Discovery of Ubiquitous Fast-Propagating Intensity Disturbances by the Chromospheric Lyman Alpha Spectropolarimeter (Clasp)

Abstract

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 Lyα 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 ′′ × 527 ′′ during the 5-minute observing time. The apparent speeds of the intensity disturbances range from 150 to 350 km s −1 , and they are comparable to the local Alfvén 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 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 magnetohydrodynamic fast mode waves.

What Causes the High Apparent Speeds in Chromospheric and Transition Region Spicules on the Sun?

“…This means that the observed motions are not caused by mass motions, which impacts the estimated mass and kinetic energy flux that these jets may provide into the solar wind (Tian et al 2014). Our results not only provide an explanation for the rapid "network jets" observed with IRIS (Tian et al 2014), but could also provide an explanation for the rapid upper-chromospheric signals that have been recently observed with the CLASP rocket instrument (Kubo et al 2016).…”

“…The transition region counterparts appear to be shorter and slower in quiet Sun than in coronal holes, presumably because of differing magnetic field configurations (Narang et al 2016). Such high apparent speeds have also been found in other upperchromospheric lines such as Lyα (Kubo et al 2016). There is, however, a large discrepancy between these high apparent speeds and the actual mass flows in spicules as deduced from Doppler shift measurements.…”

Discovery of Scattering Polarization in the Hydrogen Lyα Line of the Solar Disk Radiation

“…The intensity emission profile shows significant spatial fluctuations on scales of ∼10arcsec, which essentially corresponds to the chromospheric network that results from intense photospheric magnetic field concentrations and related heating events: bright in the network and dark in the internetwork (Figure 1(Aa); see also Kubo et al 2016). In the wings, Q/I is negative (the linear polarization is perpendicular to the limb) with amplitudes larger than 1% and increasing up to 6 % toward the limb (i.e., with a very clear center-to-limb variation, hereafter CLV).…”

Polarization Calibration of the Chromospheric Lyman-Alpha SpectroPolarimeter for a 0.1% Polarization Sensitivity in the VUV Range. Part II: In-Flight Calibration

“…The spurious polarization caused by the pointing jitter was calculated by first interpolating the jitter profile obtained by analysing the slit-jaw images (see Figure 15, Kubo et al, 2016) taken at the limb with a 0.6 s cadence to the 0.3 s cadence of the spectro-polarimeter. The jitter shows a periodicity at 4.8 s, mainly due to the image wobbling caused by the half-waveplate rotation.…”