Analysis of loop-top and foot-point sources in microwave bursts

The polarization of four microwave bursts with loop-top and foot-point sources at 17 GHz of Nobeyama Radioheliograph (NoRH) is analyzed. The loop-like structure of the four events is confirmed by the simultaneous photospheric magnetograms (SOHO/MDI) and EtJV (TRACE) image or soft x-ray image (YOHKOH/SXT). Three events are located near the limb, and the other one is located 35degrees away from the center of solar disk. The three microwave sources in a given burst are polarized in the same sense. The polarization structure call be interpreted in terms of the extraordinary mode (e-mode) emission, taking into account the polarity of the underlying magnetic field and propagation effects, which may lead to inversion of the sense of polarization in the limbward foot-point and loop-top sources of the flaring loop.