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Produced by the NASA Center for Aerospace Information (CASI) 49ASA -CH-1740341 SIUDI OF 7H8 SOLE CORON A 985-11963 USING RADIO END SPACE OBSESTATIONS ADAU41 States Heport, Nov. 1983 - Cc t. 1984 (Colorado Univ.) 37 p HC A03/fi? A01 Unclas CSCL 03B G3/92 24299 ANIIQAL STATUS REPORT November 1983 - October 1984 Grantee: The Regents of the University of Colorado Boulder, Colorado 80309 Principal Investigator: George A. Dulk Professor Department of Astrophysical, Planetary and Atmospheric Sciences University of Colorado a Boulder, Colorado 80309 Telephone: (30) 492-8788 Grant Title: Study of the Solar Corona Using Radio and Space Observations Grant Number: NASA Grant No. NSG-7287 Univ. of Colorado No. 1-5331-26 v y ^ R 1 This annual report was prepared by the principal investigator under grant no. NSG-7287 from the National Aeronautics and Space Administration. lcw) 11 CONTENTS Annual Report STUDY OF THE SOLAR CORONA USING RADIO AND SPACE OBSERVATIONS NASA Grant NSG-7287 Page Scientific Background and Scope of this Investigation . 3 1) Physics of Coronal Transients . 3 2) The Characteristics of Radiation and Accelerated Particles at the Time of Flares . 3 3) The Density-Temperature Structure of the Transition Region and Corona and the Coronal Magnetic Field . 5 Appendix A . 7 List of Papers Published, Submitted or Prepared During the Previous Year and Present Year of Grant NSG-7287 Appendix B . 9 Invited Talks and Colloquia; Contributed Papers Conferences Attended and Other Grant-Related Activities Appendix C . 12 Abstracts of Papers Published, Submitted or Prepared During the Previous Year and the Present Year of Grant NSG-7287 PM 3 In the following we detail the progress made under the three main areas of investigation: 1) the physics of coronal transients, 2) the characteristics of radiation and accelerated particles at the time of flares, and 3) the density-temperature structure of the transition region and corona and the coronal magnetic field. 1) The Physics of Coronal Transient Events Together with the HAO group led by L. House and the Australian group led by K. Sheridan, Graduate Student Dale Gary and I performed a detailed analysis of a coronal transient event that was particularly well observed by the C/P experiment on SMM and the Culgoora Radio Observatory. The analysis and interpretation composed part of Gary ' s thesis which is now complete; he is presently a Research Associate at Caltech. One part of this work, the part related to shock waves and Type II bursts, has recently been published. The main results are given in the attached abstract. The second part of this work involved one of the first quantitative analyses of SMM C/ P observations of brightness, and simultaneous radio observations of a moving Type IV radio source. The emphasis was placed on identifying whether the radio emission was due to gyrosynchrotron radiation or plasma radiation, and on whether the observations could distinguish between "loop" and "bubble" models of transients. The results have been submitted for publication and are given in the attached abstract. Analysis of another event is underway, led by Graduate Student Joe Bassi and Bill Wagner of HAO. A report on the preliminary results of this work was presented at the SMM workshop. 2) The Characteristics of Radiation and Accelerated Particles At the Time of Flares We have reported on the radio and hard X -ray characteristics of two flares ...^ No 4 observed with several instruments: the VLA, ground-based radiometers, and hard X-ray spectrometers and imaging devices on spacecraft (SMM, ISEE-3 and Hinatori). One flare (bulk, Bastian and Hurford 1983; see attached abstract) demonstrated that large source sizes and inhomogeneous structures are likely in a large flare, while the other (Dulk, Bastian and Kane 1985; see attached abstract) established the altitudes of microwave sources in two limb flares, and again emphasized the inhomogeneous nature of impulsive flare sources. The mechanism of amplified decimetric waves was proposed by Melrose and Dulk (1982a, 1982b; see attached abstracts) as an energetically important radiation source in flares. We are continuing to investigate both the maser mechanism and its consequences. Part has been published (Dulk and Melrose 1983; Melrose and Dulk 1984; see attached abstracts), and part is to be included in the chapter on energy transport of the SMM Workshops. Observationally we set the VIA to search for very small, very bright sources expected from this mechanism; so far we have not been successful in observing any flares. Theoretically, mainly under the auspices of our STTP grant, we are considering whether absorption of the maser radiation in small :sale pockets in the corona can account for the very broad ion lines (e.g. Ca XIX) observed by XRP and other instruments aboard spacecraft. We now have substantial evidence that our maser mechanism is important on stars other than the Sun, notably flare stars and AM Herculis type binaries (see attached abstracts by Du1< et al. 1983). On some stars the flares are of much greater magnitude than on the Sun, but many of the physical processes are undoubtedly the same. So far we are using knowledge gained form solar studies to help us understand processes on those stars; hopefully some processes will stand out more clearly in the different environment of stars and we will be able to transfer this knowledge back, to help us understand the Sun better. 5 In the larger heliosphere, we have undertaken a series of studies of radio bursts in the solar wind, bursts observable only at low frequencies (less than a few MHz) aboard spacecraft. In particular, we have collaborated with investigators of the Goddard/French radio experiment on ISEE-3 and used much of that data together with simultaneous data from Culgoora. Results obtained to now include investigation of propagation effects (ducting and scattering of radio waves by the inhomogeneous interplanetary medium), and whether the radiation is due to plasma emission at the fundamental or harmonic (see attached abstracts). Work is continuing on further analysis of data with particular emphasis on describing the small scale structures in the solar wind. 3) The Density-Temperature Structure of the Transition Region and Corona and The Coronal Magnetic Field Our interest is unabated in trying to reconcile or understand the reasons that models of the transition region and low corona based on EUV vs. radio observations differ so widely. On past occasions we have attempted to use the VLA to map the Sun simultaneously with rocket flights (of LASP) which measured EUV line intensities. On two occasions the rocket flights were postponed. We were finally successful in June 1984, when we obtained simultaneous, successful observations, not only with the rocket and the VLA, but with the 300' telescope at Green Bank, West Virginia. Data analysis is progressing, with preliminary reductions being very promising. One of our previous VLA observations resulted in an exceptionally fine radio picture of the Sun at 1.4 GHz that shows active regions, Coronal holes, filament cavities and quiet regions (Dulk and Gary 1983; see attached abstract). In general appearance it is much the same as when observed in soft X-rays. In addition, the measured degree of circular polarization provides a 1 E means of estimating the Coronal field strength in certain parts of active i No 6 regions, to altitudes of about 50,000 km. The inferred values in the outer parts of several active regions are in the range of 25 to 100 gauss, and the polarity is the same as on photospheric magnetograms. When this technique can be used with simultaneous measurements of soft X—ray brightness, both the density and field strength can be estimated as a function of height. Also, we have observed the Sun with the VIA in a more widespread configuration in order to obt in even better resolution, and data analysis on this is progressing. • .J^ . mil• ,, + ' `' - APPENDIX A LIST OF RECENT PAPERS Slee, O.B., Sheridan, K.V., Dulk, G.A. and Little, A.G., 1983, "Maps of Centaurus A from Molonglo and Culgoora", Proc. Astron. Soc. Australia, 5, 247-251. Hewitt, R.G., Melrose, D.B. and Dulk, G.A., 1983, "Cyclotron Maser Emission of Auroral Z-mode Radiation", J. Geophys. Res., 88, 10065-10071. White, S.M., Melrose, D.B. and Dulk, G.A., 1983, "Electron Cyclotron Masers During Solar Flares", Proc. Astron. Soc. Australia, 5, 188-191. Dulk, G.A., 1984, "The Solar Atmosphere, Magnetic Fields and Activity", Chapter 2 in Solar Radiophysics, D.J. McLean, ed., Cambridge Univ. Press, submitted. Lulk, G.A., McLean, D.J. and Nelson, G.J., 1984, "Solar Flares", Chapter 4 in Solar Rsdiophysics, D.J. McLean, ed., Cambridge Univ. Press, submitted. Suzuki, S. and Dulk, G.A., 1984, "Bursts of Type III and Type V". „hapter 12 in Solar Radiophysics, D.J. McLean, ed., Cambridge Univ. Press, submitted. Gary, D.E., Dulk, G.A., Houee, L., Illing, R., Sawyer, C., Wagner, W.J., McLean, D.J.