SOHO Joint Observing Program 051 Study of Quiet Sun UV/EUV and Halpha Jets by Joint SOHO/SUMER/EIT/CDS and BBSO/Halpha/VMG Observations Haimin Wang, Jong-Chul Chae, Terry Kucera, Joe Gurman, Dominic Zarro, Bob Bently, Chikyin Lee, Adriana Silva and Hal Zirin 1. Background High spatial resolution ultraviolet solar spectra (CIV 1548A) have been observed by Brueckner and Bartoe (1983) with HRTS (High Resolution Telescope and Spectrograph) on board rockets. Their observations reveal high-energy jets in the quiet Sun. Each jet carries 2.5X10^{26} erg of energy and 2X10^{11} g of mass, and moves at a speed of 400 km/s into the corona. The authors pointed out that the energy and mass requirements for coronal heating and solar wind can be satisfied by the jets. Brueckner and Bartoe interpreted these jets as exploding loops; however, simultaneous high-resolution magnetograph and Halpha observations were not available with UV observations. In addition, they observed "turbulent events" which show broadening of the UV lines in both red and blue wings. The speeds of these events are around 200 km/s. In search of the possible chromospheric counterparts for these jets, Wang et al. (1996a) studied Halpha-1.0A movies. The count rate for UV jets is much lower than that in spicules, so we could exclude spicules from being the counterparts of UV jets. Observations at Halpha-1.0A make most spicules invisible. Frequently, we observed the darkenings in the Halpha-1.0A images, which are always located close to network magnetic elements. The darkenings represent the high speed upward flows away from the Sun: we refer to them as Halpha-1.0A jets. The authors found that the birth rate of Halpha-1.0A jets is about 20 events/sec over the whole Sun, comparable to that of the UV jets, and much fewer than spicules. 70\% of Halpha jets are associated with converging magnetic bipoles at network boundaries, which are the sites of interaction between network and opposite-polarity IN fields. Most jets are from repeatedly ejections from the same site throughout the day. It is well known that magnetic fields play a fundamental role in defining the structure, mass and energy flow in the chromosphere and corona (Withbroe and Noyes, 1977). Simultaneous high-sensitivity magnetograms and high-resolution Halpha/UV/EUV observations of the quiet Sun, which cover a wide range of altitude from the photosphere, through the chromosphere, the transition region and up through the corona, will be able to provide comprehensive information on the dynamic features on the quiet Sun, such high-speed jets. In a quiet region, magnetic fields can be generally divided into two categories: network fields and intra-network (IN) fields. The observable fields are in the form of discrete magnetic elements. Network fields are found in the boundaries and, particularly, in the vertices of supergranule cells (Simon and Leighton, 1964; Wang, 1988). The intra-network fields are mixed-polarity magnetic elements inside the network (Livingston and Harvey, 1975). Two important processes for the creation and destruction of magnetic elements of the quiet Sun are Ephemeral Regions (ERs) (Harvey and Martin, 1973) and cancellation (Martin, 1983; Livi et al., 1985; Martin et al., 1985). Recently, we have obtained and studied a number of sequences of the best quiet Sun magnetograms obtained at BBSO. We studied the distribution of IN magnetic fluxes based on these magnetograms and found a peak in the flux distribution at 6X10^{16} Mx (Wang et al. 1995). We also applied the local correlation tracking technique to long-integration magnetograms and confirmed that intra-network fields follow supergranular flow and are swept into the network boundary. However, IN fluxes do not contribute to the formation of network fields because of their bipolar nature (Wang et al. 1996b). Furthermore, we estimated that the interaction between the network and IN fields, can produce at least 1.2X10^{28} erg/s of energy, which is comparable to the energy required to heat the corona. Obviously, these studies need to be extended to many regions, including the quiet network, the enhanced network and coronal holes, with new SOHO observations. 2. Proposed Observations Based on the above summary, our objectives are clear: (a) To establish relationships between Halpha and UV jets; (b) To find the relationship between jets and the photospheric magnetic fields, especially the evidence and effects of small-scale magnetic reconnections. (a) Magnetograph Observations BBSO Videomagnetograph (VMG) system take 4096-integration magnetograms every 3 minutes and record them digitally. The system has 16-bit integration memory, with 8-bit A-to-D conversion. The field strength calibration has been established (Varsik, 1994). We have also developed shift-and-add techniques (to register magnetograms and add them together). Although the existing BBSO VMG system is capable of providing the most sensitive magnetogram, further improvements to the magnetograph system are planned to obtain even better data to support SOHO quiet Sun Observations. We are developing a digital magnetograph system to substitute the current video magnetograph system. We will use the telescope, KDP and Zeiss filter of the BBSO VMG system, but replace its video camera with a 12-bit digital camera system, while having improved readout rate (100 frames/s) to minimize time difference between two polarizations. After the upgrade, we expect that the magnetograph system will provide a sensitivity of 1 gauss in flux density and spatial resolution of 1 arcsec, which will enhance the collaboration with SOHO. (b) BBSO Halpha Observations BBSO has three high-quality digital CCD cameras: an OSL TI 1024X1024 12-bit camera, a Kodak 1200X1500 10-bit camera, and a Kodak 1024X1024 8-bit camera. We propose to obtain best quality (10s temporal resolution, 1" or better spatial resolution) Halpha movies with the following three observing modes: (1) Halpha filter scan. We will use the OSL camera and computer-controlled Zeiss filter to scan the Halpha-0.65A, center line and +0.65A continuously. (2) Multi-Camera H$\alpha$ filtergraph Observation. We will set the OSL camera to observe at Halpha-1.0A, one Kodak camera at -0.5A, and the other Kodak camera at Halpha centerline. Halpha scans (-1.0 to 1.0A by 0.1A) are done every hour on the OSL camera and Kodak cameras; and (3) Fast Halpha spectral scans: we use the BBSO spectrograph and repeatedly drift scan an area of 600$''$ by 300$''$ near the solar disk center. To achieve high smoothness in the reconstructed spectroheliograms, the drift scan is achieved by turning off the telescope guider system before each scan begins, and the rotation of the earth is used to ``drift" the solar image. Spectrum and slit images are combined by a video mixer, and recorded in the optical disk at 30 frames/s. The optical disk stores images in analog form, but its serial port allows us to have computer control and grab every image easily. Spectroheliograms and velocitygrams are constructed off-line by automatic IDL. We have achieved 20-s temporal resolution, 1-arcsec 2-D spatial resolution and 0.05A spectral resolution simultaneously. (c) SOHO/SUMER/CDS/EIT Observations There are several instruments on board SOHO for studying the solar chromospheric and coronal phenomena. We are mostly interested in the SUMER observations. We had wished to select SUMER C IV (1548A, T=10^5K) line, which is the line that high speed UV jets were first observed (Brueckner and Bartoe, 1983). As SUMER is switching to detector B, C IV line will be out the upper limit of the detector. Si IV line at 1403A (T=6X10^4K) will be used, as jets were observed in this weaker line too. When the Si IV line is selected, several O IV lines near 1400A will be observed, from their line ratios, we expect to study electron density of jets. We will observe quiet regions near disk center, and scan an area of 100" by 100". We understand that SUMER would take tens of minutes to scan such an area, so it does have enough cadence to study the evolution of jets. However, at each SUMER slit position, there always be a silmutaneous Halpha observations, so we will use the SUMER data to establish the relationship between UV and Halpha jets, while the evolution of each jet will be studied by H$\alpha$. A test observing run was carried out in Oct. 1996. Data analyses are in progress. Hopefully, this run will help us to plan future observations. EIT provides high resolution images in four EUV emission lines: Fe IX (171A), Fe XII (195A), Fe XV (284A) and HeII (304A). With these high resolution images, we are especially interested in studying the morphology and evolution of sites which produce jets continuously. Jets may convert part of their kinetic energies to thermal energies to produce emission at different temperatures. These images will also help us to understand the small scale loop structure in the quiet Sun, and their role in producing jets and bright points. We prefer EIT to observe with a 2 X 2 block field of view (~ 100" X 100") with all four wavelengths. However, in order to obtain higher temporal resolution, we may have to choose one wavelength (either 171 \AA~ or 195 \AA). Brueckner and Bartoe (1983) found that the acceleration rate of UV jets did not decrease shortly before the jets become invisible, suggesting that material is heated to higher coronal temperature. CDS observations will provide further diagnoses of these jets if they are indeed heated to the higher coronal temperature. Example of useful lines: Mg VI 349A, Mg VII 315A and Mg VIII 315A. Same as for SUMER, we do not expect CDS to provide time resolution to study evolution of jets; it is used to establish the relationship among SUMER jets, CDS jets and Halpha jets. We propose to extend our study to compare the properties of magnetic fields and atmospheric structure inside and outside the coronal holes. Coronal hole regions are observed as darker areas in X-ray images, corresponding to open coronal fields. Although the non-thermal energy flux supplied at chromospheric levels inside and outside coronal holes is approximately the same (Withbroe and Noyes, 1977), the energy is converted predominantly into heat outside the coronal hole, and is used in accelerating the solar wind inside the coronal holes. Bohlin et al. (1975) found that macrospicules occur predominantly in coronal holes. It is interesting to study the properties of jets, and photospheric magnetic fields in these two different parts of the quiet Sun, which may provide direct diagnoses of conditions for coronal heating and solar wind. An ideal target is a boundary of the coronal hole near disk center, where both regions are covered with the same observing condition. REFERENCES Bohlin, J.D., Vogel, S.N., Purcell, J.D., Sheeley, N. R., Tousey, R. VanHoosier, M.E., 1975, Ap.J. 197, L133. Brueckner, G.E. and Bartoe, J.F., 1983, Ap. J., 272, 329. Harvey, K.L. and Martin, S.F., 1973, Solar Physics, 28, 61. Livi S.H.B., Wang, J. and Martin, S.F., 1985, Australian Journal of Physics, 38, 855. Livingston, W. C. and Harvey, J. 1975, Bull AAS 7, 346. Martin, S.F., Livi S.H.B. and Wang, J., 1985, Australian Journal of Physics, 38, 929. Simon, G.W. and Leighton, R.B. 1964, Ap. J., 140, 1120 Varsik, J. 1995, Solar Physics, 161, 207. Wang, 1988, Solar Physics, 116, 1. Wang J., Wang, H., Tang, F., Lee, J and Zirin H., 1995, Solar Physics, 160, 277. Wang H., Johanssen, A. Stage, M. and Zirin, H., 1996a, in preparation. Wang, H., Tang, F., Zirin, H. and Wang, J., 1996b, Solar Physics, 165, 223. Withbroe, G.L. and Noyes, R.W., 1977, Ann. Rev. Astron, Astrophys., 15, 363.