Recombination coefficient and the pre-noon maximum of electron density in ionospheric F2-region

Equilibrium electron distributions in the ionospheric F2-layer

[1] The effects on the high-latitude F region of the ionosphere by X-mode powerful HF radio waves injected towards the magnetic zenith (MZ) are analysed. The experiments were conducted using the EISCAT/Heating facility and UHF radar at Tromso, Norway, the CUTLASS (SuperDARN) radar and the EISCAT ionosonde (dynasonde). The results show that the X-mode HF pump wave, radiated into the magnetic zenith from the HF heater, can generate very strong small-scale artificial field aligned irregularities (AFAIs) in the F-region of the high-latitude ionosphere. These irregularities, with spatial scales across the geomagnetic field of the order of 8–15 m, are generated when the heater frequency is above the ordinary-mode critical frequency but comparable with the extraordinary-mode critical frequency. The generation of the X-mode AFAIs was accompanied by electron temperature (Te) enhancements up to 50% above the background level and an increase in the electron density (Ne) by up to 30%.

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.

Electrical explosion of aluminum wire is a very promising method for aluminum nanoparticle production. The exploding wire plasma has significant influence on the formation of the nanoparticles. In this paper, the electron temperatures and the electron densities in the plasma are estimated through Boltzmann plot and Stark broadening effect. The aluminum particle densities, charge state distributions, and the energy relaxation in the plasma are estimated accordingly. The diffusion of the plasma into protective argon gas is studied through its spatial distribution. The electron temperatures of the electrical explosion of wire (EEW) plasma with an aluminum wire in argon gas are 1~2 eV, and the electron densities are of the order of magnitude ~1019/cm3, which decrease rapidly over time after the EEW occurs. The diffusion of the EEW plasma of aluminum wire into ambient argon gas can be divided into two main phases, namely, the previous fast diffusion phase and the subsequent slow diffusion phase. The plasma is with quite different diffusion features due to the differences of the corresponding relative number density of the plasma to argon gas. For plasma with relative density much higher than 1, the diffusion velocity in the fast diffusion phase is significantly higher than that with relative density near 1, and in the slow diffusion phase, the distribution radius of the plasma can continue to increase significantly due to the considerable energy coupled from the circuit to the aluminum particles. Dependence of the plasma radii on the deposited energies are derived from the experimental data. For plasma with relative density near 1, due to the much longer relaxation time during the slow diffusion phase, very little energy can be transferred from the circuit to the aluminum particles and the plasma radii only increase slightly during this phase after the aluminum particles spent most of their kinetic energy in the previous fast diffusion phase.

World wide study of apparent horizontal movements in F2-region of the ionosphere

It has been found that the total electron content (TEC) and the ionospheric electric fields indicated by the geomagnetic data showed inconsistent changes with each other at the mid- and low latitudes in both the American and the Asian–Australian sectors during geomagnetic quiet time (GQT) from 30 November to 8 December 2019 (Kpmax = 1.7). Meanwhile, the effects of thermospheric compositions are still indistinct. In this work, we analyze the mid/low-latitude ionospheric variations during this period, utilizing multi-instrument observations. The vertical drift velocities from the Ionospheric Connection Explorer (ICON) show significant variations and are in line with the changes in TEC at low latitudes in both of the two sectors. The zonal electric fields are supposed to play the main role in the TEC changes. This is also confirmed by the ionospheric F2 layer parameters data from the ionosonde stations at Sanya in the Asian–Australian sectors. The correlation between the variations in the geomagnetic H component (ΔH) and ionospheric F-layer electric fields can be affected by solar activity levels. The geomagnetic data ΔH sometimes may not indicate the magnitude of the electric fields in the F-region ionosphere under geomagnetic quiet conditions. The column density ratio of atomic oxygen (O) to molecular nitrogen (N2) (∑O/N2) from the Global Scale Observations of the Limb and Disk (GOLD) showed a strong enhancement at mid-latitudes in the American sector on 30 November. It is speculated that the neutral compositions should make a minor contribution to the changes in TEC during this event, compared with the electric fields.

The physical mechanism by which the regions with increased or decreased total electron content, registered by measuring delays of GPS satellite signals before strong earthquakes, originate in the ionosphere has been proposed. Vertical plasma transfer in the ionospheric F 2 region under the action of the zonal electric field is the main disturbance formation factor. This field should be eastward, generating the upward component of plasma electromagnetic drift, in the cases of increased total electron content at midlatitudes and deepened minimum of the F 2 layer equatorial anomaly. Upward plasma drift increases electron density due to a decrease in the O+ ion loss rate at midlatitudes and decreases this density above the equator due to an enhancement of the fountain effect (plasma discharge into the equatorial anomaly crests). The pattern of the spatial distribution of the seismogenic electric field potential has been proposed. The eastward electric field can exist in the epicentral region only if positive and negative electric charges are located at the western and eastern boundaries of this region, respectively. The effectiveness of the proposed mechanism was studied by modeling the ionospheric response to the action of the electric field generated by such a charge configuration. The results of the numerical computations indicated that the total electron content before strong earthquakes at middle and low latitudes is in good agreement with the observations.

Multi-instrument data recorded at multi-stations are used to study the equatorial and low-latitude ionospheric response to an intense solar flare of class X7 (2B) in the current solar cycle 24 with the peak at 08:05 UT on 09 August 2011. Rapid changes in ionospheric total electron contents (TEC) measured by global positioning system (GPS) showed an enhancement of 2–3 TECU. The very low frequency (VLF) data recorded at a low latitude station Varanasi showed an enhancement of VLF signal amplitude during the solar flare period which is attributed to the sudden enhancement of D-region ionization. Ground based GPS measurements are also validated by analyzing the electron density profiles measured from COSMIC satellite mission. COSMIC-derived electron density profile shows a decrease below F2 peak altitude and increase above F2 peak. The D-region ionospheric perturbation observed during the solar flare could be caused by flare time enhanced level of photo-ionization due to X-ray flux enhancement, whereas for E and F-region ionosphere, enhanced EUV flux causes photo-ionization and hence perturbed the TEC.

Various methods for calculating electron‐ion recombination and ionization coefficients for argon (α and S) have been developed in the past. For given values of electron temperature and electron density, a large dispersion exists between the different results due to a great number of parameters. We have developed the method based on the collisional‐radiative model to calculate α and S for limited conditions (atmospheric pressure; strong resonance radiation absorption) in order to obtain realistic values applicable in real cases such as arc plasmas. Influences of resonance radiation absorption and atom‐atom collisions have been studied. The collisional‐radiative recombination coefficient has been compared with results obtained by other calculation methods: the best agreement occurs with the “bottleneck” model for high values of electron density and temperature. Finally the comparison with available experimental results shows a good agreement between our computed values and experimental values when experimental and theoretical conditions are analogous.

Neutral-air winds in the ionospheric F-region for an asymmetric global pressure system

The ionospheric effects of six intense geomagnetic storms with Dst index ≤ −100 nT that occurred in 2012 were studied at a low-latitude station, Darwin (Geomagnetic coordinates, 21.96° S, 202.84° E), a low-mid-latitude station, Townsville (28.95° S, 220.72° E), and a mid-latitude station, Canberra (45.65° S, 226.30° E), in the Australian Region, by analyzing the storm–time variations in the critical frequency of the F2-region (foF2). Out of six storms, a storm of 23–24 April did not produce any ionospheric effect. The storms of 30 September–3 October (minimum Dst = −122 nT) and 7–10 October (minimum Dst = −109 nT) are presented as case studies and the same analysis was done for the other four storms. The storm of 30 September–3 October, during its main phase, produced a positive ionospheric storm at all three stations with a maximum percentage increase in foF2 (∆foF2%) of 45.3% at Canberra whereas during the recovery phase it produced a negative ionospheric storm at all three stations with a maximum ∆foF2% of −63.5% at Canberra associated with a decrease in virtual height of the F-layer (h’F). The storm of 7–10 October produced a strong long-duration negative ionospheric storm associated with an increase in h’F during its recovery phase at all three stations with a maximum ∆foF2% of −65.1% at Townsville. The negative ionospheric storms with comparatively longer duration were more pronounced in comparison to positive storms and occurred only during the recovery phase of storms. The storm main phase showed positive ionospheric storms for two storms (14–15 July and 30 September–3 October) and other three storms did not produce any ionospheric storm at the low-latitude station indicating prompt penetrating electric fields (PPEFs) associated with these storms did not propagate to the low latitude. The positive ionospheric storms during the main phase are accounted to PPEFs affecting ionospheric equatorial E × B drifts and traveling ionospheric disturbances due to joule heating at the high latitudes. The ionospheric effects during the recovery phase are accounted to the disturbance dynamo electric fields and overshielding electric field affecting E × B drifts and the storm-induced circulation from high latitudes toward low latitudes leading to changes in the natural gas composition [O/N2] ratio.

Effects of greatly increased O + loss in the ionospheric F-region

A theoretical investigation of corpuscular radiation effects on the F-region of the ionosphere

A theoretical study of the ionospheric F region equatorial anomaly—II. results in the American and Asian sectors

Evaluations of loss coefficient at several fixed heights of ionospheric F-region by a comparatively simple method have been shown to yield reasonable values. Seasonal characteristics of the loss coefficient have been obtained and discussed in relation to concentration of atomic and molecular gases. From analysis at average heights of maximum electron densities, seasonal and solar cycle variations in the loss coefficient at temperate and sub-tropical latitudes have also been obtained. It has been found that the technique is not applicable to stations in low latitudes because of the large magnitudes of vertical drifts of ionization which have not been taken into account in the present method.