Shifts of the Caii K line in Hei 10830 dark points

We investigate the velocity field of the solar chromosphere at the location of 65 He i 10830 dark points (DP's). We have obtained spectra of such points in the vicinity of the Ca II K line. As a measure of differential chromospheric velocity, we use the shift of the K line center relative to a nearby photospheric Fe i line. We find that in He i DP's, the distribution of K line shifts is skewed towards the blue: the blueward skewing is more pronounced in He i DP's located in coronal holes. To the extent that He i DP's are proxies of coronal bright points, our study is relevant to previous reports of outflows from such bright points.     

Solar–Stellar Irradiance Comparison Experiment II (Solstice II): Instrument Concept and Design

The Solar–Stellar Irradiance Comparison Experiment II (SOLSTICE II) is one of four experiments launched aboard the Solar Radiation and Climate Experiment (SORCE) on 25 January, 2003. Its principal science objectives are to measure solar spectral irradiance from 115 to 320 nm with a spectral resolution of 1 nm, a cadence of 6 h, and an accuracy of 5% and to determine solar variability with a relative accuracy of 0.5% per year during a 5-year long nominal mission. SOLSTICE II meets these objectives using a pair of identical scanning grating monochromators that can measure both solar and stellar irradiance. Instrument radiometric responsivity was calibrated to ∼3% absolute accuracy before launch using the Synchrotron Ultraviolet Radiation Facility (SURF) at the National Institute for Standards and Technology (NIST) in Gaithersburg, MD. During orbital operations, SOLSTICE II has been making daily measurements of both the Sun and an ensemble of bright, stable, main-sequence B and A stars. The stellar measurements allow the tracking of changes in instrument responsivity with a relative accuracy of 0.5% per year over the life of the mission. SOLSTICE II is an evolution of the SOLSTICE i instrument that is currently operating on the Upper Atmosphere Research Satellite (UARS). This paper reviews the basic SOLSTICE concept and describes the design, operating modes, and early performance of the SOLSTICE II instrument.     

Contribution of chromospheric features to UV irradiance variability from spatially-resolved Ca II K spectroheliograms

We have digitized the Ca ii K spectroheliograms, observed at the National Solar Observatory at Sacramento Peak, for the period 1980 (maximum of solar cycle 21), 1985 (minimum of solar cycle 21), 1987 (beginning of the ascending phase of solar cycle 22), 1988 and 1989 (ascending phase and maximum of solar cycle 22), and 1992 (declining phase of solar cycle 22). A new method for analyzing the K spectroheliograms has been developed and applied to the K images for the time interval of 1992. Using histograms of intensity, we have segregated and measured the cumulative intensity and area of various chromospheric features like the plages, magnetic network and intranetwork elements. Also, the full width at half maximum (FWHM) derived from the histograms has been introduced as a new index for describing the chromospheric activity in the K-line. The full-disk intensity (spatial K index) has been derived from spatially-resolved K images and compared to the spectral K index derived from the line profiles for the full disk. Both the spatial K index and FWHM have been compared to the UV irradiance measured in the Mg ii h and k lines by the NOAA9 satellite and found that they are highly correlated with the Mg ii h and k c/w ratio.NRC Resident Research Associate, on leave from Indian Institute of Astrophysics, Bangalore 560034, India.     

The spectra of near-vertical structures on the solar disk

Bright emission arches in the spectra of H and the Ca II (H and K lines) are identified as the spectroscopic picture of the chromospheric network as it appears near the solar limb. Analysis of the geometrical properties of these spectroscopic arches indicates that the average network is a diverging sheet with a divergence angle of 50°. This sheet extends to 2600 km and 2000 km as an opaque emission feature in H and the Ca II (H and K) lines, respectively.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

Improvements in the Determination of ISS Ca <Emphasis Type="SmallCaps">ii</Emphasis> K Parameters

Measurements of the ionized Ca ii K line are one of the major resources for long-term studies of solar and stellar activity. They also play a critical role in many studies related to solar irradiance variability, particularly as a ground-based proxy to model the solar ultraviolet flux variation that may influence the Earth’s climate. Full disk images of the Sun in Ca ii K have been available from various observatories for more than 100 years and latter synoptic Sun-as-a-star observations in Ca ii K began in the early 1970s. One of these instruments, the Integrated Sunlight Spectrometer (ISS) has been in operation at Kitt Peak (Arizona) since late 2006. The ISS takes daily observations of solar spectra in nine spectra bands, including the Ca ii K and H lines. We describe recent improvements in data reduction of Ca ii K observations, and present time variations of nine parameters derived from the profile of this spectral line.     

Chromospheric rotation during 1972–73, years of declining activity

The rotational behaviour of the chromosphere, observed in the Ca ii K₃ line, is studied during 1972–1973, years of decreasing solar activity. Daily chromospheric filtergrams, detected at the Anacapri Observatory, are digitized by means of a flying-spot photometer, controlled by computer. The time series of the daily chromospheric data detected at central meridian, relative to 30 consecutive latitude zones, are analyzed to determine the recurrence tendency due to the rotation of long-lived chromospheric features. The computed rotation rate is independent of latitude, in agreement with the results obtained for the green corona during the years before sunspot minimum. Namely both chromospheric and coronal features, with lifetime exceeding one solar rotation, are almost not affected by differential rotation before sunspot minimum.     

The Mg II Index from SORCE

The Solar–Stellar Irradiance Comparison Experiment (SOLSTICE) and the Spectral Irradiance Monitor (SIM) on the Solar Radiation and Climate Experiment (SORCE) both measure the solar ultraviolet irradiance surrounding the Mg II doublet at 280 nm on a daily basis. The SIM instrument's resolution (1.1 nm) is similar to the Solar Backscatter Ultraviolet instruments used to compute the standard NOAA Mg II index, while SOLSTICE's resolution is an order of magnitude higher (0.1 nm). This paper describes the technique used to calculate the index for both instruments and compares the resulting time series for the first 18 months of the SORCE mission. The spectral resolution and low noise of the SOLSTICE spectrum produces a Mg II index with a precision of 0.6%, roughly a factor of 2 better than the low-resolution index measurement. The full-resolution SOLSTICE index is able to measure short-timescale changes in the solar radiative output that are lost in the noise of the low-resolution index.     

Do polar faculae on the sun predict a sunspot cycle?

The paper reports the results of the analysis of the data on polar faculae for three solar cycles (1960–1986) at the Kislovodsk Station of the Pulkovo Observatory and on polar bright points in Ca ii K line for two solar cycles (1940–1957) at the Kodaikanal Station of the Indian Institute of Astrophysics. We have noticed that the monthly numbers of polar faculae and polar bright points in Ca ii K line and monthly sunspot areas in each hemisphere of the following solar cycle have a correlation with each other. A new cycle of polar faculae and polar bright points in the Ca ii K line begins after the polar magnetic field reversal. We find that the smaller the period between the ending of the polar field reversal and the beginning of a new sunspot cycle is, the more intense is the cycle itself. The intensity of the forthcoming solar cycle (cycle 22) and the periods of strong fluctuations in activity expected in this cycle are also discussed.     

A Comparison of the Red and Green Coronal Line Intensities at the 29 March 2006 and the 1 August 2008 Total Solar Eclipses: Considerations of the Temperature of the Solar Corona

During the total solar eclipse at Akademgorodok, Siberia, Russia, on 1 August 2008, we imaged the flash spectrum with a slitless spectrograph. We have spectroscopically determined the duration of totality, the epoch of the second and third contacts and the duration of the flash spectrum. Here we compare the 2008 flash spectra with those that we similarly obtained from the total solar eclipse of 29 March 2006, at Kastellorizo, Greece. Any changes of the intensity of the coronal emission lines, in particularly those of Fe x and Fe xiv, could give us valuable information about the temperature of the corona. The results show that the ionization state of the corona, as manifested especially by the Fe xiv emission line, was much weaker during the 2008 eclipse, indicating that following the long, inactive period during the solar minimum, there was a drop in the overall temperature of the solar corona.     

Geoeffectiveness of interplanetary shocks during solar minimum (1995–1996) and solar maximum (2000)

Plasma and magnetic field parameter variations across fast forward interplanetary shocks are analyzed during the last solar cycle minimum (1995–1996, 15 shocks), and maximum year 2000 (50 shocks). It was observed that the solar wind velocity and magnetic field strength variation across the shocks were the parameters better correlated with Dst. Superposed epoch analysis centered on the shock showed that, during solar minimum, B _z profiles had a southward, long-duration variation superposed with fluctuations, whereas in solar maximum the B _z profile presented 2 peaks. The first peak occurred 4 hr after the shock, and seems to be associated with the magnetic field disturbed by the shock in the sheath region. The second peak occurred 19 hr after the shock, and seems to be associated with the ejecta fields. The difference in shape and peak in solar maximum (Dst peak =−50 nT, moderate activity) and minimum (Dst peak =−30 nT, weak activity) in average Dst profiles after shocks are, probably, a consequence of the energy injection in the magnetosphere being driven by different interplanetary southward magnetic structures. A statistical distribution of geomagnetic activity levels following interplanetary shocks was also obtained. It was observed that during solar maximum, 36% of interplanetary shocks were followed by intense (Dst≤−100 nT) and 28% by moderate (−50≤Dst <−100 nT) geomagnetic activity. During solar minimum, 13% and 33% of the shocks were followed by intense and moderate geomagnetic activity, respectively. Thus, during solar maximum a higher relative number of interplanetary shocks might be followed by intense geomagnetic activity than during solar minimum. One can extrapolate, for forecasting goals, that during a whole solar cycle a shock has a probability of around 50–60% to be followed by intense/moderate geomagnetic activity.     

Planetary nebula with a peculiar spectrum in the ultraviolet: CN 3-1

We have obtained IUE ultraviolet spectra of the low-excitation planetary nebula CN 3-1. The recordings show the well-known doublet 2800 MgII and resonance line 2852 MgI as strong absorption lines. We show that these lines cannot be of interstellar origin and that they may be formed in two envelopes surrounding the main nebula: in the transition zone (doublet 2800 MgII) and in the neutral envelope (line 2852 MgI). These envelopes possess an important property: they contain dust particles, and even a moderate amount of such particles may influence the strength of the absorption lines of MgII and MgI.The emission line 4686 HeII has no relation to the nebula CN 3-1 and belongs to its nucleus, a star of type WR. It is very probable that the nucleus of this nebula is a binary system with a WR component (T _*=50 000 K), exciting the helium lines, and a star of B0 or B2 type (T _*=26 000 K) exciting the nebular linesN ₁+N ₂ [OIII], 3727 [OII], hydrogen lines, etc.     

Two Unusual Episodes of ≈13-Day Variations II. Implications for the Solar Radio Flux Density, <Emphasis Type="Italic">F</Emphasis><Subscript>10.7 cm</Subscript>

Additional analysis of the behavior of the international sunspot number (R) series and the solar radio flux density (F_{10.7 cm}) series during two long (250–500 days) and distinct episodes of persistent ≈13-day variations (Crane, Solar Phys. 1998, 253, 177) is reported. The conclusion is that while the center-to-limb behavior of R does not change between solar minimum and solar maximum, F_{10.7 cm} exhibits significantly less limb brightening at solar maximum than at solar minimum.     

Frequency of coronal transients and solar activity

The High Altitude Observatory's white light coronagraph aboard Skylab observed some 110 coronal transients - rapid changes in appearance of the corona - during its 227 days of operation. The longitudes of the origins of these transients were not distributed uniformly around the solar surface (51 of the 100 events observed in seven solar rotations arose from a single quadrant of longitude). Further, the frequency of transient production from each segment of the solar surface was well correlated with the sunspot number and Ca ii plage (area × brightness) index in the segment, rotation by rotation. This correlation implies that transients occur more often above strong photospheric and chromospheric magnetic fields, that is, in regions where the coronal magnetic field is stronger and, perhaps, more variable. This pattern of occurrence is consistent with our belief that the forces propelling transient material outward are, primarily, magnetic. A quantitative relation between transient production from an area and the Zürich sunspot number appropriate to that area is derived, and we speculate that the relation is independent of phase in the solar activity cycle. If true, the Sun may give rise to as many as 100 white light coronal transients per month at solar cycle maximum.Currently at Los Alamos Scientific Laboratory, Los Alamos, N.M., U.S.A.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

Photochemical fractionation of16O in the space medium modeled by resonance excitation of CO by H-Lyman α

Inferences about the formation of primordial matter in our solar system rest on analysis of the earliest preserved materials in meteorites, of the structure of the solar system today, and of matter in evolving stellar systems elsewhere.The isotope distribution in meteorites suggests that molecular excitation processes similar to those observed today in circumstellar regions and dark interstellar clouds were operating in the early solar nebula. Laboratory model experiments together with these observations give evidence on the thermal state of the source medium from which refractory meteoritic dust formed. They indicate that resonance excitation of the broad isotopic bands of molecules such as¹²C¹⁶O, MgO, O₂, AlO, and OH by strong UV line sources such as H-L, MgII, H, and CaII may induce selective reactions resulting in the anomalous isotopic composition of oxygen and possibly other elements in refractory oxide condensates in meteorites.     

Anharmonicity of Stellar Cycles: A Wavelet Quantification

Two quantitative measures for the anharmonicity of stellar cycles, as recorded in the Ca II H and K chromospheric activity data as well as in simple dynamo models, are presented and discussed.     

Physical properties of solar chromospheric plages

We compute a new grid of plage models to determine the difference in temperature versus mass column density structure T(m) between plage regions and the quiet solar chromosphere, and to test whether the solar chromosphere is geometrically thinner in plages. We compare partial redistribution calculations of Mg ii h and k and Ca ii K to NRL Skylab observations of Mg ii h and k in six active regions and Ca ii K intensities obtained from spectroheliograms taken at approximately the same time as the Mg ii observations. We find that the plage observations are better matched by models with linear (in log m) temperature distributions and larger values of m ₀ (the mass column density at the 8000 K layer in the chromosphere), than by models with larger low chromosphere temperature gradients but values of m ₀ similar to the quiet Sun. Our derived temperature structures are in agreement with the grid originally proposed by Shine and Linsky, but our analysis is in contrast to the study by Kelch which implies that stellar chromospheric geometrical thickness is not affected by chromospheric activity. We conclude that either the stellar Mg ii observations upon which the Kelch study was based are of poorer quality than had been assumed, or that the spatial averaging of inhomogeneous structures, which is inherent in the stellar data, does not lead to a best fit one-component model similar in detail to that of a stellar or a solar plage.Visiting Astronomer at Kitt Peak National Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation.Staff member, Quantum Physics Division, National Bureau of Standards.     

Wave reflections in the solar atmosphere

The small phase-lag between velocities observed at different chromospheric levels is interpreted as being due to acoustic waves reflected by the very hot atmospheric layers of the chromosphere-corona transition zone. We consider first an isothermal slab, then a realistic solar atmospheric model and calculate weighting functions for velocities in Ca ii lines. It is shown that taking into account these functions and integrating over horizontal wave numbers leads to a good agreement with previous observations (Mein, 1977) in the case of 8498 and 8542 Ca ii lines. For the K line, the less good agreement shows that magnetoacoustic waves become important in the upper chromospheric layers.     

The solar corona above active regions: A comparison of extreme ultraviolet line emission with radio emission

The observation of extreme ultraviolet (EUV) emission lines of Fe ix through Fe xvi made by Orbiting Solar Observatory-1 are discussed and applied to a study of the solar corona above active regions. Ultraviolet and radio emission are determined and compared for several levels of activity classified according to the type of sunspot group associated with the active region. Both radio emission and line radiation from Fe xvi, the highest stage of ionization of Fe observed, are observed to increase rapidly with the onset of activity and are most intense over an E-spot group early in the lifetime of the active region. As activity diminishes, radiation from Fe xv and Fe xvi becomes relatively more prominent. The observations imply that the coronal temperature reaches a maximum during the period of highest activity, as indicated by sunspot-group complexity and the occurrence of chromospheric flares. A maximum coronal electron temperature of 4.0 × 10⁶ °K is estimated when taking into account the mechanism of dielectronic recombination. Concurrently, the average coronal electron density increases by a factor of 10–12. Both electron temperature and density decrease as activity subsides. The coronal temperature above the remaining Ca ii plage is estimated to be 2.5–3.0 × 10⁶ °K after flare activity has ceased and sunspots have disappeared.     

Solar Modulation of Cosmic Rays during the Declining and Minimum Phases of Solar Cycle 23: Comparison with Past Three Solar Cycles

We study solar modulation of galactic cosmic rays (GCRs) during the deep solar minimum, including the declining phase, of solar cycle 23 and compare the results of this unusual period with the results obtained during similar phases of the previous solar cycles 20, 21, and 22. These periods consist of two epochs each of negative and positive polarities of the heliospheric magnetic field from the north polar region of the Sun. In addition to cosmic-ray data, we utilize simultaneous solar and interplanetary plasma/field data including the tilt angle of the heliospheric current sheet. We study the relation between simultaneous variations in cosmic ray intensity and solar/interplanetary parameters during the declining and the minimum phases of cycle 23. We compare these relations with those obtained for the same phases in the three previous solar cycles. We observe certain peculiar features in cosmic ray modulation during the minimum of solar cycle 23 including the record high GCR intensity. We find, during this unusual minimum, that the correlation of GCR intensity is poor with sunspot number (correlation coefficient R=?0.41), better with interplanetary magnetic field (R=?0.66), still better with solar wind velocity (R=?0.80) and much better with the tilt angle of the heliospheric current sheet (R=?0.92). In our view, it is not the diffusion or the drift alone, but the solar wind convection that is the most likely additional effect responsible for the record high GCR intensity observed during the deep minimum of solar cycle 23.     

The relationship between solar activity and the H and K line cores in integrated sunlight

In this paper we present and analyze new data on the cores of the H and K lines of ionized calcium in the spectrum of integrated sunlight. The intensities of the components H _2v , H₃, H _2r , K _2v , K₃, and K _2r in the line cores were measured in terms of the continuum intensity at 4000 Å during a solar rotation in September 1969. Other data on these components, obtained at or close to the times of solar minimum (September 1964) and solar maximum (September 1968), were also included. The intensities of these features are compared with two indices of solar activity: the Ca ii plage index and the 2800 MHZ signal. The average correlation coefficients between the intensities of the measured features and those indices were 0.69 and 0.64, respectively. Our results are consistent with those of Bumba and Riková-Topolová (1967) for a solar rotation period in 1965.The method and results should provide a detailed quantitative basis for the study of the activity cycles and rotation periods of solar-type stars.First Weather Wing, Hickman Air Force Base, HI 96824, U.S.A.