Position of radio sources for burst R5₀³ at four frequencies: 80 MHz (purple), 70 MHz (blue), 60 MHz (green), and 50 MHz (yellow) observed by LOFAR. The green and purple field lines are open; black field lines are closed. The field lines from the PFSS model are based on HMI/SDO data (displayed as gray surface of the Sun). The flare-accelerated electrons propagate along closed magnetic field lines in that example.