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We estimated the accuracy of coronal magnetic fields derived from radioobservations by comparing them to potential field calculations and the DEMmeasurements using EUV observations. We derived line of sight component of thecoronal magnetic field from polarization observations of the thermalbremsstrahlung in the NOAA active region 11150, observed around 3:00 UT onFebruary 3, 2011 using the Nobeyama Radioheliograph at 17 GHz. Because thethermal bremsstrahlung intensity at 17 GHz includes both chromospheric andcoronal components, we extracted only the coronal component by measuring thecoronal emission measure in EUV observations. In addition, we derived only theradio polarization component of the corona by selecting the region of coronalloops and weak magnetic field strength in the chromosphere along the line ofsight. The upper limit of the coronal longitudinal magnetic fields weredetermined as 100 - 210 G. We also calculated the coronal longitudinal magneticfields from the potential field extrapolation using the photospheric magneticfield obtained from the Helioseismic and Magnetic Imager (HMI). However, thecalculated potential fields were certainly smaller than the observed coronallongitudinal magnetic field. This discrepancy between the potential and theobserved magnetic field strengths can be explained consistently by two reasons;(a) the underestimation of the coronal emission measure resulting from thelimitation of the temperature range of the EUV observations, (b) theunderestimation of the coronal magnetic field resulting from the potentialfield assumption.

Coronal Magnetic Fields Derived from Simultaneous Microwave and EUV Observations and Comparison with the Potential Field Model