Dust-acoustic wave modulation in the presence of q-nonextensive electrons and/or ions in dusty plasma

A study is presented of the nonlinear self-modulation of low-frequency electrostatic dust acoustic waves (DAWs) propagating in a dusty plasma, within the theoretical framework of the nonextensive statistics proposed by Tsallis. Using the reductive perturbation method (RPM), the nonlinear Schrödinger equation (NLSE) which governs the modulational instability (MI) of the DAWs is obtained. The presence of the nonextensive electron/ion distribution is shown to influence the MI of the waves. Furthermore it is observed that nonextensive distributed ions has more effect on the MI of the DAW than electrons.     

Instrumental and Observational Artifacts in Quiet Sun Magnetic Flux Cancellation Functions

Under the assumption that the photospheric quiet Sun magnetic field is turbulent, the cancellation function has previously been used to estimate the true, resolution-independent mean, unsigned vertical flux 〈|B _z |〉_true. We show that the presence of network elements, noise, and seeing complicate the measurement of accurate cancellation functions and their power law exponents κ. Failure to exclude network elements previously led to estimates that were too low for both the cancellation exponent κ and 〈|B _z |〉_true. However, both κ and 〈|B _z |〉_true are overestimated due to noise in magnetograms. While no conclusive value can be derived with data from current instruments, our Hinode/SP results of κ?0.38 and 〈|B _z |〉_true?270 gauss can be taken as upper bounds.     

On the rotational energy distributions of reactive, non-polar species in the interstellar medium

A basic model for the formation of non-equilibrium rotational energy distributions is described for reactive, homo-polar diatomic molecules and ions in the interstellar medium. Kinetic models were constructed to calculate the rotational populations of $\mathrm{C}_{2}^{+}$ under the conditions it would experience in the diffuse interstellar medium. As the non-polar ion reacts with molecular hydrogen, but not atomic hydrogen, the thermalization of a hot nascent rotational population will be arrested by chemical reaction when the H₂ density begins to be significant. Populations that deviate strongly from the local thermodynamic equilibrium are predicted for $\mathrm{C}_{2}^{+}$ in environments where it may be detectable. Consequences of this are discussed and a new optical spectrum is calculated.     

Coronal Temperature Maps from Solar EUV Images: A Blind Source Separation Approach

Multi-wavelength solar images in the extreme ultraviolet (EUV) are routinely used for analysing solar features such as coronal holes, filaments, and flares. However, images taken in different bands often look remarkably similar, as each band receives contributions coming from regions with a range of different temperatures. This has motivated the search for empirical techniques that may unmix these contributions and concentrate salient morphological features of the corona in a smaller set of less redundant source images. Blind Source Separation (BSS) does precisely this. Here we show how this novel concept also provides new insight into the physics of the solar corona, using observations made by SDO/AIA. The source images are extracted using a Bayesian positive source-separation technique. We show how observations made in six spectral bands, corresponding to optically thin emissions, can be reconstructed by a linear combination of three sources. These sources have a narrower temperature response and allow for considerable data reduction, since the pertinent information from all six bands can be condensed into a single composite picture. In addition, they give access to empirical temperature maps of the corona. The limitations of the BSS technique and some applications are briefly discussed.     

The 3D Geometry of Active Region Upflows Deduced from Their Limb-to-Limb Evolution

We analyze the evolution of coronal plasma upflows from the edges of AR 10978, which has the best limb-to-limb data coverage with Hinode’s EUV Imaging Spectrometer (EIS). We find that the observed evolution is largely due to the solar rotation progressively changing the viewpoint of nearly stationary flows. From the systematic changes in the upflow regions as a function of distance from disc center, we deduce their 3D geometrical properties as inclination and angular spread in three coronal lines (Si vii, Fe xii, and Fe xv). In agreement with magnetic extrapolations, we find that the flows are thin, fan-like structures rooted in quasi separatrix layers (QSLs). The fans are tilted away from the AR center. The highest plasma velocities in these three spectral lines have similar magnitudes and their heights increase with temperature. The spatial location and extent of the upflow regions in the Si vii, Fe xii, and Fe xv lines are different owing to i) temperature stratification and ii) line of sight integration of the spectral profiles with significantly different backgrounds. We conclude that we sample the same flows at different temperatures. Further, we find that the evolution of line widths during the disc passage is compatible with a broad range of velocities in the flows. Everything considered, our results are compatible with the AR upflows originating from reconnections along QSLs between over-pressure AR loops and neighboring under-pressure loops. The flows are driven along magnetic field lines by a pressure gradient in a stratified atmosphere. Our interpretation of the above results is that, at any given time, we observe the superposition of flows created by successive reconnections, leading to a broad velocity distribution.     

Assessing the Constrained Harmonic Mean Method for Deriving the Kinematics of ICMEs with a Numerical Simulation

In this study we use a numerical simulation of an artificial coronal mass ejection (CME) to validate a method for calculating propagation directions and kinematical profiles of interplanetary CMEs (ICMEs). In this method observations from heliospheric images are constrained with in-situ plasma and field data at 1 AU. These data are used to convert measured ICME elongations into distance by applying the harmonic mean approach, which assumes a spherical shape of the ICME front. We used synthetic white-light images, similar to those observed by STEREO-A/HI, for three different separation angles between remote and in-situ spacecraft of 30^°, 60^°, and 90^°. To validate the results of the method, the images were compared to the apex speed profile of the modeled ICME, as obtained from a top view. This profile reflects the “true” apex kinematics because it is not affected by scattering or projection effects. In this way it is possible to determine the accuracy of the method for revealing ICME propagation directions and kinematics. We found that the direction obtained by the constrained harmonic mean method is not very sensitive to the separation angle (30^° sep: ?=W7; 60^° sep: ?=W12; 90^° sep: ?=W15; true dir.: E0/W0). For all three cases the derived kinematics agree relatively well with the real kinematics. The best consistency is obtained for the 30^° case, while with growing separation angle the ICME speed at 1 AU is increasingly overestimated (30^° sep: ΔV _arr≈??50 km?s^?1, 60^° sep: ΔV _arr≈+?75 km?s^?1, 90^° sep: ΔV _arr≈+?125 km?s^?1). Especially for future L₄/L₅ missions, the 60^° separation case is highly interesting in order to improve space-weather forecasts.     

Evolution of the Fine Structure of Magnetic Fields in the Quiet Sun: Observations from Sunrise/IMaX and Extrapolations

Observations with the balloon-borne Sunrise/Imaging Magnetograph eXperiment (IMaX) provide high spatial resolution (roughly 100 km at disk center) measurements of the magnetic field in the photosphere of the quiet Sun. To investigate the magnetic structure of the chromosphere and corona, we extrapolate these photospheric measurements into the upper solar atmosphere and analyze a 22-minute long time series with a cadence of 33 seconds. Using the extrapolated magnetic-field lines as tracer, we investigate temporal evolution of the magnetic connectivity in the quiet Sun’s atmosphere. The majority of magnetic loops are asymmetric in the sense that the photospheric field strength at the loop foot points is very different. We find that the magnetic connectivity of the loops changes rapidly with a typical connection recycling time of about 3±1 minutes in the upper solar atmosphere and 12±4 minutes in the photosphere. This is considerably shorter than previously found. Nonetheless, our estimate of the energy released by the associated magnetic-reconnection processes is not likely to be the sole source for heating the chromosphere and corona in the quiet Sun.     

Empirical estimate of p-mode frequency shift for solar cycle 23

We have obtained empirical relations between the p-mode frequency shift and the change in solar activity indices. The empirical relations are determined on the basis of frequencies obtained from BBSO and GONG stations during solar cycle 22. These relations are applied to estimate the change in mean frequency for the cycle 21 and 23. A remarkable agreement between the calculated and observed frequency shifts for the ascending phase of cycle 23, indicates that the derived relations are independent of epoch and do not change significantly from cycle to cycle. We propose that these relations could be used to estimate the shift in p-mode frequencies for past, present and future solar activity cycles, if the solar activity index is known. The maximum frequency shift for cycle 23 is estimated to be 265±90 nHz, corresponding to a predicted maximum smoothed sunspot number 118.1±35.     

Characteristics of Flaring Sites in Solar Active Regions

The properties of the flaring sites in the active region NOAA 6555 and 6659 are presented in this paper. Although, several locations of these active regions displayed high magnetic shear, the X-class flares occurred only at one of them. Our investigations show that these locations are characterized by the `crossing' of magnetic and velocity field neutral lines. Based on a new parameter to define the stressed magnetic fields, we show that some of these flaring locations possessed highly stressed magnetic field which disappeared after the flare. This revised version was published online in July 2006 with corrections to the Cover Date.