Diurnal Variation Of Electron Density Research Articles

Variability of Weddell Sea ionospheric anomaly as deduced from observations at the Akademik Vernadsky station

Ionospheric Weddell Sea anomaly is an inversion of diurnal variation of the electron density in the ionosphere over Antarctic Peninsula, Weddell Sea, and neighbor territories observed during Antarctic summer. This paper aims at analyzing the reaction of the ionosphere during the Weddell Sea anomaly to changes in solar and geomagnetic activity as deduced from the data of vertical sounding of the ionosphere conducted at the Akademik Vernadsky station. The aim is achieved by comparing the monthly median values of the critical frequencies of the ionosphere (foF2) during Weddell Sea anomaly for the years of high and low solar activity; as well as by comparison of median December height-time diagrams (HT-diagrams) of foF2 calculated separately for the time intervals characterized by low or high levels of F10.7 and K indices for the period from 2007 till 2016. It was experimentally demonstrated that the Weddell Sea anomaly depends on the levels of solar ultraviolet flux and local K indices. The biggest nighttime maximum of ionization corresponds to low K indices and high values of F10.7. The most accurate inversion of diurnal variation of electron density in the F region is observed under the low values of K index and low F10.7 flux. The growth of geomagnetic activity decreases the nighttime ionization under both low and high levels of F10.7 fluxes and leads to a blur of the night maximum. Visible virtual heights of maximums increase together with F10.7 independently of the K index level. Blurring of the night maximum can be explained by destruction of the field of thermospheric winds supporting the nighttime anomaly, and/or by increasing role of plasma drifts in comparison with wind impact. The growth of visible virtual height of the nighttime maximum with increasing solar F10.7 flux could be explained by the gain of equatorward thermospheric wind with increasing solar ultraviolet flux that leads to growth of plasma upwelling effect. The Doppler frequency shift of the signals reflected from the ionosphere during nighttime in presence of the Weddell Sea anomaly is close to zero which could be explained by a stable F2 layer formed as a result of dynamic equilibrium between photochemical processes and upward plasma transport.

Mid-latitude anomalies in the diurnal variation of electron density in the ionosphere

The main morphological features of the F region of the mid-latitude ionosphere as obtained from Intercosmos-19 satellite measurements are presented. The causes of the anomalies in the diurnal variation of the electron density in certain longitudinal areas at the June and December solstice in the northern (Yakutsk anomaly) and southern (Weddell Sea anomaly (WSA)) hemispheres are determined. For both anomalies, the nighttime values of the critical frequency of the F2 layer, foF2, are higher than the daytime ones. Based on Intercosmos-19 satellite data, global maps of foF2 distribution for midday and midnight local time under high solar activity are drawn. Both anomalies occupy a large area in latitude and longitude, about 100° and 30°, respectively. The maximum difference between nighttime and daytime values of foF2 in the Yakutsk anomaly area reaches 1.0–1.5 MHz, smaller than that for the WSA (3.5–4.0 MHz). In the present work, these anomalies are reproduced with the help of a global self-consistent model of the thermosphere, ionosphere, and protonosphere (GSM TIP), and the mechanisms of their formation are preliminary investigated.

Diurnal variation of electron density in Saturn’s ionosphere: Model comparisons with Saturn Electrostatic Discharge (SED) observations

Using the Saturn Thermosphere Ionosphere Model (STIM), we present a study of the diurnal variation of electron density, with a focus on comparisons with peak electron densities (NMAX) inferred from the low-frequency cutoff of radio emission due to lightning in the lower atmosphere, called Saturn Electrostatic Discharges (SEDs). It is demonstrated that photochemistry in Saturn’s ionosphere cannot reproduce the SED-inferred diurnal variation in NMAX unless additional production and loss sources outside of the current best estimates are considered. Additional explanations of the SED-inferred diurnal variation of NMAX are presented and analyzed, such as the possibility that the low-frequency cutoff seen in SEDs is due to the presence of sharp low-altitude layers of plasma, as frequently seen in radio occultation measurements. Finally, we outline the observational constraints that must be fulfilled by any candidate explanations of the SED-inferred diurnal variation of NMAX.

Saturn's ionosphere: Inferred electron densities

During the two Voyager encounters with Saturn, radio bursts were detected that appear to have originated from atmospheric lightning storms. Although these bursts generally extended over frequencies from as low as 100 kHz to the upper detection limit of the instrument, 40 MHz, they often exhibited a sharp but variable low‐frequency cutoff below which bursts were not detected. We interpret the variable low‐frequency extent of these bursts to be due to the refraction and reflection of the radio waves as they propagate through an ionosphere that varies with local time. We obtain estimates of electron densities at a variety of latitude and local time locations. These compare well with the dawn and dusk densities measured by the Pioneer 11 and Voyager radio science investigations and with model predictions for dayside densities. However, we infer a two order of magnitude diurnal variation of electron density, which had not been anticipated by theoretical models of Saturn's ionosphere, and an equally dramatic extinction of ionospheric electron density by Saturn's rings.

Asymmetry in the diurnal variation of temperature and electron loss coefficient in the mesosphere

The diurnal and seasonal variations of electron density observed by partial reflection technique at Park Site, Saskatoon (52°N) in the mesosphere have been examined. It is found that an asymmetry in the diurnal variation of electron density exists in all the seasons in the height range 76–82 km. In summer and spring, the electron density reaches maxima about 1 h after local noon, while in winter and fall the maxima occur about 1 h before local noon. Except at 82 km, the electron density values are not always largest in summer and smallest in winter with fall and spring values lying in between them. Using an ion-chemical scheme, it is shown in this paper that asymmetry in the diurnal variation of electron density is due to the asymmetry in the diurnal variation of electron loss coefficient, which itself takes place because of an asymmetry in the diurnal variation in temperature. The mesosphere appears to cool down at times near local noon. Both experimental and theoretical work are needed to confirm these findings.

Ionospheric constraints of mesospheric nitric oxide

In view of the unreliabilities of γ-band estimates of mesospheric nitric oxide, ionospheric measurements of different types, including some controlled experiments specifically undertaken for this purpose, have been used to define an acceptable range of NO concentration. The ionospheric observations used are (i)the level of ionization reversal with solar activity ( Mitra, 1966), (ii) the gradual loss of solar control in the diurnal variation of electron density at levels below 70 km ( Mitra, 1969), (iii) magnitude and changes in the ratio of the two molecular ions NO + and O 2 +. The controlled experiment was the continuous monitoring of changes in mesospheric ionization profiles with the high power wave interaction facility at Pennsylvania State University during selected solar flare events. The flare measurements provide an NO profile similar to, but displaced downwards in height, from that given by Meira's γ-band measurements. The sharp ledge in electron density observed around 85 km requires a sharper valley in NO distribution at this height and the observed electron and positive ion densities at 70 km require that Meira's NO concentration should be increased by a factor between 5 and 7 at 70 km.

Model investigations of radio wave propagation in the lower ionosphere to determine electron densities from MF pulse sounding

In this paper full‐wave calculations are described to investigate the propagation of MF radio waves in the range from 255 to 950 kHz in the lower ionosphere. The method of investigation makes use of matrix multiplications with the ionosphere divided into homogeneous layers of 100‐m thickness. The model calculations provide conclusions from MF pulse sounding results on electron density and collision frequency profiles in the height interval from 50 to 100 km. The diurnal variation of electron density in the lower ionosphere is presented. Reflections observed from heights of about 75 and 87 km during the day are shown to be produced by steep gradients of electron density.

The diurnal variation in the mid-latitude D-region

The observed diurnal variation of electron density at a height of 77.5 km is examined in the light of two hypotheses for electron-ion recombination. In one of these q ∝ N 2, where q is the electron production and N the electron density, in the other q ∝ N. The latter assumption gives the better agreement between theory and experiment, when the electron production mechanism is ionization of nitric oxide by solar Lyman-α radiation, or ionization of O 2( 1Δg) by solar ultraviolet.

Total Electron Content in F2 Layer Over Madras During 1959

Some characteristics of the F2 layer of the ionosphere over Madras (Geographic lat. 13°05'N., Geomag. lat. 03°05'N.) for the period February 1959 to January 1960 are studied in this paper. Data for both quiet and disturbed days have been analysed.Diurnal variation of the F2 layer critical frequency for different months are described. The total electron content in a vertical column of unit cross-section below the level of maximum ionization has been calculated, on the assumption of parabolic distribution, for different times of the day and for different seasons. The diurnal variation of total electron content is smoother than that of maximum electron density for both quiet and disturbed days. The ‘bite-out’ effect observed in the diurnal variation of electron density is removed in the variation of the total electron content. The day-time values of electron density and total electron content are generally higher on disturbed days than on quiet days.Temperatures for the different seasons have been obtained from the values of scale height. The values of temperature on disturbed days are generally somewhat less than on quiet days.Scale height appears to increase when the height of maximum electron density increases.

The effects of diffusion and of attachmentlike recombination on theF2region

Using formulas developed in previous papers [Gliddon, 1959a and b; Gliddon and Kendall, 1960], we obtain quantitative results for the diurnal variation of electron density in the F2 region, taking account of diffusion and of an exponentially decreasing attachment-type law of recombination. The atmosphere is assumed to be isothermal, and for the case considered here (middle latitude) the effect of the geomagnetic field on diffusion is small enough to be ignored.

High-latitude radio observations

Observations were made on the ionosphere for nearly a year at 80° 23' N., 19° 31' E. It was found that at local noon the E region was present throughout the winter except on a few days which were magnetically disturbed. The electron-density in this region is at a minimum at midwinter and a maximum at midsummer. The F1 region is observed at noon only during the summer months with maximum electron-density at midsummer. The annual variation of maximum ionization in the F2 region is irregular and not very great, but the electron-density is at a maximum in spring and in late autumn. The diurnal variation of electron-density in the F2 region is more marked in the dark period, with a day to night ratio of 2.3: 1, than in the summer solstice period when the ratio is 1.5: 1. This latter figure which is also the ratio for the E and F1 region is in fair agreement with the ratio of 1.63: 1 deduced theoretically on the assumption that the ionizing power is proportional to the altitude of the sun. In all cases the minimum is near midnight with maxima before and after noon and a subminimum near noon. The effect of magnetic storms is to increase the electron-density in the absorbing region below the E region and, in the summer, to reduce markedly the electron-density in the F2 region. Reflections from the persistent E region persist to very high frequencies especially between 1200 and 1800 G.m.t. An intense E region, with a high reflection coefficient, occurs at all seasons during magnetically quiet conditions, and occurs almost solely between 1400 and 2300 G.m.t. No special conditions in the ionosphere obtain when the aurora is overhead, and absorption is not usually markedly increased under such conditions.