IMF Bx and By dependencies of the polar cap auroral distribution for northward IMF orientation inferred from observations at Vostok station

The effects of the IMF radial (B_x) and azimuthal (B_y) components on the distribution of polar cap arcs are examined using all-sky camera data from Vostok station for the winter months of 1977–1985. We conclude that three factors control the character of the aurora distribution: the type of the sector structure, the IMF radial component, and the IMF azimuthal component. Based on the experimental results, the following scheme for the auroral distribution in the northern and southern polar caps for different signs of B_x and B_y is put forward. The ‘garden hose’ structure (B_x > 0, B_y < 0 or B_x < 0, B_y > 0) produces symmetric auroral distributions in the morning and evening sectors of both the northern and southern polar caps; the ‘orthogonal garden hose’ structure (B_x > 0, B_y > 0 or B_x < 0, B_y < 0) is evidently inefficient in the production of aurorae. The B_x component determines the intensity of aurorae in that polar cap where geomagnetic field lines are in the opposite direction to the IMF (B_x < 0 in the case of the northern cap, and B_x > 0 for the southern cap) and produces the daytime auroral belt poleward of the auroral oval and parallel to it. The B_y component affects the auroral appearance in the morning or evening sectors of the polar cap, depending on its sign, and acts asymmetrically in the opposite polar cap. The appropriate patterns of plasma filament distributions in the high-latitude tail lobes are proposed. The characteristics of auroral movements affected by the B_y component (such as the direction and speed of the arc motion and the magnitude of displacements) are examined.     

Observations of neutral winds in the polar cap during northward IMF

Long term remote observations of neutral winds at F-region altitudes have been performed at Thule Air Base (lat. 76.5°N, long. 69.0°W), Greenland, and Søndre Strømfjord (lat. 67.0°N, long. 50.9°W), Greenland. The former site is very close to the geomagnetic pole, while the latter site is within the polar cap for several hours each night on either side of geomagnetic midnight. Wind data corresponding to clear sky conditions and Kp ⩽ 4 were sorted according to the sign of the IMF B_z component. The averaged maximum poleward flow near midnight LST was reduced by approximately one third during B_z northward conditions. If the magnitude of B_y was less than the magnitude of the northward B_z component, then the averaged poleward flow was further reduced by one half. In addition, if B_z > 5 nT, then sunward directed horizontal neutral winds were observed at the very highest latitudes near noon LST.     

Recipe for predicting the IMF Bz polarity's change of direction following solar disturbances and at the onset of geomagnetic storms

A three-dimensional, time-dependent, MHD model of solar-disturbance-caused storms (Wu, 1993; Wu et al., 1996a) is used to predict the turning direction of the interplanetary magnetic field (IMF) at Earth. More explicitly, we examine the polarity of B_z caused by solar disturbances on the Sun. Three manifestations of solar disturbances, as studied by previous workers, are examined. Firstly, twenty-nine kilometric Type II events, associated (Cane, 1985) with geomagnetic storms, are studied within the context of our three-dimensional model. Then, an additional eleven long-duration X-ray events (LDEs) with radio fluxes greater than 100 solar flux units were examined; these events were not associated with interplanetary Type II events but were also associated (Cane, 1985) with geomagnetic storms. Finally, in situ interplanetary phenomena that caused ten large (Dst < −100 nT, the intensification of the storm) geomagnetic storm episodes (Tsurutani et al., 1988) near solar maximum are also studied via the B_z predictions of our 3D MHD model. The accuracy of these B_z turning-direction-predictions is found to be as follows: (1) for the kilometric Type II events, the model's prediction was successful for 26 of the 29 events studied; (2) 10/11 for the LDE events; and (3) 7/9 for the major geomagnetic storm events. The overall prediction accuracy of these three independent data sets is 43/49. Thus, consideration of these three independent data sets strongly suggests that the recipe proposed by the basic 3D MHD model may be valid for a zero-th order prediction scheme.     

Ionospheric conductivity dependence of the cross-polar cap potential difference and global Joule heating rate

We examine the extent to which the cross-polar cap potential difference ϕ and the global Joule heating rate, U, both determined by the magnetogram-inversion method (Kamideet al., 1981, J. geophys. Res. 86, 801), depend upon the assumed conductance models. For this purpose two statistically-determined conductance models developed by Siroet al. (1982, J. geophys. Res. 87, 8215) and ahn et al. (1983b, Planet. Space Sci. 31, 641), and a realistic conductance distribution estimated from bremsstrahlung X-ray image data (Ahnet al., 1989, J. geophys. Res. 94, 2565) have been used. As expected from earlier studies, U is less affected by the choice of conductance models than is ϕ. This is because U is a globally integrated quantity, and thus the local structures of the electric potential pattern do not affect it appreciably, whereas they are crucial in determining ϕ, which is defined as the difference between the maximum and minimum potential values usually found in the dawn and dusk sectors, respectively. A comparison between Uand ϕ based on the statistical conductance models and U and ϕ based on a realistic conductance distribution shows that there are considerable similarities, thus enabling us to use statistical conductance models as a first approximation in deriving such global quantities as the cross-polar cap potential difference and the global Joule heating rate in the study of solar wind-magnetosphere coupling. Several suggestions are made for improving the present available conductance models and some limitations (possibly intrinsic ones) are also discussed.     

Field-perpendicular and field-aligned plasma flows observed by EISCAT during a prolonged period of northward IMF

The effect of a prolonged period of strongly northward Interplanetary Magnetic Field (IMF) on the high-latitude F-region is studied using data from the EISCAT Common Programme Zero mode of operation on 11–12 August 1982. The analysis of the raw autocorrelation functions is kept to the directly derived parameters N_e, T_e, T_i and velocity, and limits are defined for the errors introduced by assumptions about ion composition and by changes in the transmitted power and system constant. Simple data-cleaning criteria are employed to eliminate problems due to coherent signals and large background noise levels. The observed variations in plasma densities, temperatures and velocities are interpreted in terms of supporting data from ISEE-3 and local riometers and magnetometers. Both field-aligned and field-perpendicular plasma flows at Tromsø showed effects of the northward IMF: convection was slow and irregular and field-aligned flow profiles were characteristic of steady-state polar wind outflow with flux of order 10¹² m⁻² s⁻¹. This period followed a strongly southward IMF which had triggered a substorm. The substorm gave enhanced convection, with a swing to equatorward flow and large (5 × 10¹² m⁻² s⁻¹), steady-state field-aligned fluxes, leading to the possibility of O⁺ escape into the magnetosphere. The apparent influence of the IMF over both field-perpendicular and field-aligned flows is explained in terms of the cross-cap potential difference and the location of the auroral oval.     

试论先秦秦汉时期的射箭理论

中国古代射箭文化源远流长,影响深远。射箭技术也是古代军事技术中比较重要的一门技术,是对士兵体能和技能的双重考验。古人在长期使用弓箭的基础上,总结出了一整套射箭经验,并上升为理论,这就是在汉初被整理成文的"射法"。可惜的是,这些有关射箭技术的兵书早已亡佚。但是,在先秦秦汉的典籍中,还保存有射箭技术的只言片语,本文对之进行了较为系统的整理,并对弓箭、弩制造技术与使用技术的辩证关系进行了论述,对秦汉时期弩射技术理论的发展进步进行了总结。     

秦汉时期“赘婿”和“女户”的综合考察

秦汉时期,"赘婿"和"女户"作为独特的社会群体长期存在。学者们关于赘婿方面的研究已较为深入,女户方面的研究著作和论文也是甚多,但都没有把这两个群体结合起来做考察的,笔者认为只有把赘婿和女户做综合考察才能较全面的阐释当时社会形态下的历史内涵。秦汉时期依附于女户的赘婿群体社会地位低下,官府视其等同罪人。女户主的相关权益则受到明确保护。西汉后期随着儒家学说统治地位的确立、三纲五常伦理观念的普及以及女子社会地位的下降,赘婿逐渐从正史的记载中淡出。     

Uganda: Contradictions of the IMF Programme and Perspective

This critique of the Structural Adjustment Programme in Uganda is argued at three levels. A discussion of the immediate consequences of SAP is based on empirical data on economic performance compiled by the Government of Uganda, IMF and World Bank. Second, information for a longer-term historical analysis is culled from the author's own research. Its purpose is to raise more fundamental issues of social transformation. Finally, these perspectives are reinforced through a comparative discussion using South East Asian development experience. The author argues that there are diverse paths to capitalist development, with diverse and contradictory social and political consequences. The real issue in contemporary Uganda is not one of the state or the market, but of the transformation of relations internal to both from the point of view of democratization.     

明清时期太平及池州地区的渔业

本文从明清时期安徽太平及池州地区的渔税征收机构河泊所的设置分布及裁革情况,渔课的数量、比重及变化,渔业从业人口的数量及变化等分析和探讨了该时期这一区域的渔业经济状况及其变迁.由于拥有较为丰富的河湖水域,太平和池州地区的渔业在区域经济结构中占有一定地位.太平地区的渔业主要分布于沿江的当涂、繁昌和芜湖三县,其中又以境内湖泊水域较广的当涂县最为兴盛.池州地区的渔业主要分布在沿江的贵池、东流和铜陵县,其中又以附郭贵池县之渔业最为兴盛.     

National identity during periods of controversy: celebrating Cinco de Mayo in Phoenix,Arizona

Cinco de Mayo, celebrated by Mexican Americans as well as Americans of other ethnicities, provides an opportunity to examine the influence of ethnic festivals on broader US identity. Given the recent controversy over the immigration bill, State Bill 1070, passed in Arizona in 2010, the themes presented in newspaper articles concerning the celebration of the holiday in Phoenix, Arizona (2006–11) and the public response to these articles are examined. This examination reveals the intense contestation associated with the presentation of symbols and themes of national identity during periods of political controversy. It also illustrates that ordinary people have strong, long‐standing opinions about the future of the nation and national identity and will express their opinions when an outlet is provided to them     

Simulations of the behaviour of the polar thermosphere and ionosphere for northward IMF

The dynamics and structure of the polar thermosphere and ionosphere within the polar regions are strongly influenced by the magnetospheric electric field. The convection of ionospheric plasma imposed by this electric field generates a large-scale thermospheric circulation which tends to follow the pattern of the ionospheric circulation itself. The magnetospheric electric field pattern is strongly influenced by the magnitude and direction of the interplanetary magnetic field (IMF), and by the dynamic pressure of the solar wind. Previous numerical simulations of the thermospheric response to magnetospheric activity have used available models of auroral precipitation and magnetospheric electric fields appropriate for a southward-directed IMF. In this study, the UCL/Sheffield coupled thermosphere/ionosphere model has been used, including convection electric field models for a northward IMF configuration. During periods of persistent strong northward IMF B_z, regions of sunward thermospheric winds (up to 200 m s⁻¹) may occur deep within the polar cap, reversing the generally anti-sunward polar cap winds driven by low-latitude solar EUV heating and enhanced by geomagnetic forcing under all conditions of southward IMF B_z. The development of sunward polar cap winds requires persistent northward IMF and enhanced solar wind dynamic pressure for at least 2–4 h, and the magnitude of the northward IMF component should exceed approximately 5 nT. Sunward winds will occur preferentially on the dawn (dusk) side of the polar cap for IMF B_y negative (positive) in the northern hemisphere (reverse in the southern hemisphere). The magnitude of sunward polar cap winds will be significantly modulated by UT and season, reflecting E-and F-region plasma densities. For example, in northern mid-winter, sunward polar cap winds will tend to be a factor of two stronger around 1800 UT, when the geomagnetic polar cusp is sunlit, then at 0600 UT, when the entire polar cap is in darkness.     

陶寺遗址乃尧至禹都论

我国上古史上,在夏朝之前,是《史记·五帝本纪》中的唐尧、虞舜时期,已进入“五帝”时代了。关于“五帝”的历史,过去直至今日,仍有知名学者认为是传说乃至神话,采取了怀疑甚至否定态度。他们只承认商代才是信史。现经考古发现的一批遗址,可以补充古史资料,也在逐步成为信史了。近日,“夏商周断代工程”的专家公布了新的夏、商、周年表,确认二里头文化为夏文化,二里头遗址年代就是夏朝年代。但是,该遗址至今尚未见到文字的直接材料,也未发现城址遗迹以及带有标志性遗物。如果是个学术问题,仍有研究的余地。考古研究的另一个任…     

Architectural space in the Muisca settlement of La Maria (Chia,Colombia) during the Prehispanic and Colonial periods

Archaeological fieldwork conducted on a plot of land near the town of Chia (Colombia, South America) uncovered the remains of a small Muisca settlement occupied from the late Prehispanic period to the colonial period. The excavation program documented particular sets of features including postholes, pits, colored floors, and a burial. These elements provided a baseline for reconstructing the ground plans of perishable structures and architectural spaces. The components of built areas were key cultural referents for the peoples who lived in La Maria during the Prehispanic period. Important changes in the arrangement of the elements that comprise architectural space are observed during the colonial period, arguably as the result of important transformations in native culture.     

Cultural interactions during the Ubaid and Halaf periods: Tell Kurdu (Amuq Valley,Turkey) obsidian sourcing

In order to decipher cultural influences, the inter-regional contacts of the Tell Kurdu settlement have been investigated through obsidian sourcing for the Halaf and Ubaid phases (c. 5700–4300 cal. BC). The chemical composition of nine artifacts from three archaeological levels of the site have been determined and compared to source data obtained in our laboratory or available in the literature. Trace and major element analyses were performed respectively by inductively coupled plasma - mass spectrometry (ICP-MS) and atomic emission spectrometry (ICP-AES). The results assignments point out five distinct sources which highlight northwestward and eastward connections. Besides the “traditional” procurement areas (Göllü Dag and Nemrut Dag massifs; Bingöl region), the development of new exploitation centers (northeast Anatolia and northeast Van lake) is noteworthy. These results of obsidian provenances are compared to those of other raw materials and production originating from distant areas, in order to outline Tell Kurdu trade networks during the Halaf and Ubaid periods.     

Simultaneous ground-based observations of polar cap arcs and spacecraft measurements of particle precipitation

In order to investigate the particles which produce the polar cap aurora at the Vostok station in Antarctica, charged particle data obtained by the DMSP satellites for some days in a period from April to August 1985 were surveyed. Due to the satellite orbit the local time range in which the data were available was the morning sector. For all the events when sun-aligned arcs were observed on the ground the simultaneous DMSP measurements on almost the same field line showed an increased integral number flux J. > 10⁸ (cm⁸/s/sr)⁻¹ of the precipitating electrons with energy E_e > 200 eV. The electron spectra with double peaks are typical of intense electron precipitation in the polar cap arcs. The most noticeable feature of ion spectra in the polar cap arcs is the prominent minimum in ion flux in the energy range 0.1 < E_i < 1 keV in contrast with the oval precipitation ; this feature gives the possibility to separate the polar arcs from the aurora in the oval. In some events the satellite crossed the system of two widely separated arcs ; one of them was a sun-aligned arc whereas the other was circular at constant latitude according to the Vostok data. The analysis of the DMSP electron and ion precipitation data has shown that in these events the latitude-oriented arcs are located in the polar cap and not in the auroral oval.