Spectral observations of spicules at two heights in the solar chromosphere

An observational program at the Sacramento Peak Observatory in 1965 provided high-dispersion spectra of the solar chromosphere in several spectral regions simultaneously. These regions included various combinations of the spectral lines Hα, Hβ and H?, the D₃-line of Hei, the infrared triplet of Oi, and the H- and K-lines and the infrared triplet of Caii. With the use of an image slicer the observations were made simultaneously at two heights in the solar chromosphere separated by several thousand kilometers. From these data we draw the following conclusions:

1. Emission of different lines arises in the same chromospheric features. The intensity ratio of lines of different elements varies significantly from spicule to spicule. For the H- and K-lines of ionized calcium, this ratio remains constant, independent of wavelength throughout the line, overall intensity, and height in the chromosphere. Two rare-earth lines in the wing of the H-line show no spicular structure at all.
2. The line-of-sight velocities of many features reverse as a function of time, although most spicules show velocities in only one direction. The simultaneous spectra at two heights show most spicules to have the same line-of-sight velocity at both. There may be an additional class of features, mostly rapidly moving, whose members have line-of-sight velocities that increase with height. These features comprise perhaps 10% of the total. Velocity changes occur simultaneously, to within 20 sec, at two heights separated by 1800 km, indicating velocities of propagation of hundreds of km/sec. The velocity field of individual features is often quite complicated; many spectral features are inclined to the direction of dispersion, implying that differential mass motions are present.
3. The existence of anomalously broad H and K profiles is real. Even with high dispersion and the best seeing, such profiles are not resolved into smaller features. The central reversal in K, H and Hα appears to remain unshifted when the wings are displaced in wavelength, indicating that the reversal is non-spicular.

     

A morphological study of solar spicules

From improved spicule filtergrams obtained with the Sacramento Peak vacuum telescope we measured some spicule properties. The spicule diameter of 950 km was well resolved. A small decrease of diameter with height was observed confirming older observations. The expansion of the spicule was found to be at least an order of magnitude less than reported by Mouradian. Spicule counts are very sensitive to the threshold intensity of the observations. Counts, and their dependence on threshold intensity, height and wavelength are reported.On leave from the Astronomy Department, University of Texas, Austin, Texas.     

Observation of kink waves and their reconnection-like origin in solar spicules

We analyze the time series of Ca?ii H-line obtained from Hinode/SOT on the solar limb. We follow three cases of upwardly propagating kink waves along a spicule and inverted Y-shaped structures at the cusp of it. The time-distance analysis shows that the axis of spicule undergos quasi-periodic transverse displacement at different heights from the photosphere. The mean period of transverse displacement is ～175 s and the mean amplitude is 1 arc?sec. The oscillation periods are increasing linearly with height which may be counted as the signature that the spicule is working as a low pass filter and allows only the low frequencies to propagate towards higher heights. The oscillations amplitude is increasing with height due to decrease in density. The phase speeds are increasing until some heights and then decreasing which may be related to the small scale reconnection at the spicule basis. We conclude that transversal displacement of spicules axis can be related to the propagation of kink waves along them. Moreover, we observe signatures of small-scale magnetic reconnection at the cusp of spicules which may excite kink waves.     

Continuous spectral observations of spicules

D₃ and H line spectrograms of spicules are analysed. The spectrograms are obtained with a specific device attached to the 53 cm coronagraph of Abastumani Astrophysical Observatory. Certain results are derived, based on the observational material consisting of 70 height series spectrograms taken over a period of 44 min in H line and 60 height series spectrograms taken over a period of 30 min in D₃. Each series involves 8 spectrograms reflecting the state of spicules at eight different heights in the chromosphere.     

Non-rigid rotation of solar spicules

Hα profiles of chromospheric spicules computed for a variety of rotational behavior are compared with an observed profile, which was derived by averaging 11 Hα profiles taken near times of maximum spicule intensity. If turbulent velocity is small or equals zero, calculated profiles are in good agreement with the observed one under the conditions that rotation is non-rigid (faster rotation further away from the axis of the spicule) and the source function decreases in the direction from the spicule axis to the periphery. The comparison of calculated and observed tilts of spicule spectra relative to the direction of dispersion seems to corraborate the non-rigid character of spicular rotation.     

A statistical analysis of hard X-Ray solar flares

In this study we perform a statistical study on, 8319 X-Ray solar flares observed with the Hard X-Ray Burst Spectrometer (HXRBS) on the Solar Maximum Mission satellite (SMM). The events are examined in terms of the durations, maximum intensities, and intensity profiles. It is concluded that there is no evidence for a correlation between flare intensity, flare duration, and flare asymmetry. However, we do find evidence for a rapid fall-of in the number of short-duration events.     

On physical properties of solar spicules

New observations of solar spicules at Pulkovo, made simultaneously in 4 spectral regions, are described. The profiles of the H, D3, H, H and K lines were derived for 23 spicules.The spicules occur usually in narrow bundles and can be resolved into separate objects only due to a dispersion of radial velocities inside the bundle. The spicules in D3 are diffuse with faint interspicular emission.The emission of hydrogen, helium and Caii originate in different parts of spicules with different radial and turbulent velocities. The core of a spicule with Caii emission is a narrow rope several tens of km in diameter for the normal section. The optical thickness of a spicule in H is approximately 1.0 and the atomic density varies from 10¹¹ to 10¹² cm^–3.The helium emission in spicules seems to be produced by different mechanisms, one of them being the external radiation of corona and subcoronal matter.The model of a solar spicule is discussed.     

A statistical analysis of large-scale brightness and velocity fluctuations in the solar atmosphere

Simultaneous photoelectric recordings of the intensities and the Doppler shifts in 5 Fraunhofer lines (H, Na D₁, Mg b₂, Fe5123, Fe5223) were used to study the structure of local large-scale fluctuations of the intensity and velocity in different layers of the solar atmosphere. We derived the autocorrelation and cross-correlation functions and the powerspectra of the fluctuations. Fluctuation patterns with a characteristic size of 3–4 × 10⁴ km were found in all observed lines. The intensity of the fluctuations decreases sharply from the chromospheric H-core to the weak iron lines. The results are discussed in terms of the solar supergranulation pattern.     

Study of the brightness distribution across spicules from observations of the spicule occultation by the Moon at the partial solar eclipse

Cinematographic observation of the spicule occultation by the Moon have been carried out at the partial solar eclipse of October 2, 1978. The relative brightness distribution across a spicule in the light of H + 0.8 Å is first obtained. The diameter values for two spicules have been found to be of 280 ± 40 km and 1200 km.     

The study of magnetic reconnection in solar spicules

This work is devoted to study the magnetic reconnection instability under solar spicule conditions. Numerical study of the resistive tearing instability in a current sheet is presented by considering the magnetohydrodynamic (MHD) framework. To investigate the effect of this instability in a stratified atmosphere of solar spicules, we solve linear and non-ideal MHD equations in the x?z plane. In the linear analysis it is assumed that resistivity is only important within the current sheet, and the exponential growth of energies takes place faster as plasma resistivity increases. We are interested to see the occurrence of magnetic reconnection during the lifetime of a typical solar spicule.     

Observation of standing kink waves in solar spicules

We analyze the time series of Ca ii H-line obtained from Hinode/SOT on the solar limb. The time-distance analysis shows that the axis of spicule undergos quasi-periodic transverse displacement at different heights from the photosphere. The mean period of transverse displacement is ∼180 s and the mean amplitude is 1 arc sec. Then, we solve the dispersion relation of magnetic tube waves and plot the dispersion curves with upward steady flows. The theoretical analysis shows that the observed oscillation may correspond to the fundamental harmonic of standing kink waves.     

A spectroscopic study of solar spicules in Hα, Hβ and K

Simultaneous spectra of spicules in H, H and the Ca ii K have been analyzed. These spectra were obtained with the échelle spectrograph of Sacramento Peak Observatory and have a resolution of 1.5 s of arc. Data include absolute intensities, velocities, linewidths and the optical depth at the center of H. Electron densities range between 6 × 10¹⁰cm^–3 and 1.2 × 10¹¹cm^–3, while the range of the electron temperature is between 12000K and 15000K at a height of 5400 km above the limb. The analysis of the variation of the line of sight velocity across spicules shows that their rotation is very small. There is very good correlation in the structure of all three lines.     

Solar neutron observations and their relation to solar flare acceleration problems

We review the current observational knowledge on the production of neutrons in association with solar flares. From a study of the observations it is shown that unique information can be obtained on the spectral properties of accelerated ions produced during the flare. Also, the abundance of ³He/H in the photosphere can be directly determined. We also review the current interpretations of all available neutron observations and in particular highlight the uncertainties, and provide guide posts for future experiments.     

A statistical analysis of NaI D1 profile fluctuations at the center of the solar disk

Three radial-velocity fluctuation arrays V(Δλ, Y) and line-formation fluctuation arrays L(Δλ, Y),where Δλ is wavelength displacement from the center of Nai D₁ and Y is displacement on the Sun's surface along the spectrograph slit, were obtained from Sacramento Peak Observatory spectrograms. The variations of these line profile fluctuations are qualitatively described. The RMS_υ's, coherences, and power spectra shapes for V(Δλ, Y) fluctuations are examined at different Δλ with the corresponding effective heights of formation calculated with Mein weighting functions. Results include: (a) possible anticorrelation between continuum fluctuations and those near line center; (b) RMS _υ ^(cr) 's, which are root-mean-square values of the radial velocity corrected for instrumental and atmospheric blurring, are large (1.5 to 4.0 km s^?1) primarily due to large corrections for atmospheric blurring; (c) RMS _υ ^(cr) minima at effective heights of formation above 350 km suggest penetration of granulation velocities into the upper photosphere; (d) very rough determinations of RMS _υ ^(cr) 's, which are additionally corrected for line-of-sight averaging, range from around 5 km s^?1 in the low chromosphere to a sharp minimum ≤ 0.5 km s^?1 located in the upper photosphere; (e) power spectra shapes reflect decreasing average fluctuation scales above the temperature minimum (possibly high-frequency oscillations) and in the low and middle photosphere (possibly penetration of granulation); and (f) RMS _υ ^(cr) 's and average fluctuation scales suggest changes in the resolvable velocity field occurring near the temperature minimum.     

Antenna performance analysis for decameter solar radio observations

Decameter wavelength radio emission is finely structured in solar bursts. For their research it is very important to use a sufficient sensitivity of antenna systems. In this paper we study an influence of the radiotelescope‐antenna effective area on the results of decameter solar radio observations. For this purpose we compared the solar bursts received by the array of 720 ground‐based dipoles and the single dipole of the radiotelescope UTR‐2. It is shown that a larger effective area of the ground‐based antenna allows us to measure a weaker solar emission and to distinguish a fine structure of strong solar events. This feature has been also verified by simultaneous ground‐ and space‐based observations in the overlapping frequency range (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A statistical study of the interdependence of solar wind parameters

Correlation analysis of solar wind parameters, namely solar wind velocity, pro- ton density, proton temperature and mean interplanetary magnetic field (IMF) from the ACE spacecraft data near Earth, was done. To our best knowledge, this study is a novel one since we consider here only the parameters inside the solar wind, including the mean IMF and, hence, the solar wind is a self consistent system. We have proposed a Multiple Linear Regression (MLR) model for the prediction of the response variable (solar wind velocity) using the parameters proton density, proton temperature and mean IMF mea- sured as dally averages. About 60% of the observed value can be predicted using this model. It is shown that, in general, the correlation between solar wind parameters is sig- nificant. A deviation from the prediction at the solar maximum is interpreted. These results are verified by a graphical method.     

The Zeeman pattern of magnetic lines and their statistical properties in the Fei solar spectrum

The Zeeman patterns of magnetic lines are characterized by their first, second, and third order moments and a minimal equivalent representation is suggested for each line. The statistical properties of the Zeeman patterns of the Fe i lines in the solar optical spectrum are analyzed in detail and the various patterns are classified in three different types according to the relative position of the -components having larger strength.     

The work of the diode array: He 10 830 observations of spicules and subflares

At a spatial resolution of 1″ and with spectral passbands of 0.25–0.47 Å, the chromospheric fine structure was studied with an array of 512 silicon photodiodes. The high quantum efficiency of the diodes in the near infrared allowed low noise spectroheliograms to be constructed from observations in the lines of H i, Ca ii, and He i. Magnetograms of the underlying photosphere were obtained simultaneously. Tachograms in the He 10830 Å line revealed 1″ points and elongated features that are interpreted as spicules seen against the disk. Active regions and filaments at 10830 are compared with Hα and Ca ii (8542 Å) features. Filament contrast increases with the proximity of bright plage. Twelve subflares were studied and in eight cases, 3–5″ kernels of He I emission appeared over small, growing pores or over 5″ patches of magnetic field emerging through the photosphere. All the subflares showed 10830 emission, contrary to established belief that the 10830 line goes into emission only in the largest flares. All the subflares included at least one emission kernel over regions where the photospheric magnetic field, as seen with a resolution of 1–2″, broke down into a mosaic of both polarities with 3–5″ diam. elements.     

A statistical study of the spiral spots on the solar disc

After adding the data observed in the years from 1979 to 1982 to those obtained earlier (Ding et al., 1981), we re-examine the previous results and conclude:

1. The longitudinal distribution of spiral spots on the solar disc is generally the same as that of sunspot groups with areas of S _p ≥ 400, but their active longitudes seem to be more concentrated.
2. The distribution of spiral patterns in the southern and northern hemispheres shows that the differential rotation may be a fundamental solar dynamo for the formation of the spiral spots.
3. The statistical directions of the emerging twisted magnetic vectors in the active regions in the southern and northern hemispheres are synchronously inverse with a period of about two years. This period seems to be detected in other solar observations.