17 research outputs found
The radial variation of the solar wind turbulence spectra near the kinetic break scale from Parker Solar Probe measurements
In this study we examine the radial dependence of the inertial and dissipation range indices, as well as the spectral break separating the inertial and dissipation range in power density spectra of interplanetary magnetic field fluctuations using Parker Solar Probe data from the fifth solar encounter between ∼0.1 and ∼0.7 au. The derived break wavenumber compares reasonably well with previous estimates at larger radial distances and is consistent with gyro-resonant damping of Alfvénic fluctuations by thermal protons. We find that the inertial scale power-law index varies between approximately −1.65 and −1.45. This is consistent with either the Kolmogorov (−5/3) or Iroshnikov–Kraichnan (−3/2) values, and has a very weak radial dependence with a possible hint that the spectrum becomes steeper closer to the Sun. The dissipation range power-law index, however, has a clear dependence on radial distance (and turbulence age), decreasing from −3 near 0.7 au (4 days) to −4 [±0.3] at 0.1 au (0.75 days) closer to the Sun
Spectroscopic imaging of the sun with MeerKAT: opening a new frontier in solar physics
Solar radio emissions provide several unique diagnostics to estimate different physical parameters of the solar corona, which are otherwise simply inaccessible. However, imaging the highly dynamic solar coronal emissions spanning a large range of angular scales at radio wavelengths is extremely challenging. At gigahertz frequencies, MeerKAT radio telescope is possibly globally the best-suited instrument at present for providing high-fidelity spectroscopic snapshot solar images. Here, we present the first published spectroscopic images of the Sun made using the observations with MeerKAT in the 880–1670 MHz band. This work demonstrates the high fidelity of spectroscopic snapshot MeerKAT solar images through a comparison with simulated radio images at MeerKAT frequencies. The observed images show extremely good morphological similarities with the simulated images. Our analysis shows that below ∼900 MHz MeerKAT images can recover essentially the entire flux density from the large angular-scale solar disk. Not surprisingly, at higher frequencies, the missing flux density can be as large as ∼50%. However, it can potentially be estimated and corrected for. We believe once solar observation with MeerKAT is commissioned, it will enable a host of novel studies, open the door to a large unexplored phase space with significant discovery potential, and also pave the way for solar science with the upcoming Square Kilometre Array-Mid telescope, of which MeerKAT is a precursor
Multiwavelength Observations of Supersonic Plasma Blob Triggered by Reconnection Generated Velocity Pulse in AR10808
Using multi-wavelength observations of Solar and Heliospheric Observatory
(SoHO)/Michelson Doppler Imager (MDI), Transition Region and Coronal Explorer
(TRACE) 171 \AA, and H from Culgoora Solar Observatory at Narrabri,
Australia, we present a unique observational signature of a propagating
supersonic plasma blob before an M6.2 class solar flare in AR10808 on 9th
September 2005. The blob was observed between 05:27 UT to 05:32 UT with almost
a constant shape for the first 2-3 minutes, and thereafter it quickly vanished
in the corona. The observed lower bound speed of the blob is estimated as
215 km s in its dynamical phase. The evidence of the blob with
almost similar shape and velocity concurrent in H and TRACE 171 \AA\
supports its formation by multi-temperature plasma. The energy release by a
recurrent 3-D reconnection process via the separator dome below the magnetic
null point, between the emerging flux and pre-existing field lines in the lower
solar atmosphere, is found to be the driver of a radial velocity pulse outwards
that accelerates this plasma blob in the solar atmosphere. In support of
identification of the possible driver of the observed eruption, we solve the
two-dimensional ideal magnetohydrodynamic equations numerically to simulate the
observed supersonic plasma blob. The numerical modelling closely match the
observed velocity, evolution of multi-temperature plasma, and quick vanishing
of the blob found in the observations. Under typical coronal conditions, such
blobs may also carry an energy flux of 7.0 ergs cm
s to re-balance the coronal losses above active regions.Comment: Solar Physics; 22 Pages; 8 Figure
Local Helioseismology of Sunspots: Current Status and Perspectives (Invited Review)
Mechanisms of the formation and stability of sunspots are among the
longest-standing and intriguing puzzles of solar physics and astrophysics.
Sunspots are controlled by subsurface dynamics hidden from direct observations.
Recently, substantial progress in our understanding of the physics of the
turbulent magnetized plasma in strong-field regions has been made by using
numerical simulations and local helioseismology. Both the simulations and
helioseismic measurements are extremely challenging, but it becomes clear that
the key to understanding the enigma of sunspots is a synergy between models and
observations. Recent observations and radiative MHD numerical models have
provided a convincing explanation to the Evershed flows in sunspot penumbrae.
Also, they lead to the understanding of sunspots as self-organized magnetic
structures in the turbulent plasma of the upper convection zone, which are
maintained by a large-scale dynamics. Local helioseismic diagnostics of
sunspots still have many uncertainties, some of which are discussed in this
review. However, there have been significant achievements in resolving these
uncertainties, verifying the basic results by new high-resolution observations,
testing the helioseismic techniques by numerical simulations, and comparing
results obtained by different methods. For instance, a recent analysis of
helioseismology data from the Hinode space mission has successfully resolved
several uncertainties and concerns (such as the inclined-field and phase-speed
filtering effects) that might affect the inferences of the subsurface
wave-speed structure of sunspots and the flow pattern. It becomes clear that
for the understanding of the phenomenon of sunspots it is important to further
improve the helioseismology methods and investigate the whole life cycle of
active regions, from magnetic-flux emergence to dissipation.Comment: 34 pages, 18 figures, submitted to Solar Physic
A two-dimensional simulation of electrostatic drift wave turbulance in plasmas
SIGLEAvailable from British Library Document Supply Centre-DSC:DXN022105 / BLDSC - British Library Document Supply CentreGBUnited Kingdo
Simulation of the observed coronal kink instability and its implications for the SDO/AIA
Srivastava et al. (2010) have observed a highly twisted coronal loop, which was anchored in AR10960 during the period 04:43 UT-04:52 UT on 4 June 2007. The loop length and radius are approximately 80 Mm and 4 Mm, with a twist of 11.5 π. These observations are used as initial conditions in a three dimensional nonlinear magnetohydrodynamic simulation with parallel thermal conduction included. The initial unstable equilibrium evolves into the kink instability, from which synthetic observables are generated for various high-temperature filters of SDO/AIA. These observables include temporal and spatial averaging to account for the resolution and exposure times of SDO/AIA images. Using the simulation results, we describe the implications of coronal kink instability as observables in SDO/AIA filters