Abstract

Radio synoptic maps at 17 GHz were synthesized from daily full disk images by the Nobeyama Radioheliograph (NRH). The NRH can synthesize a full disk image every second with 10 arcsec spatial resolution. Routine observation at 17 GHz started late June 1992. We have five year data. Due to the transparency of the terrestrial atmosphere at 17 GHz including cloud, observations are not interrupted by weather conditions except heavy rain and wet snow pileup. The NRH is a good instrument for synoptic study of the Sun due to its continuous operation. Radio images near local noon were used for synoptic map synthesis. The image data covering the Carrington longitude of +/- 20 degrees centered at the disk center longitude Lo were cut out from daily maps and were pasted on the Carrington coordinate grid. More than 60 rotation maps were synthesized. A butterfly diagram was also synthesized from all the rotation maps. In each rotation, one dimensional profile along the latitudinal direction was formed from the maximum values in the rotation in each latitudinal bin. The most prominent features of the radio synoptic maps are bright areas in the polar regions (polar brightening). Annual variation of the polar brightening area is clearly seen in the butterfly diagram. The annual variation is synchronized with Bo. This suggests that the polar brightening is due to limb brightening. There is also gradual expansion of polar brightening area in the northern pole, but not in the southern pole. Results of comparison of radio synoptic map in each rotation with other synoptic maps are also shown.