Title: Spectral Observations of Spicule Dynamics ------ Authors: -------- K. Reardon (INAF/OAA) L. Teriaca (MPS) A. Sterling (NASA/MSFC) M. Carlsson (UO) V. Hansteen (UO) W. Curdt (MPS) SOHO Instruments: ----------------- SUMER Other Observatories: -------------------- NSO-DST/IBIS Hinode/SOT Hinode/XRT Hinode/EIS TRACE Update History: --------------- 11/09/2007 - Initial Proposal Scientific Objectives: ---------------------- The goal of the proposed JOP is to study the dynamics and evolution of spicules with spectrally resolved observations at multiple wavelengths, from the visible to the vacuum ultraviolet (VUV). With the observations in chromospheric lines at visible wavelengths we plan to determine velocities, both transversal and longitudinal, which will allow us to characterize the behavior of the "classical" spicules. In addition, rapid cadence imaging will permit the study of their evolution on a variety of time scales. This information will allow us to better quantify the energetics of the spicule phenomena. Spicular structures are also commonly observed in VUV lines formed at temperatures up to the transition region. Simultaneous observations in VUV spectral lines will clarify the relationship between VUV and classical spicules and determine the plasma dynamics up to coronal temperatures. Scientific Justification: ------------------------- Spicules are a fundamental and ubiquitous component of the solar chromosphere (Beckers 1968, 1972). Their energy requirements, ~ 10^6 erg cm^-2 s^-1, are comparable to the heating rate of the quiet corona. Since they extend from the chromosphere up into the corona, it is enticing to consider that they could be vehicles for the energization of the corona from the photosphere (e.g., Hollweg, Jackson, Galloway 1982; Kudoh & Shibata 1999). Their upward mass fluxes are many times larger than the outward-flowing mass flux of the solar wind, and so they may be important when considering the overall mass balance of the solar atmosphere. There are also spicule-like features seen at VUV wavelengths, indicating that spicules or related phenomena play a role in the transition region as well (e.g., Mariska, 1992). Whether VUV spicules are cospatial or the extension of the classical Halpha spicules is still uncertain, although there are strong indications that a close relation may exist (see Wilhelm 2000, A&A 360, 351 and references therein). Thus, an understanding of spicules is essential to a full understanding of the solar atmosphere. Theoretical models of spicules have examined a variety of mechanisms, and summaries of many of the older models can be found in Beckers (1968) and Sterling (2000); these include suggested mechanisms invoking shocks, granule-driven waves, and Alfven waves. More recently De Pontieu et al. (2004) have suggested that solar photospheric p-mode oscillations could be the source of spicules. To date it has been difficult to rule out absolutely particular models of spicules, in large part because their narrow widths place them at the limits of the capabilities of existing telescopes. Nearly all theories involve the magnetic field playing an active or passive role, which is supported up by the connection between the magnetically-enhanced supergranule boundary and the appearance spicule-like structures. With the launch of the Hinode spacecraft, it is now possible to observe spicules at visible wavelengths without atmospheric interference. Recent analyses of time series of broadband images from Hinode have enhanced or clarified many aspects of our knowledge of the spicule dynamics. Two classes of spicules have been observed, the "slower" spicules have periods of 3-7 minutes and are presumably driven by acoustic shocks originating in the solar chromosphere. A second class of faster spicules, with rapid onset, shorter lifetimes, and high transverse velocities is also observed. It has been suggested that these spicules are driven instead by magnetic reconnection. The broadband images contain indications that the spicules are also the sites of strong Alfven waves carrying a possibly significant amount of energy into the higher atmospheric layers. The spicules observed with the Hinode broadband images also appear often to be composed of multiple "strands" of sub-arcsecond sizes and rotational motions or oscillations are also observed. In order to help clarify the observed spicule characteristics, complementary spectral observations, which can provide, for example, direct information on velocities and wave behaviour, are necessary. In chromospheric lines, the only present means to obtain spectra is using ground-based instrumentation. Imaging spectrometers, such as IBIS, currently provide the best means to obtain such observations at the solar limb. VUV spectra of transition region lines, will provide information on which relation exist between VUV and the two different classes of Halpha spicules and indications on how the spicule behaviour relates to the plasma energetics at higher temperatures. VUV spectra of adequate spatial and spectral resolution can instead only be obtained from space-based instruments such as SUMER. TRACE images in C IV would provide the needed context to the slit spectra. Operational Considerations: --------------------------- The ground-based observations from the NSO/Dunn Solar Telescope will be focused on the hours 15:00-18:00 UT. Because of the fundamental role of IBIS in achieving the proposed science goals, we request the coordinated observations during this time frame. The observing time at the NSO/DST has been assigned in the period 02-11 November, 2007. Coordinated observations should be obtained for as much of this period as possible Detailed Observing Sequences: ----------------------------- SOHO/SUMER: With SUMER, we plan to obtain time series of observations with a fixed slit placed tangential to the limb near the equator. DST/IBIS: Imaging spectral scans of the Ca II 8542 and/or H-alpha lines with an approximately 10-20 second cadence. The IBIS field of view will be 80x40 arcseconds. TRACE: Images in the 155 nm band at 15 s cadence. Full resolution over a FOV of about 150"x150". Pairs of images at 160 and 170 nm whenever possible. HINODE/SOT: Images in Ca II H at about 10s cadence over a 150"x150" FOV. Occassional context images in Continuum and H-alpha HINODE/XRT: Images in Thin Al-Poly or Ti-Poly at about 15s cadence over a 150"x150" FOV. HINODE/EIS: Spectroheliograms in selected lines. The target will be chosen several days before the observations based on the structures present on the solar disk. We will avoid locations of active regions near the limb; During coordination with SUMER, we will chose a target region located close to the equator.