Plasma properties of an X-ray jet from multi-instrument co-observations: SUMER/SoHO, EIS/XRT/Hinode and EUVI/SECCHI/STEREO A and B
Madjarska, Maria
Armagh Observatory
15 April, 10:45

We will present unique multi-instrument observations of an X-ray jet-like event taken with SUMER/SoHO, EIS/ XRT/HInode and EUVI/SECCHI/STEREO. The phenomenon arose in a coronal bright point situated at the boundaries of an equatorial coronal hole. The combination of two spectrometers covering together the temperature range from 10 000 K to 12 MK and the three view points of XRT, EUVI A and B permitted us to derive the plasma properties and dynamics of this feature. We analysed the behaviour of different spectral lines during the micro-flaring which triggered the jet-like event. We also obtained the temperatures and densities in the reconnection site and the surrounding region. The jet dynamics and its plasma properties will be discussed in detail. We will give our suggestions for the future instrumentation (spectroscopic and imaging) and atomic calculations.

A new enthalpy-based approach to the transition region in an impulsively-heated corona
Cargill, Peter, Steve Bradshaw
Imperial College
15 April, 11:00

Observations of the solar corona reveal persistent and ubiquitous red-shifts, which correspond to bulk down-flows. For an impulsively-heated corona (e.g. by nanoflares) this indicates that a majority of the component loop structures are in the radiatively cooling phase of their lifecycle. However, the nature of the bulk downflows raises the possibility that enthalpy may play a key role in the energy balance of the loops and in particular that it powers the transition region radiation. We use one dimensional hydrodynamic simulations of loop cooling to show that enthalpy losses from the corona are easily sufficient to power the transition region radiation. This contrasts with the long-held view that downward thermal conduction powers the transition region. The traditional distinction between the transition region and the corona in terms of temperature alone is then a grossly unphysical simplification and a proper definition of the interface between these atmospheric layers requires a detailed knowledge of their energy balance. To this end we propose a robust new definition of the transition region.

Chromospheric magnetic reconnection: implications for jet-like events and coronal heating
Ding, Jiaoyang, M. S. Madjarska, J. G. Doyle, Q. M. Lu
Armagh Observatory
15 April, 11:15

Magnetic reconnection in the low atmosphere, e.g. chromosphere, is investigated in various physical environments. It is found that the temperature and velocity of the outflow jets as a result of magnetic reconnection are strongly dependent on the physical environments, e.g. the magnitude of the magnetic field strength and the plasma density. The stronger magnetic field strength or the lower mass density is, the outflow jets with higher temperature and larger velocity are obtained. Under certain physical conditions, the outflow jets can be heated upto $2\times 10^6$~K (coronal temperatures), and its maximum velocity reaches 300 - 400 km/s. In this case, both cold chromospheric jets and hot coronal jets are obtained simultaneously. This is very helpful to understand the relationship between cold and hot jets, as well as coronal heating mechanisms.

The Hydrodynamic Evolution of Impulsively Heated Coronal Loops: Explicit Analytical Approximations
Tsiklauri, David, M.J. Aschwanden
Queen Mary University of London
15 April, 11:30

We derive simple analytical approximations (in explicit form) for the hydrodynamic evolution of the electron temperature T(s, t) and electron density n(s, t), for one-dimensional coronal loops that are subject to impulsive heating with subsequent cooling. Our analytical approximations are derived from first principles, using (1) the hydrodynamic energy balance equation, (2) the loop scaling laws of Rosner-Tucker-Vaiana and Serio, (3) the Neupert effect, and (4) the Jakimiec relationship. We compare our analytical approximations with 56 numerical cases of time-dependent hydrodynamic simulations from a parametric study of Tsiklauri et al., covering a large parameter space of heating rates, heating timescales, heating scale heights, loop lengths, for both footpoint and apex heating, mostly applicable to flare conditions. The average deviations from the average temperature and density values are typically ~20% for our analytical expressions. The analytical approximations in explicit form provide an efficient tool to mimic time-dependent hydrodynamic simulations, to model observed soft X-rays and extreme-ultraviolet light curves of heated and cooling loops in the solar corona and in flares by forward fitting, to model microflares, to infer the coronal heating function from light curves of multi-wavelength observations, and to provide physical models of differential emission measure distributions for solar and stellar flares, coronae, and irradiance. M.J. Aschwanden, D. Tsiklauri, Astrophys. J. Suppl. Ser., 185, 171-185 (2009) DOI: 10.1088/0067-0049/185/1/171

Non-Linear Force-Free Model of the Solar Magnetic Carpet
Meyer, Karen, K. A. Meyer, D. H. Mackay, A. A. van Ballegooijen
University of St Andrews
15 April, 11:45

We model the dynamical evolution of the Sun's magnetic carpet, and construct a non-linear force-free coronal field based on surface motions. Rather than independently extrapolating the coronal field at each time step, we model a continuous evolution of the field through a magnetofrictional relaxation technique. So far we have studied energy build up within the field due to the basic interactions of cancellation, emergence and flyby. The magnetofrictional code has also been directly applied to Hinode/SOT magnetogram data to study the location and variation of low coronal null points.

Detailed observations and modelling of a small flare
Mitra Kraev, Urmila, G. Del Zanna, U. Mitra-Kraev, H. Mason, S. J. Bradshaw, A. Asai
University of Cambridge (DAMTP)
15 April, 12:00

We have obtained a plethora of spatially- and temporally-resolved spectral data of a B-class flare with the EIS spectrometer on-board the Hinode satellite. Together with data from the other Hinode instruments, as well as GOES, TRACE and the Nobeyama Radio Heliograph, a detailed picture of the evolution of this flare is put together. The flare shows many 'typical' features such as precursor events, brightenings in the ribbons, and hot (10 MK) emission and subsequent cooling. However, a number of features are new, such as strong blue-wing asymmetries only seen in lines formed between 1.5 and 2.2 MK. The temporal and temperature coverage of the EIS observations provides new insights into our understanding of chromospheric evaporation and cooling. A numerical simulation using the HYDRAD code to study the cooling of the 10 MK plasma is in good agreement with the observations. Line blending in some potentially useful lines for flare diagnostics is also discussed.

The optical depth of white-light flare continuum
Potts, Hugh, Hugh Hudson, Lyndsay Fletcher, Declan Diver
University of Glasgow
15 April, 12:15

The white-light continuum emission of a solar flare remains a puzzle as regards its height of formation and its emission mechanism. This continuum, and its extension into the near UV, contain the bulk of the energy radiated by a flare, and so its explanation is a high priority. We describe a method to determine the optical depth of the emitting layer and apply it to the well-studied flare of 2002 July 15, making use of the MDI intensity images. The optical depth of the visible continuum in this flare is small, consistent with the observation of Balmer and Paschen edges in other events.

Observation and 3D modelling of a coronal bright point
Huang, Zhenghua, M.S. Madjarska, K. Galsgaard, J.G. Doyle
Armagh Observatory

We use multi-wavelength observations obtained with EIS, XRT and SOT onboard Hinode to study the plasma properties and dynamics of a coronal bright point observed in an equatorial coronal hole. The evolution of the bright point was followed in spectral lines with formation temperatures from $10^4$ K to $2 \times 10^6$ K, i.e. from chromospheric to coronal temperatures. We found that the bright point has a longer lifetime as seen in lower chromospheric temperatures than in higher, coronal ones. We derived the density evolution of the bright point using the spectral line ratio Fe XII 186/195. We obtained densities which fluctuate in the range from $8 \times 10^8$ to $3 \times 10^9$ cm$^{-3}$ with an average of about $2 \times 10^9$ cm$^{-3}$. The time sequence of XRT images taken with the Al poly filter were also used to study the dynamics of the bright point. The plasma properties of the bright point will be compared with the output from a 3D MHD simulation. The 3D model is a combination of a stratified hydrostatic model atmosphere and a potential magnetic field that is obtained using potential magnetic field extrapolation from longitudinal magnetogram from SOT observations. The magnetic structure is stressed by imposing a photospheric velocity flow derived from blue continuum SOT data using ball tracking.

Calculation and application of R-matrix electron-impact excitation data for ions of interest to astrophysical diagnostic modelling
Liang, Guiyun, N.R. Badnell
University of Strathclyde

A large number of high-resolution and high-quality spectra have been, and continue to be, obtained from both the EUV (e.g. Hinode) and X-ray (e.g. Chandra, XMM-Newton, IXO) regions. Many emission lines observed in these spectra are potential diagnostics of the electron temperature and density of coronal-like hot plasmas. There are also many unidentified emission lines and large discrepancies in line intensity ratios likely due to unknown contaminants. Such diagnostics and associated line identifications require accurate atomic data, especially for electron-impact excitation.

The advantages of the intermediate-coupling frame transformation R-matrix method (Griffin et al. 1998) make it feasible to provide excitation data along K- and L-shell iso-electronic sequences covering a substantial range of astrophysically important ions at the high-level of accuracy afforded by the $R$-matrix method. This is one of the key goals of the UK Atomic Processes for astrophysical Plasmas (APAP) network. Here we will address effective collision strengths along the Ne-like iso-electronic sequence (Liang & Badnell 2010). We also look at a particular ion-Fe$^{13+}$ (Liang et al. 2010) for which a laboratory measurement has been made. We assess the accuracy of our excitation data in both cases.

Using the latest $R$-matrix electron-impact excitation data, we analyze the EUV and soft X-ray spectra of hot plasmas, e.g. stellar corona and electron-beam ion-traps. Several previous questionable line intensity ratios in Fe$^{13+}$ have been explained satisfactorily and some lines are identified in astrophysical sources for the first time with the aid of a laboratory measurement performed at the Heidelberg EBIT (Liang et al. 2010).

Alfven Ionisation in the Solar Photosphere
Mallik, Procheta, Declan A. Diver, Lyndsay Fletcher, Hugh E. Potts, Craig S. MacLachlan
University of Glasgow

Strong photospheric flows near active regions inevitably involve mixing neutral gas and magnetised plasma. Where the relative speed between neutral and plasma species exceeds a critical value at which the energy in the flow is equal to the first ionisation potential of a component species, that species will be ionised. The physical mechanism is as follows: the neutral gas impinging on the plasma collides with the positive ions and displaces them, causing pockets of negative charge imbalance. The resulting electric fields accelerate a tail of electrons to energies above the ionisation threshold for particular gas species. These new ions remain trapped in the magnetic structure, leading to enhanced abundance in the lower solar atmosphere. We present numerical simulations of the evolution of the electron distribution in such a situation, showing how a fraction of the affected population reaches energies above the ionisation threshold for particular elements. This is most relevant for low critical ionisation velocity (CIV) elements such as Xe, K, Cr, Mn, Fe etc, and is a key driver of element over-abundance.

What blinkers actually are?
Subramanian, Srividya, S. Subramanian, M.S. Madjarska, J.G. Doyle, D. Bewsher
Armagh Observatory

We investigate blinkers in an equatorial coronal hole region using spectral, imaging and magnetogram co-observations to find out what these blinkers actually represent. We used an automated identification procedure to identify blinkers in SoHO/CDS O v 629 Angstrom rasters. We also identified brightenings in STEREO/EUVI Fe IX 171 Angstrom images and Hinode/XRT Al poly images to study blinkers at lower coronal temperatures and to find their possible coronal counterparts, respectively. All CDS blinkers had EUVI 171 Å counterparts. Identified blinker events were classified into two groups, blinkers with coronal counterparts, mostly associated with coronal X-ray jets, and blinkers with no coronal counterparts which appear as pointed brightenings at transition region temperatures. The latter could be signature of chromospheric features (spicules or/and macrospicules) reaching transition region temperatures or simply represent induced flows along small scale loop structures. We believe that blinkers are transient EUV response of various dynamic events originating anywhere in the solar atmosphere which contribute to the temperature raise in the transition region.

Spicules and Coronal Heating
Vanninathan, Kamalam, Maria Madjarska, J.G. Doyle
Kamalam Vanninathan

We use multi-instrument observations of spicules, looking for evidence of whether these chromospheric features can also be detected at coronal temperatures. We analysed Ca II H images from SOT/Hinode, comparing them with data from EIS/Hinode, plus high-resolution data from SUMER/SoHO. We observe spicules at the North pole with 10 second cadence SOT data. A group of rotating spicules as seen with SOT are observed in the SUMER transition region O V 629 and N V 1238 as a macrospicule. EIS data do not show corresponding features at coronal temperatures.

Magnetic reconnection along QSLs - a major driver of active region outflows
van Driel-Gesztelyi, Lidia, D. Baker, L. van Driel-Gesztelyi, C.H. Mandrini, P. Demoulin
MSSL/UCL

The relationship between quasi-separatrix layers (QSLs), or in the limit of infinitely thin QSLs, separatrices, and various activity phenomena has been explored in many different solar magnetic configurations across all scales in recent years. In the absence of magnetic nulls, fast reconnection along QSLs, which are specific locations in the magnetic topology where field lines display strong gradients of magnetic connectivity, was identified as the main physical process at the origin of flares. Recently, it was shown that fast (tens of km/s) persistent hot plasma upflows in active regions (ARs) can also be linked to locations of QSLs. It is likely that these upflows that occur at the edges of ARs over unipolar magnetic field concentrations are accelerated by magnetic reconnection along QSLs. We will show multi-temperature spectral scan observations from Hinode’s EIS combined with magnetic modeling of QSLs in two ARs observed on 20-21 February 2007 and 11 January 2008. The latter AR is observed and modeled when it is in the vicinity of the solar central meridian where there are no projection effects, thereby eliminating ambiguity linking the origin of multi-temperature observations of AR upflows to QSLs. We use the Potential Source Surface Model to look for open field lines in the vicinity of upflows and QSL locations in order to demonstrate whether these upflows become outflows and can contribute to the solar wind.