Hinode 7: Conference Summary and Future Suggestions

This conclusion to the meeting attempts to summarise what we have learnt during the conference (mainly from the review talks) about new observations from Hinode and about theories stimulated by them. Suggestions for future study are also offered.Comment: This is the concluding summary for the Hinode 7 Conference, to be published in Pub. Astron. Soc. Japa

A Life of Fun Playing With Solar Magnetic Fields (Special Historical Review)

This invited memoire describes my fortunate life, which has been enriched by meeting many wonderful people. The story starts at home and university, and continues with accounts of St Andrews and trips to the USA, together with musings on the book "Solar MHD". The nature and results of collaborations with key people from abroad and with students is mentioned at length. Finally, other important aspects of my life are mentioned briefly before wrapping up.Comment: Invited Memoire in the Journal Solar Physic

On the nature of reconnection at a solar coronal null point above a separatrix dome

Three-dimensional magnetic null points are ubiquitous in the solar corona, and in any generic mixed-polarity magnetic field. We consider magnetic reconnection at an isolated coronal null point, whose fan field lines form a dome structure. We demonstrate using analytical and computational models several features of spine-fan reconnection at such a null, including the fact that substantial magnetic flux transfer from one region of field line connectivity to another can occur. The flux transfer occurs across the current sheet that forms around the null point during spine-fan reconnection, and there is no separator present. Also, flipping of magnetic field lines takes place in a manner similar to that observed in quasi-separatrix layer or slip-running reconnection.Comment: Accepted for publication in the Astrophysical Journa

The Effect of Hydrostatic Weighting on the Vertical Temperature Structure of the Solar Corona

We investigate the effect of hydrostatic scale heights ${\lambda}(T)$ in coronal loops on the determination of the vertical temperature structure $T(h)$ of the solar corona. Every method that determines an average temperature at a particular line-of-sight from optically thin emission (e.g. in EUV or soft X-ray wavelengths) of a mutli-temperature plasma, is subject to the emission measure-weighted contributions $dEM(T)/dT$ from different temperatures. Because most of the coronal structures (along open or closed field lines) are close to hydrostatic equilibrium, the hydrostatic temperature scale height introduces a height-dependent weighting function that causes a systematic bias in the determination of the temperature structure $T(h)$ as function of altitude $h$. The net effect is that the averaged temperature seems to increase with altitude, $dT(h)/dh > 0$, even if every coronal loop (of a multi-temperature ensemble) is isothermal in itself. We simulate this effect with differential emission measure distributions observed by {\sl SERTS} for an instrument with a broadband temperature filter such as {\sl Yohkoh/SXT} and find that the apparent temperature increase due to hydrostatic weighting is of order \Delta T \approx T_0 \times h/r_{\sun}. We suggest that this effect largely explains the systematic temperature increase in the upper corona reported in recent studies (e.g. by Sturrock et al., Wheatland et al., or Priest et al.), rather than being an intrinsic signature of a coronal heating mechanism.Comment: 7 pages, 3 figures. ApJ Letters, accepted 2000 April 6, in pres

Scaling law for the heating of solar coronal loops

We report preliminary results from a series of numerical simulations of the reduced magnetohydrodynamic equations, used to describe the dynamics of magnetic loops in active regions of the solar corona. A stationary velocity field is applied at the photospheric boundaries to imitate the driving action of granule motions. A turbulent stationary regime is reached, characterized by a broadband power spectrum $E_k\simeq k^{-3/2}$ and heating rate levels compatible with the heating requirements of active region loops. A dimensional analysis of the equations indicates that their solutions are determined by two dimensionless parameters: the Reynolds number and the ratio between the Alfven time and the photospheric turnover time. From a series of simulations for different values of this ratio, we determine how the heating rate scales with the physical parameters of the problem, which might be useful for an observational test of this model.Comment: 12 pages, 4 figures. Astrophysical Journal Letters (in press

Chromospheric and coronal heating and jet acceleration due to reconnection driven by flux cancellation : I. At a three-dimensional current sheet

Funding: P.S. acknowledges support by the ERC synergy grant 'The Whole Sun'.Context. The recent discovery of much greater magnetic flux cancellation taking place at the photosphere than previously realised has led us in our previous works to suggest magnetic reconnection driven by flux cancellation as the cause of a wide range of dynamic phenomena, including jets of various kinds and solar atmospheric heating. Aims. Previously, the theory considered energy release at a two-dimensional current sheet. Here we develop the theory further by extending it to an axisymmetric current sheet in three dimensions without resorting to complex variable theory. Methods. We analytically study reconnection and treat the current sheet as a three-dimensional structure. We apply the theory to the cancellation of two fragments of equal but opposite flux that approach each another and are located in an overlying horizontal magnetic field. Results. The energy release occurs in two phases. During Phase 1, a separator is formed and reconnection is driven at it as it rises to a maximum height and then moves back down to the photosphere, heating the plasma and accelerating a plasma jet as it does so. During Phase 2 the fluxes cancel in the photosphere and accelerate a mixture of cool and hot plasma upwards.Publisher PDFPeer reviewe

A cancellation nanoflare model for solar chromospheric and coronal heating. III. 3D simulations and atmospheric response

This research has made use of NASA's Astrophysics Data System. This work was supported by computational time granted from the Greek Research and Technology Network (GRNET) in the National HPC facility ARIS. P.S. acknowledges support by the ERC synergy grant "The Whole Sun."Inspired by recent observations suggesting that photospheric magnetic flux cancellation occurs much more frequently than previously thought, we analytically estimated the energy released from reconnection driven by photospheric flux cancellation, and propose that it can act as a mechanism for chromospheric and coronal heating. Using two-dimensional simulations we validated the analytical estimates and studied the resulting atmospheric response. In the present work, we set up 3D resistive MHD simulations of two canceling polarities in a stratified atmosphere with a horizontal external field to further validate and improve upon the analytical estimates. The computational evaluation of the parameters associated with the energy release are in good qualitative agreement with the analytical estimates. The computational Poynting energy flux into the current sheet is in good qualitative agreement with the analytical estimates, after correcting the analytical expression to better account for the horizontal extent of the current sheet. The atmospheric response to the cancellation is the formation of hot ejections, cool ejections, or a combination of both hot and cool ejections, which can appear with a time difference and/or be spatially offset, depending on the properties of the canceling region and the resulting height of the reconnection. Therefore, during the cancellation, a wide spectrum of ejections can be formed, which can account for the variety of multi-thermal ejections associated with Ellerman bombs, UV bursts, and IRIS bombs, and also other ejections associated with small-scale canceling regions and spicules.Publisher PDFPeer reviewe

Catastrophe versus instability for the eruption of a toroidal solar magnetic flux rope

The onset of a solar eruption is formulated here as either a magnetic catastrophe or as an instability. Both start with the same equation of force balance governing the underlying equilibria. Using a toroidal flux rope in an external bipolar or quadrupolar field as a model for the current-carrying flux, we demonstrate the occurrence of a fold catastrophe by loss of equilibrium for several representative evolutionary sequences in the stable domain of parameter space. We verify that this catastrophe and the torus instability occur at the same point; they are thus equivalent descriptions for the onset condition of solar eruptions.Comment: V2: update to conform to the published article; new choice for internal inductance of torus; updated Fig. 2; new Figs. 3, 5, and

Plasma Relaxation and Topological Aspects in Hall Magnetohydrodynamics

Parker's formulation of isotopological plasma relaxation process in magnetohydrodynamics (MHD) is extended to Hall MHD. The torsion coefficient alpha in the Hall MHD Beltrami condition turns out now to be proportional to the "potential vorticity." The Hall MHD Beltrami condition becomes equivalent to the "potential vorticity" conservation equation in two-dimensional (2D) hydrodynamics if the Hall MHD Lagrange multiplier beta is taken to be proportional to the "potential vorticity" as well. The winding pattern of the magnetic field lines in Hall MHD then appears to evolve in the same way as "potential vorticity" lines in 2D hydrodynamics

Emergency first responders and professional wellbeing: a qualitative systematic review

Emergency first responders (EFRs) such as police officers, firefighters, paramedics and logistics personnel often suffer high turnover due to work-related stress, high workloads, fatigue, and declining professional wellbeing. As attempts to counter this through resilience programmes tend to have limited success, there is a need for further research into how organisational policies could change to improve EFRs’ professional wellbeing. Aim: To identify the factors that may contribute to or affect EFRs’ professional wellbeing. Methods: A systematic literature review has been carried out. Three databases (Science Direct, ProQuest, and PubMed) were searched using keywords developed based on the PICo (population, interest, and context) framework. A total of 984 articles were extracted. These were then critically appraised for the quality of the evidence presented, leading to a total of five being ultimately included for review. Results: Thematic analysis revealed that although EFRs may be exposed daily to traumatic events, factors that contribute to a decline in professional wellbeing emerge from within the organisational environment, rather than from the event itself. Conclusion: The study concludes that organisational and team relations factors significantly impact EFRs ability to cope with stress. As such, organisational policy should evolve to emphasise team relations over resilience programmes