Study of the air-earth electrical current density in Athens

In the present study, we examine the daily and annual variation of the air-earth current density in Athens for all weather as well as for fair weather for a 16-year period 1965–1980.The daily variation of the air-earth current density has a definite bimodal form while the annual variation has no definitive form but simply reaches its larger values during the summer months. There has also been a Fourier analysis of the daily variation.Furthermore, and for a 3-year period 1968–70, we present the mean daily and annual variation of the electric field, air-earth current density and total conductivity of the air. Based on these parameters we have estimated the conduction and the convection current and we have correlated them to the total (measured) current. In addition, we have estimated the values of the parameter, in order to test the fulfillment of Ohm's law in atmosphere.     

A comparison of EISCAT and Dynasonde measurements of the auroral ionosphere

Incoherent-scatter radar and ionospheric sounding are powerful and complementary techniques in the study of the Earths ionosphere. The work presented here involves the use of the Tromsø Dynasonde as a correlative diagnostic with the EISCAT incoherent-scatter radar. A comparison of electron-density profiles shows how a Dynasonde can be used to calibrate an incoherent-scatter radar and to monitor changes in the system. Sky-maps of the direction of Dynasonde echoes are compared with EISCAT-derived density profiles to illustrate how a Dynasonde can be used to measure the drift velocity of auroral features. Vector velocities fitted to Dynasonde echoes are compared with EISCAT-derived plasma velocities. The results show good agreement when the data are taken during quiet to moderately active conditions and averaged over time scales of 30 min or more.     

Solar flares and their impact on potential gradient and air-earth current characteristics at high mountain stations

Summary Recordings of potential gradient and air-earth current in fair-weather conditions were made at high-elevation mountain stations; the latter were generally above the vertical-mixing layer and not disturbed by local sources. Both electrical quantities increased significantly from the day of appearance of a solar flare (or a maximum incidence of flares) till the fourth day after the event. Peak potential gradient and air-earth current exceed the normal levels measured during quiet-sun conditions by 50–60% in terms of averages. This result was compared with sferics incidence data and daily geomagnetic coefficients grouped around the selected (flare) dates. Both of the latter quantities show time histories (for the days preceding and following the selected dates) closely correlated with the atmospheric-electrical histories of the same intervals. We may conclude from these results that the total potential between the ground and the upper atmosphere increases for several days after solar flares. The results obtained by previous studies on Mauna Loa confirm this inference. The cause of the phenomenon is presumed to be enhanced thunderstorm activity attendant on solar disturbances.We wish to thank the Deutsche Forschungsgemeinschaft for a grant taht enabled us to carry out the studies described in this paper     

Further evidence for impact of solar flares on potential gradient and air-earth current characteristics at high mountain stations

Summary For the period February 1967–May 1969, a period of increasing solar activity, unrestricted substantiation was obtained of earlier results which had indicated that subsequent to H-flares potential gradient and air-earth current will increase significantly. A presupposition of this result is that the atmospheric electrical elements are recorded at stations with only minimal local climatic and aerosol physical disturbance factors, and that only meteorologically undisturbed days are used. It was ascertained that the exclusive use of fine weather days is of no influence on the results. The confirmed solar-terrestrial relation is even more pronounced when measurements are based on flares in the vicinity of the central meridian of the sun. It was further substantiated that the frequency of sferics pulses is significantly increased from the flare day on. As the cause for this a solar-triggered increase in thunderstorm frequency is suggested which, in turn, leads to an increase of the potential gradient and earth current. Proton flares have an effect analogous to that of H-flares. If H-flare key days are used on which significant changes were observed in the distribution of pressure over the northern hemisphere, a significant increase of potential gradient and air-earth current is found even with these flare key days. Thus for the first time a connection is made between solar-caused atmospheric electrical effects and synchronous global meteorological changes.     

Comparison of satellite measurements of the low-latitude nighttime upper ionosphere with IRI

In this paper, we report the results of our comparison study between satellite measurements and the International Reference Ionosphere (IRI) model on the seasonal and longitudinal changes of the low-latitude nighttime topside ionosphere during the period of solar maximum from June 2000 to July 2001. Satellite measurements were made by KOMPSAT-1 and DMSP F15 at 685 km altitude and 840 km altitude, respectively. The results show that the IRI2001 model gives reasonable density estimations for the summer hemisphere and the March equinox at both altitudes. However, the observed wintertime densities are smaller than the predictions of the IRI2001 model, especially at a higher (840 km) altitude, manifesting strong hemispheric asymmetries. The observed electron temperatures generally reside between the two estimations of IRI2001, one based on the Aeros–ISIS data and the other based on Intercosmos, and the latter estimation better represents the observations. With more or less monotonic increase with latitude, the temperature profiles of the IRI2001 model do not predict the enhancement seen around 15° magnetic latitude of the winter hemisphere. Longitudinal variation, probably caused by the zonal winds, is seen in all seasons at both altitudes, while the IRI2001 model does not show a large variation. The observed density and temperature show significant changes according to the F10.7 values in the whole low-latitude region from 40°S to 40°N geomagnetic latitude. The effect is manifested as increases in the density and temperature, but not in the hemispheric asymmetry or in the longitudinal variation.     

Response of the topside ionosphere over Arecibo to a moderate geomagnetic storm

We analyze the data obtained using the Arecibo incoherent scatter radar to examine the response of the topside ionosphere to a moderate geomagnetic storm that occurred during the period March 7–11, 2008. During this time period a magnetic storm with a non-monotonic main phase decrease in the Dst index occurred. The recovery phase also exhibited a secondary Dst decrease. During the initial phase of the storm, Te and Ti increased coincident with the arrival of the solar wind. The main phase registered an increase in proton concentration proportional to Ne while temperatures reached the lowest values. Variations in O⁺ concentration were not significant but a reduction in helium fraction was observed. Soon after the peak of the storm, the transition height between the topside ionosphere and the protonosphere, where H⁺ ions dominate composition, was lower than would be expected during quiet conditions and this behavior lasted for approximately 12 h.     

Approximation of the electron concentration measurements in the middle ionosphere at low solar activity

Geomagnetism and Aeronomy - The set of the electron concentration (N) measurements at heights of 120–200 km have been generalized using the regression equation from the semi-empirical model...     

关于暴时电离层电流分布的南北半球不对称性

采用国际上广泛认可的高层大气和电离层经验模式提供的各种参数, 通过电离层电流连续方程, 计算出强磁暴条件下6月至日和12月至日内, 磁纬±72°和磁地方时00:00～24:00之间电离层电场、电流等的分布. 计算中考虑了地磁和地理坐标间的偏离; 除中性风场感生的发电机效应外, 还包含了磁层耦合(极盖区边界的晨昏电场和二区场向电流)的驱动外源. 结果表明, 6月至日时, 磁层扰动自极光区向中低纬的穿透情况在南、北半球内基本接近, 北半球内略强; 但12月至日时, 呈现明显的不对称性, 南半球的电流穿透远强于北半球, 而电场的穿透则是在北半球更强. 无论南北半球, 在中高纬地区, 午夜至黎明时段出现较强的东向电场分量, 其[WTHX]E×B[WTBZ]的向上漂移效应, 正是解释我们以往不少研究现象中所期盼的物理机制.     

Response of equatorial ionosphere to episodes of asymmetric ring current activity

We present the characteristics of the response of equatorial ionospheric zonal electric field and F-region plasma density to the asymmetric ring current intensifications that occurred in succession on 16 December 1991, corresponding to the STEP/EITS-2 campaign period. The study is based on high-time-resolution (1-min) data of asymmetic ring current indices, ASY(H/D) and F-region vertical plasma drift, Vz measurements at Kodaikanal (10.25°N; 77.5°E; dip 4°), India and quarter-hourly ionosonde data of For-taleza (4°S; 322°E; dip -9°), Brazil. It is shown that short-lived disturbances in F-layer vertical plasma drift, Vz and height (hF/hpF2) indicative of westward and eastward electric fields prevail simultaneously in the dusk (18–21 LT) and predawn (02–05 LT) sectors, respectively, in association with the decay phase of asymmetic ring current events. Electric fields of opposite polarity do also seem to manifest at these local times, particularly in the early-morning sector in conjunction with the intensification of the asymmetric ring current. At a given location, electric field disturbances associated with individual asymmetric ring current events are thus bipolar in nature, with fields of opposite polarity during the growth and decay phases. The nature and polarity structure of the observed electric field disturbances are in agreement with the theoretical/model predictions of prompt penetration of high-latitude electric fields to the equatorial region.On sabbatical leave from Indian Institute of Astrophysics, Bangalore, India     

Spatial distribution of the field-aligned current density in the polar ionosphere and the contribution of magnetosound waves

The regular appearance of the chain of oppositely directed field-aligned current (FAC) pairs near the noon-midnight meridian during three considered substorms has been described. The FAC pairs (FACs flowing into the ionosphere in the morning and flowing out of this region in the evening and vice versa) are observed in each of three Iijima and Potemra zones. The FAC direction in the fixed LT sector periodically varies along the chain. The scenario, according to which each FAC pair (seven pairs) is identified with a hump or trough of one of the waves propagating from the Earth and toward the Earth in different magnetospheric domains, has been described. The estimated wave velocities differ from ∼100 to >1000 km/s depending on the propagation region but everywhere agree with the corresponding velocities of magnetosound waves (MSWs). The hypothesis is proposed, according to which these MSWs are excited by plasma ejection during current disruption and reconnection near the dayside magnetopause and in the near/middle regions of the nightside tail.     

Short-period fluctuations in the atmospheric electric field over the ocean

Fluctuations of short period in the atmospheric electric field were studied through the measurements of electric field and space charge density on the Mid-Pacific Ocean. The amplitude of fluctuation is about one third of the mean electric field, and the period mainly ranges from 2 to 5 min. The fluctuations are considered to be under the influence of spatial and temporal variation of space charge layer that possibly originates from the electrode effect above the sea surface. The unit of electrical irregularities in the atmosphere above the ocean has horizontal scale of the order of 1.5 km and indicates a tendency to become large as the wind speed increases. The vertical scale of space charge layer is estimated at several tens meters.     

The ionosphere over Genova during the solar eclipse of February 15, 1961

Summary The behaviour of the ionosphere over Genova during the solar eclipse of February 15, 1961 is investigated. For theE-layer the effect was very marked, but the value obtained for the recombination coefficient is above normal. The effect of the eclipse was also observed on theF2 layer; however, the behaviour here appears affected by the simultaneous occurrence of an ionospheric perturbation. Finally, the maximum reduction of the ionospheric absorption on 2 and 3 Mc/s during the eclipse was found to be of the order of about 12 db.This report belongs to a set of investigations on geophysical effects of the solar eclipse of February 15th, 1961 carried out by the «Istituto Geofisico, Università di Genova», and made possible through a financial support of the «Consiglio Nazionale delle Ricerche».     

Climatic characteristics of the ionosphere over Irkutsk. Observations and comparison with the IRI-2001 model

The morphological peculiarities of the behavior of the electron density over Irkutsk (52.3° N, 104.3° E) have been investigated by the current-median method. The observations are compared with the IRI model data at the decay phase of solar activity (2003–2006). Systematic discrepancies between the prediction and observations are discussed.     

未知OBS水平方位的SKS分裂参数测量

宽频带海底地震仪（OBS）探测是研究海底深部结构最有效的地球物理方法,其中SKS分裂参数测量已被广泛应用于上地幔各向异性的研究.传统的SKS分裂参数测量需要知道确切的OBS水平分量方位,然而OBS的投放过程是自由式的,其两个水平分量在海底的方位是不确定的.本文通过SKS快慢波的运动学特性,发展了一种在未知OBS水平分量方位的情况下直接求取SKS分裂参数的方法,分别用合成地震图和实际观测到的远震资料对该方法进行了数值检验,表明其是一种有效的获得SKS分裂参数的方法,而且相比于传统的先确定OBS水平分量方位,再进行SKS分裂的方法,此方法能够同时获得SKS分裂参数和OBS水平分量方位,应用简便,且减少了累积误差,获得的SKS分裂参数可靠性更高.

     

Field-aligned plasma diffusive fluxes in the topside ionosphere from radio occultation measurements by CHAMP

O⁺ field-aligned diffusive velocities and fluxes in the topside ionosphere have been calculated from electron density profiles retrieved from CHAMP radio occultation (RO) measurements. The velocities and fluxes from January 2002 to December 2003 at low- and mid-latitudes have been statistically analyzed. The results show that daytime diffusive fluxes changed gradually from downward to upward as altitude increases. The largest values of the upward diffusive fluxes and velocities occurred at around ±25° geomagnetic latitude. During solstices the plasma fluxes in the winter hemisphere were larger than those in the summer hemisphere.     

Atmospheric electricity measurements over the Indian Ocean

Summary Results of measurements of the atmospheric electrical conductivity and potential gradient made during the sixth Scientific Cruise of the Indian Oceanographic Ship INS Kistna in the Bay of Bengal during February–March 1963 are presented. Observations were made when the skies were generally clear and the sea calm, in the geographical area 8°N to 17°N and 80°E to 95°E, on the outward journey of INS Kistna from Madras (80°E, 13°N) to Port Blair (93°E, 12°N) and on the return journey to Madras.Over the ocean where there are no local sources of pollution, the measured values of conductivity and potential gradient are in agreement with theoretical values, assuming that an ion equilibrium exists, that ions are destroyed primarily by collision with small ions of opposite sign and that small ions are produced only by cosmic radiation. The values of electrical conductivity obtained are generally of the same order as those to be expected from theoretical considerations and in general agreement with those obtained during the Carnegie cruises in the Indian Ocean in 1920. There are, however, significant variations near the coast where the electric structure above the ocean is affected by continental sources of pollution. Conductivity values near the land are about half that in the unpolluted air over the ocean but prevailing winds prevent the extension of pollution beyond 100–200 km from the coast in this season.

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Zusammenfassung Es wird über Messungen der luftelektrischen Leitfähigkeit und des Potentialgefälles berichtet, welche während der Sechsten Wissenschaftlichen Kreuzfahrt des indischen Ozeanographischen Forschungsschiffes Ins Kistna in der Bengalischen Bucht im Februar und März 1963 ausgeführt wurden. Die Beobachtungen sind im allgemeinen bei klarem Himmel und ruhiger See gemacht worden, und zwar in dem geographischen Bereich zwischen 8 und 17°N und 80 und 95°E während der Ausfahrt der INS Kistna von Madras (80°E, 13°N) nach Port Blair (93°E, 12°N) und auf der Rückreise nach Madras. In den Bereichen des Ozeans, in denen keine örtlichen Pollutionsquellen bestehen, stimmen die gemessenen Werte der Leitfähigkeit und des Potentialgefälles mit den theoretischen Werten überein, die man erhält, wenn man annimmt, dass ein Ionengleichgewicht besteht, dass die schnellen Ionen vorwiegend durch Zusammenstoss mit schnellen Ionen des entgegengesetzten Vorzeichens vernichtet werden, und dass die schnellen Ionen nur durch die kosmische Höhenstrahlung erzeugt werden. Die Werte der Leitfähigkeit stimmen mit denen überein, die man aus theoretischen Überlegungen gewinnt, und auch mit denen, die während der Kreuzfahrten des Forschungsschiffes Carnegie im Indischen Ozean im Jahre 1920 gemessen Küste sind jedoch bedeutsame Abweichungen festzustellen, wo die elektrischen Verhältenisse über dem Ozean durch Pollutionsquellen auf dem Lande beeinflusst werden. Die Leitfähigkeitswerte nahe dem Land sind nur ungefähr halb so gross wie die in der pollutionsfreien Luft des offenen Ozeans-jedoch haben die während der Mess-Jahreszeit vorherrschenden Winde eine Ausbreitung der Pollutionszone auf einen Bereich von 100 bis 200 km von der Küste beschränkt.

     

Geoelectromagnetic variations over a sloping ocean floor up to and including the coastline

Summary The electric and magnetic field variations over an arbitrarily sloping ocean floor are represented in series of Bessel functions forH-polarized uniform plane wave excitation. Calculation of the spatial variations of electric eurrents and apparent resistivity near a coastline will determine the usefulness of the magnetotelluric method in this application.The work presented herein was conducted at the Institute for Applied Mathematics of the University of Oslo, Oslo, Norway.     

Fluctuations of total electron content in the ionosphere as deduced from measurements by single-frequency GPS receivers

Using an ionospheric diagnostic technique developed by the authors and single-frequency GPS receivers, we obtained the first results of these diagnostics. In particular, we show that the ionosphere is characterized by large-scale periodic processes with frequencies of 3–5 mHz.