First Results From SPICE EUV Spectrometer on Solar Orbiter

<p>SPICE (Spectral Imaging of Coronal Environment) is an EUV imaging spectrometer onboard Solar Orbiter. SPICE observes the Sun in two wavelength bands: 69.6-79.4 nm and 96.6-105.1 nm and is capable of recording full spectra in these bands with exposures as short as 1s. SPICE can measure spectra from the disk and low corona, and records all spectral lines simultaneously, using one of three narrow slits: 2”x11’, 4’’x11’, 6’’x11’, or a wide slit 30’’x14’. The primary mirror can be scanned in a direction perpendicular to the slit, allowing raster images of up to 16’ in size.</p><p>The first SPICE data were taken during the instrument commissioning carried out by the RAL Space team between 2020 April 21 and 2020 June 14, and at the first Solar Orbiter perihelion at 0.52AU between June 16-21.  We give examples of full spectra from the quiet Sun near disk centre and provide a list of key spectral lines from neutral hydrogen and ions of carbon, oxygen, nitrogen, neon, sulphur and magnesium. These lines cover the temperature range between 10,000 K and 1 million K (10MK in flares), providing slices of the Sun’s atmosphere in narrow temperature intervals. We show examples of raster images in several strong lines, obtained with different slits and a range of exposure times between 5s and 180s.</p><p>We have found several unusually bright, compact structures (named “beacons”) in the quiet Sun network, with extreme intensities up to 22 times greater than the average intensity across the image. The lifetimes of these sources are longer than 1 hour. We will derive plasma velocities in the beacon area, and co-align the SPICE rasters with the SDO/AIA 304 and 171 images and the HMI magnetic field to better understand the origin and properties of beacons.</p><p>We also show the first above-limb measurements with SPICE in Mg IX, Ne VIII and O VI lines, as obtained when the spacecraft pointed at the limb. Maps of Mg/Ne abundance ratios on disk can be derived and compared with in situ measurements to help confirm the magnetic connection between the spacecraft location and the Sun’s surface, and locate the sources of the solar wind.</p>

Numerical and Experimental Investigations on the Residual Stresses at the Centre of Flat Glass Disks After Thermal Tempering

Flat glass disks are thermally tempered by air-cooling with two air jets at the centre of their surfaces. Numerical modelling and photoelasticity measurements are proposed to analyze the distribution of the residual stresses through the glass thickness at the centre of the tempered disks. For the modelling, glass properties dependent of the temperature are used for the conductive heat transfer. Radiation is modelled by an improved approximation method. By taking both structural and stress relaxations into account, the transient and residual stresses are computed along the disk thickness. For experimentation, a complete procedure is proposed to access to the stress state in the centre of the disks using a scattered light polariscope. The average distribution of the residual stresses is deduced from stress profile measurements taking four radial orientations at the disk centre into consideration. Comparison between numerical and experimental values is finally discussed for the residual surface and half-thickness stresses at the disk centre.

Transverse motion of a disk through a rotating viscous fluid

A thin rigid disk translates edgewise perpendicular to the rotation axis of an unbounded fluid undergoing solid-body rotation with angular velocity Ω. The disk face, with radius a, is perpendicular to the rotation axis. For arbitrary values of the Taylor number, [Tscr ] = Ωa2/ν, and in the limit of zero Reynolds number [Rscr ]e, the linearized viscous equations reduce to a complex-valued set of dual integral equations. The solution of these dual equations yields an exact representation for the velocity and pressure fields generated by the translating disk.For large rotation rates [Tscr ] [Gt ] 1, the O(1) disturbance velocity field is confined to a thin O([Tscr ]−1/2) boundary layer adjacent to the disk. Within this boundary layer, the flow field near the disk centre undergoes an Ekman spiral similar to that created by a nearly geostrophic flow adjacent to an infinite rigid plate. Additionally, flow within the boundary layer drives a weak O([Tscr ]−1/2) secondary flow which extends parallel to the rotation axis and into the far field. This flow consists of two counter-rotating columnar eddies, centred over the edge of the disk, which create a net in-plane flow at an angle of 45° to the translation direction of the disk. Fluid is transported axially toward/away from the disk within the core of these eddies. The hydrodynamic force (drag and lift) varies as O([Tscr ]1/2) for [Tscr ] [Gt ] 1; this scaling is consistent with the viscous stresses created in the Ekman boundary layer. Additionally, an approximate expression, suitable for all Taylor numbers, is given for the hydrodynamic force on a disk translating broadside along the rotation axis and edgewise transverse to the rotation axis.

Observations of Alfvén Waves Simultaneously in Hα and K

Simultaneous spectroheliograms of a quiet region at solar disk centre in Hα + 0.29 Å, Hα − 0.29 Å, K + 0.18 Å and K − 0.18 Å show much similarity in the asymmetries in the two lines. The fibrils are identical geometrically. Both lines show patterns of line-of-sight motions propagating along the fibrils. Close to the network, the velocity of propagation is of the order of 12 km s−1 towards or away from the network; further away the patterns propagate away from the network at velocities of the order of 75 km s−1. The latter are interpreted as Alfvén waves, the former as due most likely to variations in longitudinal velocities along the fibrils.