A semi-empirical approximate method for studying some issues of aeronomy of the ionospheric D-region. III. Detailed analysis of the photochemistry of the environment under conditions of increased ionization

Abstract. A small, 54 MHz wind-profiler radar, MARA, was operated at Troll, Antarctica (72° S, 2.5° E), continuously from November 2011 to January 2014, covering two complete Antarctic winters. Despite very low power, MARA observed echoes from heights of 55–80 km (polar mesosphere winter echoes, PMWE) on 60% of all winter days (from March to October). This contrasts with previous reports from radars at high northern latitudes, where PWME have been reported only by very high power radars or during rare periods of unusually high electron density at PMWE heights, such as during solar proton events. Analysis shows that PWME at Troll were not related to solar proton events but were often closely related to the arrival of high-speed solar wind streams (HSS) at the Earth, with PWME appearing at heights as low as 56 km and persisting for up to 15 days following HSS arrival. This demonstrates that HSS effects penetrate directly to below 60 km height in the polar atmosphere. Using local observations of cosmic-noise absorption (CNA), a theoretical ionization/ion-chemistry model and a statistical model of precipitating energetic electrons associated with HSS, the electron density conditions during the HSS events are estimated. We find that PMWE detectability cannot be explained by these variations in electron density and molecular-ion chemistry alone. PWME become detectable at different thresholds depending on solar illumination and height. In darkness, PWME are detected only when the modelled electron density is above a threshold of about 1000 cm−3, and only above 75 km height, where negative ions are few. In daylight, the electron density threshold falls by at least 2 orders of magnitude and PWME are found primarily below 75 km height, even in conditions when a large proportion of negative ions is expected. There is also a strong dawn–dusk asymmetry with PWME detected very rarely during morning twilight but often during evening twilight. This behaviour cannot be explained if PMWE are caused by small-scale structure in the neutral/molecular-ion gas alone but may be explained by the presence of charged meteoric dust.

Abstract. The influence of atomic oxygen concentration on the height distribution of the main positive and negative ions and on electron density in the mesosphere is studied for the conditions prevailing during the solar proton event on 17 January 2005. It is shown by numerical modeling that the electron and ion density profiles are strongly dependent on the choice of the atomic oxygen profile. Experimental measurements of the electron density are used as the criterion for choosing the atomic oxygen profile in the mesosphere. With the help of modeling, the atomic oxygen profile in the daytime in the winter mesosphere is found to lead to a model electron density profile best matching the electron density profile obtained experimentally. As a result, with the help of modeling, we find the atomic oxygen profiles at various solar zenith angles in the winter mesosphere which lead to model electron density profiles matching the electron density profiles obtained experimentally. Alteration of the atomic oxygen concentration leads to a redistribution of the abundance of both positive and negative ion constituents, with changes in their total concentrations and transition heights. In consequence this results in changes of the electron density and effective recombination coefficient. For conditions of low concentration of atomic oxygen (during a solar proton event), the formation of cluster ions is the key process determining electron and ion densities at altitudes up to 77 km. The complex negative CO3− ion is formed up to about 74 km and the final NO3− ion, which is stable in relation to the atomic oxygen, is the dominant negative ion up to 74 km. As a result the transition heights between cluster ions and molecular ions and between negative ions and electron density are located at 77 km and 66 km, respectively.

Abstract. A numerical model of D-region ion chemistry is used to study the influence of the ozone concentration in the mesosphere on ion-composition and electron density during solar proton events (SPE). We find a strong sensitivity in the lower part of the D-region, where negative ions play a major role in the ionization balance. We have chosen the strong SPE on 29–30 October 2003 when very intense proton fluxes with a hard energetic spectrum were observed. Deep penetration into the atmosphere by the proton fluxes and strong ionisation allows us to use measurements of electron density, made by the EISCAT 224 MHz radar, starting from as low as 55 km. We compare the electron density profiles with model results to determine which ozone concentration profiles are the most appropriate for mesospheric altitudes under SPE conditions. We show that, during daytime, an ozone profile corresponding to depletion by a factor of 2 compared to minimum model concentrations for quiet conditions (Rodrigo et al., 1986), is needed to give model electron density profiles consistent with observations. Simple incorporation of minor neutral constituent profiles (NO, O and O3) appropriate for SPE conditions into ion-chemistry models will allow more accurate modeling of electron and ion densities during such events, without the need to apply a complete chemical model calculating all neutral species.

Relationships Between Cluster Secondary Ion Mass Intensities Generated by Different Cluster Primary Ions

Satellite Communication (SATCOM) systems are greatly susceptible to Electromagnetic Interference (EMI) caused by instabilities in the Ionosphere. In general, these instabilities are naturally occurring geomagnetic storms that are persistent at various regions of the Earth and differing times of the day. An artificial disturbance examined in this paper is the hypothetical occurrence of a High Altitude Nuclear Explosion (HANE) event. The electron density fluctuations induced by a HANE has a profound scintillation effect on wideband signals utilized in SATCOM. A computational model of this principle is established using multiple phase screen theory and a plasma physics based model to simulate nuclear burst effects. The significance of these results demonstrates a first principle approach to characterizing electromagnetic compatibility (EMC) effectiveness for SATCOM systems in a highly unstable Ionospheric environment. In particular, an approach to model lateral propagation paths is proposed utilizing a Chapman function electron density profile combined with computational HANE electron density data. The temporal characteristics such as the average time delay and time jitter from different transmitter and receiver locations at different phases of the nuclear detonation are presented. The results in this paper demonstrate the effectiveness of utilizing V and W frequency bands to minimize these environmental disturbances, achieving a more desired EMC compliant system.

A framework is provided to describe the enhanced sputtering yields and secondary ion yields of molecular fragments, from molecules on substrates, achieved when using cluster primary ions. Analysis of published sputtering yield measurements shows that one particular model of sputtering, which includes the thermal spike, is an excellent quantitative description of the yields for a wide range of monatomic and polyatomic primary ions. The model is valid for describing clusters of up to more than ten atoms over three orders of magnitude in sputtering yield. Using data from one primary ion, extremely good descriptions of measurements reported with other primary ions are achieved. This is then used to evaluate the important molecular ion yield behavior for static secondary ion mass spectrometry based on data for Irganox 1010. Universal dependences for the deprotonated molecular ion yields, valid for all the primary ions studied, both single atom and cluster, over five decades of emission intensity are obtained. This permits the prediction of the (M−H)− secondary ion yield for different, or new, cluster primary ions, e.g., Bin+ and C70+, for the analysis of organic materials. Optimal primary ion sources are predicted and discussed. For analyzing materials, raising the molecular secondary ion yield is extremely helpful but it is the ratio of this yield to the disappearance cross section that is critical for obtaining the maximum useful molecular yield and/or the best spatial resolution for molecular signals from molecular monolayers. Data are evaluated and a description is given to show how this ratio varies with the cluster to provide further universal dependences.

Abstract. Accurate measurements of electron density in the lower D-region (below 70 km altitude) are rarely made. This applies both with regard to measurements by ground-based facilities and by sounding rockets, and during both quiet conditions and conditions of energetic electron precipitation. Deep penetration into the atmosphere of high-energy solar proton fluxes (during solar proton events, SPE) produces extra ionisation in the whole D-region, including the lower altitudes, which gives favourable conditions for accurate measurements using ground-based facilities. In this study we show that electron densities measured with two ground-based facilities at almost the same latitude but slightly different longitudes, provide a valuable tool for validation of model computations. The two techniques used are incoherent scatter of radio waves (by the EISCAT 224 MHz radar in Tromsø, Norway, 69.6° N, 19.3° E), and partial reflection of radio-waves (by the 2.8 MHz radar near Murmansk, Russia, 69.0° N, 35.7° E). Both radars give accurate electron density values during SPE, from heights 57–60 km and upward with the EISCAT radar and between 55–70 km with the partial reflection technique. Near noon, there is little difference in the solar zenith angle between the two locations and both methods give approximately the same values of electron density at the overlapping heights. During twilight, when the difference in solar zenith angles increases, electron density values diverge. When both radars are in night conditions (solar zenith angle >99°) electron densities at the overlapping altitudes again become equal. We use the joint measurements to validate model computations of the ionospheric parameters f+, λ, αeff and their variations during solar proton events. These parameters are important characteristics of the lower ionosphere structure which cannot be determined by other methods.

A one-dimensional ionic-photochemical model of the gaseous composition of the atmosphere that describes the formation of the D layer of the ionosphere is presented. Based on this model, the vertical profiles of the concentration of electrons and ions in the D layer of the ionosphere were calculated, as were the vertical distributions of minor gaseous constituents in the atmosphere up to a height of 86 km for undisturbed conditions and after a powerful solar proton events (SPE) at the end of October 2003. The calculations showed that SPEs significantly increase NOx in the mesosphere of polar latitudes. In the lower mesosphere of polar caps, the NOx mixing ratio increases by 20–50 ppb; in the upper mesosphere it increases by 100 ppb and more. High NOx levels in zones of their formation can be retained for several weeks, producing a long-term but comparatively small ozone decrease in the lower mesosphere. The main ozone decrease is caused by a short-term HOx increase after SPEs and is also of a short-term character in the conditions of the illuminated mesosphere. After the SPE in October 2003, model calculations yield an ozone concentration decrease by 40% in the middle and upper mesosphere at 75 ° S and by 70% at the same heights at 70 ° N. The results of modeling NOx and O3 changes after the SPE in October 2003 agree well with the data of satellite measurements. The changes in minor gases of the mesosphere after the SPE obtained in the model with parameterized sources of HOx and NOx are compared with their changes obtained in the complete ionic-photochemical model. The changes in HOx, NOx, and O3 coincide rather well, whereas the changes in ClO noticeably differ, especially in the lower mesosphere. Thus, at a height of about 60 km, the parameterized photochemical model underestimated twofold the ClO formation after the SPE.

Satellite Communication (SATCOM) systems are greatly susceptible to Electromagnetic Interference (EMI) caused by instabilities in the Ionosphere. In general, these instabilities are naturally occurring geomagnetic storms that are persistent in various regions of the Earth and differing times of the day. An artificial disturbance examined in this chapter is the hypothetical occurrence of a High Altitude Nuclear Explosion (HANE) event. The electron density fluctuations induced by a HANE have a profound scintillation effect on wideband signals utilized in SATCOM. A computational model of this principle is established using multiple phase screen theory and a plasma physics-based model to simulate nuclear burst effects. The significance of these results demonstrates a first principle approach to characterizing electromagnetic compatibility (EMC) effectiveness for SATCOM systems in a highly unstable Ionospheric environment. In particular, an approach to model lateral propagation paths is proposed utilizing a Chapman function electron density profile combined with computational HANE electron density data. The temporal characteristics such as the average time delay and time jitter from different transmitter and receiver locations at different phases of the nuclear detonation are presented. The results in this chapter demonstrate the effectiveness of utilizing V and W frequency bands to minimize these environmental disturbances, achieving a more desired EMC compliant system.

We have studied the short‐term effect of the October–November 2003 series of solar proton events on the middle atmosphere. Using the proton flux measurements from the GOES–11 satellite as input, we modeled the effect of the precipitating particles between 26 October and 6 November with a one–dimensional ion and neutral chemistry model. Then we compared the results with ground‐based radio propagation measurements, as well as with NO2 and ozone profiles made by the GOMOS satellite instrument. The very low frequency signal experiences up to −7 dB absorption during the largest solar proton event, subsequently varying with time of day during the recovery phase. The model and radio propagation observations show very good agreement, suggesting that the model is capturing the impact of solar protons on the ionosphere. The model results show order‐of‐magnitude changes in odd hydrogen and odd nitrogen concentrations, as well as ozone depletion varying from 20% at 40 km altitude to more than 95% at 78 km. The magnitude and altitude distribution of ozone depletion is found to depend not only on the flux and energy of the protons but also on the diurnal cycle of atomic oxygen and ozone‐depleting constituents so that the largest depletions of ozone are seen during sunrise and sunset. The after‐event recovery of ozone is altitude‐dependent because of the differences in the recovery of odd hydrogen and odd nitrogen and also because of a relatively faster ozone production at higher altitudes. The modeled and measured NO2 profiles agree well at altitudes 35–60 km, particularly during times of large concentrations observed after the solar proton event onset. A comparison of the time series of ozone depletion shows a good agreement between the model and observations.

Time of flight secondary ion mass spectrometry (ToF-SIMS) is a powerful technique for the nanoanalysis of biological samples, but improvements in sensitivity are needed in order to detect large biomolecules, such as peptides, on the individual cell level at physiological concentrations. Two promising options to improve the sensitivity of SIMS to large peptides are the use of cluster primary ions to increase desorption of intact molecules or the use of matrix-assisted laser desorption/ionization (MALDI) matrices to increase the ionization probability. In this paper, the authors have combined these two approaches in order to improve understanding of the interaction between ionization and fragmentation processes. The peptides bradykinin and melittin were prepared as neat monolayers on silicon, in a Dextran-40 matrix and in two common MALDI matrices, 2,5-dihydroxybenzoic acid (DHB) and α-cyano-4-hydroxy cinnamic acid (HCCA). ToF-SIMS spectra of these samples were collected using a range of small Bi cluster primary ions and large Ar cluster primary ions. The trends observed in the molecular ion yield and the [M+H](+)/C4H8N(+) ratio with primary ion cluster size were sample system dependent. The molecular ion yield of the bradykinin was maximized by using 30 keV Bi3 (+) primary ions in a DHB matrix but in the HCCA matrix, the maximum molecular ion yield was obtained by using 30 keV Bi7 (+) primary ions. In contrast, the molecular ion yield for melittin in both matrices was greatest using 20 keV Ar2000 (+) primary ions. Improvements in the molecular ion yield were only loosely correlated with a decrease in small fragment ions. The data indicate a complex interplay between desorption processes and ion formation processes which mean that the optimal analytical conditions depend on both the target analyte and the matrix.

We present evidence for a correlation between solar proton events and fluctuations in the density of electrons trapped inside the Earth's magnetosphere. We examine 60 solar proton events and 53 solar proton enhancements, which took place between August 1989 and February 1999 (during solar cycles 22 and 23). It is found that 90% of the solar proton events and 85% of the solar proton enhancements are associated with fluctuations in the trapped electron density of the Earth's magnetosphere. Fifty percent of proton events occurred in complex regions. Ninety-six percent of the remaining events that occurred in simple solar active regions are associated with fluctuations of the electron density. We also examined 63 solar active regions with complex magnetic field configurations, which did not produce proton events. It is found that 57% of them were not associated with fluctuations in the trapped electron density during the period when their delta configurations existed on the solar disk. A total of 93 complex solar active regions occurred on the solar disk and 60% are associated with fluctuations of electron density. In this preliminary paper, we demonstrate the potential of invoking the correlation to improve the reliability of short-term predictions for proton events.

D-region positive and negative ion concentration and mobilities during the February 1979 eclipse

This paper presents the results of evidence-based calibration of a new semi-empirical method for studying the D-layer aeronomy. We use simultaneous measurements of altitude profiles of electron density Ne(h) and ionization rate q(h) under disturbed conditions (case 1) and mean <Ne> under various heliogeophysical conditions at low (LSA) and high (HSA) solar activity (case 2). The experimental data and methods are described in detail. It is shown that it is necessary to include temperature dependences of rate constants T(h) for all heliogeophysical conditions. Care should be taken when choosing the T(h) distribution with due regard to most of known factors having an effect on it, wherever possible. We draw a conclusion on the practicability of the use of new photodetachment rates that depend on the solar zenith angle and h. The unknown dissociative recombination rate for cluster positive ions and the photodetachment rate can be reasonably considered as free parameters, of course within due limits. Under disturbed ionospheric conditions, the evidence shows a fall in Ne at all altitudes h when q≈(1.3÷2)⋅10² cm⁻³ s⁻¹ with further increase in the parameters with q, which is confirmed by calculations using the semi-empirical model, yet for a wider range of q variations. The theoretical model that explains the aforementioned effect is the subject of future study. The results for dayside <Ne> coincide qualitatively with our knowledge on the behavior of aeronomy parameters in the D layer. The studies suggest that the presented method allows qualitative estimations under all heliogeophysical conditions and even wholly satisfactory quantitative estimations under disturbed ionospheric conditions.

Dust particle formation in silane plasmas