EUV Imaging Spectrometer Research Articles

Spectral and spatial resolution of an extreme ultraviolet broadband imaging spectrometer based on dispersion-matched zone plates

We present a combined 1D imaging and broadband spectroscopy tool for analyzing laser-produced plasma sources of extreme ultraviolet light using a tapered zone plate that is dispersion-matched to a transmission grating. Specifically, we follow up on prior work [Mostafa et al. Opt. Lett. 48, 4316 (2023)] to obtain the actual spectral and spatial resolution of the imaging spectrometer and compare it to the design values. The imaging spectrometer is shown to have a spectral resolution of 1.2 nm at 13.5 nm, close to its design value, by assessing spectra obtained from carbon laser-produced plasma in a 5–180 nm wavelength band. The spatial resolution was obtained by placing slits near the object plane and back-illuminating the slit with a tin laser-produced plasma and found to be 17(5) µm, somewhat larger than the design specifications but still well within design limits for use for diagnosing plasma.

Spectroscopic evidence of cool plasma in quiet Sun small-scale brightenings detected by HRIEUV on board Solar Orbiter

Context. A large number of small and short-lived EUV brightenings have been detected in the quiet Sun (QS) over the past three years by the High Resolution Imager of the Extreme Ultraviolet Imager (HRIEUV) on board Solar Orbiter. It remains uncertain whether these events reach coronal temperatures and, thus, whether they directly contribute to coronal heating. Aims. In this work, we evaluate the maximum temperature of 11 EUV brightenings in the QS through plasma diagnostics with UV/EUV spectroscopy and imaging. Methods. We used three QS observations coordinated alongside those of HRIEUV: Spectral Imaging of the Coronal Environment (SPICE/Solar Orbiter), EUV Imaging Spectrometer (EIS/Hinode), and Atmospheric Imaging Assembly (AIA/SDO). We detected events in HRIEUV, ranging from 0.8 to 6.2 Mm in length. We then identified nine of them in SPICE and AIA, as well as three in EIS. We investigated their temporal evolution using their light curves and applied temperature diagnostics, such as the LOCI emission measure (EM) and the differential EM (DEM). We also estimated the electron density of one event identified in EIS. Results. These events are dominated by emission of plasma at chromospheric and TR temperatures and they barely reach temperatures above 1 MK. As such, we concluded that their contribution to coronal heating is not dominant. The estimated density of one of the event is ne = (1.8 ± 1.3)×1010 cm−3.

Searching for Evidence of Subchromospheric Magnetic Reconnection on the Sun

Within the coronae of stars, abundances of those elements with low first ionization potential (FIP) often differ from their photospheric values. The coronae of the Sun and solar-type stars mostly show enhancements of low-FIP elements (the FIP effect) while more active stars such as M dwarfs have coronae generally characterized by the inverse-FIP (I-FIP) effect. Highly localized regions of I-FIP effect solar plasma have been observed by Hinode's EUV Imaging Spectrometer in a number of highly complex active regions (ARs), usually around strong light bridges of the umbrae of coalescing/merging sunspots. These observations can be interpreted in the context of the ponderomotive force fractionation model, which predicts that plasma with I-FIP effect composition is created by the refraction of waves coming from below the plasma fractionation region in the chromosphere. A plausible source of these waves is thought to be reconnection in the (high-plasma-β) subchromospheric magnetic field. In this study, we use the 3D visualization technique of Chintzoglou & Zhang combined with observations of localized I-FIP effect in the corona of AR 11504 to identify potential sites of such reconnection and its possible consequences in the solar atmosphere. We found subtle signatures of episodic heating and reconnection outflows in the expected places, in between magnetic flux tubes forming a light bridge, within the photosphere of the AR. Furthermore, on either side of the light bridge, we observed small antiparallel horizontal magnetic field components, supporting the possibility of reconnection occurring where we observe I-FIP plasma. When taken together with the I-FIP effect observations, these subtle signatures provide a compelling case for indirect observational evidence of reconnection below the fractionation layer of the chromosphere, however direct evidence remains elusive.

Observations of Nonthermal Velocities and Comparisons with an Alfvén Wave Turbulence Model in Solar Active Regions

We present a study of spectral line width measurements from the Extreme-ultraviolet Imaging Spectrometer on Hinode. We used spectral line profiles of Fe xvi 262.984 Å, Fe xiv 264.787 Å, Fe xiv 270.519 Å, Fe xiv 274.203 Å, and Fe xv 284.160 Å, and studied 11 active regions. Previous studies of spectral line widths have shown that in hot loops in the cores of active regions, the observed nonthermal velocities are smaller than predicted from models of reconnection jets in the corona or shock heating associated with Alfvén waves. The observed line widths are also inconsistent with models of chromospheric evaporation due to coronal nanoflares. We show that recent advances in higher resolution Alfvén wave turbulence modeling enables us to obtain nonthermal velocities similar to those measured in active regions. The observed nonthermal velocities for the 11 active regions in our study are in the range of 17–30 km s−1, consistent with the spectral line nonthermal widths predicted from our model of 16 interacting flux tubes, which are in the range of 15–37 km s−1.

The Temperature and Density of a Solar Flare Kernel Measured from Extreme-ultraviolet Lines of O iv

Previously unexplored diagnostics of O iv in the extreme-ultraviolet region 260–280 Å are used to derive a temperature and density for a solar flare kernel observed on 2012 March 9 with the Extreme-ultraviolet Imaging Spectrometer on the Hinode satellite. Seven lines from the 2s2p 2–2s2p3s transition array between 271.99 and 272.31 Å are both temperature- and density-sensitive relative to the line at 279.93 Å. The temperature, T, is constrained with the λ268.02/λ279.93 ratio, giving a value of log(T/K)=5.10±0.03 . The ratio λ272.13/λ279.93 then yields an electron number density, N e, of log(Ne/cm−3)=12.52 with a lower limit of 11.90 and an upper limit of 14.40. The O iv emitting volume is estimated to be 0.″4 (300 km) across. Additional O iv lines at 196, 207, and 260 Å are consistent with the derived temperature and density but have larger uncertainties from the radiometric calibration and blending. Density diagnostics of O v and Mg vii from the same spectrum are consistent with a constant pressure of 1017.0 K cm−3 through the transition region. The temperature derived from O iv supports recent results that O iv is formed around 0.10 dex lower at high densities compared to standard zero-density ionization balance calculations.

Identifying Plasma Fractionation Processes in the Chromosphere Using IRIS

Abstract The composition of the solar corona differs from that of the photosphere, with the plasma thought to fractionate in the solar chromosphere according to the first ionization potential (FIP) of the different elements. This produces a FIP bias, wherein elements with a low FIP are preferentially enhanced in the corona compared to their photospheric abundance, but direct observations of this process remain elusive. Here, we use a series of spectroscopic observations of active region AR 12759 as it transited the solar disk over a period of 6 days from 2020 April 2–7 taken using the Hinode Extreme ultraviolet Imaging Spectrometer and Interface Region Imaging Spectrograph (IRIS) instruments to look for signatures of plasma fractionation in the solar chromosphere. Using the Si x/S x and Ca xiv/Ar xiv diagnostics, we find distinct differences between the FIP bias of the leading and following polarities of the active region. The widths of the IRIS Si iv lines exhibited clear differences between the leading and following polarity regions, indicating increased unresolved wave activity in the following polarity region compared to the leading polarity region, with the chromospheric velocities derived using the Mg ii lines exhibiting comparable, albeit much weaker, behavior. These results are consistent with plasma fractionation via resonant/nonresonant waves at different locations in the solar chromosphere following the ponderomotive force model, and indicate that IRIS could be used to further study this fundamental physical process.

Solar Type J Radio Bursts and the Associated Coronal Loop

The solar type J radio burst is a variant of type III bursts, which are a probe for understanding solar energetic electrons and local electron density. This study investigates a type J burst event on 2017 September 9. We have combined the data from the extreme-ultraviolet (EUV) imaging and the EUV Imaging Spectrometer (EIS) to analyze the event. Within 4 minutes several type J bursts with similar morphology occur. Two of them, with clear fundamental and second harmonic bands, are studied in detail. We find a delay of 2 ± 0.5 s between their different harmonic bands. During type J bursts, only one coronal loop brightens significantly at its northern footpoint, in correlation with the continuous injection of erupting jets into the loop. The EUV intensity of the brightening footpoint is correlated with the radio flux at 245 and 410 MHz, with correlation coefficients of 0.2 and 0.4, respectively. These observations suggest that the type J bursts should originate from this coronal loop. By analyzing the electron number density distribution along the coronal loop diagnosed from the EIS data and the time evolution of the plasma frequency calculated from the type J burst, we determine that the velocities of the energetic electrons exciting the two type Js are 0.10 ± 0.02c and 0.12 ± 0.02c. Our results confirm previous studies on type J bursts.

The Plasma β in Quiet Sun Regions: Multi-instrument View

A joint campaign of several spaceborne and ground-based observatories, such as the GREGOR solar telescope, the Extreme-ultraviolet Imaging Spectrometer (EIS), and the Interface Region Imaging Spectrograph (Hinode Observing Plan 381, 2019 October 11–22) was conducted to investigate the plasma β in quiet Sun regions. In this work, we focus on 2019 October 13, 17, and 19 to obtain the plasma β at different heights through the solar atmosphere based on multiheight observational data. We obtained temperature, density, and magnetic field estimates from the GREGOR High-resolution Fast Imager, Infrared Spectrograph, Interface Region Imaging Spectrograph, and EIS and complementary data from the Solar Dynamics Observatory Atmospheric Imaging Assembly (AIA). Using observational data and models (e.g., FALC and PFSS), we determined the plasma β in the photosphere, chromosphere, transition region, and corona. The obtained plasma β values lie inside the expected ranges through the solar atmosphere. However, at EIS and AIA coronal heights (from 1.03 to 1.20 R ⊙), plasma β values appear in the limit defined by Gary; such behavior was previously reported by Rodríguez Gómez et al. Additionally, we obtained the plasma β in the solar photosphere at different optical depths from logτ=−1.0 to –2.0. These values decrease with optical depth. This work provides a complete picture of plasma β in quiet Sun regions through the solar atmosphere, which is a prerequisite of a better understanding of the plasma dynamics at the base of the solar corona.

Doppler signature of a possible termination shock in an off-limb solar flare

ABSTRACT We report striking Doppler velocity gradients observed during the well-observed 2017 September 10 solar flare, and argue that they are consistent with the presence of an above-the-looptop termination shock beneath the flare current sheet. Observations from the Hinode Extreme-ultraviolet Imaging Spectrometer measure plasma sheet Doppler shifts up to 35 km s−1 during the late-phase of the event. By comparing these line-of-sight flows with plane-of-sky (POS) measurements, we calculate total velocity downflows of 200+ km s−1, orientated ≈6–10° out of the POS. The observed velocities drop rapidly at the base of the hot plasma sheet seen in extreme ultraviolet, consistent with simulated velocity profiles predicted by our 2.5D magnetohydrodynamics model that features a termination shock at the same location. Finally, the striking velocity deceleration aligns spatially with the suppression of Fe xxiv non-thermal velocities, and a 35–50 keV hard X-ray looptop source observed by the Reuven Ramaty High Energy Solar Spectroscopic Imager. Together, these observations are consistent with the presence of a possible termination shock within the X8.2-class solar flare.

The Link between Nonthermal Velocity and Free Magnetic Energy in Solar Flares

The cause of excess spectral line broadening (nonthermal velocity) is not definitively known, but given its rise before and during flaring, the causal processes hold clues to understanding the triggers for the onset of reconnection and the release of free magnetic energy from the coronal magnetic field. A comparison of data during a 9 hr period from the extreme ultraviolet Imaging Spectrometer on the Hinode spacecraft—at a 3 minute cadence—and nonlinear force-free field extrapolations performed on Helioseismic and Magnetic Imager magnetograms—at a 12 minute cadence—shows an inverse relationship between nonthermal velocity and free magnetic energy on short timescales during two X-class solar flares on 2017 September 6. Analysis of these results supports suggestions that unresolved Doppler flows do not solely cause nonthermal broadening, and instead other mechanisms like Alfvén wave propagation and isotropic turbulence have a greater influence.

Optical design of sub-angular second spatially resolved solar extreme ultraviolet broadband imaging spectrometer

The slit imaging spectrometer is one of the important tools for solar extreme ultraviolet (EUV) spectral imaging detection. However, at present, there is no such instrument load in China. The research of solar physics and space weather in the field of EUV spectral diagnosis mainly depends on foreign instrument data, which seriously restricts the development of related disciplines. The spectral imaging instruments that have been launched internationally have only a spatial resolution of <inline-formula><tex-math id="Z-20240130160605">\begin{document}$2''$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20231481_Z-20240130160605.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20231481_Z-20240130160605.png"/></alternatives></inline-formula>, and it is difficult to observe the core characteristics of the plasma related to the coronal heating mechanism predicted by the theoretical model. In order to better understand the coupling process between different layers of the sun’s atmosphere, solar physics research requires the observed data with wider spectral coverage. In light of this, we propose and design a sub-angular second spatially resolved solar extreme ultraviolet broadband imaging spectrometer operating in a band range of 62–80 nm and 92–110 nm. Compared with the existing instruments, the system can achieve high spatial resolution and spectral resolution, and wide spectral range coverage. Performance evaluation results indicate that the imaging spectrometer’s spatial resolutions in both bands are better than 0.4<i>''</i>, and their spectral resolutions are both better than 0.007 nm, with spectral imaging quality approaching the diffraction limit. The system designed in this work holds significant reference value for developing the first Chinese space-based solar EUV spectroscopic instrument in the future.

Intriguing Plasma Composition Pattern in a Solar Active Region: A Result of Nonresonant Alfvén Waves?

The plasma composition of the solar corona is different from that of the solar photosphere. Elements that have a low first ionization potential (FIP) are preferentially transported to the corona and therefore show enhanced abundances in the corona compared to the photosphere. The level of enhancement is measured using the FIP bias parameter. In this work, we use data from the EUV Imaging Spectrometer on Hinode to study the plasma composition in an active region following an episode of significant new flux emergence into the preexisting magnetic environment of the active region. We use two FIP bias diagnostics: Si x 258.375 Å/S x 264.233 Å (temperature of approximately 1.5 MK) and Ca xiv 193.874 Å/Ar xiv 194.396 Å (temperature of approximately 4 MK). We observe slightly higher FIP bias values with the Ca/Ar diagnostic than Si/S in the newly emerging loops, and this pattern is much stronger in the preexisting loops (those that had been formed before the flux emergence). This result can be interpreted in the context of the ponderomotive force model, which proposes that the plasma fractionation is generally driven by Alfvén waves. Model simulations predict this difference between diagnostics using simple assumptions about the wave properties, particularly that the fractionation is driven by resonant/nonresonant waves in the emerging/preexisting loops. We propose that this results in the different fractionation patterns observed in these two sets of loops.

Updated Reference Wavelengths for Si vii and Mg vii Lines in the 272–281 Å Range

New reference wavelengths for atomic transitions of Mg vii and Si vii in the 272–281 Å wavelength range are derived using measurements from the Extreme-ultraviolet Imaging Spectrometer (EIS) on board the Hinode spacecraft. Mg vii and Si vii are important ions for measuring plasma properties in the solar transition region at around 0.6 MK. The six Si vii wavelengths are 13–21 mÅ and 7–11 mÅ longer than the values in the NIST Atomic Spectra Database (ASD) and the compilations of B. Edlén, respectively. The four Mg vii wavelengths are shorter than the values in the ASD by 8–12 mÅ but show reasonable agreement with the Edlén values. The new wavelengths will lead to more accurate Doppler shift measurements from the EIS instrument and will be valuable for spectral disambiguation modeling for the upcoming Multi-Slit Solar Explorer mission.

Variation of temperature and non-thermal velocity with height in fan loops

ABSTRACT We study the variation of temperature and non-thermal velocity with height in fan loops. For this purpose, we have used the observations recorded by the Extreme Ultraviolet Imaging Spectrometer onboard Hinode. We have employed the emission measure (EM)-loci method to estimate the temperatures of different coronal fan loops and then compute the non-thermal velocities using the obtained temperatures in Si vii 275.35 Å and Fe viii 185.21 Å lines. The EM-loci analysis provides nearly iso-thermal temperature along the fan loops. We obtain the peak temperatures in the range $\log \, T(K)$ = 5.85–5.95 for fan loops, and the subtraction of thermal broadening gives the non-thermal velocities in the range ≈5–15 and 11–29 km s−1 for Si vii 275.35 Å and Fe viii 185.21 Å, respectively. Our method provides quantitative accuracy in the measurement of non-thermal velocity, which is an important parameter in understanding the dynamics of heating of the solar atmosphere.

Are Nonthermal Velocities in Active Region Coronal Loops Anisotropic?

We have measured line widths in active region coronal loops in order to determine whether the nonthermal broadening is anisotropic with respect to the magnetic field direction. These nonthermal velocities are caused by unresolved fluid motions. Our analysis method combines spectroscopic data and a magnetic field extrapolation. We analyzed spectra from the Extreme Ultraviolet Imaging Spectrometer on Hinode. A differential emission measure analysis showed that many spectral lines that are commonly considered to be formed in the active region have a substantial contribution from the background quiet Sun. From these spectra we identified lines whose emission was dominated by the active region loops rather than background sources. Using these lines, we constructed maps of the nonthermal velocity. With data from the Helioseismic Magnetic Imager on the Solar Dynamics Observatory and the Coronal Modeling System nonlinear force-free magnetic field reconstruction code, we traced several of the magnetic field lines through the active region. Comparing the spectroscopic and magnetic data, we looked for correlations of the nonthermal velocity with the viewing angle between the line of sight and the magnetic field. We found that nonthermal velocities show a weak anticorrelation with the viewing angle. That is, the tendency is for the nonthermal velocity to be slightly larger in the parallel direction. This parallel broadening may be due to acoustic waves or unresolved parallel flows.

Small-scale EUV features as the drivers of coronal upflows in the quiet Sun

Context. Coronal upflows in the quiet Sun are seen in a wide range of features, including jets and filament eruptions. The in situ measurements from Parker Solar Probe within ≈0.2 au have demonstrated that the solar wind is highly structured, showing abrupt and near-ubiquitous magnetic field reversals (i.e., switchbacks) on different timescales. The source of these structures has been associated with supergranular structures on the solar disc. This raises the question of whether there are additional small coronal features that contribute energy to the corona and produce plasma that potentially feeds into the solar wind. Aims. During the Solar Orbiter first science perihelion, high-resolution images of the solar corona were recorded using the Extreme Ultraviolet High Resolution Imager (HRIEUV) from the Extreme Ultraviolet Imager (EUI). The Hinode spacecraft was also observing at the same location providing coronal spectroscopic measurements. Combining the two datasets allows us to determine the cause of the weak upflows observed in the quiet Sun and the associated activity. Methods. We used a multi-spacecraft approach to characterise regions of upflows. The upflows were identified in the Fe XII emission line by the Hinode EUV Imaging Spectrometer (EIS). We then used imaging data from the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory (SDO/AIA) and the High Resolution Imagers (HRI) from EUI on board the Solar Orbiter to identify coronal features and magnetic field data from the SDO Helioseismic and Magnetic Imager (HMI). Interface Region Imaging Spectrograph (IRIS) observations were also used to understand the photospheric and chromospheric driving mechanisms. Results. We have identified two regions of coronal upflows in the quiet Sun, with respective sizes and lifetimes of (20 Mm2, 20 min) and (180 Mm2, several hours), which are contrasting dynamic events. Both examples show weak flux cancellation, indicating that the source of the upflows and enhancements is related to the magnetic field changes. The first event, a larger upflow region, shows velocities of up to −8.6 km s−1 at the footpoint of a complex loop structure. We observe several distinct extreme ultraviolet (EUV) features including frequent loop brightenings and plasma blobs travelling along closed coronal loops. The second upflow region has velocities of up to −7.2 km s−1. Within it, a complex EUV feature that lasts for about 20 min can be seen. This main feature has several substructures. During its appearance, a clear mini-filament eruption takes place at its location, before the EUV feature disappears. Conclusions. Two features, with contrasting properties, show upflows with comparable magnitudes. The first event, a complex loop structure, shares several similarities with active region upflows. The second one, a complex small-scale feature that could not have been well resolved with previous instruments, triggered a cascade of events, including a mini-filament that lead to a measurable upflow. This is remarkable for an EUV feature that many instruments can barely resolve. The complexity of the two events, including small loop brightenings and travelling plasma blobs for the first and EUV small-scale loops and mini-filament for the second one would not have been identifiable as the sources of upflow without an instrument with the spatial resolution of HRIEUV at this distance to the Sun. These results reinforce the importance of the smallest-scale features in the Sun and their potential relevance for and impact on the solar corona and the solar wind.

The Merging of a Coronal Dimming and the Southern Polar Coronal Hole

We report on the merging between the southern polar coronal hole and an adjacent coronal dimming induced by a coronal mass ejection on 2022 March 18, resulting in the merged region persisting for at least 72 hr. We use remote sensing data from multiple co-observing spacecraft to understand the physical processes during this merging event. The evolution of the merger is examined using Extreme-UltraViolet (EUV) images obtained from the Atmospheric Imaging Assembly on board the Solar Dynamic Observatory and Extreme Ultraviolet Imager, which is on board the Solar Orbiter spacecraft. The plasma dynamics are quantified using spectroscopic data obtained from the EUV Imaging Spectrometer on board Hinode. The photospheric magnetograms from the Helioseismic and Magnetic Imager are used to derive the magnetic field properties. To our knowledge, this work is the first spectroscopical analysis of the merging of two open-field structures. We find that the coronal hole and the coronal dimming become indistinguishable after the merging. The upflow speeds inside the coronal dimming become more similar to that of a coronal hole, with a mixture of plasma upflows and downflows observable after the merging. The brightening of the bright points and the appearance of coronal jets inside the merged region further imply ongoing reconnection processes. We propose that component reconnection between the coronal hole and coronal dimming fields plays an important role during this merging event because the footpoint switching resulting from the reconnection allows the coronal dimming to intrude onto the boundary of the southern polar coronal hole.

Estimating Ion Temperatures at the Polar Coronal Hole Boundary

The temperatures of the heavy ions (T i ) in the solar corona provide critical information about the heating mechanism of the million-degree corona. However, the measurement of T i is usually challenging due to the nonthermal motion, instrumental limitations, and optically thin nature of the coronal emissions. We present the measurement of T i and its dependency on the ion charge-to-mass ratio (Z/A) at the polar coronal hole boundary, only assuming that heavy ions have the same nonthermal velocity. To improve the Z/A coverage and study the influence of the instrumental broadening, we used a coordinated observation from the EUV Imaging Spectrometer on board the Hinode satellite and the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) on board the Solar and Heliospheric Observatory. We found that the T i of ions with Z/A less than 0.20 or greater than 0.33 are much higher than the local electron temperature. We ran the Alfvén Wave Solar Model-realtime to investigate the formation of optically thin emissions along the line of sight (LOS). The simulation suggested that plasma bulk motions along the LOS broaden the widths of hot emission lines in the coronal hole (e.g., Fe xii, Fe xiii). We discussed other factors that might affect the T i measurement, including the non-Gaussian wings in some bright SUMER lines, which can be fitted by a double-Gaussian or a κ distribution. Our study confirms the preferential heating of heavy ions in coronal holes and provides new constraints on coronal heating models.

Understanding the Relationship between Solar Coronal Abundances and F10.7 cm Radio Emission

Sun-as-a-star coronal plasma composition, derived from full-Sun spectra, and the F10.7 radio flux (2.8 GHz) have been shown to be highly correlated (r = 0.88) during solar cycle 24. However, this correlation becomes nonlinear during increased solar magnetic activity. Here we use cotemporal, high spatial resolution, multiwavelength images of the Sun to investigate the underlying causes of the nonlinearity between coronal composition (FIP bias) and F10.7 solar index correlation. Using the Karl G. Jansky Very Large Array, Hinode/EIS (EUV Imaging Spectrometer), and the Solar Dynamics Observatory, we observed a small active region, AR 12759, throughout the solar atmosphere from the photosphere to the corona. The results of this study show that the magnetic field strength (flux density) in active regions plays an important role in the variability of coronal abundances, and it is likely the main contributing factor to this nonlinearity during increased solar activity. Coronal abundances above cool sunspots are lower than in dispersed magnetic plage regions. Strong magnetic concentrations are associated with stronger F10.7 cm gyroresonance emission. Considering that as the solar cycle moves from minimum to maximum, the sizes of sunspots and their field strength increase with the gyroresonance component, the distinctly different tendencies of radio emission and coronal abundances in the vicinity of sunspots is the likely cause of saturation of Sun-as-a-star coronal abundances during solar maximum, while the F10.7 index remains well correlated with the sunspot number and other magnetic field proxies.

On orbit performance of the solar flare trigger for the Hinode EUV imaging spectrometer

We assess the on-orbit performance of the flare event trigger for the Hinode EUV Imaging Spectrometer. Our goal is to understand the time-delay between the occurrence of a flare, as defined by a prompt rise in soft X-ray emission, and the initiation of the response observing study. Wide (266″) slit patrol images in the He II 256.32 Å spectral line are used for flare hunting, and a reponse is triggered when a pre-defined intensity threshold is reached. We use a sample of 13 > M-class flares that succesfully triggered a response, and compare the timings with soft X-ray data from GOES, and hard X-ray data from RHESSI and Fermi. Excluding complex events that are difficult to interpret, the mean on orbit response time for our sample is 2 min 10 s, with an uncertainty of 84 s. These results may be useful for planning autonomous operations for future missions, and give some guidance as to how improvements could be made to capture the important impulsive phase of flares.