Effective Loss Rate Research Articles

E-region effective electron loss rates and electron temperatures under different solar flare conditions

Presuming the total life-time for recombination of molecular ions with electrons remains constant at each altitude under different solar flare conditions, one can estimate the mean dissociative recombination coefficient and the electron temperatures, with a knowledge of the quiet time recombination coefficient and the production rate profiles under these conditions. To estimate the electron temperatures, the temperature dependence of the form (300/T e )1/2 for the electron loss coefficient has been assumed. The computations show very high electron temperatures below about 130 km for the representative solar events considered.

A new technique for estimating D-region effective recombination coefficients under different solar flare conditions

Under solar flare conditions, the intensity of the solar X-rays below 10 A increases by several orders of magnitude, while the increase in intensity of H-Lα is small. Photo-ionization rates in the various wavelength bands in theXUV spectrum have been presented graphically as a function of altitude under quiet, M3, X4, and outstanding flare conditions to show the relative importance of solar X-rays below 10 A in the height range between 50 and 90 km. Presuming the total time constant for recombination of the ions with electrons remains constant at each altitude under different flare conditions, one can obtain the effective recombination coefficient ψeff under these conditions with a knowledge of the quiet time recombination coefficient, the production rate profiles and λ profiles. The importance of the ratio λ of negative ions to electrons below 70 km in lowering the effective electron loss rates has been highlighted.

On solar radiation-driven surface transport of sodium atoms at Mercury

The ballistic motion of the exospheric sodium atoms on the surface Mercury is modeled, taking into account the solar radiation pressure acceleration and partial surface thermal accommodation. The Monte Carlo simulations show that there should be a significant degree of limb brightening as well as brightness enhancement over the poles. To maintain the observed sodium optical emission, a surface production rate on the order of 5-9 x 10 to the 24th atoms/s is needed. It is also found that, under the present set of assumptions, a reasonable agreement can be reached between theoretical results and ground-based measurements for the dependence of the disk-averaged abundance of the sodium atoms on the solar radiation pressure acceleration. If the low-altitude portion of the planetary surface is shielded from the magnetospheric convective electric field, the effective loss rate of the sodium atoms via photoionization and magnetospheric pickup may be reduced to about 2 x 10 to the 24th atoms/s, with the polar regions acting as the main area of ion outflows. 14 refs.

Comparison of parameterized nitric acid rainout rates using a coupled stochastic‐photochemical tropospheric model

A major tropospheric loss of soluble species such as nitric acid (HNO3) results from scavenging by water droplets. Several theoretical formulations have been advanced which relate an effective time independent loss rate for soluble species to statistical properties of precipitation such as the wet fraction and length of a precipitation cycle. There is not enough data available on trace species concentrations to test the computational results of alternative loss rate models against observations. Therefore in this paper, various “effective” loss rates that have been proposed are compared with the results of detailed time dependent model calculations carried out over a seasonal time scale. The model which we have developed for this purpose is a stochastic precipitation model coupled to a tropospheric photochemical model. The results of numerous time dependent seasonal model runs are used to derive numerical values for the nitric acid residence time for several assumed sets of precipitation statistics. These values are then compared with the results obtained by utilizing theoretical “effective” loss rates in time independent models.

A method for estimating muon production and penetration through a shield

An approximate expression is derived that describes muon production by high-energy protons and the subsequent attenuation of the muons in a shield. It is shown that the muon flux at x ahead of an interaction by a proton of energy ϵ GeV and where pions have a path length of Δ m in which to decay, will be given by: φ=8.5×10 −2 εΔ x 2 e −( αt ε ) μ/ m 2 , where t is the shield thickness in m and α is an effective muon energy loss rate which has a value of 22 GeV/m for iron and 7.8 GeV/m for concrete. It is further shown that the effective muon attenuation mean-free path is equivalent to 1 16 of the range of a muon with the energy of the interacting proton. The width of the muon beam that passes through the shield is also considered and it is shown that the beam profile approximates a Gaussian distribution with a diameter at half-maximum intensity of: d= 4.6x εαt m . Calculated muon fluxes are shown to correspond reasonably with those obtained by more sophisticated computer methods for proton energies up to at least 30 GeV and over the entire range of shield thicknesses of interest for radiation safety. Results of measurements of muon levels behind beam dumps under various conditions are presented and are shown to be in reasonable agreement with predictions based on the above model.

Bremsstrahlung spectra from thick-target electron beams with noncollisional energy losses

A generalization of the Brown's (1971) formulation of the relationship between bremsstrahlung spectrum and mean electron spectrum (electrons in the range 10-100 keV) is presented with an objective of demonstrating the information content of bremsstrahlung spectra from a thick target. It is shown that the observed photon spectrum can be inverted to yield an integral functional of the electron spectrum and the effective energy loss rate. Furthermore, if observational or theoretical electron injection spectrum is known, an effective 'phenomenological' energy loss function can be obtained.

Variations of the Electron Density and the Effective Electron Loss Rate in the Ionospheric D-region

Variations of the Electron Density and the Effective Electron Loss Rate in the Ionospheric D-region

Modelling of the low-pressure argon positive column

The properties and operating characteristics of the positive column of a low-pressure positive column in argon have been investigated experimentally and theoretically. In the experiments the pressure was varied from 5×10−2 to 1 Torr, the discharge current from 0.2–20 mA, and the discharge tube was 2.6 cm inside diameter. Measurements of the axial electric field, electron density and population in 3P2 metastable states are reported for various discharge conditions. A test is made of the usefulness of a two-moment theory which is applicable in the intermediate pressure range of this work, i.e., in the transition from inertia-limited to mobility-limited flow of ions to the wall, for the prediction of the operating characteristics. For this purpose, the electron excitation and ionization rates, and transport parameters were calculated from the homogeneous Boltzmann equation. The predicted similarity laws for the positive column are in reasonable agreement with the measurements only in the lower pressure region, i.e., for a pressure-radius product less than about 0.1 Torr cm. The discrepancy between theory and experiment at the higher pressure is, presumably, the result of our failure to correct the calculated ionization rate and effective electron loss rate for the effects caused by ionization from metastables and by space-charge fields.

Computer modelling of theta pinch behaviour with plasma column rotation

In order to simulate a theta pinch experiment in which the rotational energy is estimated to be comparable to the thermal energy, plasma column rotation is included through the radial pressure balance equation in a zero-dimensional, time-dependent computer model with a diffuse density profile. It is found that rotational pressure results in a suppression of the internal magnetic field, leading to an increase in the rate of flux diffusion and ohmic heating. The major effect of rotation is to increase the predicted temperature. Comparison of computer simulations with experimental temperatures at mid-plane indicates that temperature predictions of the computer simulations agree better with rotation effects included. Other features of the experiment, such as effective length and particle loss rate, are consistent with the simulation.

Narrow components in the profiles of ultraviolet resonance lines - Evidence for a two-component stellar wind for O and B stars

The presence of narrow, shifted absorption features superposed on the wide P Cygni profiles of the UV resonance lines in the spectra of O and B stars is studied and possible explanations of the narrow components are discussed. Spectra from 26 stars of spectral types O4f to B1 Ib were examined for the presence of narrow components in the absorption part of the profiles, and positive evidence was detected in 17. The central velocities of the features are found to be similar for different ions of the same star, and typically equal to 0.75 times the terminal velocity of the stellar wind. The width of the narrow absorptions is about 18% of the terminal stellar wind velocity, with a column density generally not correlated with the effective temperature or mass loss rate. Possible explanations for the narrow components include peaks in the degree of ionization, a stationary stellar shell, a plateau in the stellar wind velocity law, a decelerating stellar wind, a variable mass loss rate or a two component stellar wind with low-velocity, low-density material found at a distance greater than 2 stellar radii, which explanation appears most likely.

Ion production and effective loss rate in the mesosphere and lower thermosphere during the Western European Winter Anomaly Campaign 1975/76

As part of a campaign to study the middle latitude ionosphere during winter anomaly conditions, rocket ‘salvoes’ were launched from ‘El Arenosillo’, Spain, on 4 and 21 January 1976. On each of these days the rocket instrumentation measured solar X-ray and H-Lyman-α intensities, energetic particle precipitation, and also the height distribution of the minor constituents NO and O 2( 1Δ g) . On this basis the ion production q( h) in the height range 50–120 km was estimated. The main contribution to q( h) were X-rays (above 90 km), H-Lyman-α (70–90 km), ionization of O 2( 1Δ g (80–90 km), particles, and galactic cosmic rays (below 70 km). Combining the ion production with simultaneously measured values of electron density N ϵ ( h) an estimate of the effective electron loss rate ψ(h) = q N ϵ 2 was obtained. On both days, ψ( h) showed a characteristic rapid decrease from values about 10 −11–10 −10 m 3s −1 below 78 km to values in the range 2 × 10 −13–3 × 10 −12m 3s −1 above this height.

Integrated production and effective loss rates in the ionosphere

The total electron content data obtained at Ahmedabad through the Faraday fading records of the radio beacons abroad the satellites Explorer 22 and 27 are used to determine the overhead integrated production rate (Q 0) and integrated loss coefficient (β′) for the epoch 1965–1968. The production rate (Q 0) is shown to have two peaks during a year around the equinoctal months and for a particular monthQ 0 increases linearly with the 10·7 cm solar flux. The loss coefficient β′, too, has two equinoctial peaks within a year. The semiannual variations ofQ 0 and β′ are discussed in relation to similar variation in the [O]/[N2] ratio.

Coordinated measurements of ELF transmission anomalies and the precipitation of energetic particles into the ionosphere

Stimulated by previous findings of a positive qualitative correlation between anomalous ELF signal levels and the occurrence of significant fluxes of precipitating energetic particles, coordinated exercises were conducted between satellite measurements of the precipitating particles and ELF transmissions between the US Navy Wisconsin Test Facility and receiving stations in Maryland, Greenland, Norway, and Italy. Significant fluxes of precipitating electrons were often measured with the Lockheed pay load on the polar‐orbiting satellite 1972–076B. In March‐April 1976 the received signal strengths were found generally to increase during periods when the geomagnetic K indices were higher and when the fluxes of precipitating electrons >160 keV were greater on the average. During other coordinated exercises in March‐April 1975 the general correlations were less evident. Based on the fluxes, energy spectra, and pitch‐angle distributions of the particles, ion‐pair production profiles have been calculated and electron density profiles subsequently obtained with application of known effective electron loss rates. From the coordinated data, correlative studies between signal strengths and electron density profiles have been performed with use of an ELF waveguide mode computer program developed at the Naval Ocean Systems Center. The propagation path to each station of interest is segmented into different regions with an averaging perpendicular to the direction of propagation of the waveguide parameters. With the inclusion of data from several stations, the transmission signal strengths could be studied simultaneously under a variety of ionospheric conditions. The waveguide computer program calculations indicated that energetic electron precipitation events may cause a signal enhancement or degradation, depending upon where the disturbance is occurring along the path. The consistent occurrence during electron precipitation events of signal strength anomalies in either direction is supported by the coordinated satellite/ELF station measurements.

The winter anomaly in ionospheric absorption and the D-region ion chemistry

A detailed analysis of the D-region ion composition measurements performed by Zbinden et al. (1975), during a winter day of high ionospheric absorption, has been carried out. The study examines the interactive mesosphere- D-region processes which occur in such anomalous conditions and their implication for water cluster ion chemistry. Two clustering regimes for NO + have been observed in the data. Association with N 2 is identified as the dominant process below 76 km. Between 76 and 78 km altitude the effective loss rate of NO + drops by two orders of magnitude. Above 77 km, the three-body reaction NO + + CO 2+M→NO +CO 2+M seems to be the main NO + loss. A mesospheric temperature profile could be derived from the ion composition data. This indicates the presence of a strong inversion above 76 km altitude. The wavelike structure obtained, is shown to be consistent with in situ winter temperature measurements. The sharp suppression of the N 2 association reaction could, thus, be explained by an increase in the collisional break-up of the NO +N 2 ion because of the enhanced temperature. In conclusion, our study indicates that, besides the increase in the production of NO + and O 2 +, due to an enhancement in the minor ionizable constituents, an additional thermal mesosphere- D-region interaction seems necessary to explain this winter anomalous ion composition data.

Simultaneous satellite and radar studies of theDregion ionosphere during the intense solar particle events of August 1972

During the intense solar particle events of August 3–11, 1972, 28 cases of simultaneous data were obtained between the polar-orbiting satellite 1971-089A and the incoherent scatter radar at Chatanika, Alaska. Effective electron loss rates (ψ) in the D region ionosphere have been derived as a function of altitude, solar zenith angle (χ), and the magnitude of the production rate (Q). Production rate profiles extending from 3 × 10² to 3 × 104 ion pairs/cm³ s were calculated for the 40- to 90-km region. Electron density profiles extending from 5 × 10³ to 105 el/cm³ were measured, useful data being obtained down to altitudes as low as 50 km. Values of ψ were obtained for daytime and sunrise/sunset conditions over a range of solar zenith angles from 50.4° to 98.6°. A strong diurnal dependence in ψ was observed only at altitudes below 80 km. Twilight values of ψ at the lower altitudes were over an order of magnitude larger than the daytime values. Between 70- and 90-km altitude the present polar summer daytime values of ψ are significantly larger than those obtained in the winter daytime event of November 2, 1969. Near 80-km altitude the present results are consistent with the dominant ions being the hydrated ions H3O+ (amu = 19) and H3O+·H2O (amu = 37). A strong seasonal dependence in the effective loss rates has therefore been established. A pronounced asymmetry in ψ and Ne between the sunrise and sunset twilights was measured at altitudes <80 km, the electron density at sunset being larger than at sunrise at the same solar zenith angle. The altitude behavior of ψ and the temporal leads and lags measured in the transitions between twilight and day were found to be consistent with the interaction of the solar visible and ultraviolet wavelengths with the ozone layers above the earth, leading to the sunrise increase and sunset decay of O and O2(¹Δ). The dependence of ψ on the magnitude of the production rate during the day was found to be weak, a slight positive dependence being measured at altitudes <63 km.

A coordinated study of energetic electron precipitation andDregion electron concentrations over Ottawa during disturbed conditions

This article presents the results of a study of the energetic electron precipitation as well as important parameters of the D region over Ottawa (45°N, 76°W) during lightly to moderately disturbed conditions, using data for the period following the December 17, 1971, magnetic storm as well as data obtained on other selected days exhibiting anomalous D region absorption. Following the December 17, 1971, storm, significant fluxes of precipitating electrons of > 130 keV were observed near Ottawa, even during the poststorm period on December 20, when the geomagnetic activity had subsided (∑ Kp = 6). The excess ionization detected at D region altitudes above Ottawa can be explained as being due to ionization from a prolonged electron drizzle from the outer radiation belt. For the first time it has been proven that precipitating electrons from the radiation belt were the main cause of D region poststorm conditions of middle latitudes. The ground-based radio probing measurements of the free electron concentration have been coordinated with simultaneous satellite observations of the quasi-trapped and precipitating electron environment above the site. From the ground-based measurements, by using the partial reflection technique at two frequencies (2.66 and 6.275 MHz), electron concentration profiles for altitudes between ≈ 60 and 90 km have been derived at times when the low-altitude polar-orbiting satellite 1971-089A passed near Ottawa. On board this satellite, electron differential fluxes in 260 channels and at two pitch angles were measured at energies between ≈1 and ≈2800 keV. The ion pair production rate height profiles due to precipitating electrons were computed for D region heights by using nonisotropic energy-dependent pitch angle distributions. Effective electron loss rates were deduced for heights between 63 and 91 km. These results indicate a significant variability in loss rates in the altitude range 75–85 km.

A Saturnian gas ring and the recycling of Titan's atmosphere

Atoms which escape Titan's atmosphere are unlikely to possess escape velocity from Saturn, and can orbit the planet until lost by ionization or collision with Titan. It is predicted that a toroidal ring of between ∼1 and ∼10 3 atoms or molecules cm −3 exists around Saturn at a distance of about 10 times the radius of the visible rings. This torus may be detectable from Earth-orbit and detection of nondetection of it may provide some information about the presence or absence of a Saturnian magnetic field, and the exospheric temperature and atmospheric escape rate of Titan. It is estimated that, if Titan has a large exosphere, ∼97% or more of the escaping atoms can be recaptured by Titan, thereby decreasing the effective net atmospheric loss rate by up to two orders of magnitude. With such a reduction in atmospheric loss rates, it becomes more plausible to suggest that satellites previously thought too small to retain an atmosphere may have one. It is suggested that Saturn be examined by Lyman-α and other observations to search for the gaseous torus of Titan. If successful, these could then be extended to other satellites. The effect of a hypothetical Saturnian magnetosphere on the atmosphere of Titan is investigated. It is shown that, if Saturn has a magnetic field comparable to Jupiter's (∼10 G at the planetary surface), the magnetospheric plasma can supply Titan with hydrogen at a rate comparable to the loss rates in some of the models of Trafton (1972) and Sagan (1973). A major part of the Saturnian ionospheric escape flux (∼ 10 27 photoelectrons sec −1) could perhaps be captured by Titan. At the upper limit, this rate of hydrogen input to the satellite could total ∼0.1 atm pressure over the lifetime of the solar system, an amount comparable to estimates of the present atmospheric pressure of Titan.

D-region recombination coefficients and the short wavelength X-ray flux during a solar flare

VLF phase and amplitude measurements were made on five different frequencies at São Paulo, Brazil during a solar flare which occurred on 22nd January 1972. The phase and amplitude measurements during the decay phase of the flare were combined with the full wave solutions of Wait and Spies (1964) to calculate the recombination coefficient in the lower ionosphere. The values thus obtained are lower than those reported by Reid (1970), but are compatible with those reported by Montbriand et al. (1972) during Solar X-ray events. The effective loss rates have been utilized to calculate the ion-production at the maximum of the flare, which in turn has been utilized to calculate the incident X-ray flux as a function of wavelength at the maximum of the flare. Extensions to the calculations are discussed.

Electron content and other related measurements for a low latitude station obtained at sunspot maximum using a geostationary satellite

Electron content measurements have been made at Hong Kong (lat. 22.2°N, dip 30°) for the period July 1967–December 1968 by continuously recording the polarisation angle of a signal from the geostationary satellite Syncom 3. Monthly median peak diurnal contents exhibited a semi-annual variation with maxima occurring at the equinoxes and a ‘winter anomaly’ effect was noted during the daytime. However this latter effect was not apparent for midnight values, though the semi-annual variation remained. The rate of increase in content with solar flux since 1964-5 was greatest for the winter and during this season the measured scale heights were also greatest, thus possibly implying a seasonal increase in the composition ratios [O][O2] and/or [O][N2]. Good short term correlation between the daily peak electron content and the daily solar flux has been established. The equivalent thickness exhibited a broad daytime increase during the summer but at other seasons sharp peaks occurred after sunset and before sunrise. The present results showed no seasonal variation of equivalent thickness, in contrast with the summer maximum obtained using data from lower height transit satellites; and also appreciably higher winter content values have been obtained with geosatellite data. A possible explanation of these facts may be that there is a significant increase of ionization above 1000 km during the winter season. No increase of equivalent thickness was observed between sunspot minimum and maximum. The integrated production rate for an overhead sun roughly followed a similar seasonal variation to that of the peak content if allowance was made for the solar flux control, which was found significant only during the winter. The zenith angle of the Sun corresponding to initial ionization was observed to vary between 97.0° in winter to 93.5° in summer. After sunset the ionosphere was found to decay in two stages giving two distinct effective loss rates with different seasonal variations. In interpreting these results it has been considered likely that after sunset during the equinoxes Mitra drifts of ionization occurred moving ionization from the magnetic equator to Hong Kong and around midnight during the summer a further appreciable influx of ionization occurred.

Effective Electron Loss Rates in the Lower D Region During the Decay of Solar X‐Ray Flare Events

The ionization changes that occur during solar X‐ray (SXR) flares have been used to study electron loss rates at low altitudes in the D region. The electron production from SXR radiation was calculated from fluxes obtained by SOLRAD 9, and the changes in the ionization densities were measured by the partial‐reflection technique. Effective loss rates were determined at various heights during the SXR flare effect and for several sizes of flares at different times of the year. The rate values obtained were lower than those reported by Reid [1970], and are interpreted as resulting from a destruction of large water cluster ions during the initial stages of the SXR flare effect. These cluster ions have fairly large effective loss rates, and their disappearance would result in a reduced effective loss rate.