Height Of Maximum Electron Density Research Articles

On the Altitude Patterns of Photo‐Chemical‐Equilibrium in the Martian Ionosphere: A Special Role for Electron Temperature

AbstractThe ionosphere at Mars is governed by photo‐chemical‐equilibrium (PCE) at and below the height of maximum electron density (∼130 km), while the topside ionosphere blends PCE with other processes (e.g., plasma dynamics). We studied the altitude profile from 135 to 260 km where PCE conditions transition to the non‐PCE domain. Using MAVEN observations of electron density (Ne) and temperature (Te), CO2 densities, and integrated energy flux Fsun(5–93 nm), we tested the PCE relationship (Mendillo et al., 2017, https://doi.org/10.1002/2017ja024366). We found high correlations coefficients (CC = 80–90%) for heights 25–40 km above hmax, and then decreases to CC = 50% (defining partial PCE control). Surprisingly, CCs returned to > 50% in the 160–175 height range. We found the re‐establishment of PCE control occurs where the Te values rise sharply and thereby reduce the plasma recombination rate due to its inverse dependence on electron temperature. Enhancements in the topside ionosphere due to that process were first postulated by Fox and Yeager (2006, https://doi.org/10.1029/2006JA011697) to explain the “shoulder” seen Ne(h) profiles from radio occultation experiments. MAVEN data now provide the first comprehensive set of in situ observations to relate this enigmatic “bulge” to observed PCE parameters. Moreover, MAVEN observations reveal that additional sources are present to account for the Ne enhancements larger than possible from the thermal process alone.

Auroral ionospheric E region parameters obtained from satellite-based far ultraviolet and ground-based ionosonde observations: 1. Data, methods, and comparisons.

A large number (~1000) of coincident auroral far ultraviolet (FUV) and ground-based ionosonde observations are compared. This is the largest study to date of coincident satellite-based FUV and ground-based observations of the auroral E region. FUV radiance values from the NASA Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics (TIMED) Global Ultraviolet Imager (GUVI) and the Defense Meteorological Satellite Program (DMSP) F16 and F18 Special Sensor Ultraviolet Spectrographic Imager (SSUSI) are included in the study. A method is described for deriving auroral ionospheric E region maximum electron density (NmE) and height of maximum electron density (hmE) from N2 Lyman-Birge-Hopfield (LBH) radiances given in two channels using lookup tables generated with the Boltzmann 3-Constituent (B3C) auroral particle transport and optical emission model. Our rules for scaling (i.e., extracting ionospheric parameters from) ionograms to obtain auroral NmE and hmE are also described. Statistical and visual comparison methods establish statistical consistency and agreement between the two methods for observing auroral NmE, but not auroral hmE. It is expected that auroral non-uniformity will cause the two NmE methods to give inconsistent results, but we have not attempted to quantify this effect in terms of more basic principles, and our results show that the two types of NmE observations are well correlated and statistically symmetrical, meaning that there is no overall bias and no scale-dependent bias.

The equivalent slab thickness of Mars' ionosphere: Implications for thermospheric temperature

AbstractThe total electron content (TEC) of a planetary ionosphere is dominated by plasma near and above the height of maximum electron density (Nmax). The ratio TEC/Nmax represents the thickness (τ) of a TEC slab of uniform density (Nmax). For a photochemical ionosphere, τ relates to the scale height (H = kT/mg) of the ionized neutral gas as τ ~ 4 × H. Derived temperatures refer to ~160 km in thermosphere height—below the asymptotic temperature of the exosphere. The MARSIS instrument on Mars Express has produced data sets of TEC and Nmax. We used them to form τ patterns versus solar zenith angle and solar cycle phase. For daytime (SZA < 90°) conditions, <τ > day ~ 50 km, decreasing rapidly for solar zenith angle (SZA) > 90° to < τ > night ~ 25 km. These correspond to Tn values of 250°K and 125°K. Using Mars Global Surveyor data, τ patterns show a mild dependence upon the solar EUV flux proxy F10.7, with ΔTn(°K) ~ 0.3° per unit change in F10.7 at Mars.

Development and analysis of 3D ionosphere modeling using base functions and GPS data over Iran

In this study, a 3D-model of the electron density has been performed using the global positing system (GPS) measurements over Iran. 2D spherical harmonic functions and empirical orthogonal functions are used as base functions to model the horizontal and the vertical content of the electron density, respectively. The ionosonde data in Tehran (φ = 35.7382°, λ = 51.3851°) has been used for choosing an optimum value for the regularization parameter. To apply the method for constructing a 3D-image of the electron density, GPS measurements of the Iranian permanent GPS network (at 3-day in 2007) have been used. The instability of solution has been numerically analyzed and the Tikhonov method has been used for regularizing the solution. To come up with an optimum regularization parameter, the relative error in electron density profile computed from ionosonde measurements and their 3D model are minimized. The modeling region is between 24° to 40°N and 44° to 64°W. The result of 3D-Model has been compared to that of the international reference ionosphere model 2012 (IRI-2012). The data analysis shows that the latitudinal section of ionosphere electron density from 3D technique supports the expected time and height variations in ionosphere electron density. Moreover, these findings show that the height of maximum electron density is changed during the day and night and confirms the efficiency of multi-layer models in comparison to single-layer models. This method could recover 64–99 % of the ionosphere electron density.

Inversion of Oblique Ionograms Based on Hybrid Genetic Algorithm

AbstractThe oblique sounding is a powerful tool for acquiring ionospheric information, and we can get the structural parameters related to ionosphere by inversing the oblique ionogram. Genetic algorithm (GA) is a widely used inversion method which can reduce the non‐uniqueness of the inversion problems without depending on the initial estimation, but the accuracy and reliability of GA's inversion results may be decreased due to “premature convergence” and inferior local search ability. So an improved hybrid genetic algorithm (HGA) based on simulated annealing algorithm (SA) is proposed and firstly applied to inversion of oblique ionogram. HGA combines the advantages of GA and SA together and makes full use of them, so it has a strong global search ability and local search ability. To verify the reliability and stability of HGA's inversion results, we firstly use GA, SA, and HGA to inversion of the synthetic oblique ionogram and compare the inversion results of the three algorithms, find that HGA's results are nearest to the real values and its needed iterations are also much smaller than others. The inversion results include the critical frequency, the height of maximum electron density and half‐thickness. Then, comparing the influences on inversion results by changing the population size and the total iterations, we find that the HGA effectively reduces the influences. Lastly, we use the three algorithms to invert the real ionograms and compare the inversion results with the vertical data in the midpoint of transmitting and receiving site. The results show that the stability and the searching optimal solution ability of HGA are obviously better than the GA and SA, and its inversion results are reliable, so HGA has strong referential significance and practical value for the inversion of real ionograms.

On the variations of ionospheric parameters made at a near equatorial station in the African longitude sector: IRI validation with the experimental observations

We examine the main morphological patterns and climatological behaviour of equatorial F2 region over African sector using hourly observational values of F2 peak height of maximum electron density (h m F2), F2 layer peak electron density (N m F2/ foF2), and propagation factor (M3000F2) hitherto made by the Ibadan ionosonde at 7.4°N, 3.9°E, dip latitude 2.3°S, in Nigeria; between January to December 1958, during a period of high solar activity (yearly averaged Rz12 = 190 units) and magnetically quiet conditions (Kp ≤ 3). A direct comparison between these measurements and the International Reference Ionosphere 2007 (IRI-2007) model-predictions are also made. The results of comparisons illustrate that good advancement has been made but reveal some important discrepancies. The trends in the experimental data are found to be in excellent agreement with the trends in the simulation results for maximum electron density and propagation factor, but fair-to-good for F2 layer peak altitude. The model is unable to capture the sharp postsunset and predawn enhancements in h m F2 and M3000F2, respectively. The model results have errors ranging from approximately 8–15%, 9–17%, and 3–5%, respectively, for h m F2, N m F2, and M3000F2. On average, the percent absolute relative difference of the model from the experimental observations varies from about 0–20%, 0–30%, and 0–10% for h m F2, N m F2, and M3000F2, in that order. Our results are essentially consistent with other equatorial and low-latitude ground-based measurements over South America, India, and Southeast Asia.

Positive ionospheric storm effects at Latin America longitude during the superstorm of 20–22 November 2003: revisit

Abstract. Positive ionospheric storm effects that occurred during the superstorm on 20 November 2003 are investigated using a combination of ground-based Global Positioning System (GPS) total electron content (TEC), and the meridian chain of ionosondes distributed along the Latin America longitude of ~280° E. Both the ground-based GPS TEC and ionosonde electron density profile data reveal significant enhancements at mid-low latitudes over the 280° E region during the main phase of the November 2003 superstorm. The maximum enhancement of the topside ionospheric electron content is 3.2–7.7 times of the bottomside ionosphere at the locations of the ionosondes distributed around the mid- and low latitudes. Moreover, the height of maximum electron density exceeds 400 km and increases by 100 km compared with the quiet day over the South American area from middle to low latitudes, which might have resulted from a continuous eastward penetration electric field and storm-generated equatorward winds. Our results do not support the conclusions of Yizengaw et al. (2006), who suggested that the observed positive storm over the South American sector was mainly the consequence of the changes of the bottomside ionosphere. The so-called "unusual" responses of the topside ionosphere for the November 2003 storm in Yizengaw et al. (2006) are likely associated with the erroneous usage of magnetometer and incomplete data.

Comparison of observed hmF2 and IRI 2007 model with M(3000)F2 estimation of hmF2 at low solar activity for an equatorial station

In this paper, the ways of improving the equatorial F2 layer peak heights estimated from M(3000)F2 ionosonde data measured using the Ionospheric Prediction Service (IPS-42) sounder at Ouagadougou, Burkina Faso (geog lat +12.4°N, geog long +1.5°W, magnetic dip +5.9°N) during high solar activity year (1991) was investigated. For this purpose, the observed height of maximum electron density of F2 region (hmF2obs), deduced using an algorithm from scaled virtual heights of quiet day ionograms; and the predicted hmF2 values, which is given by the IRI 2007 model (hmF2IRI2007) have been compared with the ionosonde measured M(3000)F2 estimation of the hmF2 values (hmF2est), respectively. A strong correlation with its coefficients R 2 for all the seasons ranging 0.562 - 0.857 for hmF2obs values, and ranging 0.876 - 0.968 for the hmF2IRI2007 values was observed in the linear regressions of hmF2obs and hmF2IRI2007 with M(3000)F2 inverse. During the nighttime, estimated hmF2 (hmF2est) was found to be positively correlated with the hmF2obs values by the post-sunset peak representation, which is not represented by the hmF2IRI2007 values. Also, the validity of the hmF2est values has been investigated by finding the percentage deviations when compared with the hmF2obs and hmF2IRI2007.

Effect of Moon phases in riometer absorption and in the ionospheric and geomagnetic parameters

Variations in the frequency of occurrence of riometer absorption, minimum frequency of reflection of the ionospheric F layer, minimum height, and height of maximum electron density of the ionospheric F layer near the solar minimum have been studied. Application of the superposed epoch technique has detected the Moon phase effect on these ionospheric parameters. This effect was: three events per day in the occurrence of riometer absorption, 0.056 MHz in the minimum frequency of reflection of the F layer, and 2.6 and 6.7 km, in the change of the minimum height of reflection and height of reflection from the region with maximum electron density of the ionospheric F layer, respectively. The lunar tide action changes the ionospheric conductivity and, thus, influences the current systems of the magnetosphere. Through changes of magnetospheric currents, the Moon phase effect is exhibited in the Ap and Dst indices and is 4.3 and 4.25 nT, respectively.

Effect of horizontal gradients on ionospherically reflected or transionospheric paths using a precise homing-in method

A homing-in method is presented for determining ionospheric reflected or transionospheric paths between fixed transmitter and receiver locations in the presence of ionospheric gradients or ripples. Both initial elevation and azimuth are automatically adjusted to find the path that arrives exactly at the receiver. The method can be used for any 3D ionospheric model to find precise ray paths and phase and group delays for both magneto-ionic modes. The method takes full account of path location, geomagnetic field orientation and the bending of the ray path resulting from horizontal as well as vertical gradients of electron density. It can also find multiple paths e.g. low and high angle, 1- and 2-hops for both ordinary and extraordinary modes. Examples of its use are given for both terrestrial HF links and Earth to Satellite paths. For paths reflected from the ionosphere, the effect of gradients of both critical frequency and height of maximum electron density are determined and the comparative effect of gradients on high and low angle and 1- and 2-hops paths for both magneto-ionic modes investigated. Path variation with frequency for a fixed link is also studied and the bandwidth of the ionospheric background channel (dispersive bandwidth) and its reciprocal (the pulse rise time), important for wideband digital HF broadcasting or spread spectrum HF communications, is estimated for a range of frequencies, for high- and low-angle rays and 1- and 2-hop paths. For Earth–satellite paths, the effect of the ionosphere and horizontal ionospheric gradients is determined for a range of frequencies and elevation angles. It is shown that the method can also enable the determination of second-order errors in satellite navigation methods, such as GPS, due to ionospheric gradients and the effect of the geomagnetic field.

A model‐independent algorithm for ionospheric tomography: 2. Experimental results

This paper presents the results of an ionospheric tomography experiment over midlatitude Europe. The campaign yielded 539 reconstructions over a 45‐day period in spring 1995. Special attention is paid to the performance of the reconstruction algorithm, specifically by comparison with ionosonde data. Tomography and soundings tend to agree on electron density, but they do not agree on the height of maximum electron density: tomography seems to overestimate Hmax. Whereas tomography finds a daily oscillation in Hmax between 250 km (daytime) and 450 km (nighttime), the soundings indicate an oscillation between 200 and 250 km.

Low latitude airglow

Tropical airglow work during the last few years is reviewed. Airglow instrumentation is becoming more complex. Some of these sophisticated airglow experiments giving important information about the upper atmosphere such as ionospheric F region electron density, height of maximum electron density, dynamics of and irregularities in the F region, mesospheric neutral temperature and its variation, dynamics of mesospheric, etc. are mentioned. At the end some problems which could be tackled in near future with airglow techniques have been suggested.

A certain behavior of the ionospheric F2 region at low latitudes

The continuity equation of electron density is solved for the conditions of the F2 region at low latitude along 69°W meridian in the equinox of high solar activity. The transport term includes the electromagnetic drift observed at Jicamarca, the plasma diffusion, the vertical motion due to thermal expansion and contraction, and the neutral wind for which the direction reversal in the morning is rather late. The large‐scale irregularity which forms a bifurcated F2 layer is generated at the geomagnetic equator and travels as far as 15° latitude with a speed of about 10 km min−1. Other features of this bifurcation and the probable mechanism of its formation are described. The height of maximum electron density is strongly controlled by the electromagnetic drift at very low latitude from 0700 to midnight. The computation also shows that the large postsunset peak of NmF2 at a subtropical region is caused by the rapid sunset increase of upward drift at the equator. The late reversal of neutral wind favors the observed diurnal pattern of NmF2. Other effects of neutral wind and that of loss rate on the low latitude ionosphere are discussed.

Universal Time Control of the Polar Ionosphere

SEVERAL authors have demonstrated that, at very high latitudes, the critical frequency and height of the ionospheric F2 layer are strongly dependent on Universal Time. For example, Duncan1 has shown that, in winter, a maximum occurs in the F2 layer critical frequency (f0F2) near 0600 UT for Antarctic stations close to the magnetic pole. Piggott and Shapley2 have confirmed this and demonstrated a similar behaviour in the height of maximum electron density (hmF2). Duncan has suggested that the daily transport of the eccentric geomagnetic field through the interplanetary plasma could cause a tide in the geomagnetic field, which in turn would cause dumping of charged particles into the polar ionosphere. Hill3 has proposed that the phenomenon, being sporadic, is caused by electromagnetic drifts associated with polar-cap events. In contrast, Wilkes4 has pointed out that a global standing wave could explain the observed UT control of the polar tropospheric pressure; such an oscillation could also affect the atmosphere at ionospheric heights. Recently, King et al.5 have suggested that the phenomenon could be explained by vertical drifts in ionization, caused by atmospheric winds in the F layer.

The effect of diurnal temperature changes on the F2-layer

The paper describes time-varying solutions obtained for the F2-region continuity equation under conditions of thermal non-equilibrium. An isothermal model atmosphere is used and the continuity equation includes a movement term due to temperature variations of the neutral atmosphere. It is found that a decrease of electron temperature at sunset does not produce a ‘post-sunset’ increase of electron density. The ‘seasonal anomaly’ in F2-region electron densities also cannot be explained in terms of temperature variations. It is shown that variations of electron temperature are important in determining electron density, but the height of maximum electron density depends on variations of the neutral gas temperature.

Perturbation of a model F2-region by a small arbitrary time-dependent electrodynamic drift

Previous studies of a model F2-region ( Gliddon 1959a, b; Ferraro 1961) are extended to include the effects of a small electrodynamic drift. The drift is uniform in the space variable, but is an arbitrary function of time. The use of these results is illustrated by calculations carried out for a sinusoidal type of drift of variable phase. Height profiles of the perturbation are given for various phases at noon. The time variation of the perturbation at the height of maximum electron density is also given. Comparison with observations indicates that the magnitude of the vertical lunar tidal electrodynamic drift in the F2-region is about 0.4 m/sec, yielding a three percent variation of ƒ 0F2 .

Seasonal variation of the lunar tidal effects in the F2 layer of the ionosphere over Indian stations

The lunar semi-diurnal oscillations in the midday values of the critical frequency (f0F2) and the height of maximum electron density (hpF2) of the F2 layer are computed for all Indian ionospheric stations separately for each season of the year. The amplitude of oscillation inf0F2 is found to be larger in winter than in summer at each of the stations. There is a reversal in the phase of the oscillation inf0F2 between the equatorial and tropical latitudes and this is most evident in the winter months and is almost absent in summer. The annual average oscillation inf0F2 is in agreement with that found in a previous paper (Rastogi, 1961). The phase has a large seasonal variation of about 180° at an equatorial or a tropical latitude station. The phase and amplitude of the lunar tide inhpF2 do not vary significantly with latitude or with season.

Decay of an arbitrary plane-stratified distribution of ionization assumed to be produced instantaneously in the F2 region

An initial distribution of ionization, plane stratified and varying with altitude in an arbitrary manner, is assumed to be produced instantaneously under ambient conditions similar to those existing in the F2 region. It is shown that after a sufficiently long time the electron density develops a maximum. The behaviour of the height of maximum electron density and of times of decay are examined. Special cases considered are (i) decay of ionization produced by an intense pulse of solar radiation; (ii) decay of a thin concentrated layer of ionization.

Observed field strength in the neighborhood of the skip distance

During the decay of earth satellite 1958 O2 (Sputnik III), continuous wave signals were radiated on a frequency of 20 Mc when the satellite was in sunlight. As the signals originated at points below the height of maximum electron density, they provided an unusual means of studying sky-wave propagation from a rapidly moving vehicle. On many occasions abrupt increases or decreases of signal strength have been noted. Yeh and Swenson [1959] attributed similar phenomena observed in connection with Sputnik I to skip-distance focussing by the ionosphere, a conclusion supported by rather good agreement between computed and observed skip distances.

The electron distribution in the ionosphere over Slough—II Disturbed days

An account is given of how the heights of maximum electron density of the F1 and F2 layers and the sub-peak electron content vary over Slough (England) during magnetic storms. The parameters have been taken from detailed true-height electron density distributions calculated from observed h′( f) curves in 6 months representing three seasons in a year of low, and a year of high sunspot number. Attention is drawn to the fact that variations of h′ F2 during a storm should not be taken to represent changes of height of the F2 layer. The height of maximum electron density in the F2 layer is found to increase in storms, particularly at night. The height of maximum electron density in the F1 layer also increases. Comparison with the magnetograms recorded at Abinger during individual storms shows that ionospheric storm effects occur almost immediately after the magnetic changes. Some important changes have been noticed in the ionosphere at the time of a world-wide sudden impulse.