Prediction of coronal and heliospheric magnetic fields: The promise of SOI-MDI on SOHO

Abstract

Coronal magnetic field models developed over the years reproduce the static characteristics of coronal and heliospheric structures fairly well; however, limitations of spatial and temporal resolution and nonuniform quality of the input data are important factors limiting investigions of the response of the corona to rapidly changing photospheric conditions. The Solar Oscillations Investigation (SOI) Michelson Doppler Imager (MDI) experiment on SOHO, scheduled for launch in November 1995, will produce a series of full-disk photospheric magnetic field observations with 4″ resolution about every 96 minutes for the next several years. Higher resolution observations of the center of the disk will be available several times per day. These data should provide a basis for predicting the coronal and heliospheric field and their changes with unprecedented accuracy during the rising phase of Solar Cycle 23. Improved understanding of the structure and dynamics of the magnetized corona will require more realistic coronal magnetic field models. Our horizontal current-current sheet coronal field model includes large-scale, low-altitude, horizontal currents and the effect of thin current sheets in the streamer belt on the field above cusp type neutral points. To be self-consistent, the model now includes the effect of the streamer current sheet on the field below the cusp point. An overlying source surface can be added to simulate the effect of the accelerating solar wind. To suggest the potential of the MDI photospheric magnetic field data, we show calculations of the steady coronal magnetic field using low spatial resolution data and compare results with various observations.