The Large Scale Structure of the Solar Minimum Corona SOHO JOP Proposal 44 Douglas Biesecker and Sarah Gibson Scientific Objective: Our goal is to understand the large-scale, stable, coronal structure of equatorial helmet streamers and polar coronal holes that can persist for several solar rotations at solar minimum. Although the corona does change dramatically, even during solar minimum, when a Coronal Mass Ejection blows a huge quantity of mass outwards, it is to this stable background structure that the corona returns. This observed behavior suggests that it may prove useful to consider solar minimum CME's as perturbations of the background corona. Understanding the large-scale corona is also fundamental to understanding how and where the solar wind is accelerated. The magnetic field structure in particular is fundamental to solar wind studies: knowledge of where the coronal field is open and where it is closed, as well as an understanding of how the expansion of the field varies from a purely radial expansion, are essential to studies of how the coronal field is related to fast and slow solar wind passing the earth. We also would like to clarify where the wind becomes important to coronal force balance, i.e. where the sonic surface lies. We therefore would like to quantify the density, temperature, and magnetic field distribution throughout the large-scale, stable, mostly static solar corona (i.e. 1 Rsun - 3 Rsun). We would approach this problem by using coronal observations as constraints on magnetostatic models. In previous work (Gibson, Bagenal, & Low JGR, 101, 4813, 1996; Gibson & Bagenal, JGR, 100, 198651, 1995; Bagenal & Gibson, JGR, 96,17663, 1991), existing coronal models were used and new models were developed to investigate the balance between magnetic forces and gravitational and thermal forces in the presence of both bulk and sheet currents. These models were constrained by observations of the white light corona (Mauna Loa MkIII and SMM Coronagraphs) and, to a lesser extent, of the photospheric magnetic field (Stanford WSO Magnetographs). Density, temperature, and magnetic field distributions were found that matched the data to within observational accuracy. However, the considerable degeneracy of acceptable solutions that were found implied that in order to specify the coronal plasma properties with confidence, additional observational constraints were needed. Observational Goals - Bench-Mark Dataset of Minimum Corona: For the purposes of our modeling, we wish to combine SOHO and ground-based observations of the large-scale, solar minimum corona to create a dataset of extensive coverage and variety. We would also like photospheric magnetic field observations and possibly transition region temperature and density diagnostics to be used as lower boundary conditions. Observations of the corona above the region we will be modeling (i.e. > 3 Rsun) as well as solar wind observations, both coronal and in situ, are extremely useful as upper boundary conditions. As this project is very close to the heart of the core mission of SOHO and because it proposes to combine many data sets, we see this as an opportunity to bring the solar physics community together in a comprehensive study of the large-scale, solar minimum corona. The modelling we propose to do can utilize data from as many instruments as can be coordinated. Thus we plan to bring together a dataset combining observations from SOHO, other spacecraft, and ground-based observatories. The result will be a picture of the solar corona from the solar surface to the interplanetary medium. To that end, we propose to coordinate observations for a `Whole Sun Week' of coordinated contemporal observations from all the instruments, to be used in conjunction with observations taken in the month surrounding this week that will give a synoptic picture of the three-dimensional corona. We would act to facilitate communications between interested observers, to coordinate observations, and ultimately to analyze the coordinated data set with our models. Individual observers would retain all proprietary rights to their data. However, we envision papers written by each observing group and published together in a special journal issue. This would then serve as a benchmark reference of the large-scale, solar minimum corona. We would also include a summary of a comparison of the various results obtained, and present the results of our modelling. Such a campaign should happen in a timely manner, while solar activity is at a minimum. We propose the joint observing program begin in July or August, depending on the availability of observers and on solar activity. In order to accomplish the modeling we intend to do, certain observations are required. However, we have considerable flexibility in the types of data needed as the modeling techniques to be used are very robust. We have developed techniques utilizing genetic algorithms (Gibson and Charbonneau, BAAS, vol. 28 #2) that will make efficient use of many observational constraints in order to reduce model degeneracy and so choose the most physically realistic description of the solar minimum corona. We would like to engage all interested observers in a dialogue to determine which observables they feel would be most useful and relevant for a benchmark picture of the solar corona. Where necessary, we would like these observations to be as co-temporal and co-spatial as possible and to cover as great a spatial range of the corona as possible. Summary: Ultimately, we hope to produce a definitive model of the stable, background, solar minimum corona which fully specifies density, temperature, and magnetic field as a function of solar radius and polar angle, between approximately 1 Rsun and 3 Rsun. We bring to this task fully developed theoretical models, analytic techniques, and computer codes, as well as experience with applying these to large datasets. This scientific goal motivates the creation of a benchmark observational reference of the large scale, solar minimum corona. Such a reference would aid in future studies involving the large-scale corona, its relation to smaller scale structures, and act as a database to be used as boundary conditions on solar wind and coronal heating models.