Shape Of Electron Density Profile Research Articles

Analysis of Two Selected Solar Events in 2011 and 2015 With Mars Express Radio Occultation Data

AbstractThe temporal behavior of the Martian ionosphere is highly variable due to various dynamic processes including space weather events. Here, we study the effect of solar flares and coronal mass ejections (CMEs) on the Martian ionosphere for two selected solar events in 2011 and 2015, using the publicly available Mars EXpress (MEX) radio occultation (RO) data (MaRS). We developed a data processing software that converts the calibrated Radio Occultation (RO) Doppler data to scientifically valuable atmospheric profiles. Using this software and previously unexplored MaRS observations, the variations in ionospheric parameters (electron density profiles and total electron content (TEC)) are calculated in order to evaluate the ionospheric changes due to solar flares and CMEs. The RO measurements mostly available 1–4 days apart from the peak events, showed no evident change in the TEC nor in the shape of electron density profiles except for a possible gradual decrease in altitude of M2 (main layer) peak density following the arrival of CMEs. To better quantify the effect of solar events on electron density profiles, RO observations near the time of arrival of solar flares and CMEs are crucial. This can be achieved by frequent RO measurements by various Mars orbiters including spacecraft‐to‐spacecraft measurements assisted by multi‐instrument monitoring of the ionosphere.

Accuracy assessment of the quiet-time ionospheric F2 peak parameters as derived from COSMIC-2 multi-GNSS radio occultation measurements

The Constellation Observing System for Meteorology, Ionosphere, and Climate 2 (COSMIC-2) mission was launched into a low-inclination (24°) orbit on June 25, 2019. Six satellites, each with an advanced Tri-GNSS Radio-Occultation Receiver System (TGRS), provide a global and uniform data coverage of the equatorial region with several thousand electron density profiles daily. The COSMIC-2 electron density profiles, and specifically the derived ionospheric F2 peak parameters, are properly validated in this study with reliable “truth” observations. For this purpose, we used manually scaled ionograms from 29 ground-based ionosondes located globally at low and middle latitudes. For this validation campaign, we considered only geomagnetically quiet conditions in order to establish benchmark level of the new mission’s ionospheric observation quality and to evaluate the operational capability of the COSMIC-2 Radio Occultation (RO) payload at the background of normal day-to-day variability of the ionosphere. For reliable colocations between two independent techniques, we selected only COSMIC-2 RO profiles whose F2 peak point coordinates were within 5° of the closest ionosonde. Our comparison of the ionospheric F2 peak height (hmF2) derived from COSMIC-2 RO and ground-based ionosonde measurements showed a very good agreement, with a mean of ~5 and ~2 km at low and middle latitudes, respectively, while RMS error was of ~23 and ~14 km, respectively. That range corresponds to a deviation of only 6–9% from the reference, ionosonde observations. Examination of representative collocation events with multiple (2–5) simultaneous RO tracks near the same ionosonde with different RO geometry, multi-satellite and multi-GNSS combination give us observational evidence that COSMIC-2 RO-based EDPs derived from GPS and GLONAS links show good self-consistency in terms of the ionospheric F2 peak values and electron density profile shape. We can conclude that COSMIC-2 provides high quality data for specification the ionospheric electron density at the F2 peak region.

Transition between Isotope-Mixing and Nonmixing States in Hydrogen-Deuterium Mixture Plasmas

The transition between isotope-mixing and nonmixing states in hydrogen-deuterium mixture plasmas is observed in the isotope (hydrogen and deuterium) mixture plasma in the Large Helical Device. In the nonmixing state, the isotope density ratio profile is nonuniform when the beam fueling isotope species differs from the recycling isotope species and the profile varies significantly depending on the ratio of the recycling isotope species, although the electron density profile shape is unchanged. The fast transition from nonmixing state to isotope-mixing state (nearly uniform profile of isotope ion density ratio) is observed associated with the change of electron density profile from peaked to hollow profile by the pellet injection near the plasma periphery. The transition from nonmixing to isotope-mixing state strongly correlates with the increase of turbulence measurements and the transition of turbulence state from TEM to ion temperature gradient is predicted by gyrokinetic simulation.

Ionospheric Electron Densities at Mars: Comparison of Mars Express Ionospheric Sounding and MAVEN Local Measurements

AbstractWe present the first direct comparison of Martian ionospheric electron densities measured by the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) topside radar sounder on board the Mars Express spacecraft and by the Langmuir Probe and Waves (LPW) instrument on board the Mars Atmosphere and Volatile Evolution Mission (MAVEN) spacecraft. As low electron densities are not measured by MARSIS due to the low power radiated at low sounding frequencies, MARSIS electron density profiles between the local electron density and the first data point from the ionospheric sounding (≈104 cm−3) rely on an empirical electron density profile shape. We use the LPW electron density measurements to improve this empirical description and thereby the MARSIS‐derived electron density profiles. We further analyze four coincident events, where the two instruments were measuring within a 5° solar zenith angle interval within 1 h. The differences between the electron densities measured by the MARSIS and LPW instruments are found to be within a factor of 2 in 90% of measurements. Taking into account the measurement precision and different locations and times of the measurements, these differences are within the estimated uncertainties.

The effects of process conditions on the plasma characteristic in radio-frequency capacitively coupled SiH4/NH3/N2 plasmas: Two-dimensional simulations

A two-dimensional (2D) fluid model is presented to study the behavior of silicon plasma mixed with SiH4, N2, and NH3 in a radio-frequency capacitively coupled plasma (CCP) reactor. The plasma-wall interaction (including the deposition) is modeled by using surface reaction coefficients. In the present paper we try to identify, by numerical simulations, the effect of variations of the process parameters on the plasma properties. It is found from our simulations that by increasing the gas pressure and the discharge gap, the electron density profile shape changes continuously from an edge-high to a center-high, thus the thin films become more uniform. Moreover, as the N2/NH3 ratio increases from 6/13 to 10/9, the hydrogen content can be significantly decreased, without decreasing the electron density significantly.

On the nature of low‐latitude Es influencing the genesis of equatorial plasma bubble

The potential influence of the postsunset low‐latitude sporadic E (Es) on the genesis of equatorial plasma bubble (EPB) has been investigated using observations made with the Gadanki radar and two ionosondes, one located at the magnetic equator providing the F layer characteristics and another at magnetically low‐latitude providing the Es parameters. Observations revealed that the occurrence of EPB was associated with either the disruption of Es or presence of nonblanketing‐type Es or intermittently occurring blanketing Es at low‐latitude. In contrast, when blanketing Es occurred for a relatively long duration in the sunset hours, EPB did not occur. Model computation clearly reveals that the growth of the Rayleigh‐Taylor instability depends very much on the thickness, height, and shape of electron density profile of the Es layer. The above findings thus suggest that low‐latitude Es variability plays decisive role on the day‐to‐day variability of EPB through the growth rate of the Rayleigh‐Taylor instability.

Diurnal and seasonal variation of B0,B1 parameters during high solar activity period at low mid-latitude and their comparisons with IRI-2001 model

Diurnal and seasonal variations of bottom side electron density profile shape parameters B0, B1, representing the bottom side F2-layer thickness and shape, are examined using modern digital ionosonde observations at a low-middle latitude station, New Delhi (28.6 °N, 77.2 °E, dip 42.4 °N) for high solar activity (HSA) (2001–2002). Median values of these parameters are obtained at each hour during different seasons and compared with the predictions of the latest version of the international reference ionosphere (IRI), IRI-2001 model using both the options namely: IRI (Gulyaeva) and IRI (B0 Tab.). Results show in general, a large variability in B0, and B1 parameters during all the seasons, the variability is larger during nighttime than by daytime. The diurnal variation of median B0, in general, show more or less similar trends with diurnal maximum occurring around noontime, except during summer, when it occurs between 09 and 10 LT. Variation pattern of B1 in general, is identical in all the seasons with lower values of B1 by daytime than by night. Comparative studies of B0 with those obtained with the IRI model show that in general, IRI (B0 Tab.) option reveals better agreement with the observations during all the seasons for local times from about 10 LT to about 16 LT, while outside this time period IRI (Gulyaeva) matches well with the observations. The predicted B1 parameter, using IRI (B0 Tab.) is close to observations in terms of diurnal variation, while B1 using IRI (Gulyaeva) option, assumes a fixed value of 3 at all local times irrespective of season.

Latitudinal variation of ionospheric slab thickness

The ionospheric slab thickness τ, defined as a ratio of the total electron content (TEC) to the F-region peak electron density N mF2, is a first order measure of the shape of the electron density profile. In the present study, we use GPS-derived TEC and vertical electron content estimates ITEC from ground-based ionosonde observations together with the corresponding f oF2 (F2 layer critical frequency) and h mF2 (F2 layer peak height) at 14 world-wide stations lying at different latitude regions from the geomagnetic equator to north pole. The period of study is during 2001–2002, which is close to the solar maximum phase of the 23rd solar cycle. Hourly values of TEC, ITEC, f oF2, h mF2 and τ during the period of study are used to compare τ values from the observation and model predictions using the International Reference Ionosphere extended towards the plasmapause with the plasmasphere option of the Russian standard model of the ionosphere, IRI*. For the three latitudinal zones (high, mid and low latitudes) the IRI* predictions of τ are compared with observed τ values for the bottomside ionosphere (below h mF2), topside ionosphere (between h mF2 and 1000 km), plasmasphere (from 1000 to 20,000 km), and the total height range through the ionosphere and plasmasphere. Significant overestimation of τ has been revealed when using IRI*, particularly for the topside ionosphere at high latitudes. Relation of the topside part of slab thickness with the topside half peak density height above the F2 layer peak provides new characteristic parameter for modeling of the topside shape of electron density profile.

Electron density behaviour in the TPE-RX reversed field pinch experiment and comparison with the particle transport model of the RFX experiment

Measure of electron density along two chords is now available in TPE-RX, a large reversed field pinch (RFP) experiment (a = 0.45 m, R = 1.72 m), giving for the first time information on the shape of electron density profiles in this machine. The behaviour of density and of profiles in standard discharges in TPE-RX is analysed in this paper. Density grows almost linearly with plasma current whereas the profiles are highly peaked and flatten progressively as density increases. The presence of the locking of magnetic modes also influences the density behaviour and causes profiles to be less peaked. The behaviour of TPE-RX profiles is compared with the profiles measured at RFX, another RFP of similar size operating in a different current and density range, which exhibits flat or hollow profiles. The difference between the two machines can be explained with the different profile of the particle source, due to the different density range of operation. The comparison with RFX is extended to particle transport studies by verifying that TPE-RX results are compatible with the transport model developed at RFX after detailed analysis of the profiles measured by a 13-chords interferometer. In RFX, data showed that a magnetic transport, parametrized according to the Rechester and Rosembluth theory, can account for the particle transport in the plasma core, while an electrostatic diffusivity dominates at the plasma edge. The results presented in this work show that the same physical frame can also account for the behaviour of TPE-RX density profiles and give an indication that the transport model tailored to RFX could be considered characteristic of RFP plasmas.

Long-term changes and trends in the lower ionosphere

A brief overview of long-term trends in the lower ionosphere ( h<100 km, ionized component) is presented. The trends have been studied with the use of several different types of data sets: A3 radio wave absorption (LF–HF, oblique incidence on the ionosphere, continuous wave), A2 (cosmic radio noise) riometric absorption, IPHA (indirect measurements of phase reflection height), rocket measurements of electron density and ion composition. The A3 radio wave absorption in the lower ionosphere over Europe has been analyzed for trends in: (1) absolute values of absorption; (2) amplitudes of annual and semiannual variations; (3) inferred planetary wave activity. Trends in absolute values of absorption do not provide a consistent pattern, which may be due to their sensitivity to changes in the shape of electron density profile and to instrumental problems. Similarly, there is no consistent pattern in trends in relative amplitudes of annual variations. However, there appears to be a systematic tendency to the positive trend in amplitudes of semiannual variations. Some increase of the absorption-inferred planetary wave activity was found in 1970s and 1980s, whereas no change was found in 1960s and 1990s. Analyses of cosmic noise absorption measured by a chain of riometers in Finland do not reveal an evident trend in absorption. IPHA analyses in mid-latitudinal Europe point to a systematic decrease of the reflection height (level of constant electron density) near 80 km. This has been interpreted in terms of decreasing atmospheric pressure due to decreasing columnar temperature in 50–80 km. Rocket measurements of electron density display for non-winter electron density at 75 and 80 km an increase at middle latitudes (contrary to IPHA results). Rocket measurements of ion composition in the lower ionosphere are too rare, but models reveal dramatic changes with a large decrease of NO + concentration. Since the lower ionosphere is substantially affected by the 11-year solar cycle, data sets length of more than 20 years is very desirable in long-term trend studies. Results based on various methods and various data sets do not provide sufficiently consistent observational pattern of trends in the lower ionosphere. Therefore, further investigations, tests of data quality and homogeneity, and careful application of various methods are necessary.

Observation of three-half harmonic radiation from plasmas irradiated by a 0·26 μm wavelength laser

Time-integrated measurements have been made of three-half harmonic light energy emitted from 0·26 μm laser-produced plasmas. The main results are the experimental dependence of 3/2ω0 conversion efficiency and threshold on electron density-profile shape. Various density profiles are achieved by irradiating different kinds of target; their shapes are estimated with the help of two-dimensional hydrodynamic simulations.

Implementation of a new characteristic parameter into the IRI sub-peak electron density profile

The shape of electron density profile in the International Reference Ionosphere could be improved significantly if the height h g and electron density N g of the F region sub-peak inflexion point were entered in the set of the profile standard parameters. To study variations of these important parameters, the N(h) analysis of the statistically-summarized ionograms at the latitudes of 40–80°N of the Eastern hemisphere has been carried out for the two-hours intervals of local time, three seasons (winter, equinox and summer) and two levels of solar activities characterized by Covington indicesF 10.7 = 100 and 200. It is shown that the parameters of the inflexion point can be expressed in most cases via the peak parameters of the F2 layer ash g= 0.8 hmF2 and N g= 0.5 NmF2.

Measurements of the Columnar Electron Contents of the Ionosphere and Plasmasphere

Modulation phase and Faraday rotation observations at Boulder of the ATS 6 radio beacon transmissions have measured the total slant electron content (NT) to the satellite and the content up to an altitude of about 2000 km (NF). Monthly median hourly values of NT, the residual plasmaspheric content above 2000 km (NP), and a factor F related to the electron profile shape and the earth' magnetic field are reported for July 1974 to April 1975. The slab thickness τ was calculated by using Boulder ionograms and numerical mapping estimates of the geographic variations of foF2. The diurnal and seasonal variations of NT, NP, F, and τ are discussed in terms of analytical models for the electron density profile shape. Representative models for day and night profiles in the summer, equinoctial, and winter seasons are presented, and their reliability is discussed.