Simulations of anthropogenic change in the strength of the Brewer–Dobson circulation     

N. Butchart  A. A. Scaife  M. Bourqui  J. de Grandpré  S. H. E. Hare  J. Kettleborough  U. Langematz  E. Manzini  F. Sassi  K. Shibata  D. Shindell  M. Sigmond 《Climate Dynamics》2006,27(7-8):727-741

The effect of climate change on the Brewer–Dobson circulation and, in particular, the large-scale seasonal-mean transport between the troposphere and stratosphere is compared in a number of middle atmosphere general circulation models. All the models reproduce the observed upwelling across the tropical tropopause balanced by downwelling in the extra tropics, though the seasonal cycle in upwelling in some models is more semi-annual than annual. All the models also consistently predict an increase in the mass exchange rate in response to growing greenhouse gas concentrations, irrespective of whether or not the model includes interactive ozone chemistry. The mean trend is 11 kt s⁻¹ year⁻¹ or about 2% per decade but varies considerably between models. In all but one of the models the increase in mass exchange occurs throughout the year though, generally, the trend is larger during the boreal winter. On average, more than 60% of the mean mass fluxes can be explained by the EP-flux divergence using the downward control principle. Trends in the annual mean mass fluxes derived from the EP-flux divergence also explain about 60% of the trend in the troposphere-to-stratosphere mass exchange rate when averaged over all the models. Apart from two models the interannual variability in the downward control derived and actual mass fluxes were generally well correlated, for the annual mean.  相似文献   

A Rb/Sr record of catchment weathering response to Holocene climate change in Inner Mongolia     

Zhangdong Jin  Junji Cao  Jinglu Wu  Sumin Wang 《地球表面变化过程与地形》2006,31(3):285-291

Variation in the rubidium to strontium (Rb/Sr) ratio of the loess–palaeosol sequences has been proposed to reflect the degree of pedogenesis and weathering in the northwestern region of China. To characterize the Rb/Sr ratio of the dissolved loads of a single catchment, we analysed a 12·08 m sediment core from Daihai Lake in Inner Mongolia, north China. Dating control was provided by ²¹⁰Pb, ¹³⁷Cs and AMS‐¹⁴C. Sequential extraction experiments were conducted to investigate the concentrations of Rb and Sr on various chemical fractions in the lake sediments. Down‐core variation in the Rb/Sr ratios provides a record of Holocene weathering history. From 9 to 3·5 ka bp , accelerated chemical weathering was experienced throughout the Daihai catchment under mainly warm and humid conditions, and this reached a maximum at c. 5 ka bp . However, weathering was reduced between c. 8·25 and 7·90 ka bp , which may reflect the global 8·2 ka cooling event. After c. 2·5 ka bp , increased Rb/Sr ratios with higher frequency of fluctuations indicate reduced weathering within the Daihai catchment. The highest Rb/Sr ratios in the Little Ice Age lake sediments indicate the weakest phase of Holocene chemical weathering, resulting from a marked reduction in Sr flux into the basin. The Rb/Sr record also shows an enhancement of chemical weathering under today's climate, but its intensity is less than that of the Medieval Warm Period. Increased Rb/Sr in lake sediment corresponding to reduced catchment weathering is in striking contrast to Rb/Sr decrease in the glacial loess layers in the loess–palaeosol sequence. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Formation of astrophysical jets by a contracting magnetic accretion disk     

Shibata  Kazunari  Uchida  Yutaka 《Astrophysics and Space Science》1986,118(1-2):443-447

In the present paper, we discuss an MHD model for the formation of astrophysical jets, in which the directed flows are ejected along the rotation axis of an accretion disk formed from a cloud having a large scale magnetic field parallel to the angular momentum axis of the disk. The acceleration of jets is due to thej×B force in the relaxing magnetic twist which is produced by the rotation of the disk. The characteristic features of the jets, predicted by our mechanism and hopefully to be proven by observations, are the helical velocity and the hollow cylindrical shape of the jet, with a diameter of roughly the size of the region from which the acceretion disk collected its mass. Justification for the assumption of the perpendicular orientation of the disk, or the parallelism of the jets, to the external magnetic field may be provided by the fact that the component of rotation whose axis is perpendicular to the field may have been damped in the earlier phase of the cloud contraction.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 Septemper–6 October, 1984.  相似文献   

CO2浓度梯度对两种岩溶微藻碳酸酐酶活性的影响     

黄炳惠  李强  房君佳  曹建华  靳振江  彭文杰  卢晓漩  梁月明 《中国岩溶》2018,37(1):91-100

以经岩溶水驯化的小球藻（Chlorella vulgaris）和喜钙念珠藻(Nostoc calcicola Breb.)为实验对象,在封闭体系中用Willbur和 Anderson 方法比较研究两种不同微藻在不同CO2浓度下碳酸酐酶活性变化情况。结果表明:在低于3%CO2浓度的环境中岩溶微藻可通过快速调节自身碳酸酐酶活性来应对CO2升高带来的生境影响,在影响最大的2.5%的环境下小球藻与喜钙念珠藻碳酸酐酶活性分别提高了1.46倍和2.12倍;岩溶微藻应对CO2浓度增大带来的pH下降有着重要的恢复作用,随培养时间增长培养环境中的pH得到恢复;随着CO2浓度的增大,岩溶因子对碳酸酐酶有着重要的影响;培养48 h时Ca2+与喜钙念珠藻碳酸酐酶的相关性最高,而电导率（EC）与小球藻碳酸酐酶相关程度最高。   相似文献   

Simultaneous Observation of Solar Neutrons from the International Space Station and High Mountain Observatories in Association with a Flare on July 8, 2014     

Y. Muraki  D. Lopez  K. Koga  F. Kakimoto  T. Goka  L. X. González  S. Masuda  Y. Matsubara  H. Matsumoto  P. Miranda  O. Okudaira  T. Obara  J. Salinas  T. Sako  S. Shibata  R. Ticona  Y. Tsunesada  J. F. Valdés-Galicia  K. Watanabe  T. Yamamoto 《Solar physics》2016,291(4):1241-1265

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On the origin of strong downdrafts associated with the birth of sunspots     

Kazunari Shibata 《Solar physics》1980,66(1):61-70

During the emerging phase of sunspot pores strong downdrafts are observed in photospheric lines, whereas the upward flow is not detected within the observational accuracy. For the study of the origin of these downdrafts, we present the numerical solutions of non-steady hydrodynamic equations in one dimension along the rising magnetic flux tubes. In these solutions, it is assumed that the solar gas inside the tube is initially in the hydrostatic HSRA and then the tube rises with a given velocity and configuration. The results reproduce well the observed radial velocity distributions, hence it is concluded that the observed strong downdrafts originate from the sliding matter along the rising magnetic flux tubes.  相似文献   

Hα surges and associated Soft X-ray loops     

B. Schmieder  K. Shibata  L. Van Driel-Gesztelyi  S. Freeland 《Solar physics》1995,156(2):245-264

A recurrent H surge was observed on 7 October, 1991 on the western solar limb with the Meudon MSDP spectrograph. The GOES satellite recorded X-ray subflares coincident with all three events. During two of the surges high-resolutionYohkoh Soft X-ray Telescope (SXT) images have been taken. Low X-ray loops overlying the active region where the surges occurred were continuously restructuring. A flare loop appeared at the onset of each surge event and somewhat separated from the footpoint of the surge. The loops are interpreted as causally related to the surges. It is suggested that surges are due to magnetic reconnection between a twisted cool loop and open field lines. Cold plasma bubbles or jets squeezed among untwisting magnetic field lines could correspond to the surge material. No detection was made of either X-ray emission along the path of the surges or X-ray jets, possibly because of the finite detection threshold of theYohkoh SXT.  相似文献   

Correction of the effect of relative wind direction on wind speed derived by advanced microwave scanning radiometer     

Masanori Konda  Akira Shibata  Naoto Ebuchi  Kohei Arai 《Journal of Oceanography》2006,62(3):395-404

The sea surface wind speed (SSWS) derived by a microwave radiometer can be contaminated by changes of the brightness temperature owing to the angle between the sensor azimuth and the wind direction (Relative Wind Direction effect: RWD effect). We attempt to apply the method proposed by Konda and Shibata (2004) to the SSWS derived by Advanced Microwave Scanning Radiometer (AMSR) on Advanced Earth Observing Satellite II (ADEOS-II), in order to correct for the RWD effect. The improvement of accuracy of the SSWS estimation amounts to roughly 60% of the error caused by the RWD effect. Comparison with in situ observation at the Tropical Atmosphere Ocean (TAO) array shows that the root mean square error of the corrected SSWS is 1.1 ms⁻¹. It is found that the impact of the RWD effect on the estimation of the latent heat flux can amount to about 30 Wm⁻² on average. We applied the method to the SSWS derived by AMSR for Earth Observing System (AMSR-E) and obtained a similar result.  相似文献   

Effect of air-sea temperature difference on ocean microwave brightness temperature estimated from AMSR,SeaWinds, and buoys     

Akira Shibata 《Journal of Oceanography》2007,63(5):863-872

The effect of air-sea temperature differences on the ocean microwave brightness temperature (Tb) was investigated using the Advanced Microwave Scanning Radiometer (AMSR) aboard the Advanced Earth Observing Satellite-II (ADEOS-II) during a period of seven months. AMSR Tb in the global ocean was combined with wind data supplied by the scatterometer SeaWinds aboard ADEOS-II and air temperature given by a weather forecast model. Tb was negatively correlated with air-sea temperature difference, its ratio lying around −0.4K/°C at the SeaWinds wind speed of 14 m/s for the 6 GHz vertical polarization. Tb of AMSR-E aboard AQUA during 3.5 years was combined with ocean buoy data, and similar results were obtained.  相似文献   

岩溶作用对任丘古潜山碳酸盐岩油藏赋存的控制作用   总被引：7，自引：0，他引：7  

韩宝平  刘仁达  罗承建  于俊吉  于礼山 《中国岩溶》1998,17(1):75-80

根据大量钻井及开发动态资料,研究了任丘古潜山雾迷山组白云岩岩溶发育牲特征对油藏赋存的控制作用。溶蚀孔洞是最重要的储集空间,岩溶不发育的泥质白云岩段的分隔作用,导致在全油田统一油水界面以下有残余油区赋存,古潜山面上的溶蚀残丘等局部高点是残余油赋存的有利地段。  相似文献