki Satoh 《Meteorology and Atmospheric Physics》2014,126(3-4):105-117

In this study, we conducted a numerical simulation of a rapid development of an arctic cyclone (AC) that appeared in June 2008 using a cloud resolving global model, Nonhydrostatic ICosahedral Atmospheric Model (NICAM). We investigated the three dimensional structure and intensification mechanism of the simulated AC that developed to the minimum sea level pressure of 971 hPa in the model. According to the result, the AC indicates a barotropic structure with a warm core in the lower stratosphere and a cold core in the troposphere. The development of the AC is accompanied by an intense mesoscale cyclone (MC) showing baroclinic structure with a marked local arctic front. The upper level warm core of the AC is formed by an adiabatic heating associated with the downdraft in the lower stratosphere. The rapid development of the AC is caused by the combination of the intensification of the upper level warm core and the merging with the baroclinically growing MC in the lower level. The merging of the AC and MC and the vertical vortex coupling with the upper air polar vortex are the most important mechanisms for the rapid development of the arctic cyclone.  相似文献   

Biotic response of benthic foraminifera in Aso-kai lagoon,central Japan,to changes in terrestrial climate and ocean conditions (~AD 700–1600)     

Hiroyuki Takata  Satoshi Tanaka  Koji Seto  Saburo Sakai  Katsumi Takayasu  Boo-Keun Khim 《Journal of Paleolimnology》2014,51(3):421-435

We investigated responses of shallow-water benthic foraminifera to changes in climate and ocean conditions, using sediment core ASC2 from Aso-kai lagoon, central Japan. Six AMS ¹⁴C dates reveal that the studied interval corresponds to sediments deposited from ~AD 700 to 1600. Sulfur content of the bulk sediment and multi-dimensional scaling (MDS) axis 1 of fossil benthic foraminifera indicate that the composition of the benthic foraminifera community was closely related to dissolved oxygen (DO) concentration in the hypolimnion. The sulfur content and MDS axis 1 also revealed two shifts over the 900-year interval. In the first phase (~AD 700–1250), the Shannon–Wiener Index (H′), E (S₂₀₀), evenness and rank abundance curve (RAC) kurtosis indicate a gradual deterioration in structure of the benthic foraminifera community. In that period, there are statistically significant correlations between the faunal composition (MDS axis 1) and faunal structure [Shannon–Wiener (H′), E (S₂₀₀), evenness and RAC kurtosis]. In the second phase (~AD 1250–1600), however, faunal composition and structure show no marked correspondence. Instead, abundance of benthic foraminifera fluctuated on a scale of ~200 years. Thus, a shift in the biotic response of benthic foraminifera in Aso-kai lagoon occurred in ca. AD 1250. Gradual deterioration of benthic foraminifera, with taxonomic losses, is consistent with declining DO in the first phase, possibly associated with the increasing influence of the Tsushima Warm Current. The possibility that closure of Aso-kai lagoon and development of the sand bar affected benthic foraminifera cannot, however, be ruled out. No corresponding response was observed in the second phase, during which there was no distinct taxonomic loss. Large variations in abundance, however, were a consequence of strength of the East Asian summer and winter monsoons. The shift in the biotic response of benthic foraminifera in Aso-kai lagoon during the period AD 700–1600 was apparently a result of changes in climate and ocean conditions on the East Asian continental margin.  相似文献   

Correlation between climate sensitivity and aerosol forcing and its implication for the “climate trap”     

Katsumasa Tanaka  Thomas Raddatz 《Climatic change》2011,109(3-4):815-825

Climate sensitivity and aerosol forcing are dominant uncertain properties of the global climate system. Their estimates based on the inverse approach are interdependent as historical temperature records constrain possible combinations. Nevertheless, many literature projections of future climate are based on the probability density of climate sensitivity and an independent aerosol forcing without considering the interdependency of such estimates. Here we investigate how large such parameter interdependency affects the range of future warming in two distinct settings: one following the A1B emission scenario till the year 2100 and the other assuming a shutdown of all greenhouse gas and aerosol emissions in the year 2020. We demonstrate that the range of projected warming decreases in the former case, but considerably broadens in the latter case, if the correlation between climate sensitivity and aerosol forcing is taken into account. Our conceptual study suggests that, unless the interdependency between the climate sensitivity and aerosol forcing estimates is properly considered, one could underestimate a risk involving the “climate trap”, an unpalatable situation with a high climate sensitivity in which a very drastic mitigation may counter-intuitively accelerate the warming by unmasking the hidden warming due to aerosols.  相似文献   

Emission metrics under the 2 °C climate stabilization target     

Katsumasa Tanaka  Daniel J. A. Johansson  Brian C. O’Neill  Jan S. Fuglestvedt 《Climatic change》2013,117(4):933-941

In multi-gas climate policies such as the Kyoto Protocol one has to decide how to compare the emissions of different greenhouse gases. The choice of metric could have significant implications for mitigation priorities considered under the prospective negotiations for climate mitigation agreements. Several metrics have been proposed for this task with the Global Warming Potential (GWP) being the most common. However, these metrics have not been systematically compared to each other in the context of the 2 °C climate stabilization target. Based on a single unified modeling framework, we demonstrate that metric values span a wide range, depending on the metric structure and the treatment of the time dimension. Our finding confirms the basic salient point that metrics designed to represent different aspects of the climate and socio-economic system behave differently. Our result also reflects a complex interface between science and policy surrounding metrics. Thus, it is important to select or design a metric suitable for climate stabilization based on an interaction among practitioners, policymakers, and scientists.  相似文献