Some effects of geomagnetic activity on spread-F occurrence and ionospheric height variations in equatorial regions

AE indices have been used to investigate, at times of increased geomagnetic activity, the possibility of significant changes to both spread-F occurerence and h′F values for 3 stations in equatorial latitudes. The investigation covered a sunspot minimum period. Furthermore, data for each of these parameters have been considered for both a pre-midnight period (interval A) and a post-midnight period (interval B). The use of the AE indices at 12 different times at 2 h intervals allows the measurement of the delay times, after increased geomagnetic activity, of any significant changes in the parameters being investigated.The results show that for interval A significant suppressions of spread-F occurrence are recorded at delay times of approximately 3 h and 9 h. These delays correspond to enhanced geomagnetic activity at local times of 1800 and 1200, respectively. Also, for interval A the h′F variations suggest that h′F is suppressed at times of spread-F suppression. For interval B spread-F occurrence seems to be controlled by two opposing effects. For several hours after enhanced geomagnetic activity spread-F occurrence increases significantly, followed by a sharp decline culminating in suppressed occurrence, again related to increased geomagnetic activity at 1800 local time for the maximum effect. Also, for interval B h′F values lift abruptly a few hours after enhanced geomagnetic activity, followed by a gradual decline when delays of up to 20 h are considered. Further work on these delays may allow reliable short-term forecasting of some ionospheric behaviour in equatorial regions.     

Some effects of geomagnetic activity and ionospheric height rises on mid-latitude spread-F occurrence

The analysis investigates the base heights of the ionosphere (h′F) when spread-F is recorded at Brisbane, Australia, for 2 separate periods, namely July and August 1966 when spread-F occurs frequently and September and October 1966 when the activity is much lower. It is found that for July and August there is little tendency for spread-F to occur preferentially when the base height is above the average for the period. However, for the September–October period, spread-F occurs more often (by a factor of 2 or 3 depending on the geomagnetic activity) when the base height is above rather than below the average height. Also, this analysis shows that the overall spread-F occurrence (for both periods investigated) decreased to some extent following increased geomagnetic activity. This suppressed activity in the hours following geomagnetic activity is confirmed by superposed-epoch analyses using K indices (for Macquarie Island) as controls. It is suggested that the results of all the analyses might be explained by invoking a transition height in the ionosphere (controlled by the neutral-particle density of the upper atmosphere). Ionospheric off-vertical reflections from above this height would be recorded as spread-F traces in this model. This transition height would be low in July and August when the neutral-particle density is low and higher in September and October. It is further proposed that changes in the neutral-particle density could also be associated with reduced spread-F activity following increased geomagnetic activity, as well as influencing the diurnal, annual and sunspot-cycle variations of spread-F occurrence in mid-latitudes.     

Post-midnight equatorial scintillation activity in relation to geomagnetic disturbances

VHF amplitude scintillation measurements made during the period April 1978 through December 1982 at Calcutta (23°N, 88.5°E; 32°N dip), situated near the northern crest of the Appleton Anomaly in the Indian sector, have been used to study the association of post-midnight (as well as post-sunrise) scintillations with the occurrences of the maximum negative excursion in the variation of the Earth's horizontal magnetic intensity. The post-midnight scintillation has been found to be related to the maximum negative excursion occurring in the 0000–0600 LT interval. No such relation is observed with the pre-midnight excursions. Scintillation with onset between 0000 and 0300 LT shows remarkable correspondence with the occurrence of negative excursion (18 out of 20 available cases). Magnetic conditions with Dst < −150 nT have been found to be most effective in producing the above scintillation activity. From the present observations, a threshold value of the maximum negative excursion of Dst for producing scintillation may be obtained, Dst < −75 nT being significantly associated with the post-midnight scintillation occurrences. The results are interpreted in terms of the reversal of the equatorial horizontal electric field, under magnetically disturbed conditions, due to a coupling of the high latitude and magnetospheric current systems with the equatorial electric field.     

The vernal-autumnal asymmetry in the seasonal variation of geomagnetic activity

In intervals in which the polarity of the main solar dipole field is stabilized, a 12 month wave occurs in geomagnetic activity (indices aa, Ap, Dst) with its maximum in one of the equinoctial periods. Whether the vernal or the autumnal maximum is greater depends on the polarity of the main solar dipole; the existence of the wave may be explained by the north-south asymmetry in the main solar dipole field. The results favour the southward component of the interplanetary magnetic field as the decisive factor for geomagnetic activity.     

The effect of geomagnetic activity on north polar currents in winter

Average north polar currents for the winter season have been derived from geomagnetic hourly means at six levels of geomagnetic activity. The twin-vortex pattern, normally associated with more disturbed conditions, persisted even on the quietest (mean Ap ≈ 1) days. When Ap increased to 24, the Harang discontinuity appeared earlier by about 3.5 h, though the current system as a whole remained unchanged in orientation. The average quiet day seems to be associated with a weak IMF oriented northwards and towards the Sun, with a low solar wind velocity and low proton temperature.     

Simulation of ionospheric currents and geomagnetic field variations of Sq for different solar activity

Variations of ionospheric Sq electric currents and fields caused by changes in electric conductivity due to changes in solar activity are studied using the International Reference Ionosphere (IRI) model. Calculations are made for R (sunspot number) = 35 and 200 on the assumption of constant (1, −2)mode tidal winds. It is shown that electric fields grow when solar activity is high, because the ratio of the conductivity in the F-region to that in the E-region increases. Currents in the F-region become stronger than those in the E-region, and nocturnal currents are not negligible when solar activity becomes high. F-region currents also play an important role in the westward currents on the high latitude side of the current vortex. The calculated geomagneticH component at the equator has a depression around 1600 LT for R = 35, while it decreases smoothly from 1100 LT to 1900 LT for R = 200. This difference is consistent with the observed geomagnetic field variation. The ratio of total Sq currents obtained by our simulation is about 3.5, which is a little larger than is found in the observed results.     

The influence of sunspot number and magnetic activity on the diurnal variation of the geomagnetic field at mid to high latitudes

The variations of the diurnal range of the geomagnetic field with sunspot number and with magnetic activity was studied at mid and high latitude stations in the northern hemisphere at different seasons. The effect of increasing sunspot number is small at lower latitudes and increases with geomagnetic latitude, while the effect of increasing magnetic activity is to increase the range at all latitudes, very greatly at the higher geomagnetic latitudes.     

Seasonal trend of geomagnetic activity derived from solar-terrestrial geometry confirms an axial-equinoctial theory and reveals deficiency in planetary indices

At the magnetopause, solar wind plasma interacts with the terrestrial magnetic field, with the consequent entry of solar wind energy into the magnetosphere and the ionosphere. Geomagnetic activity is one of the results. Planetary geomagnetic indices, e.g. Kp, Ap, Am, etc, have been designed to measure solar particle radiation by its magnetic effects. Long-term averages of these indices have established that solar wind energy input into the ionosphere maximizes around equinoctial months with minima around the solstices. Although considerable progress has been made to explain qualitatively the semiannual variation o1' geomagnetic activity, its component parts, representing the axial and equinoctial hypotheses, have not so far been put together with a high degree of quantitative precision. This paper demonstrates that the semiannual trend of geomagnetic activity can be reproduced quantitatively with good precision by using accurate astronomical data relating to the Sun-Earth geometry. The key factor is the combination of the varying solar declination and the heliographic latitude of the Earth during different months. Analysis shows that the seasonal trend of solar wind-magnetopause coupling is, in fact, controlled by a combination of the two competing theories, the axial and equinoctial, which have been advanced over the years to explain the semiannual variation in geomagnetic activity. Planetary ion density of the F2 layer of the ionosphere (F2pd) is another index of relatively higher accuracy which also shows marked maxima around the equinoxes. The observed seasonal trend of F2pd can be reproduced by using the semiannual trend of geomagnetic activity as derived from astronomical data with a correlation coefficient of 0.98. This analysis also brings out another important fact that the planetary indices, Kp, Ap, Am and AA, are somewhat deficient as they respond to solar declination only and do not bring out the contribution of the heliographic latitude of the Earth.     

试论明至清前期黔中城镇的发展与特点

中国经济史的研究领域重点,多集中在中原、江南、口岸等城市,不关注西部民族地区城镇的历史状况,因此很难形成对中国城市发展起源、类型、特征总体的科学总结。笔者在日常文化遗产调研的业务工作中,发现贵州城镇中保留下来可供我们作为文化遗产观察、分析和研究的古代城市建筑物、街区、城垣等遗产已所剩不多,而究其原因是因为人们对城市发展的历史,对城镇历史遗物的文化价值、社会意义所知甚少。本文拟就明至清前期黔中地区的城镇发展史做一点粗浅论述,以引起专家学者对这一问题的关注。     

Agglomeration,foreign firms and firm exit in regions under transition: the increasing importance of related variety in Hungary

ABSTRACT

Related variety of economic activities is widely recognized to induce regional development; however, it is not clear how this mechanism takes place in regions that go through major structural and institutional transformation. Furthermore, foreign direct investment (FDI) is typically a major source of structural change in these areas; and we still need a better understanding on how foreign-owned (foreign) firms affect the dynamics of domestic-owned (domestic) companies. For these reasons we analyse firm-level exit in Hungarian city regions between 1996 and 2011, over the late post-socialist transition in manufacturing industries, focusing on the difference between foreign and domestic firms. Introducing ownership into the related variety calculation, we estimate the probability of firm exit with the region-level related variety calculated separately for foreign and domestic firms. Our results suggest that related variety of foreign firms decreases the probability of domestic firm exit earlier during the economic transition compared to the related variety of domestic firms. This finding supports the idea that FDI plays a formative role in regions under transition, and shows that domestic firms benefit from being in agglomerations where foreign firms are technologically related to each other.     

The influence of geomagnetic activity on the upper mesosphere lower thermosphere in the auroral zone. II. Horizontal winds

A spaced antenna partial reflection radar located at Mawson, Antarctica (67°S, 63°E, invariant latitude 70°S), has been used to measure the horizontal wind field in the height range 70–110 km. Three years of data (1985–1987) from the radar have been analysed in order to investigate correlations between geomagnetic activity (determined from the local K-index) and the horizontal wind. Results are analysed using a randomization technique and show that larger winds are measured during geomagnetically active periods in both the raw (or unfiltered) wind values and in the medium-frequency (2–6 h period) and high-frequency (1–3 h period) components. The raw winds tend to be shifted towards the geographic NW to NE quadrant in the early morning hours during high K-times. The observed correlation is seen down to 86 km and shows a seasonal dependence. The mean r.m.s. velocity of the radar scatterers and the angular spread of the return echoes are also found to be correlated with geomagnetic activity. The medium- and high-frequency components of the wind are polarized in the magnetic zonal direction during all seasons of the year.     

An American controversy about the localization of cutaneous sensory regions and their relation to motor regions

Three American neurologists (C. K. Mills, C. L. Dana, and M. A. Starr) explored the anatomical limits of the motor and tactile systems in the brain from 1884 to 1895. Their papers and critiques of one another show contemporary knowledge, limits of their thinking, and difficulties deciding between alternatives. The issue for them was whether there were separate sensory and motor regions or whether there was a combined sensory-motor region. They based their localization arguments on clinical and laboratory findings and on the conclusions of H. Munk and D. Ferrier. There is a discussion about why differences were unresolved.     

The influence of geomagnetic activity on the upper mesosphere/ lower thermosphere in the auroral zone. I. Vertical winds

A scanning Fabry-Perot spectrometer (FPS), located at Mawson station, Antarctica (672S, 63°E, invariant latitude 70°S) was used to obtain vertical wind, temperature, and emission intensity measurements from the λ558 nm emission of atomic oxygen. The measured temperature is used to assign an approximate emission height to the observations. A spaced-antenna partial-reflection radar was run concurrently with the FPS from which the presence of enhanced ionization in the D-region could be inferred from the return heights and strengths of the echoes. Large upwards winds of approximately 30 m s⁻¹, at altitudes less than 110 km, appear to be a direct response of the neutral atmosphere to intense auroral events. It is suggested that the observed upwelling is a result of particle heating at heights below the principal emission height. At higher altitudes, vertical winds of a similar magnitude are also measured during geomagnetically disturbed conditions, although here they do not appear to be associated with particular auroral events. In this case it is suggested that upwelling is produced by a combination of Joule and particle heating.     

Effects of geomagnetic storms in the lower ionosphere,middle atmosphere and troposphere

Geomagnetic storm effects at heights of about 0–100 km are briefly (not comprehensively) reviewed, with emphasis being paid to middle latitudes, particularly to Europe. Effects of galactic cosmic rays, solar particle events, relativistic and highly relativistic electrons, and IMF sector boundary crossings are briefly mentioned as well. Geomagnetic storms disturb the lower ionosphere heavily at high latitudes and very significantly also at middle latitudes. The effect is almost simultaneous at high latitudes, while an after-effect dominates at middle latitudes. The lower thermosphere is disturbed significantly. In the mesosphere and stratosphere, the effects become weaker and eventually non-detectable. There is an effect in total ozone but only under special conditions. Surprisingly enough, correlations with geomagnetic storms seem to reappear in the troposphere, particularly in the Northern Hemisphere. Atmospheric electricity is affected by geomagnetic storms, as well. We essentially understand the effects of geomagnetic storms in the lower ionosphere, but there is a lack of mechanisms to explain correlations found deeper in the atmosphere, particularly in the troposphere. There seem to be two different groups of effects with possibly different mechanisms—those observed in the lower ionosphere, lower thermosphere and mesosphere, and those observed in the troposphere.     

发达地区与欠发达地区贯彻落实科学发展观的路径选择

发达地区与欠发达地区所处的发展阶段不同,科学发展的条件、要求以及所要解决的难点也就不同。同时,发达地区、欠发达地区均存在着影响贯彻落实科学发展观的二重性因素,只有正视这些因素,才能趋利避害,扬长避短,寻求适当路径,使科学发展观在各地区都能得到有效的贯彻落实。发达地区与欠发达地区贯彻落实科学发展观的不同路径既有相对独立性,又需要在宏观上相互衔接和协调。     

The theory of polynuclear urban regions and its application to central Scotland

The idea of strategic planning for networks of cities and towns, encapsulated in the polynuclear urban region concept, has attracted growing interest in many European regions. Key themes include cooperation between neighbouring cities and coordination between functional policies. This article explores the theoretical benefits, including increased economies of scale and improvements in the strength and quality of internal interactions. It also applies these arguments to Central Scotland. As the largest concentration of economic activity in Scotland, with a high level of organizational fragmentation but growing cross boundary issues and coincident growth pressures and deficiencies, there are potential gains from a common strategic perspective. These include improved communications for inter‐firm collaboration and trade, more efficient labour and housing market interactions, and an institutional framework for planning and marketing important regional assets. Closer cooperation within a regional perspective could help the Central Belt to function better as an economic unit and facilitate its ongoing development.     

坚持和完善民族区域自治制度构建社会主义和谐社会

中国成功处理民族问题的经验在于实行民族区域自治制度这一马克思主义民族理论中国化的重要成果。当前,坚持和完善民族区域自治制度,对于我国全面建设小康社会以及构建社会主义和谐社会具有重大的意义。     

Behavior of various Nigerian quartz samples to repeated irradiation and heating

In the present work the sensitization of the entire glow-curve is studied in 6 different quartz samples of Nigerian origin. The investigation was applied to the un-fired “as is” samples as well as to samples fired at 900°C for 1 hour following cooling to room temperature. The results showed that in the case of “as is” glow-curve is sensitized as a whole. There is an abrupt transition from the “natural” sensitivity without any previous heating and the artificial sensitivity induced after the first heating. The sensitization is growing up strongly to the 10^th heating but to a lower rate. The sensitization factor of the TL glow-peak at “110°C” was found to be linearly correlated to the higher temperature TL peaks. In the case of annealed samples there is an initial increase between the sensitivity immediately after the end of annealing and after the first heating. As the number of heating is increased up to the 10^th heating the sensitization is stabilized at a constant value. The results are discussed in the frame-work of existing models and implications of the sensitization effect in various applications, while some explanations are attempted.     

A study of wave packets and phase jumps in low latitude Pc3 geomagnetic pulsation

An array of four low latitude induction coil magnetometer stations has been used to study the spatial and temporal characteristics of Pc3 pulsations over a longitudinal range of 17° at L = 1.8 to 2.7 in southeast Australia. A preliminary study of individual Pc3 wave packet structure at the azimuthal stations has established the existence of phase jumps between wave packets at low latitudes, similar to those observed at synchronous orbit and at higher latitude ground stations. However, there did not appear to be any obvious pattern in phase jump occurrences between stations or signal components.     

Canal projects in the isthmus of Panama and adjacent regions

This article examines some of the problems of studying patterns of internal trading and the operation of periodic market centres in the context of seventeenth‐century Scotland. The changing distribution of periodic market centres throughout the century is discussed, and the difficulties of moving from a theoretical framework based on networks of authorised centres, towards the one which existed in practice, is examined by means of a case study from Perthshire.