Alexander Ruzmaikin

The solar magnetic field and the solar wind: Existence of preferred longitudes

Direct measurements of the solar wind speed and the radial component of the interplanetary magnetic field acquired over more than three solar cycles are used to search for signatures of a persistent dependence of solar wind properties on solar longitude. Two methods of analysis are used. One finds the rotation period that maximizes the amplitude of longitudinal variations of both interplanetary and near-Earth data mapped to the Sun. The other is based on power spectra of near-Earth and near-Venus data. The two methods give the same result. Preferred-longitude effects are found for a synodic solar rotation period of 27.03 ± 0.02 days. Such high precision is attained by using several hundred thousand hourly averages of the solar wind speed and magnetic field. The 27.03-day periodicity is dominant only over long periods of time; other periodicities are often more prominent for shorter intervals such as a single solar cycle or less. The 27.03-day signal is stronger and more consistent in the magnetic field than in the solar wind speed and is stronger for intervals of high and declining solar activity than for intervals of low or rising activity. On average, solar magnetic field lines in the ecliptic plane point outward on one side of the Sun and inward on the other, reversing direction approximately every 11 years while maintaining the same phase. The data are consistent with a model in which the solar magnetic dipole returns to the same longitude after each reversal.

Intermittent turbulence in solar wind from the south polar hole

The magnetic fields measured by the Ulysses spacecraft are used to study solar wind turbulence in the fast solar wind from the south polar hole. The spacecraft was at about 46 deg south latitude and 3.9 AU. For a magnetic field with a Gaussian distribution the power spectrum (second-order structure function) is sufficient to completely characterize the turbulence. However, the actual distribution is non-Gaussian so that the effects of intermittency must be taken into account. The observed spectral exponents include effects of intermittency and cannot be directly compared with the standard second-order spectral theories such as the Kolmogorov and Kraichnan theories. To permit a better comparison of the observations with the theoretical models, we study the structure characteristics of the data. We find the exponents of the second-order structure functions (power spectra) and the higher-order normalized structure functions for the components of the magnetic fields. We show that these sets of exponents can be approximately described by two basic numbers: the spectral exponent and the intermittency exponent. The intermittency exponent characterizes correlation properties of the energy cascade from large to small scales. Before comparing the observations to the theoretically expected values, a reduction must be made to the observed spectral exponent. The amount of the reduction depends on both the intermittency exponent and the model of the energy cascade assumed in the turbulence theory. We reduce the measured spectral indices according to a simple model for Alfven turbulence that is described here. We then compare our reduced spectral indices with second-order spectral theory. The reduced spectral indices for the period range of 1 min to about a half hour are remarkably constant and in good agreement with the value of 3/2. Thus our treatment is self-consistent. Our tentative conclusion is that the high-frequency turbulence appears to agree with the model of random-phased Alfven waves. This tentative conclusion must be tested by further theoretical and observational work.

Multifractal measure of the solar magnetic field

We analyze high-resolution, digital, photoelectric images of solar photospheric magnetic fields. The line-of-sight fields are found to scale in a self-similar way with resolution and thus can be expressed in the form of a signed multifractal measure. The scaling properties of the measure are used to extrapolate field integrals, such as moments of the magnetic field, below resolvable limits. The scaling of the field moments is characteristic of highly intermittent fields. We suggest that the quiet-Sun photospheric fields are generated by local dynamo action based on random convective motions at high magnetic Reynolds number. The properties of active region images are determined by the presence of fields generated by the global, mean field dynamo

The JPL proton fluence model: an update

Abstract The development of new technologies and the miniaturization of sensors bring new requirements for our ability to predict and forecast hazardous space weather conditions. Of particular importance are protons in the energy range from 10s to 100s of MeV which cause electronic part and solar cell degradation, and pose a hazard to biological systems in space and to personnel in polar orbit. Sporadic high-energy solar particle events are a main contributor to the fluences and fluxes of such protons. A statistical model, JPL 1991 (J. Geophys. Res. 98 (1991) 13,281), was developed to specify fluences for spacecraft design and is now widely used. Several major solar proton events have occurred since that model was developed and one objective of this paper is to see if changes need to be made in the model due to these recent events. Another objective is to review the methods used in JPL 1991 in the light of new understandings and to compare the JPL methods with those used in other models. We conclude that the method used in developing JPL 1991 model is valid and that the solar events occurring since then are completely consistent with the 1991 model. Since no changes are needed we suggest that the name of the model be changed to “the JPL fluence model”.

Anomalous Diffusion of Solar Magnetic Elements

The diffusion properties of photospheric bright points associated with magnetic elements (magnetic bright points) in the granulation network are analyzed. We find that the transport is subdiffusive for times less than 20 minutes but normal for times larger than 25 minutes. The subdiffusive transport is caused by the walkers being trapped at stagnation points in the intercellular pattern. We find that the distribution of waiting times at the trap sites obeys a truncated Levy type (power-law) distribution. The fractal dimension of the pattern of sites available to the random walk is less than 2 for the subdiffusive range and tends to 2 in the normal diffusion range. We show how the continuous time random walk formalism can give an analytical explanation of the observations. We simulate this random walk by using a version of a phenomenological model of renewing cells introduced originally for supergranules by Simon, Title, & Weiss. We find that the traps that cause the subdiffusive transport arise when the renewed convection cell pattern is neither fixed nor totally uncorrelated from the old pattern, as required in Leightons model, but in some intermediate state between these extremes.

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.

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 Niles 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.

The pattern of northern hemisphere surface air temperature during prolonged periods of low solar output

We show that the reconstructed sensitivity of the sea level temperature to long term solar forcing in the Northern Hemisphere is in very good agreement with the empirical temperature pattern corresponding to changes of the North Annular Mode (NAM). This implies that long-term variations of solar output affect climate predominantly through the NAM that extends throughout the stratosphere and troposphere.

Modulation of Cosmic Ray Precipitation Related to Climate

High energy cosmic rays may influence the formation of clouds and thus impact weather and climate. Due to systematic solar wind changes, the intensity of cosmic rays incident on the magnetopause has decreased markedly during this century. The pattern of cosmic ray precipitation through the magnetosphere to the upper troposphere has also changed. Early in the century, the part of the troposphere open to cosmic rays of all energies was typically confined to a relatively small high-latitude region. As the century progressed the size of this region increased by over 25% and there was a 6.5° equatorward shift in the yearly averaged latitudinal position of the subauroral region in which cloud cover has been shown to be cosmic ray flux dependent. We suggest these changes in cosmic ray intensity and latitude distribution may have influenced climate change during the last 100 years.

Principal Components and Independent Component Analysis of Solar and Space Data

Abstract Principal components analysis (PCA) and independent component analysis (ICA) are used to identify global patterns in solar and space data. PCA seeks orthogonal modes of the two-point correlation matrix constructed from a data set. It permits the identification of structures that remain coherent and correlated or that recur throughout a time series. ICA seeks for maximally independent modes and takes into account all order correlations of the data. We apply PCA to the interplanetary magnetic field polarity near 1 AU and to the 3.25R⊙ source-surface fields in the solar corona. The rotations of the two-sector structures of these systems vary together to high accuracy during the active interval of solar cycle 23. We then use PCA and ICA to hunt for preferred longitudes in northern hemisphere Carrington maps of magnetic fields.