NRH radio contours (the level is plotted at 80% of the maximum value at each frequency). The background is AIA/SDO at 171 Å. The NRH radio contours and AIA/SDO images are given in the same heliographic coordinate system and the unit is arcseconds. The contours in different colors denote different NRH imaging frequencies. The frequencies of 151, 173, 228 and 271 MHz in (a), and 151 and 173 MHz in (b) were removed since there is no radio emission at these frequencies and at the given time. (a) The time of the radio contours is at T₁ and the AIA/SDO 171 Å image is at 14:15:21 UT. (b) The time of the radio contours is at T₃ and the AIA/SDO 171 Å image is at 14:24:33 UT. (c) The time of the radio contours is at T₄ and the AIA/SDO 171 Å image is at 14:32:45 UT. (d) The time of the radio contours is at T₅ and the AIA/SDO 171 Å image is at 14:36:57 UT.