Coordinated study for Second Whole Sun Month Campaign
An understanding of the role currents play in the corona is essential to modeling the coronal magnetic field. This JOP is designed to use magnetic field observations, both line of sight and vector where available, in the photosphere and chromosphere to test force-free & potential models. Moreover we plan to compare magnetic field structures determined from modeled extrapolations to coronal structures. Specifically, we will
This analysis will be applied to
1) structures above active regions
2) coronal hole boundary expansion
MDI Continuous Coverage is currently planned for Wednesday 12 August 1998 to Monday 17 August 1998.
To optimize the WSM-2 science, extra high-rate telemetry coverage is requested for MDI for two periods 7 days before and after the mid-time of the continuous interval. MDI will run magnetic campaigns during these intervals.
MDI has requested coverage for two approx. 48 hours intervals, the first including Saturday 8 August and the second Saturday 22 August.
Those are the times when the solar limbs observed during the continuous contact by the coronal instruments are near central meridian. Additional observations at these times will help us characterize the magnetic field better. In addition, the East Limb locations during the first interval and West Limb locations during the second interval will be at central meridian during the planned long contact. This extra coverage will aid MDI's joint observations with TRACE and SOHO's coronal instruments. For this study absolute continuity is not required (gaps of an hour or two are not a big problem), the precise length of the intervals is not crucial (20 hours on one or two days is still useful), and the timing of the intervals is flexible (a day earlier or later for either interval is acceptable).
In addition to the synoptic Ca II 8542 full-disk magnetograms (also needed during the entire duration of the WSM2 campaign: August 1 -- 28, 1998), we have requested the Spectromagnetograph of the Kitt Peak Solar Vacuum Telescope to observe line-of-sight chromospheric magnetic field in selected active regions and (if possible) at the boundary of a coronal hole. The target will be selected in coordination with the other instruments participating to this campaign. The line to be used is also the synoptic Ca II 8542 line, therefore the setup of the area scans after the synoptic observations should not be a problem.
However, it is important to maximize the time overlap with the other instruments. More specifically, we are interested in simultanous observations with the NSO Sacramento Peak ASP. We therefore have proposed to place the Ca II 8542 synoptic magnetogram first in the synoptic sequence, if possible immediately followed by area scans restricted to the particular target chosen for the day.
(Andretta, Gibson, Jones)
The primary observing tasks will be scans of the WSM-2 target regions in the $\lambda\lambda 6301.5, 6302.5$\AA\ lines with the ASP. The dates for the observations at specific targets (August 12 -- 23, 1998) are dictated by the need to coordinate with the period during which SOHO/MDI can provide continuous coverage. The targets will be selected in coordination with the other instruments participating to this campaign. If available, the HAO Mg-I prism and cameras will be used to obtain spectropolarimetry for the chromospheric magnetic fields as well. We will also attempt to record spectropolarimetry in the Na-D line (5896\AA\ ; 9th order) in a sunspot for direct comparison with the observations by the Imaging Vector Magnetograph at UH/MSO which will be observing in this line. Since the targets will include a coronal-hole boundary, a mosaic-type approach will be used to scan the entire target region.
2) Coronal structures
Active region structures: Magnetic field morphology will be coordinated with co-temporal, co-spatial observations of coronal structures organized by JOP 84 - coronal active region WSM2 study
Coronal hole boundary structure: Magnetic field expansion at coronal hole boundaries will be coordinated with and compared to coronal observations of both the lower and upper coronal hole boundary. Moreover, the location and structure of the coronal hole/streamer boundary will be compared to observations of solar wind velocity. These observations will occur under the auspices of the following studies:
SOHO JOP 35 - Coronal Hole Structure and Evolution
SOHO JOP 76 - Streamer WSM2 study
SOHO JOP 85 - Coronal hole velocity WSM2 study