scholarly journals Some new features of electron density irregularities over SHAR during strong spread F

2000 ◽  
Vol 18 (2) ◽  
pp. 141-151 ◽  
Author(s):  
S. Raizada ◽  
H. S. S. Sinha
Keyword(s):  
Growth Rate ◽  
Electron Density ◽  
Large Scale ◽  
Density Fluctuations ◽  
High Electron ◽  
Intermediate Scale ◽  
Radio Science ◽  
Ionospheric Physics ◽  
Scale Size ◽  
Spread F

Abstract. An RH-560 rocket flight was conducted from Sriharikota rocket range (SHAR) (14°N, 80°E, dip latitude 5.5°N) to study electron density and electric field irregularities during spread F. The rocket was launched at 2130 local time (LT) and it attained an apogee of 348 km. Results of electron density fluctuations are presented here. Two extremely sharp layers of very high electron density were observed at 105 and 130 km. The electron density increase in these layers was by a factor of 50 in a vertical extent of 10 km. Large depletions in electron density were observed around 175 and 238 km. Both sharp layers as well as depletions were observed also during the descent. The presence of sharp layers and depletions during the ascent and the descent of the rocket as well as an order of magnitude less electron density, in 150-300 km region during the descent, indicate the presence of strong large-scale horizontal gradients in the electron density. Some of the valley region irregularities (165-178 km), in the intermediate scale size range, observed during this flight, show spectral peaks at 2 km and can be interpreted in terms of the image striation theory suggested by Vickrey et al. The irregularities at 176 km do not exhibit any peak at kilometer scales and appear to be of new type. The growth rate of intermediate scale size irregularities, produced through generalized Rayleigh Taylor instability, was calculated for the 200-330 km altitude, using observed values of electron density gradients and an assumed vertically downward wind of 20 ms-1. These growth rate calculations suggest that the observed irregularities could be produced by the gradient drift instability.Key words: Ionosphere (equatorial ionosphere; ionospheric irregularities) - Radio science (ionospheric physics)

scholarly journals First in situ measurement of electric field fluctuations during strong spread F in the Indian zone

2000 ◽  
Vol 18 (5) ◽  
pp. 523-531 ◽  
Author(s):  
H. S. S. Sinha ◽  
S. Raizada
Keyword(s):  
Electric Field ◽  
Electron Density ◽  
Electric Fields ◽  
Vertical Direction ◽  
Intermediate Scale ◽  
Radio Science ◽  
Ionospheric Physics ◽  
Vertical Electric Field ◽  
Field Fluctuations ◽  
Spread F

Abstract. An RH-560 rocket flight was conducted from Sriharikota rocket range (SHAR) (14°N, 80°E, dip 14°N) along with other experiments, as a part of equatorial spread F (ESF) campaign, to study the nature of irregularities in electric field and electron density. The rocket was launched at 2130 local time (LT) and it attained an apogee of 348 km. Results of vertical and horizontal electric field fluctuations are presented here. Scale sizes of electric field fluctuations were measured in the vertical direction only. Strong ESF irregularities were observed in three regions, viz., 160-190 km, 210-257 km and 290-330 km. Some of the valley region vertical electric field irregularities (at 165 km and 168 km), in the intermediate-scale size range, observed during this flight, show spectral peak at kilometer scales and can be interpreted in terms of the image striation theory suggested by Vickrey et al. The irregularities at 176 km do not exhibit any peak at kilometer scales and appear to be of a new type. Scale sizes of vertical electric field fluctuations showed a decrease with increasing altitude. The most prominent scales were of the order of a few kilometers around 170 km and a few hundred meters around 310 km. Spectra of intermediate-scale vertical electric field fluctuations below the base of the F region (210-257 km) showed a tendency to become slightly flatter (spectral index n = -2.1 ± 0.7) as compared to the valley region (n = -3.6 ± 0.8) and the region below the F peak (n = -2.8 ± 0.5). Correlation analysis of the electron density and vertical electric field fluctuations suggests the presence of a sheared flow of current in 160-330 km region.Keywords: Ionosphere (Electric fields and currents; ionospheric irregularities); Radio science (ionospheric physics)

scholarly journals Modelling the main ionospheric trough using the Electron Density Assimilative Model (EDAM) with assimilated GPS TEC

2018 ◽  
Vol 36 (1) ◽  
pp. 125-138 ◽  
Author(s):  
James A. D. Parker ◽  
S. Eleri Pryse ◽  
Natasha Jackson-Booth ◽  
Rachel A. Buckland
Keyword(s):  
Electron Density ◽  
Large Scale ◽  
Western Europe ◽  
Global Scale ◽  
Electron Content ◽  
Total Electron ◽  
Radio Science ◽  
Ionospheric Physics ◽  
Main Ionospheric Trough ◽  
Plasma Distribution

Abstract. The main ionospheric trough is a large-scale spatial depletion in the electron density distribution at the interface between the high- and mid-latitude ionosphere. In western Europe it appears in early evening, progresses equatorward during the night, and retreats rapidly poleward at dawn. It exhibits substantial day-to-day variability and under conditions of increased geomagnetic activity it moves progressively to lower latitudes. Steep gradients on the trough-walls on either side of the trough minimum, and their variability, can cause problems for radio applications. Numerous studies have sought to characterize and quantify the trough behaviour. The Electron Density Assimilative Model (EDAM) models the ionosphere on a global scale. It assimilates observations into a background ionosphere, the International Reference Ionosphere 2007 (IRI2007), to provide a full 3-D representation of the ionospheric plasma distribution at specified times and days. This current investigation studied the capability of EDAM to model the ionosphere in the region of the main trough. Total electron content (TEC) measurements from 46 GPS stations in western Europe from September to December 2002 were assimilated into EDAM to provide a model of the ionosphere in the trough region. Vertical electron content profiles through the model revealed the trough and the detail of its structure. Statistical results are presented of the latitude of the trough minimum, TEC at the minimum and of other defined parameters that characterize the trough structure. The results are compared with previous observations made with the Navy Ionospheric Monitoring System (NIMS), and reveal the potential of EDAM to model the large-scale structure of the ionosphere. Keywords. Ionosphere (midlatitude ionosphere; modelling and forecasting) – radio science (ionospheric physics)

scholarly journals Statistical Measurements of Dispersion Measure Fluctuations of FRBs

2021 ◽  
Vol 922 (2) ◽  
pp. L31
Author(s):  
Siyao Xu ◽  
David H. Weinberg ◽  
Bing Zhang
Keyword(s):  
Electron Density ◽  
Large Scale ◽  
Density Fluctuations ◽  
Clear Correlation ◽  
Dispersion Measure ◽  
Large Dispersion ◽  
Dispersion Measures ◽  
The Difference ◽  
Electron Density Fluctuations ◽  
Scale Turbulence

Abstract Extragalactic fast radio bursts (FRBs) have large dispersion measures (DMs) and are unique probes of intergalactic electron density fluctuations. By using the recently released First CHIME/FRB Catalog, we reexamined the structure function (SF) of DM fluctuations. It shows a large DM fluctuation similar to that previously reported in Xu & Zhang, but no clear correlation hinting toward large-scale turbulence is reproduced with this larger sample. To suppress the distortion effect from FRB distances and their host DMs, we focus on a subset of CHIME catalog with DM < 500 pc cm−3. A trend of nonconstant SF and nonzero correlation function (CF) at angular separations θ less than 10° is seen, but with large statistical uncertainties. The difference found between SF and that derived from CF at θ ≲ 10° can be ascribed to the large statistical uncertainties or the density inhomogeneities on scales on the order of 100 Mpc. The possible correlation of electron density fluctuations and inhomogeneities of density distribution should be tested when several thousands of FRBs are available.

scholarly journals Simultaneous ground-based and in situ Swarm observations of equatorial F-region irregularities over Jicamarca

2020 ◽  
Vol 38 (5) ◽  
pp. 1063-1080
Author(s):  
Sharon Aol ◽  
Stephan Buchert ◽  
Edward Jurua ◽  
Marco Milla
Keyword(s):  
Electron Density ◽  
Seasonal Pattern ◽  
Density Fluctuations ◽  
Ionospheric Irregularities ◽  
Plasma Plumes ◽  
December Solstice ◽  
Spread F ◽  
Field Lines ◽  
Statistical Trends

Abstract. Ionospheric irregularities are a common phenomenon in the low-latitude ionosphere. They can be seen in situ as depletions of plasma density, radar plasma plumes, or ionogram spread F by ionosondes. In this paper, we compared simultaneous observations of plasma plumes by the Jicamarca Unattended Long-term Investigations of the Ionosphere and Atmosphere (JULIA) radar, ionogram spread F generated from ionosonde observations installed at the Jicamarca Radio Observatory (JRO), and irregularities observed in situ by Swarm in order to determine whether Swarm in situ observations can be used as indicators of the presence of plasma plumes and spread F on the ground. The study covered the years from 2014 to 2018, as this was the period for which JULIA, Swarm, and ionosonde data sets were available. Overall, the results showed that Swarm's in situ density fluctuations on magnetic flux tubes passing over (or near) the JRO may be used as indicators of plasma plumes and spread F over (or near) the observatory. For Swarm and the ground-based observations, a classification procedure was conducted based on the presence or absence of ionospheric irregularities. There was a strong consensus between ground-based observations of ionospheric irregularities and Swarm's depth of disturbance of electron density for most passes. Cases, where ionospheric irregularities were observed on the ground with no apparent variation in the in situ electron density or vice versa, suggest that irregularities may either be localized horizontally or restricted to particular height intervals. The results also showed that the Swarm and ground-based observations of ionospheric irregularities had similar local time statistical trends with the highest occurrence obtained between 20:00 and 22:00 LT. Moreover, similar seasonal patterns of the occurrence of in situ and ground-based ionospheric irregularities were observed with the highest percentage occurrence at the December solstice and the equinoxes and low occurrence at the June solstice. The observed seasonal pattern was explained in terms of the pre-reversal enhancement (PRE) of the vertical plasma drift. Initial findings from this research indicate that fluctuations in the in situ density observed meridionally along magnetic field lines passing through the JRO can be used as an indication of the existence of well-developed plasma plumes.

scholarly journals Characterization of VHF radar observations associated with equatorial Spread F by narrow-band optical measurements

2004 ◽  
Vol 22 (9) ◽  
pp. 3129-3136 ◽  
Author(s):  
R. Sekar ◽  
D. Chakrabarty ◽  
R. Narayanan ◽  
S. Sripathi ◽  
A. K. Patra ◽  
...  
Keyword(s):  
Large Scale ◽  
Temporal Variations ◽  
Density Fluctuations ◽  
Optical Measurements ◽  
Small Scale ◽  
Upward Movement ◽  
Vhf Radar ◽  
Equatorial Spread F ◽  
Spread F ◽  
Airglow Intensity

Abstract. The VHF radars have been extensively used to investigate the structures and dynamics of equatorial Spread F (ESF) irregularities. However, unambiguous identification of the nature of the structures in terms of plasma depletion or enhancement requires another technique, as the return echo measured by VHF radar is proportional to the square of the electron density fluctuations. In order to address this issue, co-ordinated radar backscatter and thermospheric airglow intensity measurements were carried out during March 2003 from the MST radar site at Gadanki. Temporal variations of 630.0-nm and 777.4-nm emission intensities reveal small-scale ("micro") and large-scale ("macro") variations during the period of observation. The micro variations are absent on non-ESF nights while the macro variations are present on both ESF and non-ESF nights. In addition to the well-known anti-correlation between the base height of the F-region and the nocturnal variation of thermospheric airglow intensities, the variation of the base height of the F-layer, on occasion, is found to manifest as a bottomside wave-like structure, as seen by VHF radar on an ESF night. The micro variations in the airglow intensities are associated with large-scale irregular plasma structures and found to be in correspondence with the "plume" structures obtained by VHF radar. In addition to the commonly observed depletions with upward movement, the observation unequivocally reveals the presence of plasma enhancements which move downwards. The observation of enhancement in 777.4-nm airglow intensity, which is characterized as plasma enhancement, provides an experimental verification of the earlier prediction based on numerical modeling studies.

Modelling the electron density distribution in the Io Plasma Torus using Juno radio occultations

2020 ◽  
Author(s):  
Marco Zannoni ◽  
Alessandro Moirano ◽  
Luis Gomez Casajus ◽  
Paolo Tortora ◽  
Daniele Durante ◽  
...  
Keyword(s):  
Electron Density ◽  
Temporal Variations ◽  
Parametric Models ◽  
High Electron ◽  
Path Delay ◽  
Radio Science ◽  
Ground Station ◽  
Plasma Torus ◽  
Almost All ◽  
Io Plasma Torus

&lt;p&gt;The innermost galileian moon Io hosts an intense volcanic activity, which ejects about 10&lt;sup&gt;3&lt;/sup&gt; kg/s of gas into Jupiter's magnetosphere. Here these neutrals are ionized by interaction with the background plasma and they are accelerated from keplerian velocity to corotation velocity thanks to Alfv&amp;#233;n's theorem. This plasma cloud around the planet (the so-called Io Plasma Torus or IPT) slowly diffuses across Jupiter's magnetic field, but high electron densities (&gt;1000-2000 cm&lt;sup&gt;-3&lt;/sup&gt;) are found between 5-8 R&lt;sub&gt;J&lt;/sub&gt;.&lt;/p&gt;&lt;p&gt;Juno is travelling along highly eccentric, polar orbits around the planet and flies very close to Jupiter's surface during each perijove. Thus, the radio links used for ground communication and radio science cross the IPT both in the uplink and the downlink leg. Being a dispersive medium, the torus introduces a different path delay on the X/X and Ka/Ka links established between the Ground Station and the spacecraft. Thus, the path delay can be extracted through a linear combination of the two links, and then quantitatively analyzed and fitted to different parametric models of the IPT.&lt;/p&gt;&lt;p&gt;In this work we have used almost all the available Juno radio occultations of the IPT in order to improve an already existing model by introducing both longitudinal and temporal variations of the electron density. To this end, we looked for the 2D Fourier expansion in longitude and time of the parameters of this model with the goal of minimizing the residuals of the fit and pointing out periodicities in the morphology of the torus.&lt;/p&gt;

scholarly journals <i>Letter to the Editor</i>: First direct observations of the reduced striations at pump frequencies close to the electron gyroharmonics

1999 ◽  
Vol 17 (9) ◽  
pp. 1235-1238 ◽  
Author(s):  
F. Honary ◽  
T. R. Robinson ◽  
D. M. Wright ◽  
A. J. Stocker ◽  
M. T. Rietveld ◽  
...  
Keyword(s):  
Large Scale ◽  
Electromagnetic Emission ◽  
Theoretical Models ◽  
Small Scale ◽  
Radio Waves ◽  
Radio Science ◽  
Ionospheric Physics ◽  
F Region ◽  
Direct Observations ◽  
Electron Gyrofrequency

Abstract. It is well known that the ionospheric plasma response to high-power HF radio waves changes drastically as the heater frequency approaches harmonics of the electron gyrofrequency. These include changes in the spectrum of the stimulated electromagnetic emission, reduction in the anomalous absorption of low-power diagnostic waves propagating through the heated volume, and reduction in the large scale F-region heating. Theoretical models as well as previous experimental evidence point towards the absence of small-scale field-aligned plasma density irregularities at pump frequencies close to electron gyroharmonics as the main cause of these changes. Results presented in this paper are the first direct observations of the reduced striations at the 3rd gyroharmonic made by the CUTLASS radar. In addition, simultaneous EISCAT observations have revealed that the "enhanced ion-line" usually present in the EISCAT ion-line spectrum during the first few seconds after heater switch on, persisted at varying strengths while the heater was transmitting at frequencies close to the 3rd electron gyroharmonics.Key words. Ionosphere (active experiments; ionospheric irregularities) · Radio science (ionospheric physics)

scholarly journals Spatial structure of auroral day-time ionospheric electron density irregularities generated by a powerful HF-wave

1998 ◽  
Vol 16 (7) ◽  
pp. 812-820 ◽  
Author(s):  
E. D. Tereshchenko ◽  
B. Z. Khudukon ◽  
M. T. Rietveld ◽  
A. Brekke
Keyword(s):  
Statistical Analysis ◽  
Radio Wave ◽  
Electron Density ◽  
Large Scale ◽  
Density Fluctuations ◽  
Small Scale ◽  
Ionospheric Heating ◽  
Mean Values ◽  
Hf Wave ◽  
Electron Density Irregularities

Abstract. We describe an experiment in satellite radio-wave probing of the ionosphere, modified by powerful waves from the HF heating facility at Tromsø (Norway) in May 1995. Amplitude scintillations and variations of the phase of VHF signals from Russian navigational satellites passing over the heated region were observed. We show that both large-scale electron density irregularities (several tens of kilometers in size) and small-scale ones (from hundreds of meters to kilometers) can be generated by the HF radiation. Maximum effects caused by small-scale irregularities detected in the satellite signals are observed in the directions sector approximately parallel to the geomagnetic field lines although large-scale structures can be detected within a much larger area. The properties of small-scale irregularities (electron density fluctuations) are investigated by applying a statistical analysis and by studying experimental and model mean values of the logarithm of the relative amplitude of the signal. The results indicate that satellite radio probing can be a supporting diagnostic technique for ionospheric heating and add valuable information to studies of effects produced by HF modification.Key words. Satellite radio-wave probing · HF radiation · Electron density irregularities · Statistical analysis · Ionospheric heating

scholarly journals Renormalization group method for Farley-Buneman fluctuations: basic results

1996 ◽  
Vol 3 (1) ◽  
pp. 41-46
Author(s):  
A. M. Hamza
Keyword(s):  
Renormalization Group ◽  
Large Scale ◽  
Closed Form Solution ◽  
Power Spectra ◽  
Random Force ◽  
Form Solution ◽  
Density Fluctuations ◽  
Group Method ◽  
Ionospheric Physics ◽  
Weakly Ionized

Abstract. Sudan and Keskinen in [1979] derived a set of equations governing the nonlinear evolution of density fluctuations in a low-pressure weakly ionized plasma driven unstable by the E x B or gradient-drift instability. This problem is of fundamental importance in ionospheric physics. The nonlinear nature of the equations makes it very hard to write a closed form solution. In this paper we propose to use "Dynamical Renormalization Group" methods to study the long-- wavelength, long-time behaviour of density correlations generated in this ionospheric plasma stirred by a Gaussian random force characterized by a correlation function (fk fk) k. The effect of the small scales on the large scale dynamics in the limit k -> 0 and infinite "Reynolds" number, can be expressed in the form of renormalized coefficients; in our case renormalized diffusion. If one assumes the power spectra to be given by the kolmogorov argument of cascading of energy, then one can not only derive a subgrid model based on the results of RNG, and this has been done by Hamza and Sudan [1995], but one can also extract the skewness of the spectra as we do in this paper.

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