Oscillations Above Sunspots

The 3-min oscillations in the sunspot atmosphere are discussed, based on joint observing with the Transition Region and Coronal Explorer – TRACE and the Solar and Heliospheric Observatory – SOHO. We find that the oscillation amplitude above the umbra increases with increasing temperature, reaches a maximum for emission lines formed close to 1–2× 10⁵ K, and decreases for higher temperatures. Oscillations observed with a high signal-to-noise ratio show deviations from pure linear oscillations. The results do not support the sunspot filter theory, based on the idea of a chromospheric resonator. Whereas the filter theory predicts several resonant peaks in the power spectra, equally spaced 1 mHz in frequency, the observed power spectra show one dominating peak, close to 6 mHz. Spectral observations show that the transition region lines contribute less than 13 percent to the TRACE 171 Å channel intensity above the umbra. The 3-min oscillations fill the sunspot umbra in the transition region. In the corona the oscillations are concentrated to smaller regions that appear to coincide with the endpoints of sunspot coronal loops, suggesting that wave propagation along the magnetic field makes it possible for the oscillations to reach the corona.     

Quasi-harmonic faraday-rotation fluctuations of radio waves when sounding the outer solar corona

A statistical analysis of the Faraday-rotation fluctuations (FRFs) of linearly polarized radio signals from the Helios 1 and Helios 2 spacecraft shows that the FRF time power spectra can be of three types. Spectra of the first type are well fitted by a single power law in the range of fluctuation frequencies 1–10 mHz. Spectra of the second type are a superposition of a power law and two quasi-harmonic components with fluctuation frequencies of about v₁=4 mHz (fundamental frequency) and v₂=8 mHz (second harmonic). Spectra of the third type exhibit only one of the two quasi-harmonic components against the background of a power law. The spectral density of the quasi-harmonic components can be represented by a resonance curve with a fairly broad [Δυ ≈ (0.5–1.3)υ_1,2] distribution relative to the v=v_{1, 2} peak. The intensity of the quasi-harmonic FRF has a radial dependence that roughly matches the radial dependence for the background FRF, while their period at the fundamental frequency is approximately equal to the period of the wellknown 5-min oscillations observed in the lower solar atmosphere. The fluctuations with 5-min periods in FRF records can be explained by the presence in the outer corona of isolated trains of Alfvén waves generated at the base of the chromosphere-corona transition layer and by acoustic waves coming from deeper layers.     

Enhanced acetylene emission near the north pole of jupiter

We report observations of acetylene emission lines near 13.3 μm on Jupiter recorded at the NASA Infrared Telescope Facility in July 1984. A strong enhancement in the intensity of R₁₀ line of the ν₅ band was recorded within a well-localized region coincident with the southern extension of footprint of the Io magnetic lines and with previous observations of localized enhanced emission of CH₄ lines. The line intensity was fairly constant outside this “bright spot.” Moreover, weak lines of the hot bands 2ν₅ - ν₅, and (ν₄ + ν₅) - ν₅ were observed within the bright spot. From the field of view and the precision of the pointing, the zone of activity of the bright spot is found to be: latitude = 59 ± 10° and longitude = 178 ± 10° (System III, 1965). The location of the spot was found to be constant over a 3-day period. Two interpretations are proposed to explain these observations: (1) a variation of the C₂H₂ abundance and (2) an alteration of the thermal profile in the bright spot. Either may result from precipitation of charged particles near and below the Jovian homopause.     

New light on solar infrared intensity oscillations

The detection of large-amplitude infrared solar intensity oscillations in the 5-min region is reported. Using a broad-band multichannel photometer, the peak-to-peak intensity variation at 2.23 m is found to be as high as 2.4% for a circular aperture of 1 arc min and 0.8% in the full disk observations, i.e., remarkably higher than at the other four observed wavelength regions.The spatially-integrated power spectrum shows the 5-min oscillation plus a strong feature near 4 mHz. This feature coincides in frequency with the fundamental p-mode resonance of the chromosphere. However, a power-spectrum autocorrelation as well as a second-order Fourier transform of the data suggest that a high-frequency tail of the 5-min power spectrum is a more likely interpretation of this feature.     

The necessity of fundamental emission in type III bursts

Observations of some type III radio bursts in the hectometer and kilometer wave range are compared with theoretical predictions. It is shown that the burst emission must be near the plasma frequency in the region between 10 R _⊙ and 50 R _⊙ in order to be consistent with the observed steep rise in brightness temperature for these bursts. The results of Fainberg, Malitson et al., and Haddock and Alvarez are discussed and compared with the interpretation of emission near the plasma frequency.     

On the possibility of heating of local solar chromospheric regions by magnetoacoustic-gravity waves in a thin flux tube

The response of an isothermal atmosphere of a thin vertical magnetic flux tube to the presence of an acoustic-gravity wave field in the external medium is considered. The Laplace transform method is used to solve a problem with initial conditions. The structure of the solution for disturbances in the tube is a superposition of forced oscillations at the source frequency and oscillations decaying as ～ t ^?3/2 (the so-called wave wake). Both components are analogues of the corresponding disturbances in an external medium with a modified amplitude. The excitation under consideration is shown to be effective in the ranges of external oscillation frequencies 0 mHz ≤ v ≤ 3.3 mHz and v ≥ 6.5 mHz. The time-averaged energy flux density for high-frequency magnetoacoustic-gravity waves in the tube is estimated to be ∝ 3.0 × 10⁷ erg cm^?2 s^?1, a value of the same order of magnitude as that required for heating local regions in the solar chromosphere, ∝ 10⁷ erg cm^?2 s^?1.     

Peak Frequency Dynamics in Solar Microwave Bursts

We analyze the dynamics of the broadband frequency spectrum of 338 microwave bursts observed in the years 2001?–?2002 with the Owens Valley Solar Array. A subset of 38 strong microwave bursts that show a single spectral maximum are studied in detail. Our main goal is to study changes in spectral peak frequency ν _pk with time. We show that, for a majority of these simple bursts, the peak frequency shows a high positive correlation with flux density – it increases on the rise phase in ≈83% of 24 bursts where it could be cleanly measured, and decreases immediately after the peak time in ≈62% of 34 bursts. This behavior is in qualitative agreement with theoretical expectations based on gyrosynchrotron self-absorption. However, for a significant number of events (≈30?–?36%) the peak frequency variation is much smaller than expected from self-absorption, or may be entirely absent. The observed temporal behavior of ν _pk is compared with a simple model of gyrosynchrotron radio emission. We show that the anomalous behavior is well accounted for by the effects of Razin suppression, and further show how an analysis of the temporal evolution of ν _pk can be used to uniquely determine the relative importance of self-absorption and Razin suppression in a given burst. The analysis technique provides a new, quantitative diagnostic for the gyrosynchrotron component of solar microwave bursts. Applying this analysis technique to our sample of bursts, we find that in most of the bursts (60%) the spectral dynamics of ν _pk around the time of peak flux density is caused by self-absorption. On the other hand, for a significant number of events (≈70%), the Razin effect may play the dominant role in defining the spectral peak and dynamics of ν _pk, especially on the early rise phase and late decay phase of the bursts.     

Power spectrum analysis of limb and disk spicule using Hinode Ca H-line broadband filter

We present observations of a solar quiet region obtained using the Hinode Solar Optical telescope (SOT) in the Ca II H-line with broadband filter taken on November 2006. We study off-limb and on-disk spicules to find a counterpart of the limb spicule on the disk. This investigation shows a strong correspondence between the limb and near limb spicules (on-disk spicules that historically were called dark or bright mottles, especially when observed in Hα, being a rather cool line) from the dynamical behavior (e.g., periodicity). An excellent time sequence of images obtained near the equatorial region with a cadence of 8 s was selected for analysis. 1D Fourier power spectra made at different positions on the disk and above the limb are shown. We take advantage of the so-called mad-max operator to reduce the effects of overlapping and improve the visibility of these hair-like features. A definite signature with strong power in the 3-min (5.5 mHz) and 5-min (3.5 mHz) oscillations for both places exists. A full range of oscillations was found and the high frequency intensity fluctuation (greater than 10 mHz or less than 100 s) corresponding to the occurrence of the so-called type II spicules and, even more impressively, dominant peaks of Fourier power spectra are seen in a wide range of frequencies and for all places of “on” and “off” disk spicules, in rough agreement with what historical works report regarding disk mottles and limb spicules. Also, some statistically significant behavior, based on the power spectrum computed for different positions, is discussed. The power for all kinds of power spectra is decreasing with increasing distance from the limb, except for photospheric oscillations (5 min or p-mode), which show a dominant peak for on-disk power spectra.     

On the discovery of new behaviour in the oscillation of HD 101065

A 9 h of observation through high-speed B photometry was carried out on HD 101065 using the 0.5-m telescope of the South African Astronomical Observatory (SAAO). These photometric data were obtained between 2013 April 21 and June 19, in search of temporal variations in the oscillation of HD 101065. The frequency analysis of our data sets shows that the known principal frequency of oscillation (${\nu }_1=1.37287$ mHz) is still much intact. On nightly basis, we detected the presence of secondary frequencies (ν₂) that are well resolved from the principal frequency (ν₁) in the region of 1.0 mHz (P ∼ 17 min). These frequencies with very good signal-to-noise ratio have no harmonic period ratio with the principal frequency (ν₁). Furthermore, the amplitude spectra of individual nights reveal that the newly detected frequency (ν₂) is undergoing amplitude modulation on a short time-scale of few hours.     

Variations of microwave emission from solar active regions

Based on observational data obtained with the RT-22 Crimean Astrophysical Observatory radio telescope at frequencies of 8.6 and 15.4 GHz, we investigate the quasi-periodic variations of microwave emission from solar active regions with periods T_p<10 min. As follows from our wavelet analysis, the oscillations with periods of 3–5 min and 10–40 s have the largest amplitudes in the dynamic power spectra, while there are virtually no oscillations with T_p<10 s. Our analysis shows that acoustic modes with T_p?1 min strongly dissipate in the lower solar corona due to thermal conduction losses. The oscillations with T_p=10–40 s are associated with Alfvén disturbances. We analyze the influence of acoustic and Alfvén oscillations on the thermal mechanisms of microwave emission in terms of the homogeneous model. We discuss the probable coronal heating sources.     

Frequency splitting in stria bursts: Possible roles of low-frequency waves

The kinematics of the process L ± F→ L′ are explored where L represents a parallel Langmuir wave, F represents a low frequency fluctuation and L′ represents a secondary Langmuir wave, and the results are used to discuss (a) a possible interpretation of the frequency splitting in stria bursts in terms of the processes L ± F → L′, L′ ± F′ → t, where t represents a transverse wave, and (b) second harmonic emission due to the processes L ± s→ L′, L + L′ → t, where s represents an ion sound wave. The following results are obtained:

1. The processes L ± s → L′ are allowed only for k _s < 2k _L ± k ₀, respectively, with k ₀ = ω _p /65 V _e .
2. The inclusion of a magnetic field does not alter the result (1) and adds further kinematic restrictions related to angles of propagation; the kinematic restriction T _e > 5 × 10⁵ K for second harmonic emission through process (b) above is also unchanged by inclusion of the magnetic field. The effect of a spread in the wavevectors of the Langmuir waves on this restriction is discussed in the Appendix.
3. For parallel Langmuir waves the process L - F → L′ is forbidden for lower hybrid waves and for nearly perpendicular resonant whistlers, and the process L + F → L′ is allowed only for resonant whistlers at ω _F ? 1/2ω _p (Ω _e /ω _p )².
4. The sequential three wave processes L ± s → L′, L′ ± s → t and L + F → L′, L′ ± F′ → t encounter difficulties when applied to the interpretation of the splitting in split pair and triple bursts.
5. The four-wave process L ± F ± F′ → t is kinematically allowed and provides a favourable qualitative interpretation of the splitting when F denotes a resonant whistler near the frequency mentioned in (3) above. The four wave processes should saturate under conditions which are not extreme and produce fundamental plasma emission with brightness temperature T _t equal to the effective temperature T _L of the Langmuir waves.

     

Electron plasma oscillations associated with type III radio emissions and solar electrons

An extensive study of the IMP-6 and IMP-8 plasma and radio wave data has been performed to try to find electron plasma oscillations associated with type III radio noise bursts and low-energy solar electrons. This study shows that electron plasma oscillations are seldom observed in association with solar electron events and type III radio bursts at 1.0 AU. In nearly four years of observations only one event was found in which electron plasma oscillations are clearly associated with solar electrons. For this event the plasma oscillations appeared coincident with the development of a secondary maximum in the electron velocity distribution functions due to solar electrons streaming outwards from the Sun. Numerous cases were found in which no electron plasma oscillations with field strengths greater than 1 μV m^?1 could be detected even though electrons from the solar flare were clearly detected at the spacecraft. For the one case in which electron plasma oscillations are definitely produced by the electrons ejected by the solar flare the electric field strength is relatively small, only about 100 μV m^?1. This field strength is about a factor of ten smaller than the amplitude of electron plasma oscillations generated by electrons streaming into the solar wind from the bow shock. Electromagnetic radiation, believed to be similar to the type III radio emission, is also observed coming from the region of the more intense electron plasma oscillations upstream of the bow shock. Quantitative calculations of the rate of conversion of the plasma oscillation energy to electromagnetic radiation are presented for plasma oscillations excited by both solar electrons and electrons from the bow shock. These calculations show that neither the type III radio emissions nor the radiation from upstream of the bow shock can be adequately explained by a current theory for the coupling of electron plasma oscillations to electromagnetic radiation. Possible ways of resolving these difficulties are discussed.     

A search for 5 min periodic structure in solar 2 cm emission

Two hundred and eighty-five hours of solar data obtained from the University of Iowa 2 cm radiometer during 1968–1969 were analyzed for evidence of periodic structure related to the 5 min periodic chromospheric oscillations detected in optical line emissions. A power spectral analysis of the data failed to show any statistically significant (> 96 % confidence) periodic activity in the frequency range 1–15 mHz (periods of 1–16 min) for data organized according to solar activity in H, soft solar X-rays (2–12 ), and several microwave frequencies (3–15 GHz).A small shift in power from low to higher frequencies in the power spectrum of the 2 cm data was found to be correlated with H and X-ray activity. This power shift is attributed to a relative increase in chromospheric turbulence at altitudes common to H, X-ray, and 2 cm emission.Consistent statistical analyses of previous works reporting evidence for oscillations at microwave and extreme-ultraviolet frequencies indicate that confidence in these previous results is marginal.A model for chromospheric oscillation bursts in quiescent supergranules is incorporated into a statistical analysis of the power spectrum detectability of the oscillations to understand the negative results obtained.     

Global Pc5 wave activity observed using SuperDARN radars and ground magnetometers during an extended period of northward IMF

Observations are presented of long-lived global Pc5 ULF wave activity observed at a wide range of local times. The event was monitored in the high latitude ionosphere (∼60–80° magnetic latitude) by several SuperDARN HF radars and 5 magnetometer chains in Scandinavia, Greenland, Canada, Alaska and Russia. The event coincided with a protracted period (∼36 h) of northward interplanetary magnetic field (IMF). The study focuses on 4 h during which distinct dawn/dusk asymmetries in the wave characteristics were observed with multiple field line resonance (FLR) structures observed in the dawn flank at 1.7, 2.6, 3.3, 4.2 and 5.4 mHz and compressional oscillations in the dusk flank at 1.7 and 2.3 mHz. The data indicated an anti-sunward propagation in both the dawn and dusk flanks and a low azimuthal m number (∣m∣∼6) suggesting a generation mechanism external to the Earth's magnetosphere. A sudden increase in the solar wind dynamic pressure followed by a period of strongly northward, B_z dominated IMF, coincides with the observations and also a large increase in Pc5 wave power observed in the dawn flank. The observed enhancements in the wave activity and FLR structures are thought to be due to a Kelvin–Helmholtz driven waveguide mode. Additionally, there is no evidence that the frequencies of the FLRs are intrinsic to the solar wind. It thus seems that the frequencies were determined by the dimensions of the magnetospheric cavity.     

Measurements of the Matter Density Perturbation Amplitude from Cosmological Data

The various measurements of the linear matter density perturbation amplitude obtained from the observations of the cosmic microwave background (CMB) anisotropy, weak gravitational lensing, galaxy cluster mass function, matter power spectrum, and redshift space distortions are compared. The Planck data on the CMB temperature anisotropy spectrum at high multipoles, ? > 1000 (where the effect of gravitational lensing is most significant), are shown to give a measurement of the matter density perturbation amplitude that contradicts all other measurements of this quantity from both Planck CMB anisotropy data and other data at a significance level of about 3.7σ. Thus, at present these data should not be combined together for the calculations of constraints on cosmological parameters. Except for the Planck data on the CMB temperature anisotropy spectrum at high multipoles, all the remaining measurements of the density perturbation amplitude agree well between themselves and give the following constraints: σ₈ = 0.792± 0.006 on the linear matter density perturbation amplitude, Ω_m = 0.287± 0.007 on the matter density parameter, and H₀ = 69.4 ± 0.6 km s^?1 Mpc^?1 on the Hubble constant. Various constraints on the sum of neutrino masses and the number of neutrino flavors can be obtained by additionally taking into account the data on baryon acoustic oscillations and (or) direct Hubble constant measurements in the local Universe.     

The Sun and the transcendental world of binaries

The theory of gravity says that a binary with orbital frequency ν should be a source of gravitational waves at the double frequency and higher harmonics. This implies that long-term exposure of an ensemble of binaries to gravity waves with frequency ν _G can result in (a) a lack of binaries with frequencies near frequency ν _G /2 and its higher harmonics (the effect of unstable orbits) and/or (b) an excess of binaries whose orbital frequencies are “absolutely” incommensurable with ν _G /2 and its higher harmonics (the effect of stable orbits). It is assumed that the stable-orbit frequencies are almost equal to multiples of πν _G /2 and ν _G /2π, where π plays the role of a “perfect” factor ensuring the best antiresonance of binaries. The statistical analysis of frequencies of 5774 Galactic close binary systems (CBSs) with periods P less than 10 days is based on calculating the resonance spectrum that indicates the best common multiple for a given set of frequencies with allowance for the factor π. The CBS distribution turns out to be modulated by the frequency ν _G = 104.4(5) μHz, and this effect is the most pronounced for superfast and compact rotators, such as cataclysmic variables (CVs) and related objects. The frequency ν _G is, within the error, equal to the “enigmatic” frequency ν₀ = 104.160(1) μHz com discovered earlier in the power spectra of the Sun and brightness variations of some extragalactic sources. This confirms the existence of a “coherent cosmic oscillation” of the Universe with frequency ν₀(ν _G ). The new astrophysical phenomenon naturally explains an “CV period gap” at frequencies ≈πν _G /3 (P ≈ 153 min) and maxima at the neighboring frequencies ≈πν _G /2 and ≈πν _G /4 (P ≈ 102 and ≈204 min, respectively). The remarkable and “mysterious” role of the transcendental number π for the world of binaries is emphasized, and the mystery of physical nature of the “universal” oscillation ν₀(ν _G ) is highlighted.     

Frequency Fine Structures of Type III Bursts Due to Localized Medium-Scale Density Structures Along Paths of Type III Beams

Predictions from large-scale kinetic simulations are presented for the effects on coronal type III bursts of localized, medium-scale, enhanced density structures superposed on the coronal background along the paths of type III beams. The simulations show that these density structures can produce pronounced frequency fine structures in type III spectra. Flux intensifications and reductions of f _p and 2f _p emission relative to those for the unperturbed background corona occur at frequencies corresponding to the density structures, where f _p is the local electron plasma frequency. Frequency fine structures that are intense, slowly drifting, and narrowband, and thus resemble the characteristics of stria bursts, are predicted for the 2f _p emission. The 2f _p results are consistent with the qualitative proposal of Takakura and Yousef (Solar Phys. 40, 421, 1975) for the interpretation of stria/type IIIb bursts. However, the predicted f _p emission is much weaker than the 2f _p emission and generally below observable levels, and the predicted frequency fine structures do not always show stria characteristics. The predictions are thus inconsistent with the qualitative suggestion of Takakura and Yousef and the interpretations of many observers that stria bursts occur more often in f _p than in 2f _p emission. The significant discrepancies for f _p emission between our numerical calculations and the qualitative proposition of Takakura and Yousef (1975) are mainly caused by: i) differences in the detailed emission processes, ii) neglect of scattering of f _p emission off small-scale density fluctuations by Takakura and Yousef (1975), and iii) other simplifications made in both works. Possible improvements to the simulations are discussed, including improvements to the emission processes and the coronal and beam conditions (e.g., beam speed), in order to produce realistic stria/type IIIb bursts in f _p emission.     

Spectral properties of hydromagnetic fluctuations near 4 and 5 a.u.

Power spectra of vector components of interplanetary magnetic field fluctuations near 4–5 a.u. during quiet intervals show a frequency dependence very close to f^s over the frequency range 4 × 10^?5 to 9 × 10^?3 Hz (corresponding to periods of 7 h-2 min). While the spectra are generally very close to power law in frequency, variations in slope among the spectra exceed those expected from random errors and may represent true temporal variations. Mean slopes corrected for systematic error are s = ? 1.50±0.02 (Pioneer 10, mean heliocentric distance 5.3 a.u.) and s = ? 1.52±0.02 (Pioneer 11, mean heliocentric distance 3.9 a.u.) and are consistent with several determinations of spectral slope for magnetic fluctuations near 1 a.u. Radial evolution of the perturbations is investigated by choosing data samples in which Pioneer 10 and 11 and the sun are nearly colinear. The dependence on heliocentric distance of σ_c², the composite vector variance, and of σ_c/B_mag, where B_mag is the mean magnitude of the magnetic field, show that the radial variation of fluctuation amplitude is highly variable in time with a dependence on heliocentric distance typically in the range R^?1 to R^?1.5. These observations are compared with theoretical models of outward propagating Alfven waves of solar origin and of MHD turbulence. The mean slopes agree well with that expected for turbulence. The significant variability observed in spectral slopes and in the radial dependence of fluctuation amplitude in data selected specifically for conditions of relative magnetic quiet is noteworthy and urges caution in modeling heliospheric magnetic microstructure in studies of galactic cosmic ray modulation.     

EGRET observations of > 30 MeV emission from the brightest bursts detected by BATSE

EGRET on the Compton Gamma Ray Observatory has detected 5 gammaray bursts above 30 MeV. The sub-MeV emission, as detected by BATSE, for these 5 bursts has the largest fluence,F, and peak intensity,I, of any of the BATSE detected bursts within the EGRET field of view. The BATSE data reported in the 2B catalog and the EGRET exposure,E, are combined to select additional bursts with largeF ×E andI ×E. The EGRET data for these bright BATSE bursts are searched for prompt, as well as delayed, emission above 30 MeV. The average properties of the >30 MeV emission are obtained by adding the EGRET data from the 5 bursts. On average the fluence is greater than 15% of the fluence detected by BATSE below an MeV, and the average spectrum is flatter than the spectrum from 1-30 MeV.     

Forecasting the intensity of solar proton events from the time characteristics of solar microwave bursts

A survey of the main characteristics of solar microwave bursts in relation to their usefulness for indicating the intensity of associated solar proton emissions suggests that time parameters give much better results than intensity or spectrum parameters. In particular, best results are obtained by using the effective, or mean, burst duration defined by $$T_M = 1/P_{max} \int_0^T {P(t)dt} $$ where T is the overall burst duration, P is the power density at time T, and P _max is the maximum power density. For proton energies > 10 MeV the proton flux N _p is given approximately by N _p = 0.034 T _M ³ particles ster^?1 cm^?2 s^?1, where T _m is in minutes, with a correlation factor of 0.8. Corresponding coefficients have been derived for a number of energy ranges. Using this parameter solar proton warnings and intensity estimates can be made with observations at only one frequency, preferably in the range 5–20 GHz.