Number Densities Of N2 Research Articles

Vertical Variations in Thermospheric O/N2 and the Relationship Between O and N2 Perturbations During a Geomagnetic Storm

AbstractThe ratio of O to N2 number densities (O/N2) at different altitudes is an important parameter in describing thermospheric neutral composition changes and their effects on the ionosphere during geomagnetic storms. However, storm‐induced vertical variations in O/N2 and its dependence on the O and N2 perturbations are still not fully understood. Here, the Thermosphere/Ionosphere Electrodynamics General Circulation Model simulations were used to investigate the responses of thermospheric composition at different pressure levels to the super geomagnetic storm occurred on November 20 and 21 in 2003. Our analysis shows that the behaviors of O/N2 perturbations on different pressure levels are similar above ∼180 km altitude. In the middle and low thermosphere of below ∼300 km, the storm‐time O/N2 decrease is mainly caused by a large reduction of O number density. However, N2 enhancement plays a vital role in O/N2 decreases in the upper thermosphere. The O/N2 enhancement is mainly attributed to the N2 decreases at all pressure levels. The changes of O and N2 number densities at a constant pressure level can be explained by the perturbations of their mass mixing ratio (mmr) and total mass density (ρ). The regions of the O/N2 decrease are characterized by the O mmr decrease and N2 mmr enhancement, whereas the regions of the O/N2 increase are characterized by the O mmr increase and N2 mmr decrease. The ρ value that shows the decrease globally at most pressure levels during the storm either enhance or reduce the O and N2 perturbations.

The altitude of green OI 557.7 nm and blue N2+ 427.8 nm aurora

Abstract. We have performed a large statistical study of the peak emission altitude of green O(1D2–1S0) (557.7 nm) and blue N2+ 1 N (427.8 nm) aurora using observations from a network of all-sky cameras stationed across northern Finland and Sweden recorded during seven winter seasons from 2000 to 2007. Both emissions were found to typically peak at about 114 km. The distribution of blue peak altitudes is more skewed than that for the green, and the mean peak emission altitudes were 114.84 ± 0.06 and 116.55 ± 0.07 km for green and blue emissions, respectively. We compare simultaneous measurements of the two emissions in combination with auroral modelling to investigate the emission production mechanisms. During low-energy electron precipitation (<∼ 4 keV), when the two emissions peak above about 110 km, it is more likely for the green emission to peak below the blue emission than vice versa, with the difference between the two heights increasing with their average. Modelling has shown that under these conditions the dominant source of O(1S), the upper state of the green line, is energy transfer from excited N2 (A3Σu+), with a rate that depends on the product of the N2 and O number densities. Since both number densities decrease with higher altitude, the production of O(1S) by energy transfer from N2 peaks at lower altitude than the N2 ionisation rate, which depends on the N2 number density only. Consequently, the green aurora peaks below the blue aurora. When the two emissions peak below about 110 km, they typically peak at very similar altitude. The dominant source of O(1S) at low altitudes must not be energy transfer from N2, since the rate of that process peaks above the N2 ionisation rate and blue emission due to quenching of the long-lived excited N2 at low altitudes. Dissociative recombination of O2+ seems most likely to be a major source at these low altitudes, but our model is unable to reproduce observations fully, suggesting there may be additional sources of O(1S) unaccounted for.

Generation and decay of N2(A3Σu +) molecules in reacting CO2 and CH4 plasmas

Time-resolved number densities of N2(A3Σu +, v = 0, 1) molecules in diffuse ns pulse discharge plasmas in N2, N2–H2, N2–CH4, N2–CO2, and N2–CO2–CH4 are measured by tunable diode laser absorption spectroscopy (TDLAS). The first series of measurements is made in the discharge pulse bursts at a relatively low pulse repetition rate (3 kHz), when the N2(A3Σu +) generation and decay after individual discharge pulses is fully resolved. The second set of data is taken during a sequence of two pulse bursts generated at a higher pulse repetition rate (100 kHz), for different delay times between the first and second bursts. This approach is used to determine the effect of accumulation and decay of reacting species generated in the plasma, including N, H, and O atoms, CO molecules, and C2 hydrocarbon product species, on the rate of N2(A3Σu +) production and quenching. The effect of these species can be isolated since the rates of N2(A3Σu +) quenching by the initial reactant species (H2, CH4, and CO2) are slow. Comparison of the measurement results with the kinetic modeling predictions is used to obtain insight into the plasma chemical reaction kinetics. The results complement the measurements of N, H, O, and CO in high-pressure reacting plasmas, and help quantify the plasma chemical processes driven by the electron impact dissociation, electronic excitation, and reactive quenching of the excited electronic states. The present results may be used for the development and validation of higher fidelity kinetic models of reacting plasmas, incorporating state-specific electronic and vibrational energy transfer and chemical reactions.

Middle‐Low Latitude Neutral Composition and Temperature Responses to the 20 and 21 November 2003 Superstorm From GUVI Dayside Limb Measurements

AbstractTIMED/Global Ultraviolet Imager (GUVI) limb measurements of far‐ultraviolet airglow emission have been used to investigate middle‐low latitude thermospheric composition and neutral temperature responses to the 20 and 21 November 2003 (day of year [DOY] 324 and 325) superstorm. Altitude profiles of O, N2 number densities and temperature, as well as O/N2 column density ratio (∑O/N2), on the storm days along the GUVI limb tracks are compared with those on DOY 323 (quiet time). The storm‐time composition and temperature responses were global and evolved continuously as the storm progressed. Specially, N2 and temperature increased almost globally at all altitudes during the storm and their perturbation structures were similar. The magnitudes of their enhancements both increased with altitude and latitude. The storm‐induced O perturbations decreased in the lower thermosphere but increased in the upper thermosphere. Transition heights of O perturbations from decrease to increase changed with latitude and time. During the storm main and recovery phases, the storm‐induced ∑O/N2 decreases were mostly related to the O depletion in the low‐middle thermosphere, whereas ∑O/N2 increases during the storm were primarily caused by N2 depletion. There was a remarkable hemispheric asymmetry in composition responses as they have different morphologies and lifetime, especially during the storm recovery phase.

Seasonal Variation of O/N2 on Different Pressure Levels From GUVI Limb Measurements

AbstractThe ratio of O number density to N2 number density (O/N2) is an important parameter to describe thermospheric composition changes and its effects on the ionosphere. Based on Global Ultraviolet Imager (GUVI) limb measurements, we investigate the seasonal behaviors of O/N2 volume density ratio on different constant pressure levels during geomagnetically quiet periods. The global O/N2 shows the prominent annual and semiannual variations with solar activity dependence. An empirical model considering the solar activity and annual/semiannual variations can reasonably reproduce the original O/N2. The modeled O/N2 captures the hemispheric asymmetry of the annual variations in both length and magnitude. Global maps of the seasonal harmonic components of the modeled O/N2 indicate the latitudinal and altitudinal dependence of O/N2 seasonal variations. The annual component dominates over the semiannual component at mid‐latitudes, but it is smaller than the semiannual component at low latitudes. In the Northern Hemisphere, and at low geomagnetic latitudes of the Southern Hemisphere, the annual component peaks around December solstice at all altitudes, whereas at middle geomagnetic latitudes of the Southern Hemisphere, it peaks around June solstice. The semiannual component peaks at the equinoxes in almost all regions over the globe at all altitudes. The annual and semiannual amplitudes both increase with altitude. In addition, O/N2 annual variations and solar activity dependence are more influenced by the thermal expansion and contraction.

Comparison of Reference Heights of O/N2 and ∑O/N2 Based on GUVI Dayside Limb Measurement

AbstractWe define a new thermospheric concept, the reference heights of O/N2, referring to a series of thermospheric heights corresponding to the fixed ratios of O to N2 number density. Here, based on Global Ultraviolet Imager (GUVI) limb measurement, we compare O/N2 column density ratio (∑O/N2) and the reference heights of O/N2. We choose the transition height of O and N2 (transition height hereafter), a special reference height at which O number density is equal to N2 number density, to verify the connection with ∑O/N2 during geomagnetically quiet periods. It is found that transition height and ∑O/N2 have noticeable negative correlation with correlation coefficient of ‐0.887. An empirical model of transition height (O/N2 model hereafter) is established based on nonlinear least‐squares‐fitting method. The considerable correlation (greater than 0.96), insignificant errors (less than 4%) and the great influencing weight of ∑O/N2 to reference heights indicate the validity of O/N2 model and the existence of quantitative relation between ∑O/N2 and transition height. Besides, it is verified that the similar quantitative relation also exists between ∑O/N2 and reference heights of other O/N2 values. Namely, using the O/N2 model coefficients, we can roughly get the whole altitude profiles of O/N2 within 6% precision for any given ∑O/N2.

Discussion on population kinetics and number densities of excited species of low‐pressure discharge nitrogen plasma

A numerical model is constructed to calculate the number densities of some excited species of nitrogen in low‐pressure discharge nitrogen plasma, together with simultaneous solution of the self‐consistent electron energy distribution function and N2‐vibration distribution function. We consider species N2(X), N2(A), N2(B), N2(C), N2(a), N2(a′), N2+, N4+, N(4S) ande−. In addition to electron collisional reactions, diffusion losses and molecular relations are included. It is found that the ratio of number densities of N2(B) and N2(C) states can be a good measure of the electron kinetic temperature. The N2(C) state is found to be almost in a corona equilibrium, whereas the N2(B) state becomes mainly populated by N2(X,v≥6) + N2(A) reaction and depopulated by collisional relaxation by the ground‐state N2(X) molecule. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Space and time analysis of the nanosecond scale discharges in atmospheric pressure air: I. Gas temperature and vibrational distribution function of N2 and O2

Reliable experimental data on nanosecond discharge plasmas in air become more and more crucial considering their interest in a wide field of applications. However, the investigations on such nonequilibrium plasmas are made difficult by the spatial non-homogeneities, in particular under atmospheric pressure, the wide range of time scales, and the complexity of multi-physics processes involved therein. In this study, we report spatiotemporal experimental analysis on the gas temperature and the vibrational excitation of N2 and O2 in their ground electronic state during the post-discharge of an overvoltage nanosecond-pulsed discharge generated in a pin-to-plane gap of air at atmospheric pressure. The gas temperature during the pulsed discharge is measured by optical emission spectroscopy related to the rotational bands of the 0–0 vibrational transition N2(C 3 Πu, v = 0) → N2(B3 Πg, v = 0) of nitrogen. The results show a rapid gas heating up to 700 K in tens of nanoseconds after the current rise. This fast gas heating leads to a high gas temperature up to 1000 K measured at 150 ns in the first stages of the post-discharge using spontaneous Raman scattering (SRS). The spatiotemporal measurements of the gas temperature and the vibrational distribution function of N2 and O2, also obtained by SRS, over the post-discharge show the spatial expansion of the high vibrational excitation of N2, and the gas heating during the post-discharge. The present measurements, focused on thermal and energetic aspect of the discharge, provide a base for spatiotemporal analysis of gas number densities of N2, O2 and O atoms and hydrodynamic effects achieved during the post-discharge in part II of this investigation. All these results provide space and time database for the validation of plasma chemical models for nanosecond-pulsed discharges at atmospheric pressure air.

An anomalous subauroral red arc on 4 August, 1972: comparison of ISIS-2 satellite data with numerical calculations

Abstract. This study compares the Isis II satellite measurements of the electron density and temperature, the integral airglow intensity and volume emission rate at 630 nm in the SAR arc region, observed at dusk on 4 August, 1972, in the Southern Hemisphere, during the main phase of the geomagnetic storm. The model results were obtained using the time dependent one-dimensional mathematical model of the Earth's ionosphere and plasmasphere (the IZMIRAN model). The major enhancement to the IZMIRAN model developed in this study to explain the two component 630 nm emission observed is the analytical yield spectrum approach to calculate the fluxes of precipitating electrons and the additional production rates of N+2, O+2, O+(4S), O+(2D), O–(2P), and O+(2P) ions, and O(1D) in the SAR arc regions in the Northern and Southern Hemispheres. In order to bring the measured and modelled electron temperatures into agreement, the additional heating electron rate of 1.05 eV cm–3 s–1 was added in the energy balance equation of electrons at altitudes above 5000 km during the main phase of the geomagnetic storm. This additional heating electron rate determines the thermally excited 630 nm emission observed. The IZMIRAN model calculates a 630 nm integral intensity above 350 km of 4.1 kR and a total 630 nm integral intensity of 8.1 kR, values which are slightly lower compared to the observed 4.7 kR and 10.6 kR. We conclude that the 630 nm emission observed can be explained considering both the soft energy electron excited component and the thermally excited component. It is found that the inclusion of N2(v > 0) and O2(v > 0) in the calculations of the O+(4S) loss rate improves the agreement between the calculated Ne and the data on 4 August, 1972. The N2(v > 0) and O2(v > 0) effects are enough to explain the electron density depression in the SAR arc F-region and above F2 peak altitude. Our calculations show that the increase in the O++N2 rate factor due to the vibrationally excited nitrogen produces the 5–19% reductions in the calculated quiet daytime peak density and the 16–24% decrease in NmF2 in the SAR arc region. The increase in the O++N2 loss rate due to vibrationally excited O2 produces the 7–26% decrease in the calculated quiet daytime peak density and the 12–26% decrease in NmF2 in the SAR arc region. We evaluated the role of the electron cooling rates by low-lying electronic excitation of O2(a1Δg) and O2(b1Σg+), and rotational excitation of O2, and found that the effect of these cooling rates on Te can be considered negligible during the quiet and geomagnetic storm period 3-4 August, 1972. The energy exchange between electron and ion gases, the cooling rate in collisions of O(3P) with thermal electrons with excitation of O(1D), and the electron cooling rates by vibrational excitation of O2 and N2 are the largest cooling rates above 200 km in the SAR arc region on 4 August, 1972. The enhanced IZMIRAN model calculates also number densities of N2(B3Πg+),N2(C3Πu), and N2(A3Σu+) at several vibrational levels, O(1S), and the volume emission rate and integral intensity at 557.7 nm in the region between 120 and 1000 km. We found from the model that the integral intensity at 557.7 nm is much less than the integral intensity at 630 nm.Key words. Atmospheric composition and structure (airglow and aurora; thermosphere – composition and chemistry) · Ionosphere (ionosphere – magnetosphere interactions)

An anomalous subauroral red arc on 4 August, 1972: comparison of ISIS-2 satellite data with numerical calculations

This study compares the Isis II satellite measurements of the electron density and temperature, the integral airglow intensity and volume emission rate at 630 nm in the SAR arc region, observed at dusk on 4 August, 1972, in the Southern Hemisphere, during the main phase of the geomagnetic storm. The model results were obtained using the time dependent one-dimensional mathematical model of the Earth's ionosphere and plasmasphere (the IZMIRAN model). The major enhancement to the IZMIRAN model developed in this study to explain the two component 630 nm emission observed is the analytical yield spectrum approach to calculate the fluxes of precipitating electrons and the additional production rates of N+2, O+2, O+(4S), O+(2D), O–(2P), and O+(2P) ions, and O(1D) in the SAR arc regions in the Northern and Southern Hemispheres. In order to bring the measured and modelled electron temperatures into agreement, the additional heating electron rate of 1.05 eV cm–3 s–1 was added in the energy balance equation of electrons at altitudes above 5000 km during the main phase of the geomagnetic storm. This additional heating electron rate determines the thermally excited 630 nm emission observed. The IZMIRAN model calculates a 630 nm integral intensity above 350 km of 4.1 kR and a total 630 nm integral intensity of 8.1 kR, values which are slightly lower compared to the observed 4.7 kR and 10.6 kR. We conclude that the 630 nm emission observed can be explained considering both the soft energy electron excited component and the thermally excited component. It is found that the inclusion of N2(v > 0) and O2(v > 0) in the calculations of the O+(4S) loss rate improves the agreement between the calculated Ne and the data on 4 August, 1972. The N2(v > 0) and O2(v > 0) effects are enough to explain the electron density depression in the SAR arc F-region and above F2 peak altitude. Our calculations show that the increase in the O++N2 rate factor due to the vibrationally excited nitrogen produces the 5–19% reductions in the calculated quiet daytime peak density and the 16–24% decrease in NmF2 in the SAR arc region. The increase in the O++N2 loss rate due to vibrationally excited O2 produces the 7–26% decrease in the calculated quiet daytime peak density and the 12–26% decrease in NmF2 in the SAR arc region. We evaluated the role of the electron cooling rates by low-lying electronic excitation of O2(a1Δg) and O2(b1Σg+), and rotational excitation of O2, and found that the effect of these cooling rates on Te can be considered negligible during the quiet and geomagnetic storm period 3-4 August, 1972. The energy exchange between electron and ion gases, the cooling rate in collisions of O(3P) with thermal electrons with excitation of O(1D), and the electron cooling rates by vibrational excitation of O2 and N2 are the largest cooling rates above 200 km in the SAR arc region on 4 August, 1972. The enhanced IZMIRAN model calculates also number densities of N2(B3Πg+),N2(C3Πu), and N2(A3Σu+) at several vibrational levels, O(1S), and the volume emission rate and integral intensity at 557.7 nm in the region between 120 and 1000 km. We found from the model that the integral intensity at 557.7 nm is much less than the integral intensity at 630 nm.Key words. Atmospheric composition and structure (airglow and aurora; thermosphere – composition and chemistry) · Ionosphere (ionosphere – magnetosphere interactions)

Reactive crossed beam scattering of a Ti plasma and a N2 pulse in a novel laser ablation method

The interaction and energy transfer of a laser ablation plasma of Ti with a pulsed N2 supersonic expansion are investigated using time-of-flight quadrupole mass spectroscopy and Langmuir probe techniques. The Ti ablation target and the exit nozzle of the pulsed gas source are positioned so that the plasma plume and gas pulse interact near to their respective origins, where the number density is still high, which hence results in strong coupling of the nascent plasma with the gas pulse. The timing between the gas pulse and ablation plume is shown to be critical in determining the scattering processes and the chemical nature of the films grown by this method, an example of which is presented. The degree of ionization of the plasma when crossed with the gas pulse compared to that for expansion into vacuum increases from less than 10−3 to 0.28±0.11, which is attributed to collision-induced ionization of Ti atoms. Further increasing the N2 number density quenches the ion signal. The effective bimolecular cross section for scattering of Ti with the high density N2 pulse is about 4 times larger than that with a static background of low pressure N2, while the fractional depletion of the N2 pulse by the Ti plume depends on the N2 number density in the pulse, indicating that at these high local pressures, collective effects prevail. We propose a simple model for the resulting evolution of the plasma based on electrostatic considerations.

Temperature, N2, and N density profiles of Triton's atmosphere: Observations and model

Improved analysis of the Voyager Ultraviolet Spectrometer (UVS) observations of the solar occultation by Triton yields the isothermal temperature and N2 number densities in the altitude range 475–675 km: T = 102 ± 3 K, [N2]= (4 ± 0.4) × 108 cm−3 at 575 km. A distinct steplike absorption feature at 850 Å is due to the atomic nitrogen ionization continuum. It allows a measurement of N number densities in the range from 170 to 570 km, which correspond to diffusive equilibrium above 300 km with [N] = (1±0.25) ×108 cm−3 at 400 km and T = 100±7 K. Deviations from diffusive equilibrium become important below 300 km, and [N] = (5 ± 2.5) × 108 cm−3 at 200 km. The exobase altitude is 870 km, and the total escape rate of atomic nitrogen is (1±0.3) × 1025 s−1. The main condensible product of methane chemistry is ethylene, C2H4, with a peak number density of 6 × 106 cm−3 near 25 km. The striking similarity of the thermospheric properties at both occultation sites despite substantial differences in latitudes, seasons, local time, and incoming flux of magnetospheric electrons implies very effective winds and suggests that one‐dimensional modeling is applicable. Temporal variations of the temperature profile should be rather small in spite of strong variations of the electron flux. The presence of CO in the atmosphere as suggested by recent measurements of the CO absorption bands in the surface ice results in cooling by the rotational lines, deactivation and radiation of vibrational excitation of N2, and heating by quenching of N(2D). Heating efficiencies of electron precipitation and solar EUV radiation in the ranges of the N2 continuum and bands are calculated equal to 0.2–0.29, 0.24, and 0.19, respectively. The column integrated cooling by the CO lines is weaker than the thermospheric heating and cannot form a mesosphere. A CO mixing ratio of up to 10−2 is consistent with thermal balance calculations. Sixteen optimized versions of the model are considered with profiles of T and [N2] which agree with the measurements. Profiles of N, H2, and H densities are calculated. The calculated profile of atomic nitrogen and its escape rate are in excellent agreement with the measured values. Mixing ratios of H2 and H at 400 km are equal to 240 and 23 ppm, respectively. The total escape rate of hydrogen atoms (H + 2H2) is determined by photolysis of methane by H Lyman α radiation, does not depend on the ionospheric processes which transform H2 to H, and is equal to 2.3 × 1026 s−1. The ratio of H to N escape rates on Triton, 20, does not correspond to the measured ratio H+/N+∼ 2–3 in Neptune's magnetosphere and should be taken into account in its modeling. The recommended model for Triton's atmosphere is based on the temperature profile calculated for a CO mixing ratio of 10−3, a ratio of the average to the maximum electron fluxes of 0.162, and includes data on temperature, N2, N, CH4, H2, and H number densities.

Energy transfer studies on N2(X 1Σ+g,v) and N2(B 3Πg)

We have developed a novel discharge–flow technique for studying the quenching of N2(X 1Σ+g,v″≥5) and N2(B 3Πg) by a variety of molecules. The technique involves adding small number densities of N2(A 3Σ+u) to a flow of N2(X,v) producing, thereby, N2(B). By comparing N2(B) fluorescence intensities generated when a quencher is added to the N2(X,v) flow 2–3 ms before N2(A) addition with intensities observed after the N2(X,v) and quencher have been mixed for times of 10–30 ms, we can separate the effects of N2(B) fluorescence quenching from effects of N2(X,v) quenching. Our results indicate that CH4, CO2, CO, O2, and N2O quench N2(B) at rates approaching gas kinetic while H2, N2, SF6, and CF4 are about ten times slower. Rate coefficients for N2(X,v″≥5) quenching by H2 and N2 are on the order of 10−15 cm3 molecule−1 s−1, those for CO2, CH4, and CF4 roughly an order of magnitude faster, and CO and N2O yet another order of magnitude faster.

On the global mean structure of the thermosphere

A self‐consistent global average model of the coupled thermosphere and ionosphere has been developed and used to examine the global mean structure of these regions for solar minimum and maximum conditions. The model uses a parameterized version of the solar EUV and UV flux measured from the Atmospheric Explorer satellite to calculate photoionization rates of the major ion species and photo‐dissociation rates for O2 and N2. The ionospheric calculation solves for the vertical distributions of O+, including ambipolar diffusion, and of NO+, O2+, N2+, and N+, assuming photochemical equilibrium with respect to O+. It also solves the electron and ion energy equations as well as the coupled minor neutral constituent diffusion equations for N(²D), N(4S), and NO. The neutral gas energy equation is solved considering heating from photoelectrons, O2 absorption in the Schumann‐Runge continuum and bands, excess energy from exothermic ion‐neutral and neutral‐neutral chemical reactions, thermal electron, ion, and neutral collisions, O3 absorption in the Hartley bands, and atomic oxygen recombination and cooling from molecular and eddy thermal conduction and NO and CO2 IR radiation. The O2 photodissociation rates are used in a model of major species diffusion to solve for the O, O2, and N2 number densities. From specified lower‐boundary conditions and arbitrary initial conditions, both the thermospheric and the ionospheric structure evolve self consistently with time for specified solar flux values. The calculated globally averaged thermospheric and ionospheric structure compares well with the globally averaged structure predicted by the thermospheric and ionospheric empirical models based on data for both solar minimum and maximum conditions by considering solar EUV and UV radiation and aurora particle precipitation and joule heat sources to represent high‐latitude processes. Total joule heating is 7 × 1010 W for geomagnetic quiet conditions for both solar minimum and maximum. The model results show that the dominant heat sources for the thermosphere are collisions between ambient electrons, ions, and neturals above about 250 km, exothermic ion‐neutral chemical reactions between 200 and 250 km, exothermic neutral‐neutral chemical reactions between 200 and 150 km, and heating in the Schumann‐Runge continuum and bands below 150 km. Dominant cooling mechanisms are downward molecular thermal conduction above 150 km and NO and CO2 radiation below 150 km. The results also show that NO cooling must be considered in the thermal energy balance if the effect of minor neutral constituent chemical heating is considered in a definition of the neutral gas solar heating efficiency. Otherwise, the heat input into the thermosphere is overestimated.

Effect of a neutral N2 cloud on the electrical charging of an electron beam‐emitting rocket in the ionosphere: Echo IV

During the Echo IV electron beam rocket flight, 114 moles of neutral N2 was injected for the attitude stabilization system. The interaction of the 40‐kV 80‐mA beam with this relatively dense cloud was studied as a ‘gas plume’ to enhance the flow of neutralizing return current to the rocket body. It was found that the currents preferentially followed a route back through the region where the beam interacted with the N2. A complex luminous discharge was observed photometrically to accompany beam injection. This discharge was strongly roll modulated as the rotating beam swept through the injected gas near the rocket. The neutral N2 number density was measured by observing 3914‐Å emission produced by the beam impact, and reached nearly 1015 cm−3 at times. During a 1‐s 40‐kV 80‐mA beam injection pulse the discharge became oscillatory and ‘flickered’ with a frequency near 22 Hz, somewhat lower than the N2+ ion gyrofrequency. The injected N2 on one occasion apparently acted as a flourescent screen, and a photometric pulse was observed from a conjugate hemisphere beam echo. Ionospheric positive ions have been used to measure E × B drifts by their flow pattern at rocket altitudes, but it was found that the N2 cloud interacted by collision to isotropize and thermalize the flow patterns, so electric fields could not be studied by this technique.

A two-satellite study of the neutral atmosphere response to a major geomagnetic storm

Simultaneous measurements of neutral composition from both Esro 4 and Aeros-A have provided a complementary set of data for studying the temporal and spatial characteristics of the thermosphere during a major geomagnetic storm. From the correlative studies of Ar and N2 number densities, the magnetic index Aps, and ground-based magnetograms, it is found that the Ap index only reflects the gross features of atmospheric disturbances. Superposed on the global component are localized regions of 'hot spots' which appear correlated with ground-based magnetograms. Because of these localized disturbances, the interpretation of the atmospheric response to geomagnetic storms becomes ambiguous.

Profile of an anisentropic nitrogen nozzle expansion

Hypersonic N2 flow fields were produced using a conical nozzle of 1.04 mm throat diameter and an exit plane area ratio of 13.4. The reservoir pressure was varied over the range of 1.93 to 13.6 atm at the reservoir temperature of 285 K, and the reservoir conditions were such that both isentropic and anisentropic conditions existed within the axial region investigated. The N2 number density and rotational temperature axial and radial profiles were measured using laser Raman scattering, and comparisons are presented with the method of characteristics isentropic prediction. The onset of condensation and subsequent cluster growth were observed using laser Rayleigh scattering and depolarization measurements as well as photographic recording. The Rayleigh and Raman scattering data were used to obtain estimates of the axial variation of the cluster size as well as the variation of the depolarization ratio with the mean number of molecules of the cluster.

A mass spectrometric determination of the neutral constituents in the lower thermosphere above Sardinia

On December 11, 1965, at 0505 MET an ESRO Centaure rocket (ESRO C07/2) was launched from the range of Salto di Quirra, Sardinia, carrying a quadrupole mass filter. The number densities of N2, O2, O, and Ar were determined in the altitude range from 112 to 158 km. A high content of atomic oxygen was found, as can be seen from the number density ratio n(O)/n(O2) = 7.3 at 150 km. The relative Ar concentration was low, this indicating an onset of diffusive separation well below 110 km.

Time-Dependent Structure of the Upper Atmosphere

The physical properties of the upper atmosphere are determined mainly by heat conduction, the heat sources and the barometric law. An analysis of the integro-differential equation which describes these physical processes has been carried out. It is found that heating of the thermosphere due to absorption of the solar extreme ultraviolet (EUV) radiation alone cannot explain the observed diurnal variation of density and temperature, since it would yield a maximum of these properties at about 17h local time, instead of 14h where it is observed. Secondly, if the EUV flux is adjusted to give the observed average temperature, then the diurnal variation in density would be much too large compared with the observed amplitude. Thirdly, it would require an extremely high efficiency for the conversion of EUV radiation into heat, if we compare the required flux with Hinteregger's measurements of the EUV flux. Thus, it is necessary to have another heat source in addition to the heating due to absorption of EUV radiation. If an additional beat source is used, which has a maximum at about 9h local time and a flux of 1 erg cm−1 sec−1, a time-dependent model of the upper atmosphere is obtained that is in good agreement with the observed densities. There is evidence that this additional heat source derives its energy ultimately from the solar corpuscular radiation. In this paper we present the results of calculations for a model in the equatorial and temperature zones of the earth, for those times when the average solar activity corresponds to a solar radiation flux of 200×110−22 Wm−2 (cps)−1 at 10.7-cm wavelength. The physical properties (temperature, density, pressure, scale height, mean molecular weight and the number densities of N2, O2, O, He and H) are given as a function of local time and for the altitudes between 120 km and 2050 km.