Small-scale microwave background anisotropies due to tangled primordial magnetic fields

An inhomogeneous cosmological magnetic field creates vortical perturbations that survive Silk damping on much smaller scales than compressional modes. This ensures that there is no sharp cut-off in anisotropy on arc-minute scales. As we had pointed out earlier, tangled magnetic fields, if they exist, will then be a potentially important contributor to small-angular scale CMBR anisotropies. Several ongoing and new experiments, are expected to probe the very small angular scales, corresponding to multipoles with l>1000. In view of this observational focus, we revisit the predicted signals due to primordial tangled magnetic fields, for different spectra and different cosmological parameters. We also identify a new regime, where the photon mean-free path exceeds the scale of the perturbation, which dominates the predicted signal at very high l. A scale-invariant spectrum of tangled fields which redshifts to a present value B_{0}=3\times 10^{-9} Gauss, produces temperature anisotropies at the 10 micro Kelvin level between l ~ 1000-3000. Larger signals result if the univese is lambda dominated, if the baryon density is larger, or if the spectral index of magnetic tangles is steeper, n > -3. The signal will also have non-Gaussian statistics. We predict the distinctive form of the increased power expected in the microwave background at high l in the presence of significant tangled magnetic fields. We may be on the verge of detecting or ruling out the presence of tangled magnetic fields which are strong enough to influence the formation of large-scale structure in the Universe.Comment: 5 pages, 2 figures, submitted to MNRAS Letter

Extratropical signature of the quasi-biennial oscillation

Using the assimilated data from the National Centers for Environmental Prediction (NCEP) reanalysis, we show that the extratropical signature of the tropical quasi-biennial oscillation (QBO) is seen mostly in the North Annular Mode (NAM) of atmospheric variability. To understand the extratropical manifestation of the QBO, we discuss two effects that have been suggested earlier: (1) The extratropical circulation is driven by the QBO modulation of the planetary wave flux, and (2) the extratropical circulation is driven by the QBO-induced meridional circulation. We found that the first effect is seen in wave 1 in the beginning of winter and in wave 2 in the end of winter. The QBO-induced circulation affects midlatitude regions over the entire winter. To investigate the QBO-NAM coupling, we use an equation that relates the stream function of the meridional circulation and the polar cap averaged temperature, which is a proxy for the NAM index. In addition to the annual Ω_a and the QBO frequency Ω_Q the spectrum of its solutions indicates the satellite frequencies at Ω_a ± Ω_Q

Nonlinear mean-field dynamo and prediction of solar activity

We apply a nonlinear mean-field dynamo model which includes a budget equation for the dynamics of Wolf numbers to predict solar activity. This dynamo model takes into account the algebraic and dynamic nonlinearities of the alpha effect, where the equation for the dynamic nonlinearity is derived from the conservation law for the magnetic helicity. The budget equation for the evolution of the Wolf number is based on a formation mechanism of sunspots related to the negative effective magnetic pressure instability. This instability redistributes the magnetic flux produced by the mean-field dynamo. To predict solar activity on the time scale of one month we use a method based on a combination of the numerical solution of the nonlinear mean-field dynamo equations and the artificial neural network. A comparison of the results of the prediction of the solar activity with the observed Wolf numbers demonstrates a good agreement between the forecast and observations.Comment: 15 pages, 6 figures, jpp.cls, final versio

Climate Stability and the Origin of Agriculture

Although modern man had developed long before the migration from Africa began ∼ 55,000 years ago, no agricultural societies developed until about ∼ 10,000 years ago. But in the next 5000 years, agricultures developed in several unrelated regions of the world. It was not a chance occurrence that new agricultures independently appeared in the same 5000 years. The question is what inhibited agriculture worldwide for 44,000 years and what changed ∼ 10,000 years ago? We suggest that a major factor influencing the development of agricultural societies was climate stability. From the experience of several independent cultures, we estimate that the development of agriculture needed about 2000 years of climate free from significant climate variations on time scales of a few centuries

The Sun's Preferred Longitudes and the Coupling of Magnetic Dynamo Modes

Observations show that solar activity is distributed non-axisymmetrically, concentrating at "preferred longitudes". This indicates the important role of non-axisymmetric magnetic fields in the origin of solar activity. We investigate the generation of the non-axisymmetric fields and their coupling with axisymmetric solar magnetic field. Our kinematic generation (dynamo) model operating in a sphere includes solar differential rotation, which approximates the differential rotation obtained by inversion of helioseismic data, modelled distributions of the turbulent resistivity, non-axisymmetric mean helicity, and meridional circulation in the convection zone. We find that (1) the non-axisymmetric modes are localised near the base of the convection zone, where the formation of active regions starts, and at latitudes around $30^{\circ}$; (2) the coupling of non-axisymmetric and axisymmetric modes causes the non-axisymmetric mode to follow the solar cycle; the phase relations between the modes are found. (3) The rate of rotation of the first non-axisymmetric mode is close to that determined in the interplanetary space.Comment: 22 pages, 18 figures. Accepted for publication in the Astrophysical Journa

Dual strings and magnetohydrodynamics

We investigate whether dual strings could be solutions of the magnetohydrodynamics equations in the limit of infinite conductivity. We find that the induction equation is satisfied, and we discuss the Navier-Stokes equation (without viscosity) with the Lorentz force included. We argue that the dual string equations (with a non-universal maximum velocity) should describe the large scale motion of narrow magnetic flux tubes, because of a large reparametrization (gauge) invariance of the magnetic and electric string fields. It is shown that the energy-momentum tensor for the dual string can be reinterpreted as an energy-momentum tensor for magnetohydrodynamics, provided certain conditions are satisfied. We also give a brief discussion of the case when magnetic monopoles are included, and indicate how this can lead to a non-relativistic "electrohydrodynamics" picture of confinement.Comment: 10 pages. LaTex. A minor correction has been mad

Is solar variability reflected in the Nile River?

We investigate the possibility that solar variability influences North African climate by using annual records of the water level of the Nile collected in 622–1470 A.D. The time series of these records are nonstationary, in that the amplitudes and frequencies of the quasi-periodic variations are time-dependent. We apply the Empirical Mode Decomposition technique especially designed to deal with such time series. We identify two characteristic timescales in the records that may be linked to solar variability: a period of about 88 years and one exceeding 200 years. We show that these timescales are present in the number of auroras reported per decade in the Northern Hemisphere at the same time. The 11-year cycle is seen in the Nile's high-water level variations, but it is damped in the low-water anomalies. We suggest a possible physical link between solar variability and the low-frequency variations of the Nile water level. This link involves the influence of solar variability on the atmospheric Northern Annual Mode and on its North Atlantic Ocean and Indian Ocean patterns that affect the rainfall over the sources of the Nile in eastern equatorial Africa

Fermion Density Induced Instability of the W-Boson Pair Condensate in Strong Magnetic Field

The electroweak vacuum structure in an external magnetic field close to the lower critical value is considered at finite fermion density. It is shown that the leading effect of the fermions is to reduce the symmetry of the W-pair condensate in the direction of the magnetic field. The energy is minimized by the appearance of a helicoidal structure of the condensate along the magnetic field.Comment: 9 pages, LaTex, JHU-TIPAC-93000