Comparison of Far-Side STEREO Observations of Solar Activity and Active Region Predictions from GONG

Abstract

On 6 February 2011, the two Solar TErrestrial Relations Observatory (STEREO) spacecraft reached 180° separation and began imaging the entire far-side hemisphere of the Sun in extreme ultraviolet light (EUV). Here, we compare STEREO’s observations of far-side solar activity, as evidenced by bright regions in the EUV images, to predictions of far-side active regions from helioseismology using National Solar Observatory Global Oscilla-tion Network Group (GONG) observations. GONG produces seismic Carrington maps of strong magnetic field regions, labeling far-side regions with a probability ≥ 70%. By visual comparison of these GONG maps with STEREO EUV Carrington maps, we determine whether or not solar activity is observed at the locations of the predicted active regions. For data from February – June 2011, we find that for 139 of 157 comparisons activity is observed in EUV at the predicted site, yielding an 89% success rate. For 18 comparisons, no activity was seen at the predicted region (11% false predictions). We also investigated GONG’s success at predicting large active regions before they appear at the east limb as viewed from Earth. Of 15 such east-limb active regions, eight were predicted by GONG at least once in the seven days preceding their Earth-side appearance. STEREO B observations of activity in the days preceding the appearance of the other seven large East-limb active regions indicated that, while three were possibly too small for GONG to make a prediction, four seemed as large and active as other active regions that had been predicted successfully by GONG.