A new model for heating of Solar North Polar Coronal Hole

This paper presents a new model of North Polar Coronal Hole (NPCH) to study dissipation/propagation of MHD waves. We investigate the effects of the isotropic viscosity and heat conduction on the propagation characteristics of the MHD waves in NPCH. We first model NPCH by considering the differences in radial as well as in the direction perpendicular to the line of sight (\textit{los}) in temperature, particle number density and non-thermal velocities between plumes and interplume lanes for the specific case of \ion{O}{VI} ions. This model includes parallel and perpendicular (to the magnetic field) heat conduction and viscous dissipation. Next, we derive the dispersion relations for the MHD waves in the case of absence and presence of parallel heat conduction. In the case of absence of parallel heat conduction, we find that MHD wave dissipation strongly depends on the viscosity for modified acoustic and Alfven waves. The energy flux density of acoustic waves varies between $10^{4.7}$ and $10^7 \,erg\,cm^{-2}\,s^{-1}$ while the energy flux density of Alfven waves turned out to be between $10^6-10^{8.6} \,erg\,cm^{-2}\,s^{-1}$. But, solutions of the magnetoacustic waves show that the parallel heat conduction introduce anomalous dispersion to the NPCH plasma wherein the group velocity of waves exceeds the speed of light in vacuum. Our results suggests all these waves may provide significant source for the observed preferential accelerating and heating of \ion{O}{VI} ions, in turn coronal plasma heating and an extra accelerating agent for fast solar wind in NPCH.Comment: 17 pages, 11 figures, Submitted to MNRA

ACUTE RESIDUAL EFFECTS OF SHORT AND LONG DURATION STATIC STRETCHING ON COUNTER MOVEMENT JUMP PERFORMANCES IN WELL-TRAINED FEMALE COMBAT ATHLETES

Duration of static stretching is the most crucial factor associated with static stretch-induced impairments in explosive muscular performances. The aim of this study was to investigate the acute residual effects of lower body short (S-SS) and long duration static stretching protocols (L-SS) on counter movement jump (CMJ) performances in skilled female combat athletes. Twelve well-trained female combat athletes (training experience: 11.5 ∓ 3.6 years) performed S-SS (6 min of total stretch duration) and L-SS (12 min of total stretch duration) separated by 48 hours in a randomized, balanced order. After each protocol, participants performed, respectively, counter movement jump with arm swing (CMJAS) and with hands on hip (CMJHH) separated by 30-second rest interval at the 15th second and 1st, 5th, 10th, 15th, and 20th minute of the 20-minute recovery period. An insignificant interaction effect was found for Protocol × Time in CMJ heights (p = 0.722) indicating that both S-SS and L-SS reduced CMJ heights to a similar extent over the course of 20 min recovery period. S-SS and L-SS led to a mean CMJ height reduction of 6.29% (p < 0.05, d = 0.603) and 6.74% (p < 0.05, d = 0.610), respectively. Greater than 50% of participants experienced a reduction in CMJAS height exceeding minimum detectable change score with 90% confidence at each time point during the recovery period without exception. Use of static stretching protocols ≥ 6 minutes prior to competitions and/or training sessions may lead to impairment in lower body explosive strength of well-trained female combat athletes that persists at least 20 minutes. This impairment may also indirectly hinder their sport-specific performance since combat sports include a great deal of movement patterns related to lower body explosive strength.   Article visualizations

Finite Larmor Radius Effects on Weakly Magnetized, Dilute Plasmas

We investigate the stability properties of a hot, dilute and differentially rotating weakly magnetized plasma which is believed to be found in the interstellar medium of galaxies and protogalaxies and in the low-density accretion flows around some giant black holes like the one in the Galactic center. In the linear MHD regime, we consider the combined effects of gyroviscosity and parallel viscosity on the magnetorotational instability. The helical magnetic field is considered in the investigation. We show that the gyroviscous effect and the pitch angles cause a powerful gyroviscous instability. Furthermore, in most of the cases, plasma with the above mentioned properties is unstable and the growth rates of the unstable modes are larger than that of the magnetorotational instability.Comment: 7 pages, 4 figures. Accepted for publication in MNRA

Drift waves in the corona: heating and acceleration of ions at frequencies far below the gyro frequency

In the solar corona, several mechanisms of the drift wave instability can make the mode growing up to amplitudes at which particle acceleration and stochastic heating by the drift wave take place. The stochastic heating, well known from laboratory plasma physics where it has been confirmed in numerous experiments, has been completely ignored in past studies of coronal heating. However, in the present study and in our very recent works it has been shown that the inhomogeneous coronal plasma is, in fact, a perfect environment for fast growing drift waves. As a matter of fact, the large growth rates are typically of the same order as the plasma frequency. The consequent heating rates may exceed the required values for a sustained coronal heating by several orders of magnitude. Some aspects of these phenomena are investigated here. In particular the analysis of the particle dynamics within the growing wave is compared with the corresponding fluid analysis. While both of them predict the stochastic heating, the threshold for the heating obtained from the single particle analysis is higher. The explanation for this effect is given.Comment: To appear in MNRAS (2010

Solar off-limb line widths: Alfven waves, ion-cyclotron waves, and preferential heating

Alfven waves and ion-cyclotron absorption of high-frequency waves are frequently brought into models devoted to coronal heating and fast solar-wind acceleration. Signatures of ion-cyclotron resonance have already been observed in situ in the solar wind (HELIOS spacecrafts) and, recently, in the upper corona (UVCS/SOHO remote-sensing results). We propose a method to constrain both the Alfven wave amplitude and the preferential heating induced by ion-cyclotron resonance, above a partially developed polar coronal hole observed with the SUMER/SOHO spectrometer. The instrumental stray light contribution is first substracted from the spectra. By supposing that the non-thermal velocity is related to the Alfven wave amplitude, it is constrained through a density diagnostic and the gradient of the width of the Mg X 625 A line. The temperatures of several coronal ions, as functions of the distance above the limb, are then determined by substracting the non-thermal component to the observed line widths. The effect of stray light explains the apparent decrease with height in the width of several spectral lines, this decrease usually starting about 0.1-0.2 Rs above the limb. This result rules out any direct evidence of damping of the Alfven waves, often suggested by other authors. We also find that the ions with the smallest charge-to-mass ratios are the hottest ones at a fixed altitude and that they are subject to a stronger heating, as compared to the others, between 57" and 102" above the limb. This constitutes a serious clue to ion-cyclotron preferential heating.Comment: 15 pages, 12 figures, 3 table

Pulse-driven nonlinear Alfv\'en waves and their role in the spectral line broadening

We study the impulsively generated non-linear Alfv\'en waves in the solar atmosphere, and describe their most likely role in the observed non-thermal broadening of some spectral lines in solar coronal holes. We solve numerically the time-dependent magnetohydrodynamic equations to find temporal signatures of large-amplitude Alfv\'en waves in the model atmosphere of open and expanding magnetic field configuration, with a realistic temperature distribution. We calculate the temporally and spatially averaged, instantaneous transversal velocity of non-linear Alfv\'en waves at different heights of the model atmosphere, and estimate its contribution to the unresolved non-thermal motions caused by the waves. We find that the pulse-driven nonlinear Alfv\'en waves with the amplitude $A_{\rm v}$=50 km s$^{-1}$ are the most likely candidates for the non-thermal broadening of Si VIII $\lambda$1445.75 \AA\ line profiles in the polar coronal hole as reported by Banerjee et al. (1998). We also demonstrate that the Alfv\'en waves driven by comparatively smaller velocity pulse with its amplitude $A_{\rm v}$=25 km s$^{-1}$ may contribute to the spectral line width of the same line at various heights in coronal hole without any significant broadening. The main conclusion of this paper is that non-linear Alfv\'en waves excited impulsively in the lower solar atmosphere are responsible for the observed spectral line broadening in polar coronal holes. This is an important result as it allows us to conclude that such large amplitude and pulse-driven Alfv\'en waves do indeed exist in solar coronal holes. The existence of these waves and their undamped growth may impart the required momentum to accelerate the solar wind