Streamer study for second Whole Sun Month Campaign (August 1 - August 28, 1998)

Sarah Gibson, David Alexander, Doug Biesecker, Andrzej Fludra, Don Hassler, Helen Mason, Leonard Strachan, Barbara Thompson

Abstract. The corona is characterized by an array of structures of various temporal and spatial scales, each providing a clue to its global physical properties. These structures are intrinsically linked to the coronal magnetic field, and range from small-scale, quickly varying structures in the lower corona to large-scale, quasi-static structures in the upper corona. We are interested in using observations of the solar corona in spectral emission and scattered white light to study the connections between lower, smaller-scale coronal structures and large-scale coronal ``streamer'' structures for the ascending phase of the solar cycle. Specifically, we propose to use observations from a variety of coronal telescopes including SOHO/CDS, SOHO/EIT, SOHO/LASCO, SOHO/SUMER, SOHO/UVCS, YOHKOH/SXT and HAO Mauna Loa Mark 3 during the proposed second Whole Sun Month Campaign (August 1-28, 1998 - CROT 1939). We plan to use these data to:

In so doing, we hope to gain insight into the physics of the stable and dynamic coronal structures which directly affect the properties of the solar wind and its interaction with the earth.

Proposed Study

As solar maximum approaches, the axisymmetric streamer belt disappears to be replaced by individual streamers of finite extent centered at various latitudes and longitudes, as in Figure 1 . Because white light observations depend upon the integral of coronal density along the line of sight, it is not possible to tell from a single image whether the streamers are centered in the plane of the sky, or whether they are projections of streamers centered away from the edge (or limb) of the solar disk. Multiple white-light images of streamers rotating past the solar limb, along with on-disk lower coronal observations of their boundaries are needed to determine streamer morphology. Moreover, active regions will increasingly dominate the lower corona as we move into solar maximum. We would like to study the relation between these hot, highly structured regions and the upper coronal streamers.

We plan to study the physical properties of a few selected ascending phase streamers as they rotate past the solar limbs during WSM2. Specifically, we will try to determine for each streamer selected, using upper and lower coronal observations:

We will use the results of this analysis, particularly regarding the thermodynamics and morphology of the streamers, to expand upon theoretical models of the solar minimum corona and to gain understanding about the coronal magnetic field, its role in coronal force balance, and the connections between large- and small-scale structures.

Finally, it is a distinct possibility we will observe one of our chosen streamers blow out in a coronal mass ejection (CME). CMEs are directly connected to occasionally damaging geomagnetic storms. Because emission corona observations are not limited to observations of the limb, lower coronal signatures of CMEs would be particularly helpful for predicting such potential disruptions of ground- and space-based systems. (See SOHO JOP 3 for an existing lower coronal CME study.) Since the rate of CMEs observed in white light by SOHO is high, and expected to increase as we move toward solar maximum, we stand a good chance of seeing one during our study. If so, we will have detailed information about the temperature and density profile at the base of the streamer, as well as the white light streamer structure, both before and after the eruption. We could then ask, how is the streamer morphology changed by the CME, and does it return to its original state? Where does the mass of the CME come from? Is the CME heated, and if so where? The answers to these questions would yield important constraints on existing CME models.