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Empirical relations between major UV and extreme UV spectral lines are one of the inputs for models of chromospheric and coronal spectral radiances and irradiances. They are also needed for the interpretation of some of the observations of the Solar Orbiter mission. We aim to determine an empirical relation between the intensities of the HI 121.6 nm and HeII 30.4 nm Lyman $\alpha$ lines. Images at 121.6 nm from the Chromospheric Lyman Alpha Spectro Polarimeter (CLASP) and Multiple XUV Imager (MXUVI) sounding rockets were co-registered with simultaneous images at 30.4 nm from the EIT and AIA orbital telescopes in order to derive a spatially resolved relationship between the intensities. We have obtained a relationship between the HI 121.6 nm and HeII 30.4 nm intensities that is valid for a wide range of solar features, intensities, and activity levels. Additional SUMER data have allowed the derivation of another relation between the HI 102.5 nm (Ly$\beta$) and HeII 30.4 nm lines for quiet-Sun regions. We combined these two relationships to obtain a Ly$\alpha$/Ly$\beta$ intensity ratio that is comparable to the few previously published results. The relationship between the HI 121.6~nm and HeII 30.4 nm lines is consistent with the one previously obtained using irradiance data. We have also observed that this relation is stable in time but that its accuracy depends on the spatial resolution of the observations. The derived Ly$\alpha$/Ly$\beta$ intensity ratio is also compatible with previous results.

In JT-60U, simultaneous excitation of n = 1 helical cores (HCs) and m/n = 2/1 Tearing Modes (TMs) was observed [T. Bando et al., Plasma Phys. Control. Fusion 61 115014 (2019)]. In this paper, we have investigated the excitation mechanism of n = 1 HCs with m/n = 2/1 TMs based on the experimental observations and a simple quasi-linear MHD model. In the previous study, it was reported that a "coupling" on the phase of the MHD mode is observed between n = 1 HCs and m/n = 2/1 TMs. In this study, it is found that the coupling is observed with the mode frequency from several Hz to 6 kHz. This indicates that the resistive wall and the plasma control system do not induce the coupling because the both time scales are different from the mode frequency. In addition, n = 1 HCs appear to be the non-resonant mode from the two observations: n = 1 HCs do not rotate with the plasma around the q = 1 surface in the core and the coupling is also observed even when qmin > 1. It is also observed that the electron fluctuation due to an n = 1 HC in the core region disappears with the stabilization of an m/n = 2/1 neoclassical tearing mode by electron cyclotron current drive, implying that n = 1 HCs are driven by m/n = 2/1 TMs. This perspective, n = 1 HCs are driven by m/n = 2/1 TMs, is supported by the observation that the saturated amplitude of the m/n = 1/1 component of the radial displacement in the core is smaller than that of the m/n = 2/1 component. Finally, we revisit a quasi-linear MHD model where the m/n = 1/1 HC is induced directly by the sideband of the current for the m/n = 2/1 TM, which allows to excite the non-resonant m/n = 1/1 mode. The model also describes the characteristic of the coupling, fm/n=1/1(HC) = 2fm/n=2/1(TM).

The Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) is a suborbital rocket experiment that on 3rd September 2015 measured the linear polarization produced by scattering processes in the hydrogen Ly-$\alpha$ line of the solar disk radiation, whose line-center photons stem from the chromosphere-corona transition region (TR). These unprecedented spectropolarimetric observations revealed an interesting surprise, namely that there is practically no center-to-limb variation (CLV) in the $Q/I$ line-center signals. Using an analytical model, we first show that the geometrical complexity of the corrugated surface that delineates the TR has a crucial impact on the CLV of the $Q/I$ and $U/I$ line-center signals. Secondly, we introduce a statistical description of the solar atmosphere based on a three-dimensional (3D) model derived from a state-of-the-art radiation magneto-hydrodynamic simulation. Each realization of the statistical ensemble is a 3D model characterized by a given degree of magnetization and corrugation of the TR, and for each such realization we solve the full 3D radiative transfer problem taking into account the impact of the CLASP instrument degradation on the calculated polarization signals. Finally, we apply the statistical inference method presented in a previous paper to show that the TR of the 3D model that produces the best agreement with the CLASP observations has a relatively weak magnetic field and a relatively high degree of corrugation. We emphasize that a suitable way to validate or refute numerical models of the upper solar chromosphere is by confronting calculations and observations of the scattering polarization in ultraviolet lines sensitive to the Hanle effect., Comment: Accepted for publication in The Astrophysical Journal Letters

On 3rd September 2015, the Chromospheric Lyman-Alpha SpectroPolarimeter (CLASP) successfully measured the linear polarization produced by scattering processes in the hydrogen Lyman-$\alpha$ line of the solar disk radiation, revealing conspicuous spatial variations in the $Q/I$ and $U/I$ signals. Via the Hanle effect the line-center $Q/I$ and $U/I$ amplitudes encode information on the magnetic field of the chromosphere-corona transition region (TR), but they are also sensitive to the three-dimensional structure of this corrugated interface region. With the help of a simple line formation model, here we propose a statistical inference method for interpreting the Lyman-$\alpha$ line-center polarization observed by CLASP., Comment: Accepted for publication in The Astrophysical Journal

The Chromospheric Lyman Alpha Spectropolarimeter (CLASP) observed the Sun in H I Lyman-{\alpha} during a suborbital rocket flight on September 3, 2015. The Interface Region Imaging Telescope (IRIS) coordinated with the CLASP observations and recorded nearly simultaneous and co-spatial observations in the Mg II h&k lines. The Mg II h and Ly-{\alpha} lines are important transitions, energetically and diagnostically, in the chromosphere. The canonical solar atmosphere model predicts that these lines form in close proximity to each other and so we expect that the line profiles will exhibit similar variability. In this analysis, we present these coordinated observations and discuss how the two profiles compare over a region of quiet sun at viewing angles that approach the limb. In addition to the observations, we synthesize both line profiles using a 3D radiation-MHD simulation. In the observations, we find that the peak width and the peak intensities are well correlated between the lines. For the simulation, we do not find the same relationship. We have attempted to mitigate the instrumental differences between IRIS and CLASP and to reproduce the instrumental factors in the synthetic profiles. The model indicates that formation heights of the lines differ in a somewhat regular fashion related to magnetic geometry. This variation explains to some degree the lack of correlation, observed and synthesized, between Mg II and Ly-{\alpha}. Our analysis will aid in the definition of future observatories that aim to link dynamics in the chromosphere and transition region., Comment: Accepted by ApJ

There is a thin transition region (TR) in the solar atmosphere where the temperature rises from 10,000 K in the chromosphere to millions of degrees in the corona. Little is known about the mechanisms that dominate this enigmatic region other than the magnetic field plays a key role. The magnetism of the TR can only be detected by polarimetric measurements of a few ultraviolet (UV) spectral lines, the Lyman-$\alpha$ line of neutral hydrogen at 121.6 nm (the strongest line of the solar UV spectrum) being of particular interest given its sensitivity to the Hanle effect (the magnetic-field-induced modification of the scattering line polarization). We report the discovery of linear polarization produced by scattering processes in the Lyman-$\alpha$ line, obtained with the Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) rocket experiment. The Stokes profiles observed by CLASP in quiet regions of the solar disk show that the $Q/I$ and $U/I$ linear polarization signals are of the order of 0.1 % in the line core and up to a few percent in the nearby wings, and that both have conspicuous spatial variations with scales of $\sim 10$ arcsec. These observations help constrain theoretical models of the chromosphere-corona TR and extrapolations of the magnetic field from photospheric magnetograms. In fact, the observed spatial variation from disk to limb of polarization at the line core and wings already challenge the predictions from three-dimensional magnetohydrodynamical models of the upper solar chromosphere.

A sounding-rocket program called the Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) is proposed to be launched in the summer of 2014. CLASP will observe the solar chromosphere in Ly-alpha (121.567 nm), aiming to detect the linear polarization signal produced by scattering processes and the Hanle effect for the first time. The polarimeter of CLASP consists of a rotating half-waveplate, a beam splitter, and a polarization analyzer. Magnesium Fluoride (MgF2) is used for these optical components, because MgF2 exhibits birefringent property and high transparency at ultraviolet wavelength.

High cadence spectroscopic observations by CLASP reveal that intensity fluctuations of blue and red peaks of the hydrogen Lyman-alpha line (121.57 nm) recurrently appear in the quiet Sun at short timescale. The intensity fluctuations of the blue and red peaks are opposite in phase to each other: the blue peak is enhanced during the decease of the red peak, and vice versa. Similar intensity fluctuations also can be seen in Mg II h & k profiles observed with IRIS. It is suggested that the short-timescale oscillatory or torsional phenomena take place in the transition region or the upper chromosphere.

The 400 arcsec spectrograph slit of CLASP crossed predominantly quiet regions of the solar chromosphere, from the limb towards the solar disk center. Interestingly, in the CLASP slit-jaw images and in the SDO images of the He I line at 304 A, we can identify a filament channel (FC) extending over more than 60 arcsec crossing the spectrograph slit. In order to interpret the peculiar spatial variation of the Q/1 and U/1 signals observed by CLASP in the hydrogen Ly-alpha line (1216 A) and in the Si Ill line (1206 A) in such a filament channel, it is necessary to perform multi-dimensional radiative transfer modeling. In this contribution, we show the first results of the two-dimensional calculations we are carrying out in given filament models, with the aim of determining the filament thermal and magnetic structure by comparing the theoretical and the observed polarization signals.

The Chromospheric Lyman-alpha SpectroPolarimeter (CLASP) is a sounding rocket experiment launched on September 3, 2015 to investigate the solar chromosphere, and the slit-jaw (SJ) optical system took Lyα images with the high time cadence of 0.6 s. By the CLASP/SJ observation, many time variations in the solar chromosphere with the time scale of <1 minute were discovered (see the poster by Kubo et al., Pa-13). We focused on an active region and investigated the short (<30 s) time variations and relation to the coronal structure observed by SDO/AIA. We compared the Ly(alpha) time variations at footpoints of coronal magnetic fields observed by AIA 211 Å (approx.2 MK) and AIA 171 Å (0.6 MK), and non-loop regions. As the result, we found the <30 s Ly(alpha) time variations had more in the footpoint regions. On the other hand, the <30 s time variations had no dependency on the temperature of the loop.

High cadence observations by the slit-jaw (SJ) optics system of the sounding rocket experiment "the Chromospheric Lyman Alpha SpectroPolarimeter (CLASP)" reveal ubiquitous intensity disturbances that recurrently propagate in either the chromosphere, transition region, or both at a speed much higher than the sound speed.

The Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) is a sounding-rocket instrument developed at the National Astronomical Observatory of Japan (NAOJ) as a part of an international collaboration. The in- strument main scientific goal is to achieve polarization measurement of the Lyman-alpha line at 121.56 nm emitted from the solar upper-chromosphere and transition region with an unprecedented 0.1% accuracy. For this purpose, the optics are composed of a Cassegrain telescope coated with a "cold mirror" coating optimized for UV reflection and a dual-channel spectrograph allowing for simultaneous observation of the two orthogonal states of polarization. Although the polarization sensitivity is the most important aspect of the instrument, the spatial and spectral resolutions of the instrument are also crucial to observe the chromospheric features and resolve the Ly- pro les. A precise alignment of the optics is required to ensure the resolutions, but experiments under vacuum conditions are needed since Ly-alpha is absorbed by air, making the alignment experiments difficult. To bypass this issue, we developed methods to align the telescope and the spectrograph separately in visible light. We will explain these methods and present the results for the optical alignment of the CLASP telescope and spectrograph. We will then discuss the combined performances of both parts to derive the expected resolutions of the instrument, and compare them with the flight observations performed on September 3rd 2015.

We developed a polarization modulation unit (PMU), a motor system to rotate a waveplate continuously. We applied this PMU for the Chromospheric Lyman-alpha SpectroPolarimeter (CLASP), a sounding rocket experiment to observe the linear polarization of the Lyman-alpha emission (121.6 nm vacuum ultraviolet) from the upper chromosphere and transition region of the Sun with a high polarization sensitivity of 0.1% for the first time and investigate the vector magnetic field. Rotation non-uniformity of the waveplate causes error in the polarization degree (i.e. scale error) and crosstalk between Stokes components. In the ground tests, we confirmed that PMU has superior rotation uniformity. CLASP was successfully launched on September 3, 2015, and PMU functioned well as designed. PMU achieved a good rotation uniformity during the flight and the high precision polarization measurement of CLASP was successfully achieved.

High cadence observations by the slit-jaw (SJ) optics system of the sounding rocket experiment known as the Chromospheric Lyman Alpha SpectroPolarimeter (CLASP) reveal ubiquitous intensity disturbances that recurrently propagate in one or both of the chromosphere or transition region at a speed much higher than the sound speed. The CLASP/SJ instrument provides a time series of 2D images taken with broadband filters centered on the Ly(alpha) line at a 0.6 s cadence. The fast propagating intensity disturbances are detected in the quiet Sun and in an active region, and at least 20 events are clearly detected in the field of view of 527′′ x 527′′ during the 5-minute observing time. The apparent speeds of the intensity disturbances range from 150 to 350 km/s, and they are comparable to the local Alfven speed in the transition region. The intensity disturbances tend to propagate along bright elongated structures away from areas with strong photospheric magnetic fields. This suggests that the observed propagating intensity disturbances are related to the magnetic canopy structures. The maximum distance traveled by the intensity disturbances is of about 10′′, and the widths are a few arcseconds, which is almost determined by the pixel size of 1.′′03. The timescale of each intensity pulse is shorter than 30 s. One possible explanation of the fast propagating intensity disturbances observed by CLASP is magneto-hydrodynamic fast mode waves.

The Chromospheric Lyman-Alpha SpectroPolarimeter is a sounding rocket experiment design to measure for the first time the polarization signal of the Lyman-Alpha line (121.6nm), emitted in the solar upper-chromosphere and transition region. This instrument aims to detect the Hanle effect's signature hidden in the Ly-alpha polarization, as a tool to probe the chromospheric magnetic field. Hence, an unprecedented polarization accuracy is needed ((is) less than 10 (exp -3). Nevertheless, spatial and spectral resolutions are also crucial to observe chhromospheric feature such as spicules, and to have precise measurement of the Ly-alpha line core and wings. Hence, this poster will present how the telescope and the spectrograph were separately aligned, and their combined spatial and spectral resolutions.