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The Ionospheric Data Assimilation Four-Dimensional (IDA4D) technique has been coupled to Sami3, which is another model of the ionosphere (SAMI3). In this application, ground-based and space-based GPS total electron content (TEC) data have been assimilated into SAMI3, while in-situ electron densities, autoscaled ionosonde NmF2, and reference GPS stations have been used for validation. IDA4D/SAMI3 shows that night-time ionospheric localized enhancements (NILE) are formed following geomagnetic storms in November 2003 and August 2018. The NILE phenomenon appears as a moderate, longitudinally extended enhancement of NmF2 at 30°-40°N MLAT, occurring in the late evening (20-24 LT) following much larger enhancements of the equatorial anomaly crests in the main phase of the storms. The NILE appears to be caused by upward and northward plasma transport around the dusk terminator, which is consistent with eastward polarization electric fields. Independent validation confirms the presence of the NILE, and indicates that IDA4D is effective in correcting random errors and systematic biases in SAMI3. In all cases, biases and root-mean-square errors are reduced by the data assimilation, typically by a factor of 2 or more. During the most severe part of the November 2003 storm, the uncorrected ionospheric error on a GPS 3D position at 1LSU (Louisiana) is estimated to exceed 34 m. The IDA4D/SAMI3 specification is effective in correcting this down to 10 m.

We present the Volume Emission Rate Tomography (VERT) technique for inverting satellite-based, multi-sensor limb and nadir measurements of atmospheric ultraviolet emission to create whole-orbit reconstructions of atmospheric volume emission rate. The VERT approach is more general than previous ionospheric tomography methods because it can reconstruct the volume emission rate field irrespective of the particular excitation mechanisms (e.g., radiative recombination, photoelectron impact excitation, energetic particle precipitation in auroras); physical models are then applied to interpret the airglow. The technique was developed and tested using data from the Special Sensor Ultraviolet Limb Imager (SSULI) and Special Sensor Ultraviolet Spectrographic Imager (SSUSI) instruments aboard the Defense Meteorological Satellite Program F-18 spacecraft, and planned for use with upcoming remote sensing missions. The technique incorporates several features to optimize the tomographic solutions, such as: use of a non-negative algorithm (Richardson-Lucy; RL) that explicitly accounts for the Poisson statistics inherent in optical measurements; capability to include extinction effects due to resonant scattering and absorption of the photons from the lines-of-sight; a pseudo-diffusion-based regularization scheme implemented between iterations of the RL code to produce smoother solutions; and the capability to estimate error bars on the solutions. Tests using simulated atmospheric emissions verify that the technique performs well in a variety of situations, including daytime, nighttime, and even in the challenging terminator regions. Lastly, we consider ionospheric nightglow and validate reconstructions of the nighttime electron density against ALTAIR incoherent scatter radar data.

We present a new model of the South Atlantic Anomaly (SAA) particle flux intensity for low Earth orbit, based a new data set, i.e., particle noise pulses in an ultraviolet photomultiplier. The data set is unique in that it provides daily monitoring of the strength of the particle radiation at a fixed altitude and local time and provides a consistent set of observations across the deep solar minimum. The observations show the following: (1) a development over the decline of solar cycle 23 into a deep solar minimum and the subsequent rise of cycle 24, (2) the slow motion drift of the SAA centroid with time at the rate—longitude drift =0.36 ± 0.06°W/yr, and latitude drift =0.16 ± 0.09°N/yr, (3) a higher particle flux at solar minimum than at solar maximum, and (4) a yearly cyclical variation. These particle rates are deduced from electric noise pulses generated in the photometers when an energetic charged particle hits the detector and causes an electron to be liberated from the detector material. The model described here can be used to monitor and even spatially predict the changes in particle fluxes seen by instruments in contemporaneous low Earth orbits through the SAA.

This paper examines the relationships between the integrated solar EUV (26–34 nm and 5–45 nm) flux and the measured radiance in the N2 Lyman-Birge-Hopfield (LBH) 140–150 nm range (LBHS) under sunlit conditions. We find that both the (26–34 nm) and (5–45 nm) solar fluxes are linearly correlated with the daily median LBHS radiances with correlation coefficients of 0.979 and 0.963 respectively. Such a linear correlation can provide an alternative way to estimate the integrated solar EUV flux, a key heating and ionization source for the thermosphere and ionosphere. A direct measurement of the solar EUV spectrum is challenging due to a rapid degradation of EUV instruments. We demonstrate that using an FUV instrument to infer the change in the solar EUV flux, to the accuracy needed for aeronomic applications, leads to a more stable estimation of the solar EUV inputs especially over the long time scales that are important for understanding secular changes in the upper atmosphere.

First results of a Cosmic Microwave Background (CMB) anisotropy experiment conducted at the Observatorio del Teide (Tenerife, Spain) are presented. The instrument is a four channel (3.1, 2.1, 1.3 and 1.1 mm) $^3$He bolometer system coupled to a 45 cm diameter telescope. The resultant configuration is sensitive to structures on angular scales ~ 1-2 degrees. We use the channels at the two highest frequencies for monitoring the atmosphere, and apply a simple method to subtract this contribution in channels 1 (3.1 mm) and 2 (2.1 mm). The most intense structure at these two frequencies is the Galactic crossing with peak amplitudes of ~ 350 micro-K. These crossings have been clearly detected with the amplitude and shape predicted. This demonstrates that our multifrequency observations allow an effective assessment and subtraction of the atmospheric contribution. In the section of data at high Galactic latitude we obtain sensitivities ~ 40 micro-K per beam. The statistical analyses show the presence of common signals between channels 1 and 2. Assuming a simple Gaussian auto-correlation model with a scale of coherence $\theta_c=1.32$ degrees for the signal, a likelihood analysis of this section of data reveals the presence of fluctuations with intrinsic amplitude $C_{0}^{1/2} = 76^{+43}_{-32}$ micro -K (68 % CL including a ~ 20% calibration uncertainty). Since residual atmospheric noise might still contaminate our results, we also give our result as an upper limit of 118 micro-K at 95% c.l., Comment: uuencoded, g-zipped tar file containing a 14 page (AASTEX) LaTEX file with 3 PostScript figures. Revision: Minor revisions made; this is the verion which will appear in Astroph. J. Lett

We examine the correlation between the arrival direction of ultra high energy cosmic ray showers and gamma ray bursts in the third BATSE catalog. We find no correlation between the two data sets. We also find no correlations between a pre-BATSE burst catalog and the Haverah Park Ultra High Energy shower set that cover approximately the same period of time.

We have used the data from the COBE satellite to search for delayed microwave emission (31 - 90 GHz) from Gamma Ray Bursts (GRBs). The large $7^\circ$ beam of COBE is well matched to the large positional uncertainties in the GRB locations, although it also means that fluxes from (point source) GRB objects will be diluted. In view of this we are doing a statistical search of the GRBs which occurred during the currently released COBE DMR data (years 1990 and 1991), which overlap $\sim 200$ GRBs recorded by GRO. Here we concentrate on just the top 10 GRBs (in peak counts/second). We obtain the limits on the emission by comparing the COBE fluxes before and after the GRB at the GRB location. Since it is thought that the microwave emission should lag the GRB event, we have searched the GRB position for emission in the few months following the GRB occurrence.

Global Assimilation of Information for Action (GAIA) is a new initiative at The Johns Hopkins University connecting decision-makers with the research community. GAIA's focus is on the near- and long-term effects of weather, climate, and climate disruption on society and national security. The GAIA initiative, http://gaia.jhuapl.edu, makes use of collaborative tools to bring together decision makers to address focused problems in settings that range from symposia and workshops to specific socio-political-economic "games" to explore how decisions can be made and risks assessed. GAIA includes a suite of visualization tools, documentation, analyses, and social networking capabilities. Here, we will discuss the GAIA collaboration and recent GAIA projects, in particular the development of climate change national security gaming scenarios and studies in public health, and how the GAIA project can aide in assessing national security and public health concerns.

Formulas are derived for describing the evolution of fluctuations in the density of collisionless particles in the expanding universe using the gauge-invariant fluid description. The formulas use the “gauge-invariant” variables proposed by Bardeen to describe cosmological perturbations. These variables are hydrodynamic in nature and we show the behavior of the equations when the particles have streaming lengths large compared to the scales of interest. We also show how these equations couple gravitationally when other species of matter are present in significant densities. Using the “fourteen moment” approximation for the particle distribution function, we get a simple set of ordinary differential equations which are much easier to use than a direct integration of the Boltzmann equation. This formulation is especially useful when we are considering universes with more than one cosmologically significant component of matter density. An example of a numerical integration of the evolution equations is presented for comparison of this method to other work. A formula for calculating fluctuations in the cosmic microwave background radiation is also given.

The usual cosmological bound on axions can be significantly relaxed if the universe experienced a period of entropy production between the time axions were produced and nucleosynthesis. We discuss a scenario in which a large amount of entropy is generated by decaying particles of mass 1–10 TeV. We find that nucleosynthesis constraints the decay lifetimes to be less than about 0.03 seconds. Using this limiting lifetime, we derive cosmological limits on the axion mass and find that m a ≳ 9 × 10 −8 eV if the axion density is dominated by radiation from strings. This limit is far from the limit m a ≲ 10 −3 based on supernova 1987A, thus showing clearly a case where axionic strings do not need to be inflated away. If the strings were inflated away, we can relax the axion mass bound to m a ≳ 5 × 10 −9 eV.

The GLAST Balloon Flight Engineering Model (BFEM) represents one of 16 towers that constitute the Large Area Telescope (LAT), a high-energy (>20 MeV) gamma-ray pair-production telescope being built by an international partnership of astrophysicists and particle physicists for a satellite launch in 2006. The prototype tower consists of a Pb/Si pair-conversion tracker (TKR), a CsI hodoscopic calorimeter (CAL), an anti-coincidence detector (ACD) and an autonomous data acquisition system (DAQ). The self-triggering capabilities and performance of the detector elements have been previously characterized using positron, photon and hadron beams. External target scintillators were placed above the instrument to act as sources of hadronic showers. This paper provides a comprehensive description of the BFEM data-reduction process, from receipt of the flight data from telemetry through event reconstruction and background rejection cuts. The goals of the ground analysis presented here are to verify the functioning of the instrument and to validate the reconstruction software and the background-rejection scheme., 5 pages, 4 figures, to be published in IEEE Transacations on Nuclear Science, August 2002

Results from the third campaign of a ground-based multiband observation of the millimeter emission of the sky from Tenerife (Canary Islands) are presented. The instrument consists of a 0.45 m diameter off-axis telescope equipped with a four-band multimode 3He cooled photometer working at 1.1, 1.3, 2.1, and 3.1 mm wavelengths. The beam is well approximated by a Gaussian with 1°.35 FWHM at all wavelengths. The wide wavelength coverage of our instrument allows us to characterize and reduce both the atmospheric and Galactic contamination in our data. The cosmic microwave background radiation data is analyzed in six multipole bands whose centers span the range l = 39 to l = 134 at the two longest wavelengths (2.1 and 3.1 mm). A likelihood analysis indicates that we have detected fluctuations in all bands at the two wavelengths. We have evidence of a rise in the angular power spectrum from low l to high l. Our measured spectrum is consistent with current popular theories of large-scale structure formation, COBE, and other recent balloon-borne experiments with similar wavelength coverage.

We have used the 2- year Differential Microwave Radiometer data from the COsmic Background Explorer (COBE) satellite to systematically search for millimetric (31 - 90 GHz) emission from the Gamma Ray Bursts (GRBs) in the Burst And Transient Source Experiment (BATSE) GRB 3B catalog. The large beamsize of the COBE instrument (7 degs FWHM) allows for an efficient search of the large GRB positional error boxes, although it also means that fluxes from (point source) GRB objects will be somewhat diluted. A likelihood analysis has been used to look for a change in the level of millimetric emission from the locations of 81 GRB events during the first two years (1990 & 1991) of the COBE mission. The likelihood analysis determined that we did not find any significant millimetric signal before or after the occurance of the GRB. We find 95% confidence level upper limits of 175, 192 and 645 Jy or, in terms of fluxes, of 9.6, 16.3 and 54.8 10^{-13} erg/cm^2/s, respectively at 31, 53 and 90 GHz. We also look separately at different classes of GRBs, including a study of the top ten (in peak flux) GRBs, the "short burst" and "long burst" subsets, finding similar upper limits. While these limits may be somewhat higher than one would like, we estimate that using this technique with future planned missions could push these limits down to \sim 1 mJy., 21 pages, 5 figures, to be published in The Astrophysical Journal

We consider a supersymmetric model of inflation in which the primordial density fluctuations are nearly scale invariant (the spectral index n is approximately 0.98) with amplitude proportional to (M/M_{Planck})^2, where M ~ 10^{16} GeV denotes the scale of the gauge symmetry breaking associated with inflation. The 60 or so e-foldings take place when all relevant scales are close to M, which helps suppress supergravity corrections. The gravitino and baryogenesis (via leptogenesis) constraints help determine the two heaviest right handed neutrino masses to be approximately 2 x 10^{13} GeV and 6 x 10^9 GeV., Comment: The title has been changed to better reflect the content, the formulas now more accurate, and the reasons for the lack of SUGRA corrections are further clarified. 8 pages REVTEX

We explore the implications of possible neutrino oscillations, as indicated by the solar and atmospheric neutrino experiments, for the cold plus hot dark matter scenario of large scale structure formation. We find that there are essentially three distinct schemes that can accommodate the oscillation data and which also allow for dark matter neutrinos. These include (i) three nearly degenerate (in mass) neutrinos, (ii) non-degenerate masses with $\nu_\tau$ in the eV range, and (iii) nearly degenerate $\nu_\mu-\nu_\tau$ pair (in the eV range), with the additional possibility that the electron neutrino is cosmologically significant. The last two schemes invoke a `sterile' neutrino which is light (< or ~ eV). We discuss the implications of these schemes for $\bar{\nu}_\mu - \bar{\nu}_e$ and $\nu_\mu - \nu_\tau$ oscillation, and find that scheme (ii) in particular, predicts them to be in the observable range. As far as structure formation is concerned, we compare the one neutrino flavor case with a variety of other possibilities, including two and three degenerate neutrino flavors. We show, both analytically and numerically, the effects of these neutrino mass scenarios on the amplitude of cosmological density fluctuations. With a Hubble constant of 50 km s$^{-1}$ Mpc$^{-1}$, a spectral index of unity, and $\Omega_{baryon} = 0.05$, the two and three flavor scenarios fit the observational data marginally better than the single flavor scheme. However, taking account of the uncertainties in these parameters, we show that it is premature to pick a clear winner., Comment: 1 LaTEX file plus 1 uuencoded Z-compressed tar file with 3 postscript figures

We consider the growth of density perturbations in the presence of self--interacting dark matter, SIDM, proposed by Carlson, Machacek and Hall (1992). We determine the range of values for the coupling constant $\lambda$ and the particle mass $m^\prime$, for which the power spectrum lies in the ``allowed" range based on constraints from the IRAS galaxy survey and damped Lyman--$\alpha $ systems. Our results show that no combination of parameters can meet both limits. We consider constraints on the $\2-2$ scatterings which keep the SIDM particles in pressure equilibrium, and we show that if such interactions maintain pressure equilibrium down to the present, they will be strong enough to disrupt galaxy mergers and may lead to stripping of galaxy halos as galaxies move through the dark matter background of these particles. Hence, we also investigate the evolution of large-scale structure in the SIDM model when the particles drop out of pressure equilibrium at some higher redshift. The resulting free-streaming leads to an additional suppression of small-scale perturbations, but it does not significantly affect our results., Comment: 19 pages compressed post-script (3 figures included)

We give an improved formalism for calculating the evolution of density fluctuations and temperature perturbations in flat universes. Our equations are general enough to treat the perturbations in collisionless relics like massive neutrinos. We find this formulation to be simpler to use than gauge dependent and other gauge-invariant formalisms. We show how to calculate temperature fluctuations (including multipole moments) and transfer functions, including the case of collisionless relics like massive neutrinos. We call this formalism "quasi-Newtonian" because the equations for the potential and cold matter fluctuation evolution have the same form as the Newtonian gravitational equations in an expanding space. The density fluctuation variable also has the same form inside and outside of the horizon which allows the initial conditions to be specified in a simple intuitive way. Our sample calculations demonstrate how to use these equations in cosmological models which have hot, cold, and mixed dark matter and adiabatic (isentropic) or isocurvature modes. We also give an approximation which may be used to get transfer functions quickly., Comment: 1 LaTEX text file (29 pages), and a uuencoded gzip'ed tar file containing 7 Postscript figures

The Sachs-Wolfe temperature fluctuations produced by primordial density perturbations are proportional to the potential field \phi, which is a weighted integral over the density field \delta. Because of the central limit theorem, \phi can be approximately Gaussian even when \delta is non-Gaussian. Using the Wold representation for non-Gaussian density fields, \delta(\rvec) = \int f(|\rvec - \rvec^\prime|) \Delta(\rvec^\prime) d^3 \rvec^\prime, we find conditions on \Delta and f for which \phi must have a Gaussian one-point distribution, while \delta can be non-Gaussian. Sufficient (but not necessary) conditions are that the density field have a power spectrum (which determines f) of P(k) \propto k^n, with -2 < n \le +1, and that \Delta(\rvec) be non-Gaussian with no long-range correlations. Thus, there is an infinite set of non-Gaussian density fields which produce a nearly Gaussian one-point distribution for the Sachs-Wolfe effect., Comment: 13 pages + 4 figs., uuencoded, compressed postscript files, (Repaired error in uudecode unpacking.)

We explore constraints on the spectral index $n$ of density fluctuations and the neutrino energy density fraction $\Omega_{HDM}$, employing data from a variety of large scale observations. The best fits occur for $n\approx 1$ and $\Omega_{HDM} \approx 0.15 - 0.30$, over a range of Hubble constants $40-60$ km s$^{-1}$ Mpc$^{-1}$. We present a new class of inflationary models based on realistic supersymmetric grand unified theories which do not have the usual `fine tuning' problems. The amplitude of primordial density fluctuations, in particular, is found to be proportional to $(M_X /M_P)^2$, where $M_X (M_P)$ denote the GUT (Planck) scale, which is reminiscent of cosmic strings! The spectral index $n = 0.98$, in excellent agreement with the observations provided the dark matter is a mixture of `cold' and `hot' components., Comment: LaTEX, 14 pp. + 1 postscript figure appended

We explore constraints on inflationary models employing data on large scale structure mainly from COBE temperature anisotropies and IRAS selected galaxy surveys, taking care not to apply linear perturbation theory to data in the non-linear regime. In models where the tensor contribution to the COBE signal is negligible, we find the spectral index of density fluctuations $n$ must exceed 0.7. Furthermore the COBE signal cannot be dominated by the tensor component, implying $n>0.85$ in such models. The data favors cold plus hot dark matter models with $n$ close to unity and $\Omega_{HDM} \sim 0.20 - 0.35$. We present realistic grand unified theories, including supersymmetric versions, which produce inflation with these properties., Comment: 42 pages, in REVTEX 3.0. 9 figures available from authors

A precision measurement of atmospheric electron fluxes has been performed on a Japanese commercial airliner (Enomoto, {\it et al.}, 1991). We have performed a monte carlo calculation of the cosmic ray secondary electron fluxes expected in this experiment. The monte carlo uses the hadronic portion of our neutrino flux cascade program combined with the electromagnetic cascade portion of the CERN library program GEANT. Our results give good agreement with the data, provided we boost the overall normalization of the primary cosmic ray flux by 12\% over the normalization used in the neutrino flux calculation., in REVTEX, 12 pages + 4 figures available upon request

The predictions of the inflationary cosmology are compared with the expected sensitivity of the COBE satellie. It is noted that detection of large angle temperature fluctuations in the usual biased cold dark matter version of inflation requires COBE to reduce systematic errors to the level of the detector sensitivity. However, the difficulty the usual biased cold dark matter scenario has in fitting recent large scale structure observations leads us to consider a variety of possible modifications of inflation. These changes generally increase the amplitude of the temperature fluctuations to a more detectable level, although the amount of increase depends on the specific modification. Thus we would expect that COBE will easily see temperature fluctuations in a realistic model of large scale structure formation based on inflation.

We consider several factors concerning the design of observing strategies in Cosmic Microwave Background (CMB) anisotropy experiments. First we consider the number of independent points on the sky one should observe given a fixed observing time. Given an assumed level of sky temperature fluctuations, $\sigma_{sky}$ and the presence of instrumental noise $s$ in units of K s$^{-1/2}$ and a total observing time $t_{obs}$, we find there is an optimum number of points in the sky to maximize the confidence level of a detection. This number is a function of the signal to noise ratio $R^2 = \sigma_{sky}^2 t_{obs}/s^2$. We verify this analytical result with a monte carlo simulation, which also includes the correlation between different positions in the sky. Furthermore, using an $n=1$ spectrum of Gaussian fluctuations, we show that arranging the observing patterns along a (great) circle, a raster scan, or a randomized pattern yields results which are indistinguishable in Monte carlos.

We calculate distortions in the microwave background radiation from the Sunyaev-Zel'dovich effect, produced by hot gas in large (approximately 100 Mpc) pancakes. The large-scale distribution of the pancakes is taken to be that of a Voronoi foam. Fluctuations for this scenario are estimated to be on the order of delta T/T is approximately 10(exp -5). Using computer simulations, we produce several 32 deg x 32 deg images with 0.25 deg resolution. These images show characteristic linear features produced when a pancake is viewed nearly edge-on. By calculating the two-point and the degenerate three-point correlation functions, we are able to statistically detect such non-Gaussian features even in the presence of a relatively large amount of Gaussian noise. The degenerate three-point correlation function is found to be particularly useful since it is insensitive to correlated Gaussian noise. We also smooth our data over a 7 deg Full Width at Half Maximum (FWHM) Gaussian window to simulate the Cosmic Background Explorer Satellite (COBE) observations. We find that under such low-resolution conditions, the features are highly suppressed.

The effect of a small admixture of hot dark matter (HDM) to the «standard» cold dark matter (CDM) model for galaxy formation is examined. With equal amounts of HDM and CDM, the growth of galactic scale density peaks in the CDM component is highly damped and galaxy formation is problematic, as has been discussed elsewhere. However, if the HDM contribution is 30% then the damping is not so severe and galaxies can still form by a reasonable redshift

An account is given of a course of study encompassing the numerous considerations involved in aircraft gas turbine system definition within an aerothermodynamic framework; these considerations range over engine cycle type, air flowpath design, control integration, inlet and exhaust integration, acoustics, survivability, reliability, and mechanical subsystems. The integration of these factors is stressed. The systems approach is employed throughout. Over the years of the course's use, student suggestions have led to a relative deemphasis of the design-related aspects of the subject matter.

We prove that the S-matrix can be correctly obtained from the gauge-invariant effective action in the background field approach to gauge theories. In addition, we present a computation of the two-loop fermionic contributions to the Yang-Mills β-function.

For some time we have known that the standard big bang nucleosynthesis (BBN) strongly limits the amount of baryonic matter in the universe. The recently proposed inhomogeneous nucleosynthesis2 (IN) would invalidate that bound. In view of this possibility, we review constraints from the isotropy of the microwave background on pure baryonic universes and show that these constraints are not likely to be avoided by hiding the baryons in ‘‘lumps’’ left over from an inhomogeneous nucleosynthesis era.

We present an extensive comparison of models of structure formation with observations, based on linear and quasi-linear theory. We assume a critical matter density, and study both cold dark matter models and cold plus hot dark matter models. We explore a wide range of parameters, by varying the fraction of hot dark matter $\Omega_{\nu}$, the Hubble parameter $h$ and the spectral index of density perturbations $n$, and allowing for the possibility of gravitational waves from inflation influencing large-angle microwave background anisotropies. New calculations are made of the transfer functions describing the linear power spectrum, with special emphasis on improving the accuracy on short scales where there are strong constraints. For assessing early object formation, the transfer functions are explicitly evaluated at the appropriate redshift. The observations considered are the four-year {\it COBE} observations of microwave background anisotropies, peculiar velocity flows, the galaxy correlation function, and the abundances of galaxy clusters, quasars and damped Lyman alpha systems. Each observation is interpreted in terms of the power spectrum filtered by a top-hat window function. We find that there remains a viable region of parameter space for critical-density models when all the dark matter is cold, though $h$ must be less than 0.5 before any fit is found and $n$ significantly below unity is preferred. Once a hot dark matter component is invoked, a wide parameter space is acceptable, including $n\simeq 1$. The allowed region is characterized by $\Omega_\nu \la 0.35$ and $0.60 \la n \la 1.25$, at 95 per cent confidence on at least one piece of data. There is no useful lower bound on $h$, and for curious combinations of the other parameters it is possible to fit the data with $h$ as high as 0.65., Comment: 19 pages LaTeX file (uses mn.sty). Figures *not* included due to length. We strongly recommend obtaining the full paper, either by WWW at http://star-www.maps.susx.ac.uk/papers/lsstru_papers.html (UK) or http://www.bartol.udel.edu/~bob/papers (US), or by e-mailing ARL. Final version, to appear MNRAS. Main revision is update to four-year COBE data. Miscellaneous other changes and reference updates. No significant changes to principal conclusions

Several particle physics models suggest the simultaneous existence of both cold and hot forms of dark matter particles. Assuming a Harrison-Zel'dovich spectrum of primordial density fluctuations and Omega = 1, the formation of structure in a universe dominated by a combination of cold dark matter and massive neutrinos is explored. It is found that the presence of the hot dark matter component can cause enough power on large scales to explain some recent observations, while there is still sufficient power on small scales to allow galactic structure formation. Spatial anisotropies in the microwave background radiation are computed and found to be compatible with observational limits.

A general, gauge-invariant analysis of the large-scale anisotropies in the cosmic background radiation produced by arbitrary scalar, vector, or tensor perturbations in open, closed, or flat Robertson-Walker spacetimes (with no cosmological constant) is presented. The multipole moment predictions for the scale invariant spectrum and Omega = 1 universe predicted by inflationary cosmologies are contrasted with those for other spectra and for open and closed universes. Using the measured value of the dipole moment, limits are set on the expected value of the quadrupole moment as a function of Omega for various spectra.

Data covering a complete solar cycle (1965–1976) have been analyzed in a comprehensive investigation of the nature of transient modulations of relativistic galactic cosmic rays associated with interplanetary magnetic field intensity excursions in the vicinity of the earth. It had been recognized earlier that the correlation coefficient between the cosmic ray intensity and the IMF magnitude is small. In fact, it remains less than 0.5 throughout the solar cycle. In order to understand the nature of field-related modulations and to minimize the complications arising from the effects of other features of solar plasma, the data are here analyzed by the method of superposed epochs. Following newly developed procedures for evaluating the statistical significance of the results obtained with this type of analysis, it is demonstrated that, while the days characterized by high IMF magnitude B are associated with intensity decreases, the IMF rarefactions (low B) cause an increase in the flux. In contrast to the case of geomagnetic disturbances, which respond more rapidly, maximum cosmic ray intensity variations associated with both high and low B occur 1 day after the key days characterized by field departures from average values. This indicates that the modulation mechanism becomes efficient only when the plasma engulfment of the earth extends at least a gyroradius beyond 1 AU. Finally, while the geomagnetic index Ap follows the interplanetary magnetic field changes rather closely, the polar nucleonic intensity shows a prolonged recovery time (7–10 days) following magnetic enhancements as well as rarefactions. These results suggest that, on average, interplanetary magnetic field intensity variations which are presumably related to disturbances traveling from the sun are effective transient modulators of the relativistic particles and that the corotation of the modulating region plays a significant role in the recovery of the cosmic ray intensity. An investigation of the spectra of the cosmic ray intensity variations produced by interplanetary magnetic field enhancements and rarefactions, respectively, over the rigidity range covered by ground-based nucleonic intensity detectors has revealed that a power law of the form Kp−1 fits the data in both cases. This result is relevant to further theoretical studies of cosmic ray modulation processes.