Estimation of initial auroral proton energy fluxes from Doppler profiles

An energetic auroral proton entering the atmosphere will, by charge exchange in collisions with atmospheric constituents, alternate between being a proton H⁺ and a neutral hydrogen atom H. This study provides a procedure to evaluate the auroral Doppler shifted and broadened hydrogen Balmer profile as a function of initial energy, flux, pitch angle and view angle relative to the geomagnetic field. The differential proton energy flux entering the atmosphere is deduced using ground-based measurements of H_α and H_β from Nordlysstasjonen in Adventdalen, Longyearbyen. The main assumptions are that the geomagnetic field lines are: parallel and vertical, and that the pitch angle of the H/H⁺-particle is preserved in collisions with atmospheric constituents before being thermalized. This numerical method estimates the fate of the auroral H/H⁺-particle in the atmosphere, and from measured Doppler profiles the corresponding incoming particle flux can be deduced. Optimization of the method will continue through extensive use of observational data.     

Calculation of auroral Bahner volume emission height profiles in the upper atmosphere

Energetic protons entering the atmosphere will either travel as auroral protons or as neutral hydrogen atoms due to charge-exchange and excitation interactions with atmospheric constituents. Our objective is to develop a simple procedure to evaluate the Balmer excitation rates of H_α and H_β, and produce the corresponding volume emission rates vs height, using semi-empirical range relations in air, starting from proton spectra observed from rockets above the main collision region as measured by Reasoneret al. [(1968) J. geophys. Res.73, 4185] and Søbraaset al. [(1974) J. geophys. Res.79, 1851]. The main assumptions are that the geomagnetic field is parallel and vertical, and that the pitch angle of the proton/hydrogen atom is preserved in collisions with atmospheric constituents before being thermalized. Calculations show that the largest energy losses occur in the height interval between 100 and 125 km, and the corresponding volume emission rate vs height profiles have maximum values in this height interval. The calculted volume emission rate height profile of H_β compares favorably with that measured with a rocket-borne photometer.     

Outlook

Abstract

The heavy ion research described in these reviews focussed predominantly on collision energies around the nuclear Coulomb threshold. To put this energy in perspective one could say that the relative velocity of two nuclei impinging on each other is small compared to the so-called Fermi velocity at which individual nucleons move inside the nucleus. As a consequence nuclear matter tends to be in or close to thermal equilibrium at all times during the nuclear collisions because the energy is quickly dissipated inside the nucleus through moving nucleons. However, one may anticipate a change in this situation if the energy of the heavy ion beams increases further. Then a nucleus smashing into another nucleus may cause shock waves or the same phenomena which are observed if an airplane exceeds the speed of sound. Furthermore, nuclear compression and heating might be considerable. At even higher energies, the heavy ion exceeds many thresholds, like the one for the production of pions and other strange particles like lambda and sigma particle and even antiprotons. At the end of such a process the nuclear liquid may be compressed and heated so much that nucleons with their three quarks in a bag lose their individuality, quark are deconfined and form an extended bag of many quarks and gluons, according to today's knowledge of the ultimate constituents of matter. And even the atomic physics may b taken to the extreme by depriving uranium atom of all electrons, leaving a tripped and naked uranium nucleus behind.     

Energy deposition by precipitating keV range protons and neutral hydrogen atoms into the equatorial atmosphere: dependence on the neutral atmosphere model

The problem of the precipitation of keV range protons and neutral hydrogen atoms into the equatorial atmosphere is studied by the Monte-Carlo technique, and the energy deposition is calculated for different atmospheric models corresponding to low, medium and high solar activity conditions. It is found that the total energy deposited is independent of the atmospheric model and is equal to 16% of the incident energy, but the energy deposition profile varies. The dependence of the profile parameters on the neutral atmospheric model is examined in detail. An empirical model of the Chapman type distribution, involving only the neutral atmospheric density, has been developed to represent the energy deposition profile for any solar activity condition.     

Poker Flat MST radar observations of high latitude neutral winds at the mesopause during and after solar proton events

Observations with the Poker Flat, Alaska, MST radar during and after solar proton events in 1982 and 1984 suggest that winds in the altitude range of ~ 80–90 km were altered as a consequence of the influx of energetic charged particles and large electric fields at high latitudes. The atmospheric changes accompanying these events appear to result in a reduction of the semidiurnal tide and an enhancement in the diurnal tide. It is suggested that these changes could result from the alteration of the local tidal heating distribution produced by the particle precipitation, either through changes in the local ozone distribution or as a result of mesospheric Joule heating.     

In-situ observations of magnetospheric electron scattering by a VLF transmitter

High resolution pitch angle measurements of outer zone electrons in the energy range 12 keV−1.6 MeV were obtained at high altitude in the region of the high power VLF transmitter UMS [300 kW radiated at 17.1 kHz (Watt A. D., 1967, VLF Radio Engineering, Pergamon Press, Oxford)] while a resonant wave-particle interaction was in progress. Additional complementary electron measurements in the range of 36–316 keV were obtained in the drift loss cone by another satellite at low altitude along the drift path 75° east of the interaction region. The data from the low-altitude satellite confirm that UMS was precipitating particles in the inner zone, in the slot, and in the outer zone at the time that the high-altitude satellite was obtaining its data. The high-altitude pitch angle distributions indicate that, for this event, two types of scattering interactions were in progress. Particles with small pitch angles, up to 17.2° at the Equator, were being removed, resulting in an enhanced loss cone. Particles which were mirroring between 6500 km and the altitude of the spacecraft (7200) km were also being strongly scattered, resulting in a relative minimum in the pitch angle distribution around 90°. The data are interpreted as indicating that a cyclotron mode interaction with UMS waves was precipitating electrons with equatorial pitch angles up to 17.2° and that another process, perhaps electrostatic (ES) waves arising from the UMS radiations through a mode-conversion process, was present in the region above 6500 km and was efficiently scattering those particles which mirrored in that region     

A case study of the reaction of the auroral atmosphere to local energy inputs

EISCAT data taken along the Tromsø geomagnetic field line, on 25 March 1986, 1800–2400 UT, have been used to study the reaction of the neutral atmosphere to temporal and localized energy inputs. A periodic variation of the electron temperature with a period of ~25 min following a temporal heating event is interpreted as being due to a corresponding oscillation of the neutral atmosphere. A model to simulate the dynamic behaviour of the atmosphere is briefly described. The observations can well be explained provided the energy deposition is localized. Then horizontal gradients and thus horizontal atmospheric motions are established and these also affect the amplitude and period of vertical motions.     

Satellite and rocket studies of relativistic electrons and their influence on the middle atmosphere

Magnetospheric electrons from hundreds of keV to over 10MeV in energy have been systematically measured at geostationary altitude (6.6 R_E) for well over a decade. We find evidence of significant diurnal, solar-rotational (27-day), annual, and solar-cycle (11-yr) variations in the fluxes of the relativistic electron component. We have also used low-altitude satellite data and sounding rocket measurements to characterize the location and strength of the relativistic electron precipitation into the atmosphere. We conclude that the magnetospheric electrons, when dumped into the middle atmosphere, represent a very significant ionization source which affects the pattern of conductivity, electric fields, and atmospheric chemistry. These measurements—when combined with global atmospheric modeling—suggest that relativistic electrons provide a robust coupling mechanism to impose long-term solar wind and magnetospheric variability onto the Earth's deep atmospheric regions. A strong 11-yr cycle of relativistic electron effects is found in available atmospheric data sets.     

Calculation of ionospheric effects due to acoustic radiation from an underground nuclear explosion

Within the framework of the ionospheric detection of underground nuclear tests, we have developed an analytic computing technique for the acoustic effect of a confined nuclear explosion on upper layers of the Earth's atmosphere. The relationship (32) is obtained, which relates the nuclear test parameters (depth, explosion yield, and mechanical properties of the rock) to the vertical displacement of the ionosphere produced by the shock wave over the explosion's epicentre. It is also shown that most of the acoustic energy produced by a confined underground nuclear explosion escapes upward, with only a small fraction being captured by the atmospheric waveguide.     

Solar-induced variation of proton precipitation near the equator

This paper reports the solar condition dependences of the quasi-trapped component (low energy) of the proton population of energy 0.65–35 MeV which peaks in the equatorial zone centered on the minimum magnetic field equator in the altitude range 170–850 km. The proton populations compared pertain to AZUR observation in 1969–1970, S81-1 mission observation in 1982 and EXOS-C observation during 1984–1986. In the equatorial zone, the dependence of the flux normalization constant, which represents the absolute proton population, upon factors like L (1.1–1.3), B (0.29–0.32 gauss), latitude ( ± 20°), longitude (0–360°) and anisotropy index q (~6–12) of the pitch angle distribution function is not so significant in the given range of these factors as it is upon the solar epoch. It is found that the absolute proton flux in 1982 was, at least, forty times that in 1984–1986 and, almost, three times that in 1969–1970, possibly, due to, varying solar conditions in those epochs.     

Trimpi events on low latitude paths: An investigation of gyroresonance interactions at low L-values

We report on Trimpi events observed at Durban (L = 1.69, 29°53′S, 31°00′E) and investigate the efficacy of gyroresonance scattering in precipitating electrons into the atmosphere at low L (<2). The rate of occurrence of Trimpis at Durban is less than one per day. Our observations include a number of daytime events on OMEGA signals from La Reunion. Using the full relativistic equations of motion, a test particle simulation is employed to find the region in parameter space where large pitch angle scattering occurs. We find that at low L the conditions for pitch angle scattering are less favourable than at higher L (L ∼ 4). Resonant electrons have high (relativistic) energies, interaction times are of the order of milliseconds (T_i ∼ 5 ms) and large wave amplitudes (B_w ∼ 200 pT) are required at whistler frequencies to produce pitch angle changes of greater than 1°. Large pitch angle scattering is needed near Durban since particles near the loss cone will have been lost in the South Atlantic Geomagnetic Anomaly. We note that the radio frequencies transmitted into the magnetosphere from lightning are too low to give effective electron scattering at low L. We suggest an explanation for the low rate of occurrence of Trimpis at Durban.     

Forcing atmospheric oscillations by long-period seismic oscillations: a case study

Using synchronous measurements made by microbarograph and a seismograph with a vertical pendulum, the sign of the vertical direction of the wave energy flux in the atmosphere at the ground has been derived for oscillations in the ∼0.5–4 h period range and which occur simultaneously in the Earth and atmosphere. The seismic oscillations shown could generate atmospheric oscillations by the ‘piston’ mechanism. A change of sign of the flux direction is also observed.     

Eighteenth‐Century Meissen Porcelain Reference Data Obtained By Proton‐Beam Analysis (PIXE–PIGE)

Prior to their restoration, the porcelain bodies of broken pieces from 31 authentic Meissen objects of the early 18th century were investigated by proton‐beam analysis. Attention was paid so that the proton beam probed only the bare porcelain paste areas of fractures. Thus, contributions to the measured X‐ray and γ‐ray spectra from adjacent surface glaze were prevented. The chemical compositions, obtained by simultaneous detection of elements with Z ≥ 13 (X‐rays) and lighter elements Z ≤ 14 (γ‐rays), represent rather consistent mixtures of paste ingredients. This result highlights the durable recipes and raw materials used in early Meissen porcelain production in the years 1725–50. Mean concentration values of element oxides, deduced from the detailed measurements, prove suitable for use as a database for Meissen porcelain paste identification. Material authentication of intact objects, without access to the bare porcelain body, is demonstrated by inspection of the white glaze. Unique museum objects are examined in atmosphere and without sampling. A low proton‐beam intensity and a short irradiation time ensure non‐destructive analysis. Simultaneous radiation and backscattered particle detection allow complete composition analysis, using the established ion beam techniques of particle‐induced X‐ray emission (PIXE), particle‐induced gamma‐ray emission (PIGE) and Rutherford backscattering spectrometry (RBS).     

Interactions between whistler-mode waves and energetic electrons in the coupled system formed by the magnetosphere,ionosphere and atmosphere

The physical mechanism of a cyclotron resonance interaction between trapped energetic electrons and whistler-mode waves in the magnetosphere is discussed. Not only do the electrons have their pitch angles reduced in this interaction, so that they may be precipitated into the upper atmosphere, but also the waves can be amplified. Such a flux of precipitating electrons can, either by direct ionisation or via bremsstrahlung radiation, cause a pimple to be produced on the bottom of the ionosphere. That can significantly modify the amplitude and/or phase of very low frequency radio signals propagating in the Earth-ionosphere waveguide. Various experimental observations that demonstrate the reality of such effects are reviewed. The conditions necessary for a positive feedback situation are discussed, and some evidence for its existence assessed.     

Auroral rays: filamentation in the auroral accelerator

In situ measurements of particles, fields and optical emissions from a rocket that encountered auroral rays are reported. The measurements give insight into the production of rays, as well as the production of large fluctuations in electric fields perpendicular to the magnetic field. The fine structure and rapid variations of the electron energy flux associated with the rays are apparently produced by modulation in the degree of electron acceleration. Rays are produced when the energy flux increases in localized regions to values even higher than those normally encountered in bright auroral forms. Close and consistent similarities in the variations of the electron energy flux, the light and the electric fields suggest that the field variations were produced as a direct result of the changes in the stream of accelerated electrons. In examining possible causes of the velocity changes that produce the rays, two acceleration processes are considered; acceleration as a consequence of a potential difference between the magnetosphere and the atmosphere and acceleration by waves.     

Calculations and ground-based observations of pulsed proton events in the dayside aurora

A procedure is established to evaluate the Balmer excitation rates of Hα and Hβ to produce the corresponding volume emission rates versus height, using semi-empirical range relations of protons in air. The calculations are carried out with identified ion-energy particle spectra of the dayside aurora obtained by low altitude satellites. The calculated emission intensities of Hα and Hβ indicate that they are indeed observable by ground-based optical detection. Measurements of the dayside aurora from Nordlysstasjonen in Adventdalen, Svalbard, are discussed in relation to these calculations. Periodic bursts of auroral Hα and Hβ emissions are observed in the dayside aurora by ground-based photometers and spectrometers. The mean period between proton events is found to be 10 min on average. Furthermore, it is found that when the time between successive bursts decreases, the emission ratio of Hα and Hβ fluctuates indicating a step-like behaviour in the primary initial proton energy.     

Nitric oxide and lower ionosphere quantities during solar particle events of October 1989 after rocket and ground-based measurements

The most dramatic demonstrations of solar activity are solar proton flares. One such very strong flare, accompanied by a solar proton event (SPE) and a large ground level enhancement of cosmic rays on Earth, was observed in October 1989. During this SPE, ion density and nitric oxide concentration profiles were measured by rockets launched from the Soviet research vessel ‘Akademik Shirshov’ in the southern part of the Indian Ocean. The rocket experiment yielded the first in-situ measurement of NO concentration increased by SPE. The NO concentrations estimated from ion-pair production rates due to measured fluxes of high energy particles agree fairly well with the observed NO concentrations in the stratopause region. The results of rocket measurements are compared with measurements of the radio wave absorption in the lower ionosphere performed at similar latitudes in central Europe. Model calculations of absorption show that while the night-time enhancement of absorption can be explained by increased electron density related to the measured increase of ion density as a consequence of enhanced penetration of high energy particles, the daytime increase of absorption needs to be explained mainly in terms of the observed increase of nitric oxide concentration.     

Observation of low energy particle precipitation at low altitude in the equatorial zone

Precipitation of protons (~ 1 MeV) in the equatorial zone was investigated by the Phoenix-1 experiment on board the S81-1 mission from May–November, 1982. The protons show a precipitation peak along the line of minimum magnetic field strength with a full width at half maximum (FWHM) of 13°. The index of equatorial pitch angle distribution is q ~ 19. The peak proton flux shows a fifth-power altitude dependence, and the proton flux shows approximately a factor of 3 times increase in 1982 compared to that in 1969 due, possibly, to the stronger (~ 1.2 times) solar maximum conditions of 10.7cm radiation in 1982.     

Quasi-periodic particle precipitation and Trimpi activity at Halley,Antarctica

The relationship between quasi-periodic VLF emissions and micropulsations is briefly reviewed, and then discussed with reference to an event recorded at Halley, Antarctica, on day 257 in 1986. VLF emissions at 2 kHz with a quasi-period of 9 s were observed simultaneously with Pi1 and Pe1 micropulsations. Also observed was a quasi-periodic Trimpi event on the amplitudes and phases of the VLF transmitters NAA and NSS. It is deduced that the VLF emissions are modulated in the generation region by a hydromagnetic wave, giving rise to particle precipitation. The emissions are also modulated by the bounce period of the generating particles. The Trimpi effect is due to 120 keV electrons being precipitated into the lower ionosphere by the interaction with the VLF emissions. This event shows that the Trimpi effect can be used to detect particle precipitation occurring during the ULF/VLF interaction, and can give information which helps to define the mechanism reponsible for the interaction.     

An experimental investigation of atmospheric electricity and lightning activity to be performed during the descent of the Huygens Probe onto Titan

No terrestrial-like electrical activity was observed during the Voyager 1 flyby of Titan on 12 November 1980, in spite of a predicted global lightning energy dissipation rate of 4 × 10⁻⁶ Wm⁻². This lack of evidence does not, however, rule out the existence of electrical discharges with magnitudes, rates of occurrence and spectral characteristics drastically different from those known on Earth, owing to large dissimilarities between the temperatures, chemical compositions and, especially, electrical conductivities of the two atmospheres. Towards the end of the year 2004, the ESA probe Huygens will be jettisoned from the NASA Saturn orbiter, Cassini. This probe will descend onto Titan and perform in situ measurements during a period of 3 h, from an altitude of 170 km down to the satellite surface where the atmospheric pressure reaches 1.6 × 10⁵ Pa. The Huygens scientific payload will include a set of instruments entirely dedicated to the detection of lightning and to the characterization of the electrical properties of the atmosphere and surface. An electric antenna will search for natural emissions in the frequency range 0–10 kHz, at altitudes lower than those of ionized layers opaque to electromagnetic waves, and measure the magnitude of static electric fields due to charge separation. The conductivity of the atmosphere and the existence of free electrons will be checked during the whole descent with a combination of quadrupolar and relaxation probes; a microphone will also record acoustic phenomena associated with electrical discharges and atmospheric processes. The impedance of the surface will be evaluated from the measurements collected with a radar during the descent and a quadrupolar array after touch down.