The high latitude circulation and temperature structure of the thermosphere near solstice

The neutral gas temperature and circulation of the thermosphere are calculated for December solstice conditions near solar cycle maximum using NCAR's thermospheric general circulation model (TGCM). High-latitude heat and momentum sources significantly alter the basic solar-driven circulation during solstice. At F-region heights, the increased ion density in the summer hemisphere results in a larger ion drag momentum source for the neutral gas than in the winter hemisphere. As a result there are larger wind velocities and a greater tendency for the neutral gas to follow the magnetospheric convection pattern in the summer hemisphere than in the winter hemisphere. There is about three times more Joule heating in the summer than the winter hemisphere for moderate levels of geomagnetic activity due to the greater electrical conductivity in the summer E-region ionosphere.

The results of several TGCM runs are used to show that at F-region heights it is possible to linearly combine the solar-driven and high-latitude driven solutions to obtain the total temperature structure and circulation to within 10–20%. In the lower thermosphere, however, non-linear terms cause significant departures and a linear superposition of fields is not valid.

The F-region winds at high latitudes calculated by the TGCM are also compared to the meridional wind derived from measurements by the Fabry-Perot Interferometer (FPI) and the zonal wind derived from measurements by the Wind and Temperature Spectrometer (WATS) instruments onboard the Dynamics Explorer (DE−2) satellite for a summer and a winter day. For both examples, the observed and modeled wind patterns are in qualitative agreement, indicating a dominant control of high latitude winds by ion drag. The magnitude of the calculated winds (400–500 m s⁻¹) for the assumed 60 kV cross-tail potential, however, is smaller than that of the measured winds (500–800 m s⁻¹). This suggests the need for an increased ion drag momentum source in the model calculations due to enhanced electron densities, higher ion drift velocities, or some combination that needs to be further denned from the DE−2 satellite measurements.     

Observation of a thin Es-layer by the eiscat radar

High resolution E-region measurements carried out on 16 November 1983 using the EISCAT incoherent scatter radar are presented. The experiment was monostatic with a vertical radar beam, and it was based on a Barker-coded four-pulse code on one frequency channel and Barker-coded single pulses on three channels. The basic integration time was 15 s and the spatial resolution 450 m. The results reveal a short-lived but intense thin sporadic E-layer at 18:00–18:06 U.T. at an altitude of about 106 km. Both before and during the event, downward ion velocities of the order of 100 m s⁻¹ are observed above this height. A convergent null in the vertical ion speed is occasionally seen at the layer altitude. The layer occurrence is associated with auroral arcs drifting across the radar beam. Simultaneous observations of the STARE radar show an ionospheric electric field of 25–30 mV m⁻¹. The field always has a westward component, which is in accordance with the observed downward plasma flow. Most of the time when the layer is intense, the field points into the NW-sector. Theoretically, this field direction should create convergent vertical plasma motion. Therefore it is suggested that the observed E_s-layer is created by the action of the auroral electric field rather than by the wind shear mechanism.     

Nightside ionosphere of Venus

Venera 9, 10 measurements of the nightside ionospheric profile and the night airglow were used for investigating ionosphere formation processes. The upper ionospheric layer may be formed by HeI 584 Å radiation; the lower layer by meteorite ionization. Upper limits on the electron energy flux, <4 × 10⁸eV cm⁻² s⁻¹, the helium ion flux <10⁷ cm⁻² s⁻¹, the nitric oxide mixing ratio, <1.5 × 10⁻⁴ and the atomic sulphur mixing ratio, <10⁻⁶, are deduced for ionospheric altitudes.     

Interpreting vertical plasma drift in the mid-lattitude ionosphere using ionosonde measurements

Measurements of the density at the F₂ peak (N_mF₂) were obtained by the Boulder, Colorado, ionosonde as part of the SUNDIAL-86 campaign. The measurements were made during a period of low to moderate geomagnetic activity following a “disturbed” day. These measurements were then used to estimate the height of the F₂ peak (h_mF₂). A three-dimensional time-dependent model of Earth's ionosphere was used to calculate N_mF₂ and h_mF₂ using the vertical plasma drift as a free parameter. Since the plasmasphere-ionosphere exchange flux can remain upward during the night for these conditions, different feasible flux scenarios were inputed to the ionospheric model. These different flux scenarios had a large effect on the “induced” vertical plasma drifts required to match the measurements (i.e. at times greater than a factor of 2 in speed or a difference in direction). Futhermore, uncertainty in the O⁺---O collision frequency changes the required vertical plasma drift at night. Despite knowledge of h_mF₂, interpretation of the vertical plasma drifts as meridional neutral winds is compromised by a lack of knowledge of the plasmasphere-ionosphere exchange flux following disturbed days.     

OH masers in W 33A

This paper presents observations of OH maser lines of W 33A for the transitions ²Π_3/2, J = 3/2, F = 1 → 1 and F = 2 → 2. Two models, a thin tube and a sphere, were used for modelling the masing region and a molecular hydrogen density of about 10⁷ cm⁻³ was obtained. To give a maser photon emission of the order of 10⁴⁶ s⁻¹, both models require a pump rate of 1 OH cm⁻³s⁻¹, while the sphere model requires a higher pump efficiency.     

Some aspects of Sporadic-E at mid-latitudes

Evidence is presented to suggest that the ƒ₀E_s value tends to be high at positions in the E_s-layer where trough slope-lines and crest slope-lines of F2-layer irregularities meet the E_s-layer. These slope-lines are drawn through the troughs and crests, respectively, of the characteristic kinks in the F2-layer ionization contours, which are associated with F2-layer irregularities.

A rotating-loop direction-finding system has allowed an estimation of the distribution of ionization, which gives rise to Sporadic-E echoes. Analysis of Sporadic-E occurrence, on two occasions, suggests that the reflecting surfaces are frontal in nature, the fronts having a separation from each other of some tens of kilometres, and probably existing as closed curves, with diameters of the order of several hundreds of kilometres. A possible association between these structures and the occurrence of the green line of the airglow, is discussed.

A distribution of ionization, which will give contours showing “clouds” of ionization at some frequencies and a ripple structure at other frequencies, is proposed, in an endeavour to explain the apparent dual nature of Sporadic-E occurrence.

The evidence seems to indicate that the mechanism operating at the E_s-layer level, producing the phenomenon of Sporadic-E, is the same as that which produces the F2-layer irregularities which are responsible for “Spread-F”.     

Galactic kinematics derived from classical cepheids

On the basis of radial velocity and Hipparcos proper motion data, we have analyzed the galactic kinematics of classical Cepheids. Using the 3-D Ogorodnikov-Milne model we have determined the rotational velocity of the Galaxy to be V₀ = 240.5 ± 10.2 km/s, on assuming a glactocentric distance of the Sun of R₀ = 8.5 kpc. The results clearly indicate a contracting motion in the solar neighbourhood of (∂V_θ∂θ)/R = −2.60 ± 1.07 km s⁻¹ kpc⁻¹, along the direction of galactic rotation. Possible reason for this motion is discussed. The solar motion found here is S = 18.78 ± 0.86 km/s in the direction l = 54.4° ± 2.9° and b = +26.6° ± 2.6°.     

An auroral F-region study using in situ measurements by the Atmosphere Explorer-C satellite

On 14 July 1974 the Atmosphere Explorer-C satellite flew through an aurora at F-region altitudes just after local midnight. The effects of the particle influx are clearly evident in the ion densities, the 6300 Å airglow, and the electron and ion temperatures. This event provided an opportunity to study the agreement between the observed ion densities and those calculated from photochemical theory using in situ measurements of such atmospheric parameters as the neutral densities and the differential electron energy spectra obtained along the satellite track. Good agreement is obtained for the ions O₂⁺, NO⁺ and N₂⁺ using photochemical theory and measured rate constants and electron impact cross sections. Atomic nitrogen densities are calculated from the observed [NO⁺]/[O₂⁺] ratio. In the region of most intense electron fluxes (20 erg cm⁻² sec⁻¹) at 280 km, the N density is found to be between 2 and 7 × 10⁷ cm⁻³. The resulting N densities are found to account for approx. 60% of the production of N⁺ through electron impact on N and the resonant charge exchange of O⁺(²P) with N(⁴S). This reaction also provides a significant source of O(¹S) in the aurora at F-region altitudes. In the region of intense fast electron influx, the reaction with atomic nitrogen is found to be the main loss of O⁺(²P).     

Satellite beacon measurements of protonospheric fluxes

The ionospheric and protonospheric regions of the plasmasphere, which are dominated by the O⁺ and H⁺ ionic species, respectively, interact by means of proton fluxes within tubes of magnetic force. The present study is concerned with the determination of these fluxes by the beacon satellite technique as used in the ATS-6 experiment in relation to three observing sites: Boulder, Colorado; Lancaster, U.K.; and Fairbanks, Alaska. From plasmasphere models based on solutions of the time dependent O⁺ and H⁺ momentum and continuity equations, it is shown that the time differential of the “residual content” as measured at Lancaster, provides a good estimate of the protonospheric flux at 4000km altitude in the L = 1.8 magnetic shell under quite geomagnetic conditions. The effect of the neutral thermospheric wind on the protonospheric flux is also investigated. Fluxes determined by the beacon technique for the period from September 1975 to July 1976 are shown, and these are compared with typical results derived from other techniques.     

A prediction for three neutrino masses and mixings and similarity between quark and lepton mixings

If neutrinos have mass, we give reasons for a possible pattern of three (squaed) mass eigenvalues: m₁² (2.8−5.8) (eV)², m₂² 0.01 (eV)², m₃² (1.5−1) × 10⁻⁴ (eV)². The flavor states ν_μ and ν_e are mixtures of the eigenstates with m₂ and m₃ with a significant mixing, corresponding to an effective mixing angle of about 0.45. The ν_τ is nearly the state with m₁; the other two effective mixing angles are about an order of magnitude smaller than 0.45. There is a marked similarity to mixing in the quark sector.     

Ducted propagation of hydromagnetic waves in the upper ionosphere

This paper presents a theoretical investigation of the ducting of Pc1 hydromagnetic waves in an ionospheric layer situated above the F₂ region. Theoretical calculations show that this upper ionospheric duct may also sustain horizontal propagation of Pc1 pulsations over appreciable distances. It is found that there is a low-frequency cutoff as in the case of the F₂ layer waveguide. The group velocity of waves in the upper ionospheric duct is considerably greater, and dispersion is more pronounced compared to the ducted propagation in the F₂ region.     

The odd zonal harmonics in the Earth's gravitational potential

The odd zonal harmonics in the Earth's gravitational potential are determined by analysing the changes in the eccentricities of six satellites having orbital inclinations spaced as uniformly as possible between 28° and 96°. The most satisfactory representation of the potential is found to be in terms of four coefficients, and their values are, in the usual notation: 10⁶J₃ = −2.56, 10⁶J₅ = −0.15, 10⁶J₇ = −0.44, 10⁶J₉ = 0.12. The resulting potential is compared with that obtained by other authors. Three and five-coefficient solutions are also presented.     

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

A detailed analysis of the D-region ion composition measurements performed by Zbinden et al. (1975), during a winter day of high ionospheric absorption, has been carried out. The study examines the interactive mesosphere-D-region processes which occur in such anomalous conditions and their implication for water cluster ion chemistry. Two clustering regimes for NO⁺ have been observed in the data. Association with N₂ is identified as the dominant process below 76 km. Between 76 and 78 km altitude the effective loss rate of NO⁺ drops by two orders of magnitude. Above 77 km, the three-body reaction NO⁺ + CO₂+M→NO⁺CO₂+M seems to be the main NO⁺ loss. A mesospheric temperature profile could be derived from the ion composition data. This indicates the presence of a strong inversion above 76 km altitude. The wavelike structure obtained, is shown to be consistent with in situ winter temperature measurements. The sharp suppression of the N₂ association reaction could, thus, be explained by an increase in the collisional break-up of the NO⁺N₂ ion because of the enhanced temperature. In conclusion, our study indicates that, besides the increase in the production of NO⁺ and O₂⁺, due to an enhancement in the minor ionizable constituents, an additional thermal mesosphere-D-region interaction seems necessary to explain this winter anomalous ion composition data.     

Rotational discontinuities in an anisotropic plasma

A general theory of rotational discontinuities is developed and the changes in the components of the plasma pressure, p_| and p, and in the magnetic induction, B, are found. For a given value of λ=(p_| − p) 4πμ/B² upstream only a limited range of downstream anisotropies are possible. If λ>0.6 upstream then isotropy is not possible downstream. Some special solutions are analysed and the identification of rotational discontinuities is the solar wind is discussed.     

Median ionospheric height variations over a sunspot cycle in the Australian-Japanese longitudinal sector

The monthly median virtual height (h′F) of the F-region was studied for a period of 6 years (1980–1985) from sunspot maximum to minimum, using data from 11 ionosonde stations in the Japanese-Australian longitudinal sector, in an invariant latitude range: 37°N to 54°S. The night-time maximum in the median height progressively decreases equatorwards, particularly in the local winter and spring, while a reverse weak tendency is observed in summer. The median height reaches peak in both hemispheres from 1 to 2 years after sunspot maximum then decreases towards sunspot minimum. A second diurnal maximum in h′F, preceded by a well-defined minimum, was consistently observed over the solar cycle close to the sunrise time at the F-region, mainly at low invariant latitudes (9–20°). The second maximum has a distinct seasonal variation, being most pronounced in winter and diminishing in summer. It is envisaged that the second peak in h′F is associated with the wave disturbance generated by the supersonic motion of the sunrise terminator. Possible effects of the background height variations on the propagation of the magnetic storm-induced travelling ionospheric disturbances are discussed.     

The HNCO ring in the Sgr B2 region

The large-scale structure associated with the 2′N HNCO peak in Sgr B2 [Minh, Y.C., Haikala, L., Hjalmarson, Å., Irvine, W.M., 1998. ApJ 498, 261 (Paper I)] has been investigated. A ring-like morphology of the HNCO emission has been found; this structure may be colliding with the Principal Cloud of Sgr B2. This “HNCO Ring” appears to be centered at (l,b) = (0.7°,−0.07°), with a radius of 5 pc and a total mass of 1.0 × 10⁵ to 1.6 × 10⁶ M. The expansion velocity of the Ring is estimated to be 30–40 km s⁻¹, which gives an expansion time scale of 1.5 × 10⁵ year. The morphology suggests that collision between the Ring and the Principal Cloud may be triggering the massive star formation in the Sgr B2 cloud sequentially, with the latest star formation taking place at the 2′N position. The chemistry related to HNCO is not certain yet, but if it forms mainly via reaction with the evaporated OCN⁻ from icy grain mantles, the observed enhancement of the HNCO abundance can be understood as resulting from shocks associated with the collision between the Principal Cloud and the expanding HNCO Ring.     

Spectrum of the relic neutrino background from past supernovae and cosmological models

It is greatly expected that the relic neutrino background from past supernovae will be detected by Superkamiokande (SK) which is now under construction. We calculate the spectrum and the event rate at SK systematically by using the results of simulations of a supernova explosion and reasonable supernova rates. We also investigate the effect of a cosmological constant, Λ, on the spectrum, since some recent cosmological observations strongly suggest the existence of Λ. We find following results. (1) The spectrum has a peak at about 3 MeV, which is much lower than that of previous estimates (6–10 MeV). (2) The event rate at SK in the range from 10 MeV to 50 MeV, where the relic neutrinos from past supernovae are dominant, is about 25h₅₀²(R_SN/0.1 yr⁻¹)(n_Gh₅₀⁻³/0.02 Mpc⁻³) events per year, where R_SN is the supernova rate in a galaxy, n_G is the number density of galaxies, and h₅₀ = H₀/(50 km/s Mpc), where H₀ is the Hubble constant. (3) The event rate is almost insensitive to Λ. The flux increases in the low energy side (< 10 MeV) with increasing Λ, but decreases in the high energy side (> 10 MeV) in models in which the integrated number of supernovae in one galaxy is fixed.     

Electron excitation and auroral emission parameters

Auroral luminosities of the main emission lines in the aurora have been calculated for excitation by an isotopic primary electron flux with spectra of the form J(E) = AE exp (−E/E₁) + B(E₂)E exp (−E/E₁). The variation of emissions from O and N₂⁺ with height are shown, as are the variations of column integrated intensities and pertinent intensity ratios with the characteristic energy E₂, this leading to a method of estimating the electron spectrum from ground observation.     

Density profiles of dark matter halos with anisotropic velocity tensors

We present density profiles, that are solutions of the spherical Jeans equation, derived under the following two assumptions: (i) the coarse grained phase-density follows a power-law of radius, ρ/σ³ ∝ r⁻, and (ii) the velocity anisotropy parameter is given by the relation β_a(r)=β₁+2β₂ (r/r_*)/[1+(r/r_*)²] where β₁, β₂ are parameters and r_* equals twice the virial radius, r_vir, of the system. These assumptions are well motivated by the results of N-body simulations. Density profiles have increasing logarithmic slopes γ, defined by γ=−d ln ρ/d ln r. The values of γ at r=10^−2.5r_vir, a distance where the systems could be resolved by large N-body simulations, lie in the range 1.0–1.6. These inner values of γ increase for increasing β₁ and for increasing concentration of the system. On the other hand, slopes at r=r_vir lie in the range 2.42–3.82. A model density profile that fits well the results at radial distances between 10⁻³r_vir and r_vir and connects kinematic and structural characteristics of spherical systems is described.     

The upper ionospheres of Jupiter and Saturn

We use a 1-D chemical diffusive model, in conjunction with the measured neutral atmospheric structure, to analyze the Voyager RSS electron density, n_e, profiles for the ionospheres of Jupiter and Saturn. As with previous studies we find serious difficulties in explaining the n_e measurements. The model calculates ionospheres for both Jupiter and Saturn with n_e peaks of 10 times the measured peaks at altitudes which are 900–1000 km lower than the altitude of peaks in the RSS electron densities. Based on our knowledge of neutral atmospheric structure, ionization sources, and known recombination mechanisms it seems that, vibrational excitation of H₂ must play some role in the conversion of slowly radiatively recombining H⁺ ions to the relatively more rapidly recombining H₂⁺ and H₃⁺ ions. In addition, vertical ion flow induced by horizontal neutral winds or electric fields probably also play some role in maintaining the plasma peaks observed both for Jupiter and Saturn to be at high altitudes. For the ionosphere of Saturn, the electron densities are affected by a putative influx of H₂O molecules, Φ_H2O, from the rings. To reproduce the RSS V2 exit n_e results model requires an influx of Φ_H2O 2 × 10⁷ molecules cm⁻² s⁻¹ without invoking H_2f vibrational excitation. To maintain the model n_e peak at the measured altitude vertical plasma drift maintained by meridional winds or vertical electric fields is required. The amounts of H₂O are consistent with earlier estimates of Connerney and Waite (1984) and do not violate any observational constraints.