Cross-Calibration of MDI, NSO/KP, and GONG Magnetograms

Harrison P. Jones
NASA/GSFC, Laboratory for Astronomy and Solar Physics Southwest Solar Station c/o NSO PO Box 26732 Tucson, AZ 85726 hjones@noao.edu (520) 318-8354


The importance of the magnetic field in shaping a wide range of solar phenomena is universally acknowledged. Many studies, particularly those which attempt to extrapolate photospheric observations to greater heights, rely on quantitative inputs. Although different magnetographs produce morphologically similar data, quantitative differences are substantial and better appreciated than understood. The MDI magnetograms will have good spatial resolution free from atmospheric degradation at a cadence better suited for evolutionary studies than has been previously available and will thus doubtless be used for numerous studies which rely on quantitative stability if not overall accuracy. Thus, I propose to compare roughly co-temporal MDI, NSO/KP, and GONG full-disk magnetograms at intervals throughout the SOHO mission to establish mappings between the individual flux scales, to attempt to identify causes of any systematic differences in response, and to look for possible slow temporal trends. I intend to rely mostly on histogram equating--a very rapid method which does not require elaborate geometrical re-mappings for co-alignment--and check the results less often with pixel-by-pixel comparison.

MDI Data Requirements:
The above three data sets with their full-disk fields of view and continuity of observation provide an ideal opportunity to examine the effects of seeing and spatial resolution without organizing special campaigns. However, past experience suggests that I will not be alone in wishing to compare magnetograph data from diverse sources. Although I have not yet explored community interest in such an enterprise in the context of SOHO, I would be happy to cooperate with and, indeed, to help organize such an effort if needed.

No additional text was submitted for this proposal.