Effective Recombination Coefficient Research Articles

Ionospheric Effects of Cosmic γ-ray Bursts

It has been suggested that the recently discovered bursts of gamma rays of cosmic origin might produce observable ionospheric effects. Since gamma rays are absorbed at a relatively low altitude compared with most other types of ionising radiation it was thought that these bursts would produce additional ionisation that might be strong enough to affect vlf radio propagation, and if data from several paths were obtained it might be possible to obtain information concerning the location of the sources. Calculations are reported that were made using a Monte Carlo code that was developed to calculate x-ray and gamma -ray transport in a model atmosphere. Above 120 km the atmosphere is assumed to show negligible proton attenuation. Several simplifying assumptions were made concerring the nature of the source, and the spectrum was assumed to be independent of time. It is considered that the best chance of observing the bursts would be at low geomagnetic latitudes, where the ionisation induced by galactic cosmic rays would be of lower magnitude than that produced by the burst. The burst would produce only a very transient effect, since at the altitudes at which peak ionisation occurs the effective recombination coefficient is a very rapidly increasingmore » function of decreasing altitude. This requires that data be recorded on a finer time scale than is usually the case, as for example when the effects of geomagnetic activity are being studied. (UK)« less

E-region model parameters

The formation of any E-region model is dependent upon a number of key parameters some of which are reviewed in this paper. Particular emphasis is placed on the mean dissociative recombination coefficient of the -region, α M , the most important E-region parameter. It appears that 3 × 10 −7 (300/ T) cm 3 sec −1 is a reasonable value for α M , based on laboratory measurements. Ionospheric studies yield α E , the effective recombination coefficient of the E-region, the deduction of which appears to have suffered from various inadequacies in the past. While normally α E = α M , it is shown how they sometimes differ. Ionization of NO by the direct H Lyman-α flux is significant at twilight, and ionization of NO by scattered H Ly-α is important below about 100 km at night. The E-region above 100 km at night is apparently maintained by H Ly-β. The interrelationships between α E , α M , NO, H Ly-α and H Ly-β during night and twilight are stressed. Electron precipitation is not thought to be a common source of the mid-latitude night-time E-region and it is demonstrated how the presence of a night-time meteor ion layer can lead to erroneous conclusions concerning the source. The influence of transport is briefly discussed as well as some effects of the O O 2 ratio.

Electron and positive ion density altitude distributions in the equatorial D-region

Simultaneous measurements of D-region ionization sources and electron and ion densities have been made in one day aboard three rockets. Electron density profiles for solar zenith angles of 53.2, 27.8 and 48.3° are displayed. The profiles are found to be quite similar to those reported for midlatitudes under non-winter quiet conditions. Simultaneous measurement of the X-ray flux together with NO ionization estimates based on recent measurements of NO by Meira (1971) and O 2( 1Δ g) ionization rates by Huffman et al. (1971), are used to compute the ion-pair production rate. It is demonstrated that the charged particle distribution can be explained using this production rate and an effective recombination coefficient compatible with recent laboratory measurements of the dissociative recombination coefficient for electrons with hydrated cluster ions.

Ionospheric effects of solar flares—VI. Changes in D-region ion chemistry during solar flares

Evidence has been presented by Rows et al. (1970) and in some of the preceding papers of this series showing a drastic decrease of the effective recombination coefficient during solar flares. In this paper, the sixth in the series, we examine the nature and magnitude of the decrease as a function of flare flux, develop model recombination coefficient profiles for different flare conditions, and then offer a theory of how these decreases can occur. A new ion chemical scheme consisting of a six-ion (four positive and two negative) model is presented. It is shown that this decrease is due to different relative increases in the electron density and the negative ion density, or to a change in the dominant positive ion from a complex hydrated ion with a large recombination coefficient to a simple ion with a smaller recombination coefficient. At 70 km the former effect seems to be operating, while at 80 km the latter effect operates.

Measurement of E‐Layer Effective Recombination Coefficient During Solar Flares

Simultaneous measurements of flare‐enhanced electron density in the E layer and of flare‐enhanced solar X‐ray flux were used to evaluate the ionospheric relaxation time constant at E‐layer heights. The method is an extension of Appleton's ionospheric “filter” idea to the case in which radiation flux and electron density fluctuations are simultaneously measured. Electron density measurements were made using the Thomson scatter technique at the National Astronomy and Ionosphere Center, Arecibo, Puerto Rico. X‐ray flux data in the 2‐ to 12‐Å band were obtained from instruments aboard the Explorer 33 satellite. Measured values of time constant were converted to an effective recombination coefficient using the familiar Appleton formula and known values of the ambient electron density. Values for the effective recombination coefficient of the order 10−7 cm3/sec were obtained at E‐layer heights.

Ionization changes in the lower ionosphere during the solar eclipse of 7 March 1970

Measurements in the lower ionosphere (65–150 km) of 2.66 MHz differential absorption and of Langmuir probe currents were obtained using four rockets launched in Nova Scotia, Canada during the 7 March 1970 solar eclipse. It was found that the eclipse caused a maximum decrease in the electron number density by more than a factor of 10 below 80 km, but by only 3–5 above 85 km. Below 80 km, the smallest densities were observed on the third flight, 7–20 s after 3rd contact, and the D-region ledge between 65 and 75 km had disappeared. On the last flight, 360 s later, this ledge had begun to redevelop; however, the lowest densities in the 85–90 km and 125–150 km ranges were observed on this flight. Densities of about 60 electrons cm −3 at 80 km, 700 at 85, 7000 at 95 and 30,000 above 105 km were the minimum ones recorded. The paper compares these electron number densities to those measured at night by other experiments. The height dependence of the rate of disappearance of electrons leads to values of the effective recombination coefficient which decrease from about 10 −4 cm 3 s −1 at 80km to 3 × 10 −7 cm −3 s −1 at 95 km and indicates an increase in the ratio of negative ions to electrons below about 80 km.

Recombination and Ionization in a Molecular-Ion-Dominated Helium Afterglow

An intense source of free electrons has been observed to strongly influence the time history of the electron density in a high-pressure (> 15-Torr) helium afterglow. The electronic recombination coefficient $\ensuremath{\alpha}$ of molecular helium ions was measured by utilizing this source and was found to be over five times larger than the effective recombination coefficient obtained by equating the net loss rate of free electrons to the recombination loss rate in the usual manner. If $\ensuremath{\alpha}$ is assumed to be of the form $\ensuremath{\alpha}={\ensuremath{\alpha}}_{0}+{k}_{p}p$, then ${\ensuremath{\alpha}}_{0}=1.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}$ ${\mathrm{cm}}^{3}$ ${\mathrm{sec}}^{\ensuremath{-}1}$ and ${k}_{p}=4.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}$ ${\mathrm{cm}}^{3}$ ${\mathrm{sec}}^{\ensuremath{-}1}$ ${\mathrm{Torr}}^{\ensuremath{-}1}$ over the pressure range from 15 to 56 Torr. A model is presented which indicates that ionizing metastable-metastable collisions are responsible for the source of free electrons.

Ionospheric effects of solar flares—V. The flare event of 30 January 1968 and its implications

From riometer and pulse absorption measurements on three frequencies for the large X-ray flare event that occurred on 30 January 1968, electron density profiles are derived for the entire course of the flare. The time variation of the electron production rate is obtained for this event from satellite measurements of X-rays in the bands 0–3 A, 0–8 A and 8–20 A. A comparison of these profiles with the electron production rates deduced from the X-rays reveals a decrease in the effective recombination coefficient or of the negative ion to electron ratio λ, in agreement with the results reported by Rowe et al. (1970).

Theoretical Estimate of the Effective Recombination Coefficient in the D Region

In the presence of a large number of positive and negative ionic species, an analytical expression for the effective recombination coefficient of electrons in the D region is derived in the same from, a' = + lambda ( alpha /sub ion/), as is customarily used in the uppe r regions. Here, ( alpha /sub e/) is the electronic recombination coefficient averaged with weights proportional to the abundance of various kinds of positive ions, and ( alpha /sub ion/) is the weighted mean of the various ionic recombination coefficients according to the composition of positive and negative ions. The effective loss rate of electrons is given as (1 + lambda )a' in which the negative ion-electron ratio, lambda , changes in a wide range as a function of altitude. Under the assumption of a model atmosphere containing eight minor constituents, the density distributions of thirteen species of positive ions and seven species of negative ions as well as of electrons are calculated. Based on the result, the effective recombination coefficient is estimated to be 4.2 x 10/ sup -7/ cm/sup 3/ sec/sup -1/ a t the 80 km-level, 1.5 x 10/sup -6/ cm/sup 3/ sec/ sup -1/more » at 70 km, and 1 9 x 10/s up -5/ cma sec/sup -1/ at 60 km, while lambda increases rapidly with decreasing height, being about 5.3 x 10/sup -3/ at 80 km, 7.9 x 10/sup -1/ at 70 km, and 1.0 x 10/sup -1/ at 60 km in a daytime condition. The effective loss rate estimated is shown to be consistent with the results derived from observations of solar eclipse, SID, and PCA events. (auth)« less

Study on the Solar Activity Dependence of the E Region Peak Electron Density and Some Atmospheric Parameters

The sunspot number (R) dependence of the E region maximum electron density (Nm) near noon is studied under the form Nm=N00√1+ρeR (cosχ)(1+Γ)/2, based on f0E obtained at 28 stations around the world. It is found that (1) the N00 for intermediate latitudes is lower than that for low latitudes, and greater in winter than in summer, (2) the N00 for high latitudes is much lower, (3) two groups having different N00's exist in low latitudes, and (4) the ρe always increases with χ irrespective of seasons and latitudes. Based on some theoretical investigation, the difference in atmospheric temperature due to seasons and latitudes is discussed and some arguments are given on the height dependence of the effective recombination coefficient. Finally, empirical formulae to give Nm as a function of R and χ for different seasons and latitudes are tentatively given.

Study of Sudden Cosmic Noise Absorption in Relation to Corresponding X-Ray Flares

In this paper an exhaustive study of X-ray flare which occurred on 13 April 1966 between 0706 and 0716 UT has been made. Raw data for this X-ray flare have been converted to the flux energy in erg cm−2 sec−1 and the corresponding time curves have been plotted. N-h profiles for the D-region for χ values of 30°, 50° and 60° have been worked out at the maximum of the flare. N-h profiles for the χ values of 50° and 60° correspond respectively to Manila and Ondrejov.The SCNA data for Manila on 18 Mc/s and for Ondrejov on 29 Mc/s have been employed to work out a model of effective recombination coefficient (αeff).The height of maixmum electron density comes to about 72 km and the corresponding maximum of absorption is found to occur at about 68 km. This is in agreement with the result of Mitra et al. (1966).

The decay of optically thick helium plasmas, taking into account ionizing collisions between metastable atoms or molecules

The effective recombination rate of a helium afterglow plasma, which is optically thick towards the resonance lines, is calculated from the coupled rate equations for the number densities of free electrons and of metastable atoms or molecules. The model employed is a neutral plasma consisting of one kind of ion and one kind of metastable. The ions are lost by electron-ion recombination only, with subsequent formation of metastables, which are then deactivated in collisions with free electrons or with other metastables: in the latter case one electron is regained to the free state. When the rate constants for these various processes are time independent, it is found that after a certain transition time a transient equilibrium between the number densities of electrons and metastables is attained. In a dense afterglow plasma, where the recombination coefficient may be large, the transient equilibrium density of metastables may become significantly higher than the quasi-equilibrium value obtained by equating the time derivative of the metastable density to zero, and the effective recombination coefficient may be reduced by much more than a factor of two.

Study on Electron Density Profile in the Lower Ionosphere

The daytime N(h) profiles in the E and D regions are obtained for summer, spring and fall, and winter, based on data available from rocket experiment. The profiles cover the periods of low, medium and high solar activity.The Nmax in the normal E region obtained by routine ionosonde observation is studied to compare with the rocket data and to obtain the solar activity dependence of Nmax or Φ0, the solar photon flux density at λ=1025.7A and 977A, which controls the Nmax in the E region. From the satellite observation of the solar X ray flux at λ=1-8A, the solar activity dependence of the X ray flux, which controls the ionization at the lower part of the E region, is tentatively estimated.Based on the result of the above study the N(h) profiles are calculated, following the current theory of the E region formation, for each case of the observed N(h) profiles as described above. Fairly good agreement is found between the theory and experiment. Thus we can know the N(h) profile for any season in any solar activity.Some nighttime profiles are studied from rocket data and the nocturnal variation of the N(h) in the E region is obtained. Based on this result the electron production rate of geocorona, a possible nighttime source of ionization, and the effective recombination coefficient are estimated.Finally the N(h) profile during winter absorption anomaly is calculated, based on some atmospheric temperature models, which are available from actual rocket observations. It is found that the E layer comes down and this enables one to interpret the lowering of the reflection height of the Loran waves during anomaly reported by other workers.

Interpretation of D‐Region Electron Densities

D‐region electron densities measured by rockets during the November 12, 1966, solar eclipse are shown to imply an effective recombination coefficient at an altitude of about 80 km of the order of 10−5 cm3 sec−1. The D‐region electron densities between 65 and 83 km are computed for full‐sun conditions assuming this value of recombination coefficient, the [37+] profile of Narcisi and Bailey [1965], and the NO profiles of Barth [1966], Pearce [1969], and Hesstvedt and Jansson [1969]. Electron densities between 60 and 65 km are estimated on the basis of the above‐mentioned NO profiles and the negative‐ion model of LeLevler and Branscomb [1968]. Also, electron densities between 80 and 90 km are computed by assuming an effective electron‐ion recombination coefficient for NO+ and O2+ of 10−6 cm3 sec−1. There is a reasonable agreement between the computed electron densities and those measured by rockets launched from Wallops Island near 60° solar zenith angle. These results suggest that variability of D‐region electron densities may be caused by changes in H2O vapor concentration induced by atmospheric circulation or eddy transport effects.

A two-ion model of electron-ion recombination in the D-region

This note discusses the effective recombination coefficient, α eff , in a D-region where two positive ions, X 1 + and X 2 +, having different recombination coefficients are present, and where the production rate of the rapidly recombining ion, X 2 +, is proportional to the number density of the more slowly recombining ion species, X 1 +. It is shown, that for the assumed model, the effective recombination coefficient α eff is related to the number density N of free electrons. It is pointed out that this effect may have bearing on a number of problems in our understanding of D-region processes.

VLF phase disturbances, HF absorption, and solar protons in the events of August 28 and September 2, 1966

The VLF phase disturbances and HF absorption observed during the proton events of August 28 and September 2, 1966, were quantitatively connected to the proton intensities, energies, and cutoff latitudes observed by satellite 1963-38C, at 1100 km in a polar orbit. The connection is achieved through considerations that include a model of the ionospheric D region described in terms of an effective recombination coefficient related to the four generalized ionic reactions. The complementary use of the VLF and HF observations tends to reduce ambiguities often present in the formation of D-region models. The VLF is the more sensitive indicator of ionization effects due to solar protons in comparison to the HF absorption (especially at night) because the VLF responds to ionization enhancements over a relatively narrow altitude range varying with the proton energies and intensities.

Comparison of auroral light emission and electron density

Simultaneous measurements of the auroral light emission and the electron density have been made during three rocket flights into auroral glow. The optical measurements were made on the (0–1) First Negative band of N 2 + at 4278 Å, and the volume emission rate vs. altitude has been obtained. The electron density measurements were made by a propagation experiment based upon the Faraday rotation technique. From the observed emission rate of photons Q, the production rate of ion pairs q, is deduced, and assuming equilibrium conditions, the effective recombination coefficient α is derived as the ratio between q and the square of the electron density N. The recombination rates so derived are in fairly good agreement with laboratory measurements.

Some relationships between solar X-ray bursts and SPA's produced on VLF propagation in the lower ionosphere

This paper discusses SPA's measured at long VLF propagation paths in the lower ionosphere and their association with solar X-ray bursts observed by USNRL satellites in the 0–3 A, 0–8 A and 8–20 A bands. Excellent correlations were found between the SPA importances (in degrees per Mm) and the logarithm of the X-ray burst peak intensities. A hardening of the X-ray burst spectra is evident for increasing importance of SPA's; the threshold energy required for the occurrence of such anomalies was estimated, it is 4.3×10−5 ergs cm−2 sec−1 in the main ionizing band of 0–3 A. It was also possible to derive the effective recombination coefficient at the normal D-region height of 70 km, this beingαr≈6×10−6 cm3 sec−1; furthermore ion production rates were estimated during SPA's at heights below the reference level.

A measurement of the effective recombination coefficient in the lower ionosphere

Effective recombination coefficient in lower ionosphere determined from charged particle spectra obtained by rocket sounding in Canada

Origin of water cluster ions in theDregion

Laboratory studies of the ions produced by the addition of water vapor into flowing streams of O2+ (or NO+) ions have led to a vapor phase reaction scheme starting with O2+ that seems likely to be responsible for the formation of the observed water cluster ions H3O+, H5O2+, H7O3+, etc. in the D region of the earth's ionosphere. Experimental difficulties have precluded quantitative rate constant measurements so far, and in addition the D-region water vapor concentration is uncertain so that only a qualitative scheme is possible at this time. The O2(¹Δg) photoionization source recently proposed by Hunten and McElroy is presumed to be the necessary precursor O2+ source. The reaction scheme involves O4+ and O2+·H2O as intermediate ions; these ions are possibly present in observable concentrations in the D region. Nitrous acid (HNO2) production is proposed to be an end result of successive hydrations of atmospheric NO+. The hydration of the atmospheric NO+ and O2+ ions and the formation of O4+ are expected to increase somewhat the effective electron recombination coefficient in the ionosphere.