The SUMER Data in the SOHO Archive

We have released an archive of all observational data of the VUV spectrometer Solar Ultraviolet Measurements of Emitted Radiation (SUMER) on SOHO that have been acquired until now. The operational phase started with ‘first light’ observations on 27 January 1996 and will end in 2014. Future data will be added to the archive when they become available. The archive consists of a set of raw data (Level 0) and a set of data that are processed and calibrated to the best knowledge we have today (Level 1). This communication describes step by step the data acquisition and processing that has been applied in an automated manner to build the archive. It summarizes the expertise and insights into the scientific use of SUMER spectra that has accumulated over the years. It also indicates possibilities for further enhancement of the data quality. With this article we intend to convey our own understanding of the instrument performance to the scientific community and to introduce the new, standard FITS-format database.     

Multiresolution wavelet analysis of SUMER/SOHO observations in a solar prominence

We have studied through a multiresolution wavelet analysis the oscillations in a limb prominence. Intensity fluctuations in time and height corresponding to different lines of Siiv and Oiv observed with SUMER on board SOHO have been analyzed in the wavelet bands of J₃= 1 min 36 s to 3 min 12 s and J₄=3 min 12 s to 6 min 24 s. For all species, oscillations in the J₄ band were dominant. We found relevant differences between the behavior of line D₁ (1393.76 Å) corresponding to Siiv and the set D₂ (1401.16 Å), D₃ (1404.81 Å), D₄ (1402.77 Å) corresponding to Oiv, Oiv and Siiv respectively. We also report the identification of a pulse in the intensity of the line D₁ that appears in the range of 15–20 min. This disturbance seems to travel with a speed of about 170 km s^–1.     

Statistical Analysis of Solar Events Associated with Storm Sudden Commencements over One Year of Solar Maximum During Cycle 23: Propagation from the Sun to the Earth and Effects

Taking the 32 storm sudden commencements (SSCs) listed by the International Service of Geomagnetic Indices (ISGI) of the Observatory de l’Ebre during 2002 (solar activity maximum in Cycle 23) as a starting point, we performed a multi-criterion analysis based on observations (propagation time, velocity comparisons, sense of the magnetic field rotation, radio waves) to associate them with solar sources, identified their effects in the interplanetary medium, and looked at the response of the terrestrial ionized and neutral environment. We find that 28 SSCs can be related to 44 coronal mass ejections (CMEs), 15 with a unique CME and 13 with a series of multiple CMEs, among which 19 (68%) involved halo CMEs. Twelve of the 19 fastest CMEs with speeds greater than 1000 km?s^?1 are halo CMEs. For the 44 CMEs, including 21 halo CMEs, the corresponding X-ray flare classes are: 3 X-class, 19 M-class, and 22 C-class flares. The probability for an SSC to occur is 75% if the CME is a halo CME. Among the 500, or even more, front-side, non-halo CMEs recorded in 2002, only 23 could be the source of an SSC, i.e. 5%. The complex interactions between two (or more) CMEs and the modification of their trajectories have been examined using joint white-light and multiple-wavelength radio observations. The detection of long-lasting type IV bursts observed at metric–hectometric wavelengths is a very useful criterion for the CME–SSC events association. The events associated with the most depressed Dst values are also associated with type IV radio bursts. The four SSCs associated with a single shock at L1 correspond to four radio events exhibiting characteristics different from type IV radio bursts. The solar-wind structures at L1 after the 32 SSCs are 12 magnetic clouds (MCs), 6 interplanetary coronal mass ejections (ICMEs) without an MC structure, 4 miscellaneous structures, which cannot unambiguously be classified as ICMEs, 5 corotating or stream interaction regions (CIRs/SIRs), one CIR caused two SSCs, and 4 shock events; note than one CIR caused two SSCs. The 11 MCs listed in 3 or more MC catalogs covering the year 2002 are associated with SSCs. For the three most intense geomagnetic storms (based on Dst minima) related to MCs, we note two sudden increases of the Dst, at the arrival of the sheath and the arrival of the MC itself. In terms of geoeffectiveness, the relation between the CME speed and the magnetic-storm intensity, as characterized using the Dst magnetic index, is very complex, but generally CMEs with velocities at the Sun larger than 1000 km?s^?1 have larger probabilities to trigger moderate or intense storms. The most geoeffective events are MCs, since 92% of them trigger moderate or intense storms, followed by ICMEs (33%). At best, CIRs/SIRs only cause weak storms. We show that these geoeffective events (ICMEs or MCs) trigger an increased and combined auroral kilometric radiation (AKR) and non-thermal continuum (NTC) wave activity in the magnetosphere, an enhanced convection in the ionosphere, and a stronger response in the thermosphere. However, this trend does not appear clearly in the coupling functions, which exhibit relatively weak correlations between the solar-wind energy input and the amplitude of various geomagnetic indices, whereas the role of the southward component of the solar-wind magnetic field is confirmed. Some saturation appears for Dst values \(< -100\) nT on the integrated values of the polar and auroral indices.     

FESTIVAL: A Multiscale Visualization Tool for Solar Imaging Data

Since 4 December 2006, the SECCHI instrument suites onboard the two STEREO A and B probes have been imaging the solar corona and the heliosphere on a wide range of angular scales. The EUVI telescopes have a plate scale of 1.7 arcseconds pixel⁻¹, while that of the HI2 wide-angle cameras is 2.15 arcminutes pixel⁻¹, i.e. 75 times larger, with the COR1 and COR2 coronagraphs having intermediate plate scales. These very different instruments, aimed at studying Coronal Mass Ejections and their propagation in the heliosphere, create a data visualization challenge. This paper presents FESTIVAL, a SolarSoftware package originally developed to be able to map the SECCHI data into dynamic composite images of the sky as seen by the STEREO and SOHO probes. Data from other imaging instruments can also be displayed. Using the mouse, the user can quickly and easily zoom in and out and pan through these composite images to explore all spatial scales from EUVI to HI2 while keeping the native resolution of the original data. A large variety of numerical filters can be applied, and additional data (i.e. coordinate grids, stars catalogs, etc.) can be overlaid on the images. The architecture of FESTIVAL is such that it is easy to add support for other instruments and these new data immediately benefit from the already existing capabilities. Also, because its mapping engine is fully 3D, FESTIVAL provides a convenient environment to display images from future out-of-the-Ecliptic solar missions, such as Solar Orbiter or Solar Probe.     

A Contribution to the Understanding of Chromospheric Oscillations

We present SUMER/SOHO UV measurements of chromospheric oscillations of intensity, velocity, and linewidth observed in C i, S i, O i, and C ii lines, which are formed in the altitude range from 1000 km to 2000 km above τ ₅₀₀=1. Oscillations in lines originating at similar altitudes exhibit different behaviors which we discuss in terms of the formation of the lines.     

Dynamics of a Quiescent Solar Prominence Observed with the SUMER/SOHO Instrument

We present the results obtained from analyzing SUMER/SOHO observational data of a quiescent solar prominence. The studied prominence is made of complex structures. From the 1-hr data set, we derive characteristic frequencies in terms of intensity and velocity oscillations, as measured in 4 transition-region lines. The presence of different types of frequencies is detected: chromospheric oscillations and intermediate periods (6 min to 12 min). This result suggests that these oscillations are transmitted by the magnetic fields from the chromosphere to the transition region.     

Studying Sun–Planet Connections Using the Heliophysics Integrated Observatory (HELIO)

The Heliophysics Integrated Observatory (HELIO) is a software infrastructure involving a collection of web services, heliospheric data sources (e.g., solar, planetary, etc.), and event catalogues – all of which are accessible through a unified front end. In this paper we use the HELIO infrastructure to perform three case studies based on solar events that propagate through the heliosphere. These include a coronal mass ejection that intersects both Earth and Mars, a solar energetic particle event that crosses the orbit of Earth, and a high-speed solar wind stream, produced by a coronal hole, that is observed in situ at Earth (L1). A ballistic propagation model is run as one of the HELIO services and used to model these events, predicting if they will interact with a spacecraft or planet and determining the associated time of arrival. The HELIO infrastructure streamlines the method used to perform these kinds of case study by centralising the process of searching for and visualising data, indicating interesting features on the solar disk, and finally connecting remotely observed solar features with those detected by in situ solar wind and energetic particle instruments. HELIO represents an important leap forward in European heliophysics infrastructure by bridging the boundaries of traditional scientific domains.     

High-chromosphere and low-transition-region network: A different organization in an equatorial coronal hole?

In order to investigate the high chromosphere and the low transition region in a coronal hole, we have analysed Ca ii, Mg ii and hydrogen resonance lines, recorded by the OSO-8 spectrometer in 1975. We present the comparison between average profiles observed in and out of the equatorial coronal hole which was at the center of the solar disk between 27 and 29 November, 1975. We separate internetwork and quiet-Sun (network+internetwork) profiles: for the internetwork, we observe that the hydrogen and Mg ii profiles recorded in the hole are stronger than the profiles recorded out of the hole; a similar result, but with a much lower contrast, is found for the quiet Sun. We discuss this surprising result.     

Oscillations of the upper chromosphere

Variations of intensity and wavelength in several UV lines have been observed with the SUMER spectroheliometer onboard SOHO, and they have been analysed to obtain oscillation spectra and phase differences between lines of different ions. Lines intensities of neutral or singly ionized atoms (with temperature of formation 30000 K) exhibit an increase of oscillatory power between 2.5 and 7 mHz, which may be considered as the signature of p modes. Lines of highly ionized elements (with a temperature of formation 50000 K) yield power spectra which are continuously decreasing with frequency. Brightness variations of the continuum at different wavelengths between 1000 and 1400 Å present oscillations in the same frequency range. Thus, p modes seem to be efficiently stopped by the transition region. No clear evidence is found for the existence of a chromospheric oscillation mode. Phase comparisons between lines formed at different altitudes (in particular Sii and Siii) indicate that these lines oscillate in phase, within the precision of the measurements.     

Joint EUV/Radio Observations of a Solar Filament

In this paper we compare simultaneous extreme ultraviolet (EUV) line intensity and microwave observations of a filament on the disk. The EUV line intensities were observed by the CDS and SUMER instruments on board SOHO and the radio data by the Very Large Array and the Nobeyama radioheliograph. The main results of this study are the following: (1) The Lyman continuum absorption is responsible for the lower intensity observed above the filament in the EUV lines formed in the transition region (TR) at short wavelengths. In the TR lines at long wavelengths the filament is not visible. This indicates that the proper emission of the TR at the filament top is negligible. (2) The lower intensity of coronal lines and at radio wave lengths is due to the lack of coronal emission: the radio data supply the height of the prominence, while EUV coronal lines supply the missing hot matter emission measure (EM). (3) Our observations support a prominence model of cool threads embedded in the hot coronal plasma, with a sheath-like TR around them. From the missing EM we deduce the TR thickness and from the neutral hydrogen column density, derived from the Lyman continuum and Hei absorption, we estimate the hydrogen density in the cool threads.