Quasi-trapped VLF propagation in the outer magnetosphere.
Quasi-trapped whistler mode propagation and generation by trapped electrons in magnetosphere, noting refraction index and wave reflection
MAGNETOSPHERE↗
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Measurements of Partial Reflections at 3.18 Mhz Using the CW Radar Technique
An equipment for measuring partial reflections using the FM-CW-radar principle at 3.18 MHz, installed at the Ionospheric Observatory Juliusruh of the CISTP (HHI), is described. The linear FM-chirp of 325 kHz bandwidth is Gaussian-weighted in amplitude and gives a height resolution of 1.5 km (chirp length is 0.6 sec). Preliminary results are presented for the first observation period in winter 1982/83.
Priese, J.↗
Using GPS Reflections for Satellite Remote Sensing
GPS signals that have reflected off of the ocean's surface have shown potential for use in oceanographic and atmospheric studies. The research described here investigates the possible deployment of a GPS reflection receiver onboard a remote sensing satellite in low Earth orbit (LEO). The coverage and resolution characteristics of this receiver are calculated and estimated. This mission analysis examines using reflected GPS signals for several remote sensing missions. These include measurement of the total electron content in the ionosphere, sea surface height, and ocean wind speed and direction. Also discussed is the potential test deployment of such a GPS receiver on the space shuttle. Constellations of satellites are proposed to provide adequate spatial and temporal resolution for the aforementioned remote sensing missions. These results provide a starting point for research into the feasibility of augmenting or replacing existing remote sensing satellites with spaceborne GPS reflection-detecting receivers.
Mickler, David↗
Major Pathways to Electron Distribution Function Formation in Regions of Diffuse Aurora
This paper discusses the major pathways of electron distribution function formation in the region of diffuse aurora. The diffuse aurora accounts for about of 75% of the auroral energy precipitating into the upper atmosphere, and its origin has been the subject of much discussion. We show that an earthward stream of precipitating electrons initially injected from the Earth's plasma sheet via wave-particle interactions degrades in the atmosphere toward lower energies and produces secondary electrons via impact ionization of the neutral atmosphere. These electrons of magnetospheric origin are then reflected back into the magnetosphere along closed dipolar magnetic field lines, leading to a series of reflections and consequent magnetospheric interactions that greatly augment the initially precipitating flux at the upper ionospheric boundary (700-800 km). To date this, systematic magnetosphere-ionosphere coupling element has not been included in auroral research models, and, as we demonstrate in this article, has a dramatic effect (200-300%) on the formation of the precipitating fluxes that result in the diffuse aurora. It is shown that wave-particle interaction processes that drive precipitating fluxes in the region of diffuse aurora from the magnetospheric altitudes are only the first step in the formation of electron precipitation at ionospheric altitudes, and they cannot be separated from the atmospheric collisional machine that redistributes and transfers their energy inside the magnetosphere-ionosphere-atmosphere coupling system.
magnetospheric↗
Ionosphere-Magnetosphere Energy Interplay in the Regions of Diffuse Aurora
Both electron cyclotron harmonic (ECH) waves and whistler mode chorus waves resonate with electrons of the Earths plasma sheet in the energy range from tens of eV to several keV and produce the electron diffuse aurora at ionospheric altitudes. Interaction of these superthermal electrons with the neutral atmosphere leads to the production of secondary electrons (E500600 eV) and, as a result, leads to the activation of lower energy superthermal electron spectra that can escape back to the magnetosphere and contribute to the thermal electron energy deposition processes in the magnetospheric plasma. The ECH and whistler mode chorus waves, however, can also interact with the secondary electrons that are coming from both of the magnetically conjugated ionospheres after they have been produced by initially precipitated high-energy electrons that came from the plasma sheet. After their degradation and subsequent reflection in magnetically conjugate atmospheric regions, both the secondary electrons and the precipitating electrons with high (E600 eV) initial energies will travel back through the loss cone, become trapped in the magnetosphere, and redistribute the energy content of the magnetosphere-ionosphere system. Thus, scattering of the secondary electrons by ECH and whistler mode chorus waves leads to an increase of the fraction of superthermal electron energy deposited into the core magnetospheric plasma.
Khazanov, G. V.↗
The case of the noisy derivatives - Evidence for a spacecraft-plasma interaction
Data from the retarding potential analyzers on Atmosphere Explorers C and D indicate the existence of 2-m irregularities in the ion flux to the satellite. These irregularities are seen only occasionally, and usually very near the magnetic dip equator. They occur both in sunlight and eclipse and span at least two decades of ion concentration. They tend to be present when the spacecraft is moving nearly parallel to the magnetic field vector and are not seen at all from the low latitude AE-E orbit. It is believed that the irregularities, whose amplitude is of the order of 1% of the background ion flux, are the result of a spacecraft interaction with the ionospheric plasma. A mechanism for producing this interaction that utilizes a fast beam of ambient ions reflected upstream from the satellite to produce a two-stream instability is examined in some detail.
Hanson, W. B.↗
F region airglow - Are ground-based observations consistent with recent satellite results
The Atmosphere Explorer photochemistry is used to interpret simultaneous observations made at the Arecibo Observatory of the OI (6300 A) and NI (5200 A) airglow surface brightness and electron density and temperature profiles measured by incoherent scatter radar. It was found that the theory and the experiment agree for the 5200-A emission; however, it was not possible to obtain to a complete agreement for the 6300-A nightglow. It is suggested that the source of the discrepancy results from one of the parameters used to calculate the production rate of O(lD); the data show evidence of an asymmetrical behavior of the ionosphere between times when the F layer is descending and when it is ascending, with asymmetry probably reflecting the effects of transport on molecular ion densities in the bottom side of the F region.
Cogger, L. L.↗
Wind regime peculiarities in the lower thermosphere in the winter of 1983/84
Temporal variations of prevailing winds at 90 to 100 km obtained from measurements carried out in winter 1983 to 1984 at three sites in the USSR and two sites in East Germany are reported. These variations are compared with those of the thermal stratospheric regime. Measurements were carried out using the drifts D2 method (meteor wind radar) and the D1 method (ionospheric drifts). Temporal variations of zonal and meridional prevailing wind components for all the sites are given. Also presented are zonal wind data obtained using the partial reflection wind radar. Wind velocity values were obtained by averaging data recorded at between 105 and 91 km altitude. Wind velocity data averaged in such a way can be related to about the same height interval to which the data obtained by the meteor radar and ionospheric methods at other sites, i.e., the mean height of the meteor zone (about 95 km). The results presented show that there are significant fluctuations about the seasonal course of both zonal and meridional prevailing winds.
Lysenko, I. A.↗
HydroCube Mission Concept: P-Band Signals of Opportunity for Remote Sensing of Snow and Root Zone Soil Moisture
We have developed the HydroCube mission concept with a constellation of small satellites to remotely sense Snow Water Equivalent (SWE) and Root Zone Soil Moisture (RZSM). The HydroCube satellites would operate at sun-synchronous 3-day repeat polar orbits with a spatial resolution of about 1-3 Km. The mission goals would be to improve the estimation of terrestrial water storage and weather forecasts. Root-zone soil moisture and snow water storage in land are critical parameters of the water cycle. The HydroCube Signals of Opportunity (SoOp) concept utilizes passive receivers to detect the reflection of strong existing P-band radio signals from geostationary Mobile Use Objective System (MUOS) communication satellites. The SWE remote sensing measurement principle using the P-band SoOp is based on the propagation delay (or phase change) of radio signals through the snowpack. The time delay of the reflected signal due to the snowpack with respect to snow-free conditions is directly proportional to the snowpack SWE. To address the ionospheric delay at P-band frequencies, the signals from both MUOS bands (360-380 MHz and 250-270 MHz) would be used. We have conducted an analysis to trade off the spatial resolution for a space-based sensor and measurement accuracy. Through modeling analysis, we find that the dual-band MUOS signals would allow estimation of soil moisture and surface roughness together. From the two MUOS frequencies at 260 MHz and 370 MHz, we can retrieve the soil moisture from the reflectivity ratio scaled by wavenumbers using the two P-band frequencies for MUOS. A modeling analysis using layered stratified model has been completed to determine the sensitivity requirements of HydroCube measurements. For mission concept demonstration, a field campaign has been conducted at the Fraser Experimental Forest in Colorado since February 2016. The data acquired has provided support to the HydroCube concept.
Derksen, Chris↗
Theoretical investigation of EM wave generation and radiation in the ULF, ELF, and VLF bands by the electrodynamic orbiting tether
The problem of electromagnetic wave generation by an electrodynamic tethered satellite system is important both for the ordinary operation of such systems and for their possible application as orbiting transmitters. The tether's ionospheric circuit closure problem is closely linked with the propagation of charge-carrying electromagnetic wave packets away from the tethered system. Work is reported which represents a step towards a solution to the problem that takes into account the effects of boundaries and of vertical variations in plasma density, collision frequencies, and ion species. The theory of Alfen wave packet generation by an electrodynamic tethered system in an infinite plasma medium is reviewed, and brief summary of previous work on the problem is given. The consequences of the presence of the boundaries and the vertical nonuniformity are then examined. One of the most significant new features to emerge when ion-neutral collisions are taken into account is the coupling of the Alfven waves to the fast magnetosonic wave. This latter wave is important, as it may be confined by vertical variations in the Alfven speed to a sort of leaky ionospheric wave guide, the resonances of which could be of great importance to the signal received on the Earth's surface. The infinite medium solution for this case where the (uniform) geomagnetic field makes an arbitrary angle with the vertical is taken as the incident wave-packet. Even without a full solution, a number of conclusions can be drawn, the most important of which may be that the electromagnetic field associated with the operation of a steady-current tethered system will probably be too weak to detect on the Earth's surface, even for large tethered currents. This is due to the total reflection of the incident wave at the atmospheric boundary and the inability of a steady-current tethered system to excite the ionospheric wave-guide. An outline of the approach to the numerical problem is given. The use of numerical integrations and boundary conditions consistent with a conducting Earth is proposed to obtain the solution for the horizontal electromagnetic field components at the boundary of the ionosphere with the atmospheric cavity.
Estes, Robert D.↗
Natural environment design criteria for the Solar Electric Propulsion Stage (SEPS)
The natural environment design criteria are given for six different solar electric propulsion stage missions. These environment data include the neutral atmosphere; ionosphere, trapped radiation; free-space radiation environment; and meteoroid, asteroid, and comet environments. The electromagnetic radiation environment (direct, reflected, or scattered) at the planets and interplanetary regions is also included.
Wright, J. J.↗
Dynamics of Mars' magnetosphere
If Mars has a small intrinsic magnetic moment, Mars' magnetosphere could vary on time scales of a few minutes due to reconnection with the solar wind magnetic field. The day-side magnetopause will be one or two reflected-ion Larmor radii from the bow shock. Substorms will have scale-times of about six minutes. Mars' high ionospheric conductance will virtually stop polar cap convection, and create a magnetic 'topological crisis' unless convecting magnetic flux finds a dissipative way to return to the day-side. The strong magnetic shear induced by magnetospheric convection above the ionosphere could be tearing unstable. The magnetic field might diffusively 'percolate' through the tearing layer. This shearing also draws field aligned currents from the ionosphere which could inject few KeV heavy ionospheric ions into the magnetotail.
Kennel, C. F.↗
Ionospheric effects of X-ray source Scorpius XR-1
A simple two-ion model was employed to evaluate the ionospheric effects of various nocturnal ionization sources. The model was used to calculate the decay of the electron number density at 90 km with and without illumination by Scorpius XR-1 X rays. Reflection parameters for the determination of the effect of cosmic x-ray sources on radio wave propagation were also obtained. The results obtained in the investigation do not support the proposal made by Anathakrishnan and Ramanathan (1969) that the X-ray source in Scorpius XR-1 affects the nighttime lower ionosphere of the earth.
Poppoff, I. G.↗
Comparisons of techniques for measurement of D-region electron densities
This paper reviews the ground-based and rocket techniques that are presently being used to determine electron density profiles in the ionospheric D region. Ground-based techniques include VLF, LF, and MF sounding; differential absorption and differential phase measurements using partial reflections; wave interaction; and incoherent scatter. Rocket techniques include differential absorption and Faraday rotation in association with high-resolution dc probes calibrated by means of the radio measurements. The characteristics of the aforementioned techniques are presented, including time and height resolution, accuracy estimates, preferred height ranges, and problems encountered. Electron density profiles obtained with these techniques are presented for comparable solar zenith angles and undisturbed solar and geophysical conditions.
Sechrist, C. F., Jr.↗
Assessment of atmospheric height uncertainties for high precision satellite altimeter missions to monitor ocean currents
The influence of the atmosphere on nadir directed signal associated with satellite altimeters are examined. Frequencies at 6, 13.5, and 35 GHz are selected so as to provide a parameter study. Uncertainties are summarized in both existing and proposed techniques which establish ionospheric and tropospheric height corrections. The error summary thus gives values describing the best you can do in height resolution (as dictated by atmospheric parameters) for a satellite borne altimeter system. The results presented reflect data gleaned from the literature, at large, as well as from the existing body of published literature associated with the Seasat A Altimeter Experiment. Specifically considered are: (1) the effects of precipitation on altimeter signals, (2) range errors due to refractive index variations in both the clear atmosphere (convective and nonconvective) and clouds, and (3) range errors introduced by the ionosphere. A preliminary analysis is pursued establishing the feasibility of incorporating rain rate range gates in a future satellite-borne altimeter system.
Goldhirsh, J.↗
What Processes are Defining the Ionospheric Conductivity and its Variability During Geomagnetic Disturbances?
Modeling of electrodynamic coupling between the magnetosphere, ionosphere, and upper atmosphere (MIA) depends on accurate specification of ionospheric conductance produced by auroral precipitation of high-energy electrons and ions. The precipitation of energetic electrons into the ionosphere is the result of a three-step process that relies on the proper selections of the simulation tools for the ionospheric conductivity studies, while observation can only measure the results of the three steps. In the region of diffuse aurora, the first step is the initiation of electron precipitation into both magnetically conjugate foot points from the Earth’s magnetosphere via wave-particle interactions. The second step is the multiple atmospheric backscatters (or reflections) of electrons at the two magnetic conjugate points, which produces secondary superthermal electron fluxes. The third step is namely the self-consistent electric and magnetic fields that influence magnetospheric particle transport and re-distribute precipitating electrons and ions through the ionospheric electrodynamics. These steps are especially important for revealing electron precipitation dynamics that carry most of the energy in the aurora, resulting also from ion precipitation production and the formation of ionospheric conductance during geomagnetic disturbances. We demonstrate all above results based on SuperThermal Electron Transport (STET), Superthermal Proton, Electron and Atomic Hydrogen tRansport in the Ionosphere and Thermosphere (SPEAH-RIT), and Comprehensive Inner Magnetosphere and Ionospere (CIMI) codes developed at NASA Goddard Space Flight Center.
George V. Khazanov↗
Kinesonde observations of ionosphere modification by intense electromagnetic fields from Platteville, Colorado.
Observations by the Kinesonde (a multifrequency, spaced antenna, digitized complex-amplitude radio sounding system) of ionospheric responses to excitation by the high-power transmitter at Platteville, Colo., are described. Increases of echo scintillation rate and intensity at frequencies reflected near and far from the excitation level are shown. Significant onset delays of these responses suggest disturbance propagation velocities of a few kilometers per second. Calculated echolocations show a time-dependent development toward the excitation region, again with a delayed response. Comments are offered regarding the relative utility of ionogram and Kinesonde observations for study of these phenomena.
Wright, J. W.↗
HF sideband generation in the ionosphere
The temporal development of sidebands excited near sunrise by two strong HF waves separated by a few hertz is presented. Sidebands are not observed before sunrise when the ionospheric critical frequency is less than the heater frequency. As the ionospheric density increases following sunrise and overdense conditions are established, strong sidebands emerge. Even though these results favor a mechanism which phase modulates the reflected HF wave over one which first downconverts the HF power to ULF before exciting sidebands, it is possible that either mechanism could at times contribute to sideband production.
Noble, S. T.↗