Title: ============== Coronal Magnetic Fields above an Emerging Flux region Lead Investigator: ======= Jeongwoo Lee, Univ. of Maryland Team Members: ================== Stephen White M. R. Kundu Technical Summary: ================== We propose to use MDI magnetograms and Dopplergrams for a correlative study of the emergence of NOAA 7978 on 1996 July 6 from 14:00 UT to 24:00 UT. We will compare the change of the magnetogram images with that of radio images which we have obtained using the VLA. We have already processed the VLA data to determine the change of radio flux, area, and intensity associated with the EFR event. MDI magnetograms of this region will be used to identify locations of foot-points of the coronal magnetic fields where the radio emission comes from. We will examine the positional and temporal correlation of the radio images with the magnetogram images to investigate which physical parameter is the most responsible for the increase of radio emission associated with the EFR. We also hope to learn how the magnetic fields expands and forms an arch filament as they rise above the coronal base by matching the locations of polarized radio sources with those of the photospheric magnetic fields seen on the magnetograms. Proposal Text: ======================= An EFR is a pattern in which new bipolar active regions emerge from below the solar photosphere. EFRs have received attention for they may carry information of magnetic fields in the subphotosphere and for they evolve to active regions or arch filaments. Physical and dynamical natures of EFRs have been studied mainly by observing optical emissions such as H\alpha and HeD3 (Chou and Zirin, 1988). The photospheric magnetic field change during of EFRs has been quantified with use of magnetograms. A radio observation of an EFR provides unique information of the corresponding change of EFRs at the coronal level since solar radio emission preferentially comes from the coronal magnetic fields. In particular, radio observations are sensitive to the strength of fields in the coronal loops associated with the newly-emerging flux. On 1996 July 6 we have observed, probably for the first time, an EFR in radio wavelengths using the VLA at three radio bands, C, X, and U at 32 time intervals during 14-24 UT. Our radio maps reveal that the emergence of magnetic flux though the corona starts at 18:00 UT near a tiny spot located at S09E21. The monotonic increase of in radio flux and intensity continued until the end of our observation at 24:00 UT. A detailed look at the radio maps led us to find that the EFR consists of at least three components. Two of the radio sources show low polarization corresponding to the magnetic field polarity shown in MDI magnetograms and probably are regions of magnetic flux tubes. The brightest radio source lies in the middle of these two components with little polarization for which we suspect it as either a top portion of a magnetic loop or a field free region filled by dense materials and surrounded by magnetic flux tubes. To resolve this ambiguity we need magnetograms of this region that show details of the field configuration underneath the coronal EFR phenomenon seen at radio wavelengths. Comparison of the temporal change of the magnetogram images with that of radio images are expected to provide information on dynamics of the EFR in 3-D space. To specify our scientific goals, (1) we hope to identify the physical parameters mainly responsible for the morphological change of radio emission associated with the flux emergence by cross-checking the positional correlation of the radio brightness, magnetogram, and soft X-rays. (2) We will attempt to determine the field strength and density of EFR materials at the coronal level using the radio diagnostics to see how the physical conditions of the coronal region has been affected by the EFR. (3) Magnetic fields in EFRs are expected to expand as they reach the upper atmosphere as gas pressure drops rapidly with height. By examining locations of polarized radio images relative to the magnetogram and Dopplergram images we hope to tell how the magnetic fields reconfigure themselves and how it leads to formation of an arch filament structure, of which presence is indicated by radio images. The full-disk magnetograms and Dopplergrams acquired by MDI every 90 minutes will be ideal for studying this emergence. We also plan to use Yohkoh SXT data in order to study the density evolution in the corona. See Also: ========= Chou, D.-Y. and Zirin, H. 1988 ApJ 333, 420.