Yoichiro Hanaoka

Nobeyama Radio Observatory, NAOJ, Minamimaki, Minamisaku, Nagano 384-130, Japan

Flux emergence in solar active regions eventually causes a collision between the emerging loop and an overlying loop. This is a typical cause of solar flares and related active phenomena. We analyzed such flares observed with Yohkoh and the Nobeyama Radioheliograph, and derived the following conclusions.

(1) Two of the footpoints of the loops, one from the emerging loop and the other from the overlying loop, are included in a single magnetic polarity patch. The two loops form a `three-legged' structure, and the magnetic field has a `bipolar + remote unipolar' structure. Therefore, the magnetic field of the two loops are not anti-parallel.

(2) Relative timing analysis of the brightness of the microwave and the hard X-ray sources shows that the brightness fluctuation of one of the microwave sources, which is distant from the interaction region of the two loops, lags for 400-600 ms behind that of the other microwave source located at the interaction region. This is the evidence that the electron acceleration site is located at the interaction region of the two loops.

In addition, I would like to mention the prospect of the observations in radio and X-rays of the flares caused by the flux emergence during the next solar maximum abound 2001.