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1.
Summary The lunar tide in theE-layer of the ionosphere above Istanbul has been determined by the analysis of thefo E parameter from 1964–1967. Semi-diurnal variations were found to be significant. The seasonal and monthly variations of the amplitude and phase of the lunar tide show very little differences.  相似文献   

2.
Some anomalous TV receptions in India on band I have been interpreted as being propagated viaF-layer artificially modified by high power broadcast transmitters. In this paper, the possibility of VHF communication by artificially modifiedE-layer is discussed. The presented theoretical analysis shows that high-power broadcast trasmitters can produce substantial changes in temperature and ionisation in theE-layer. The rate of energy transfer from the wave to the medium particles has also been computed. Model calculations are made for a transmitter located near Calcutta. The possibility of the extra-ionisation producing field-aligned structures to support VHF communication is discussed.  相似文献   

3.
Summary The model originally constructed for theF1-layer is adapted to enable an investigation of both theF-layers. Essential premises are: The ionization of a single constituent of atmosphere by monochromatic radiation. A positive temperature gradient in theFl-region, a temperature—independent from height—in theF2-region and a negative temperature gradient above the height of theF2-electron-peak; furthermore during the daytime strong heating in theF2-region. It is further assumed that the rate of electron loss in theF1-layer is proportional to the square of the density of the electrons, and in theF2-layer is in simple proportion to this density. It is also assumed that this electron loss stands in proportion to the powerk of the pressurep, and to the powern of the absolute temperatureT, as assumed in the originalF1-layer model.The above mentioned assumption as to temperature conditions are essential to an understanding of the transition from static to dynamic conditions observed in theF2-layer. During the night and in the morning theF2-layer can be treated as a static problem, movement of air-masses being of no great importance. Later in the day however an labile stratification of air-masses gives rise to such movement that theF2-layer can only be handled as a dynamic problem, particular attention being paid to the movement of the air.Numerous observational data are referred to in order to prove the practicability of the new model and, with the help of this model, to justify new assertions. It has been possible for example, to calculate the yearly temperature variation at a constant level in theF1-layer.A critical report upon the models published recently by other authors concludes this paper.
Zusammenfassung Das seinerzeit nur für dieF1-Schicht aufgestellte Modell wird so erweitert, daß eine Deutung beiderF-Schichten möglich wird. Wesentliche Voraussetzungen sind: Ionisierung eines einzigen Bestandteiles der Luft durch eine monochromatische Strahlung. Ein positiver Temperaturgradient im Bereich derF1-Schicht, eine höhen-unabhängige Temperatur im Bereich derF2-Schicht und ein negativer Temperaturgradient oberhalb des Ionisationsmaximum, derF2-Schicht. Weiters wird vorausgesetzt, daß der Elektronenvernichtungsprozeß in derF1-Schicht dem Quadrat der Elektronendichte proportional sei, in derF2-Schicht soll er dagegen der Elektronendichte einfach proportional sein. Eine Abhängigkeit dieses Prozesses von derk-ten Potenz des Druckes,p und von dern-ten Potenz der absoluten TemperaturT wird hier vom ursprünglichenF1-Schicht-Modell übernommen.Erst die genannten Annahmen über die Temperaturverhältnisse machen den beobachteten Übergang von statischen zu dynamischen Verhältnissen in derF2-Schicht verständlich. Während der Nacht und am Morgen bis in die ersten Vormittagsstunden kann dieF2-Schicht als statisches Problem behandelt werden, die Bewegungsvorgänge der Luftmassen spielen eine nur untergeordnete Rolle. Darnach aber ruft eine labile Schichtung der Luftmassen kräftige Luftbewegungen hervor, sodaß dieF2-Schicht nur mehr als dynamisches Problem mit besonderer Berücksichtigung von Luftmassenverschiebungen behandelt werden kann.Zahlreiche Beobachtungsdaten werden herangezogen, um die Anwendbarkeit des neuen Modells zu beweisen und um mit Hilfe des Modells zu neuen Aussagen zu gelangen. Es gelingt so z. B., den Jahresgang der Temperatur in einem konstant gehaltenen Druckniveau derF1-Schicht anzugeben.Eine kritische Betrachtung der Modelle, die in letzterer Zeit von anderen Autoren veröffentlicht wurden, beschließt die Arbeit.
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4.
Zusammenfassung Die Theorie der Schichtbildung durch eine monochromatische Strahlung wird für beliebige Temperaturverteilungen in der Atmosphäre erweitert. Unter gewissen Voraussetzungen ergeben sich durch Ionisation einer einzigen Komponente des Luftgemisches bereits zwei Maxima der Ionenbildung. Es wird vermutet, daß dieser Vorgang bei der häufig beobachteten Aufspaltung der F-Schicht in dieF 1- undF 2-Schicht vorliegt; aus der Theorie ergibt sich dann, daß die Temperatur in derF 2-Schicht tiefer sein muß als in derF 1-Schicht, weiters können verschiedene bisher bestandene Schwierigkeiten hinsichtlich derF 2-Schicht behoben werden.
Summary The ion-production of a monochromatic radiation in an atmosphere with variable temperature in various heights is considered. A stratification ofF-layer intoF 1-andF 2-layer appears by a heat zone between these layers. But always the temperature of theF 2-layer is lower as this ofF 1-layer. Thus some difficulties ofF 2-layer can be removed.
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5.
This paper presents results from the TIME-GCM-CCM3 thermosphere–ionosphere–lower atmosphere flux-coupled model, and investigates how well the model simulates known F2-layer day/night and seasonal behaviour and patterns of day-to-day variability at seven ionosonde stations. Of the many possible contributors to F2-layer variability, the present work includes only the influence of ‘meteorological’ disturbances transmitted from lower levels in the atmosphere, solar and geomagnetic conditions being held at constant levels throughout a model year.In comparison to ionosonde data, TIME-GCM-CCM3 models the peak electron density (NmF2) quite well, except for overemphasizing the daytime summer/winter anomaly in both hemispheres and seriously underestimating night NmF2 in summer. The peak height hmF2 is satisfactorily modelled by day, except that the model does not reproduce its observed semiannual variation. Nighttime values of hmF2 are much too low, thus causing low model values of night NmF2. Comparison of the variations of NmF2 and the neutral [O/N2] ratio supports the idea that both annual and semiannual variations of F2-layer electron density are largely caused by changes of neutral composition, which in turn are driven by the global thermospheric circulation.Finally, the paper describes and discusses the characteristics of the F2-layer response to the imposed ‘meteorological’ disturbances. The ionospheric response is evaluated as the standard deviations of five ionospheric parameters for each station within 11-day blocks of data. At any one station, the patterns of variability show some coherence between different parameters, such as peak electron density and the neutral atomic/molecular ratio. Coherence between stations is found only between the closest pairs, some 2500 km apart, which is presumably related to the scale size of the ‘meteorological’ disturbances. The F2-layer day-to-day variability appears to be related more to variations in winds than to variations of thermospheric composition.  相似文献   

6.
Summary The geomagnetic records obtained at Genova during the eclipse of February 15th, 1961 are quantitatively interpreted with the aim of separating the eclipse effect. Using the ionospheric observations also made at Genova, the result is well confirmed by the calculations carried out applying both theChapman-model and theVolland-scheme for estimating the geomagnetic effect as originated by the changes of the current system flowing in theE-layer.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».  相似文献   

7.
Zusammenfassung Es wird versucht, die beobachtete Aufspaltung derF-Schicht, die zur Ausbildung derF1- undF2-Schicht führt, dadurch zu erklären, daß zwei — in ihrer Wellenlänge verschiedene — Strahlungsanteile als Ionisationsquellen angenommen werden. Die aus dieser Annahme folgenden mathematischen Beziehungen werden abgeleitet, für die Lösung der komplizierten Gleichungen wird eine graphische Methode verwendet. Vergleiche mit dem aus Beobachtungen folgenden Verhalten der F1- und F2-Schicht führen jedoch zum Ergebnis, daß die Aufspaltungserscheinungen derF-Schicht auf diese Art nicht in befriedingender Weise erklärt werden können.
Summary The bifurcation of theF-layer is tried to be explained by the assumption of two radiation-components of distinct wavelength. Mathematical formulas derived for this statement are resolved by a graphical method. In comparison with observed behaviour of theF1- andF2-layer results the fact, that the bifurcation can not be explained in a satisfactory way by such a statement.
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8.
Annual, seasonal and semiannual variations of F2-layer electron density (NmF2) and height (hmF2) have been compared with the coupled thermosphere-ionosphere-plasmasphere computational model (CTIP), for geomagnetically quiet conditions. Compared with results from ionosonde data from midlatitudes, CTIP reproduces quite well many observed features of NmF2, such as the dominant winter maxima at high midlatitudes in longitude sectors near the magnetic poles, the equinox maxima in sectors remote from the magnetic poles and at lower latitudes generally, and the form of the month-to-month variations at latitudes between about 60°N and 50°S. CTIP also reproduces the seasonal behaviour of NmF2 at midnight and the summer-winter changes of hmF2. Some features of the F2-layer, not reproduced by the present version of CTIP, are attributed to processes not included in the modelling. Examples are the increased prevalence of the winter maxima of noon NmF2 at higher solar activity, which may be a consequence of the increase of F2-layer loss rate in summer by vibrationally excited molecular nitrogen, and the semiannual variation in hmF2, which may be due to tidal effects. An unexpected feature of the computed distributions of NmF2 is an east-west hemisphere difference, which seems to be linked to the geomagnetic field configuration. Physical discussion is reserved to the companion paper by Rishbeth et al.  相似文献   

9.
Summary The existence of temperature gradients and temperature variations in the heigh atmosphere change in a big rate the linear dependence between the variation of the maximal electron production in theF1 layer and the relative sunspot number is shown. The variations of the intensity of the ionizing source extremely with the increase of the solar activity. In order to obtain sensible data is necessary to use only the mean of the penetration frequency ofF1 layer in the midday hours of the summer season.  相似文献   

10.
The companion paper by Zou et al. shows that the annual and semiannual variations in the peak F2-layer electron density (NmF2) at midlatitudes can be reproduced by a coupled thermosphere-ionosphere computational model (CTIP), without recourse to external influences such as the solar wind, or waves and tides originating in the lower atmosphere. The present work discusses the physics in greater detail. It shows that noon NmF2 is closely related to the ambient atomic/molecular concentration ratio, and suggests that the variations of NmF2 with geographic and magnetic longitude are largely due to the geometry of the auroral ovals. It also concludes that electric fields play no important part in the dynamics of the midlatitude thermosphere. Our modelling leads to the following picture of the global three-dimensional thermospheric circulation which, as envisaged by Duncan, is the key to explaining the F2-layer variations. At solstice, the almost continuous solar input at high summer latitudes drives a prevailing summer-to-winter wind, with upwelling at low latitudes and throughout most of the summer hemisphere, and a zone of downwelling in the winter hemisphere, just equatorward of the auroral oval. These motions affect thermospheric composition more than do the alternating day/night (up-and-down) motions at equinox. As a result, the thermosphere as a whole is more molecular at solstice than at equinox. Taken in conjunction with the well-known relation of F2-layer electron density to the atomic/molecular ratio in the neutral air, this explains the F2-layer semiannual effect in NmF2 that prevails at low and middle latitudes. At higher midlatitudes, the seasonal behaviour depends on the geographic latitude of the winter downwelling zone, though the effect of the composition changes is modified by the large solar zenith angle at midwinter. The zenith angle effect is especially important in longitudes far from the magnetic poles. Here, the downwelling occurs at high geographic latitudes, where the zenith angle effect becomes overwhelming and causes a midwinter depression of electron density, despite the enhanced atomic/molecular ratio. This leads to a semiannual variation of NmF2. A different situation exists in winter at longitudes near the magnetic poles, where the downwelling occurs at relatively low geographic latitudes so that solar radiation is strong enough to produce large values of NmF2. This circulation-driven mechanism provides a reasonably complete explanation of the observed pattern of F2 layer annual and semiannual quiet-day variations.  相似文献   

11.
A self-consistent method for daytime F-region modelling was applied to EISCAT observations during two periods comprising the very disturbed days 3 April 1992 and 10 April 1990. The observed strong Ne decrease at F2-layer heights originated from different physical mechanisms in the two cases. The negative F2-layer storm effect with an NmF2 decrease by a factor of 6.4 on 3 April 1992 was produced by enhanced electric fields (E 85 mV/m) and strong downward plasma drifts, but without any noticeable changes in thermos-pheric parameters. The increase of the O+ + N2 reaction rate resulted in a strong enrichment of the ionosphere with molecular ions even at F2-layer heights. The enhanced electric field produced a wide mid-latitude daytime trough on 03 April 1992 not usually observed during similar polarization jet events. The other strong negative storm effect on 10 April 1990 with a complete disappearance of the F2-layer maximum at the usual heights was attributed mainly to changes in neutral composition and temperature. A small value for the shape parameter S in the neutral temperature profile and a low neutral temperature at 120 km indicate strong cooling of the lower thermosphere. We propose that this cooling is due to increased nitric oxide concentration usually observed at these heights during geomagnetic storms.  相似文献   

12.
Further development of the method proposed by Danilov and Mikhailov is presented. The method is applied to reveal the foF2 long-term trends on 30 Northern Hemisphere ionosonde stations. Most of them show significant foF2 trends. A pronounced dependence of trend magnitude on geomagnetic (invariant) latitude is confirmed. Periods of negative/positive foF2 trends corresponding to the periods of long-term increasing/decreasing geomagnetic activity are revealed for the first time. Pronounced diurnal variations of the foF2 trend magnitude are found. Strong positive foF2 trends in the post-midnight-early-morning LT sector and strong negative trends during daytime hours are found on the sub-auroral stations for the period with increasing geomagnetic activity. On the contrary middle and lower latitude stations demonstrate negative trends in the early-morning LT sector and small negative or positive trends during daytime hours for the same period. All the morphological features revealed of the foF2 trends may be explained in the framework of contemporary F2-region storm mechanisms. This newly proposed F2-layer geomagnetic storm concept casts serious doubts on the hypothesis relating the F2-layer parameter long-term trends to the thermosphere cooling due to the greenhouse effect.  相似文献   

13.
The applicability of the method proposed by Titheridge [1995] to the estimations of the ionization vertical drift velocity V is studied. The values of the F2-layer maximum height, h m F2, obtained from the measurements using the DPS-4 digital ionosonde at Irkutsk (Institute of Solar-Terrestrial Physics) in 2003–2006, are the initial data. The neutral gas parameters were calculated from the [Hedin, 1987] thermospheric model. The obtained calculations of the vertical ionization drift velocity are estimated by comparing with the [Hedin et al., 1991] empirical model. In some cases, good agreement with this model has been obtained. However, such agreement is registered not always, and the cause of such discrepancies is still unclear. The diurnal variations in the vertical ionization drift velocity in different seasons are also discussed.  相似文献   

14.
Summary This note deals with the great and abrupt falls of air temperature in Athens which occur especially during the cold season of the year. The frequency of these falls, the greatest falls noted per month and the weather situations associated with these falls are examined separately. It was found that the weather situations which cause the great falls of air temperature in Greece can be classified in four categories:A, B, C andD. In theA belong the anticyclones of N and NW Europe both moving and not. TheB comprises the extensions of the anticyclone of the Azorez over Europe. In theC belong the extension of the Russian anticyclones and theD comprises the cold fronts of depressions moving from W to E.  相似文献   

15.
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».  相似文献   

16.
Summary Results of sunspot cycle influence on solar and lunar ranges at a low latitude station, Alibag, outside the equatorial electrojet belt, show that the sunspot cycle association in solar ranges is three times that of the lunar ranges in thed- andj-seasons. This is in general agreement with the earlier results for non-polar latitude stations. The association with sunspot number of individual lunar amplitudes is greatest for lunar semidiurnal harmonic in thej-season. During this season, the sunspot cycle influence on lunar variations is more than that on solar variations, thereby indicating that the lunar current is situated at a level more favourable for sunspot cycle influence than the level of the current associated with solar variations. With the increase in solar activity a shift appears in the times of maxima of semidiurnal lunar variation towards a later lunar hour ine- andj-seasons and in the year.  相似文献   

17.
The spatial variations of the ionospheric F2-layer vertical incidence critical frequency (foF2) and GPS-derived vertical total electron content (vTEC) under geomagnetically quiet and disturbed days are examined using measurements from the latitudinal and longitudinal chains of ionospheric stations and GPS receivers over the European area. Plots produced for January 2005 are used to discuss temporal structures in terms of the prevailing solar-terrestrial conditions. Then the line trends procedure has been applied to simultaneous data collected from a limited number of measuring stations during quiet monthly median ionospheric conditions as well as during the storm period of 16–23 January 2005. The procedure is explained involving an application of the least squares method to define latitudinal and longitudinal dependence of foF2 and vTEC at different locations. Examples of coefficients of determination thereby produced show that the linear regression equations are very helpful in predicting longitudinal and latitudinal vTEC and foF2 variations during the quiet as well as disturbed ionospheric conditions.  相似文献   

18.
Variation with solar activity level of the ratios of the critical frequencies of the F2 layer, foF2, is considered for various pairs of local time moments T1 and T2 for two seasons (winter and summer). It is found that, as a rule, the foF2(T1)/foF2(T2) behavior with the solar activity index F10.7 is different in winter and summer. The variations of foF2(T1)/foF2(T2) with F10.7 obtained from experimental data are considered from the viewpoint of the current theory of F2-layer formation. It is shown that the majority of observed characteristics of these variations are explained using the above-indicated theory. However, special cases of foF2(T1)/foF2(T2) behavior with solar activity are found for which there is still no physical explanation.  相似文献   

19.
New ionospheric activity indices are derived from automatically scaled online data from several European ionosonde stations. These indices are used to distinguish between normal ionospheric conditions expected from prevailing solar activity and ionospheric disturbances caused by specific solar and atmospheric events (flares, coronal mass ejections, atmospheric waves, etc.). The most reliable indices are derived from the maximum electron density of the ionospheric F 2-layer expressed by the maximum critical frequency foF 2. Similar indices derived from ionospheric M(3000)F 2 values show a markedly lower variability indicating that the changes of the altitude of the F 2-layer maximum are proportionally smaller than those estimated from the maximum electron density in the F 2-layer. By using the ionospheric activity indices for several stations the ionospheric disturbance level over a substantial part of Europe (34°N–60°N; 5°W–40°E) can now be displayed online.  相似文献   

20.
The variations of the upper atmosphere air density during geomagnetic disturbances have been investigated by many authors. According to the analysis of satellite orbits, in most cases an increase in the air density may be observed when the indexA phas a maximum. Having ionospheric data from stations in Europe, Asia and Australia we might be able to study the global behaviour of the electron density in theF 2 region during such geomagnetic disturbances when an increase of the air density had been observed. In these cases we found, that at the peak of the ionospheric layer, the electron density decreased 0–3 days later than theA pmaximum.  相似文献   

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